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    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY

    ENVIRONMENTAL HEALTH CRITERIA 87



                           ALLETHRINS

                           -  Allethrin
                           -  d-Allethrin
                           -  Bioallethrin
                           -  S-Bioallethrin










    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Labour Organisation,
    and the World Health Organization

    World Health Orgnization
    Geneva, 1989


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CONTENTS
                                                           
ENVIRONMENTAL HEALTH CRITERIA FOR ALLETHRINS

INTRODUCTION 

1. SUMMARY 

    1.1. Identity, physical and chemical properties, analytical 
          methods 
    1.2. Production and uses 
    1.3. Residues in food 
    1.4. Environmental fate   
    1.5. Kinetics and metabolism  
    1.6. Effects on experimental animals and  in vitro test systems 
    1.7. Effects on organisms in the environment  

2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS 

    2.1. Identity  
    2.2. Physical and chemical properties 
    2.3. Analytical methods 

3. SOURCES IN THE ENVIRONMENT, ENVIRONMENTAL TRANSPORT, 
    DISTRIBUTION AND TRANSFORMATION, ENVIRONMENTAL LEVELS AND HUMAN 
    EXPOSURE  

    3.1. Industrial production  
    3.2. Use patterns   
    3.3. Environmental transport, distribution, and transformation 
    3.4. Environmental levels and human exposure  
          3.4.1. Residues in food 

4. KINETICS AND METABOLISM  

    4.1. Metabolism in mammals  
    4.2. Enzymatic systems for biotransformation  

5. EFFECTS ON ORGANISMS IN THE ENVIRONMENT  

    5.1. Aquatic organisms  
    5.2. Terrestrial organisms  

6. EFFECTS ON EXPERIMENTAL ANIMALS AND  IN VITRO TEST SYSTEMS 

    6.1. Acute toxicity 
    6.2. Short-term studies 
          6.2.1. Allethrin  
          6.2.2. d-Allethrin  
          6.2.3. Bioallethrin   
          6.2.4. S-Bioallethrin   
    6.3. Primary irritation 
          6.3.1. Eye irritation 
          6.3.2. Skin irritation  
    6.4. Sensitization  

    6.5. Long-term studies and carcinogenicity  
    6.6. Mutagenicity and related end-points  
    6.7. Reproductive effects, embryotoxicity, and teratogenicity 
    6.8. Potentiation 
    6.9. Mechanism of toxicity - mode of action 

7. EFFECTS ON MAN 

8. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT 

    8.1. Evaluation of human health risks 
    8.2. Evaluation of effects on the environment 

9. CONCLUSIONS  

10. RECOMMENDATIONS  

11. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES   

REFERENCES 

APPENDIX   

WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR ALLETHRINS AND 
RESMETHRINS
                                                               
 Members

Dr L.A. Albert-Palacios, National Institute of Biological Resources 
   Research, Xalapa, Veracruz, Mexicoa

Dr V. Benes, Institute of Hygiene and Epidemiology, Prague, 
   Czechoslovakia

Dr A.H. El-Sabae, Faculty of Agriculture, Alexandria University, 
   Alexandria, Egypt

Dr Y. Hayashi, National Institute of Hygienic Sciences, Tokyo,
   Japan

Dr S. Johnson, US Environmental Protection Agency, Hazard 
   Evaluation Division, Washington DC, USA

Dr S.K. Kashyap, National Institute of Occupational Health,
   Ahmedabad, India  (Vice-Chairman)

Dr J.H. Koeman, Agricultural University, Wageningen, Netherlandsa

Dr Yu. I. Kundiev, Research Institute of Labour, Hygiene and
   Occupational Diseases, Kiev, USSR  (Chairman)

Dr J.P. Leahey, ICI Agrochemicals Division, Jealotts Hill Research 
   Station, Bracknell, Berkshire, United Kingdom  (Rapporteur)

Dr M. Matsuo, Sumitomo Chemical Co. Ltd, Takarazuka Research 
   Center, Takarazuka, Hyogo, Japan

Dr G.U. Oleru, College of Medicine, University of Lagos, Lagos, 
   Nigeria

 Observers

Mr J.-M. Pochon, International Group of National Associations of 
   Agrochemical Manufacturers, Brussels, Belgium

Dr L.M. Sasynovitch, Research Institute of Hygiene and Toxicology 
   of Pesticides, Polymers and Plastics, Kiev, USSR

 Secretariat

Dr Z.P. Grigorevskaja, Centre for International Projects, Moscow, 
   USSR

___________________________________________________________________

a Invited but unable to attend.

 Secretariat (contd.)

Dr K.W. Jager, International Programme on Chemical Safety, World 
   Health Organization, Geneva, Switzerland  (Secretary)

Dr J. Sekizawa, National Institute of Hygienic Sciences, Tokyo, 
   Japan  (Rapporteur)
                                  

NOTE TO READERS OF THE CRITERIA DOCUMENTS

    Every effort has been made to present information in the 
criteria documents as accurately as possible without unduly 
delaying their publication.  In the interest of all users of the 
environmental health criteria documents, readers are kindly 
requested to communicate any errors that may have occurred to the 
Manager of the International Programme on Chemical Safety, World 
Health Organization, Geneva, Switzerland, in order that they may be 
included in corrigenda, which will appear in subsequent volumes. 

                            *    *    *

    A detailed data profile and a legal file can be obtained from 
the International Register of Potentially Toxic Chemicals, Palais 
des Nations, 1211 Geneva 10, Switzerland (Telephone no. 988400 - 
985850). 

ENVIRONMENTAL HEALTH CRITERIA FOR ALLLETHRINS

    A WHO Task Group on Environmental Health Criteria for 
Allethrins and Resmethrins met in Moscow from 16 - 20 November 
1987.  The meeting was convened with the financial assistance of 
the United Nations Environment Programme (UNEP) and was hosted by 
the Centre for International Projects of the USSR State Committee 
on Science and Technology.  On behalf of the USSR Commission for 
UNEP (UNEPCOM), Dr M. I. Gounar opened the Meeting and welcomed the 
participants.  Dr K.W. Jager welcomed the participants on behalf of 
the Heads of the three IPCS cooperating organizations (UNEP/ILO/WHO).  
The Group reviewed and revised the draft Environmental Health 
Criteria and Health and Safety Guides and made an evaluation of the 
risks for human health and the environment from exposure to 
allethrins and resmethrins. 

    The first drafts of the documents were prepared by Dr J. 
Miyamoto and Dr M. Matsuo of Sumitomo Chemical Co. Ltd, with the 
assistance of the staff of the National Institute of Hygienic 
Sciences, Tokyo, Japan.  Dr I. Yamamoto of the Tokyo University of 
Agriculture and Dr M. Eto of Kyushu University, Japan, assisted in 
the finalization of the draft. 

    The second draft was prepared by Dr J. Sekizawa of the National 
Institute of Hygienic Sciences, Tokyo, incorporating comments 
received following the circulation of the first draft to the IPCS 
contact points for Environmental Health Criteria documents. 

    The help of the Sumitomo Chemical Company Ltd, Japan and 
Roussel Uclaf, France in making their toxicological proprietary 
information on allethrins and resmethrins available to the IPCS and 
the Task Group is gratefully acknowledged.  This enabled the Task 
Group to make their evaluation on a more complete data base. 

    The efforts of all who helped in the preparation and 
finalization of the documents are gratefully acknowledged. 

                            *    *    *

    Partial financial support for the publication of this criteria 
document was kindly provided by the United States Department of 
Health and Human Services, through a contract from the National 
Institute of Environmental Health Sciences, Research Triangle Park, 
North Carolina, USA - a WHO collaborating Centre for Environmental 
Health Effects.  The United Nations Environment Programme (UNEP) 
generously supported the costs of printing. 

                            *    *    *

 NOTE:  The proprietary information contained in this document 
cannot replace documentation for registration purposes, because the 
latter has to be closely linked to the source, the manufacturing 
route, and the purity/impurities of the substance to be registered.  
The data should be used in accordance with paragraphs 82 - 84 and 
recommendations paragraph 90 of the 2nd FAO Government Consultation 
(1982). 

INTRODUCTION

SYNTHETIC PYRETHROIDS-A PROFILE

1.    During investigations to modify the chemical structures of 
      natural pyrethrins, a certain number of synthetic pyrethroids 
      were produced with improved physical and chemical properties 
      and greater biological activity.  Several of the earlier 
      synthetic pyrethroids were successfully commercialized, 
      mainly for the control of household insects.  Other more 
      recent pyrethroids have been introduced as agricultural 
      insecticides because of their excellent activity against a 
      wide range of insect pests and their non-persistence in the 
      environment. 

2.    The pyrethroids constitute another group of insecticides in 
      addition to organochlorine, organophosphorus, carbamate, and 
      other compounds.  Pyrethroids commercially available to date 
      include allethrin, resmethrin, d-phenothrin, and tetramethrin 
      (for insects of public health importance), and cypermethrin, 
      deltamethrin, fenvalerate, and permethrin (mainly for 
      agricultural insects).  Other pyrethroids are also available 
      including furamethrin, kadethrin, and tellallethrin (usually 
      for household insects), fenpropathrin, tralocythrin and 
      tralomethrin, cyhalothrin, lambda-cyhalothrin, tefluthrin, 
      cyfluthrin, flucythrinate, fluvalinate, and biphenate (for 
      agricultural insects). 

3.    Toxicological evaluations of several synthetic pyrethroids 
      have been performed by the FAO/WHO Joint Meeting on Pesticide 
      Residues (JMPR).  The acceptable daily intake (ADI) or 
      temporary ADI has been estimated by the JMPR for 
      cypermethrin, deltamethrin, fenvalerate, permethrin, 
      phenothrin, cyfluthrin, cyhalothrin, and flucythrinate. 

4.    Chemically, synthetic pyrethroids are esters of specific 
      acids (e.g., chrysanthemic acid, halo-substituted 
      chrysanthemic acid, 2-(4-chlorophenyl)-3-methylbutyric acid) 
      and alcohols (e.g., allethrolone, 3-phenoxybenzyl alcohol).  
      For certain pyrethroids, the asymmetric centre(s) exist in 
      the acid and/or alcohol moiety, and the commercial products 
      sometimes consist of a mixture of both optical (1R/1S or d/1) 
      and geometric ( cis/trans)-isomers.  However, most of the 
      insecticidal activity of such products may reside in only one 
      or two isomers.  Some of the products (e.g., d-phenothrin, 
      deltamethrin) consist only of such active isomer(s). 

5.    Synthetic pyrethroids are neuropoisons acting on the axons 
      in the peripheral and central nervous systems by interacting 
      with sodium channels in mammals and/or insects.  A single 
      dose produces toxic signs in mammals, such as tremors, 
      hyperexcitability, salivation, choreoathetosis, and 
      paralysis.  The signs disappear fairly rapidly, and the 
      animals recover, generally within a week.  At near-lethal 
      dose levels, synthetic pyrethroids cause transient changes in 

      the nervous system, such as axonal swelling and/or breaks and 
      myelin degeneration in sciatic nerves.  They are not 
      considered to cause delayed neurotoxicity of the kind induced 
      by some organophosphorus compounds.  The mechanism of 
      toxicity of synthetic pyrethroids and their classification 
      into two types are discussed in the Appendix. 

6.    Some pyrethroids (e.g., deltamethrin, fenvalerate, 
      flucythrinate, and cypermethrin) may cause a transient 
      itching and/or burning sensation in exposed human skin. 

7.    Synthetic pyrethroids are generally metabolized in mammals 
      through ester hydrolysis, oxidation, and conjugation, and 
      there is no tendency to accumulate in tissues.  In the 
      environment, synthetic pyrethroids are fairly rapidly 
      degraded in soil and in plants.  Ester hydrolysis and 
      oxidation at various sites on the molecule are the major 
      degradation processes.  The pyrethroids are strongly adsorbed 
      on soil and sediments, and hardly eluted with water.  There 
      is little tendency for bioaccumulation in organisms. 

8.    Because of low application rates and rapid degradation in the 
      environment, residues in food are generally low. 

9.    Synthetic pyrethroids have been shown to be toxic for fish, 
      aquatic arthropods, and honey-bees in laboratory tests.  But, 
      in practical usage, no serious adverse effects have been 
      noticed, because of the low rates of application and lack of 
      persistence in the environment.  The toxicity of synthetic 
      pyrethroids in birds and domestic animals is low. 

10.    In addition to the evaluation documents of FAO/WHO, there 
      are several reviews and books on the chemistry, metabolism, 
      mammalian toxicity, environmental effects, etc. of synthetic 
      pyrethroids, including those by Elliot (1977), Miyamoto 
      (1981), Miyamoto & Kearney (1983), and Leahey (1985). 

1.  SUMMARY

1.1  Identity, Physical and Chemical Properties, Analytical 
Methods

    Allethrin was the first synthetic pyrethroid to be synthesized 
(in 1949) and was marketed in 1952.  Chemically, it is an ester 
of chrysanthemic acid (CA), 2,2-dimethyl-3-(2,2-dimethylvinyl)
cyclopropanecarboxylic acid with allethrolone and it 
is a racemic mixture of 8 stereoisomers: [1R, trans;1R]-, 
[1R, trans;1S]-, [1R, cis;1R]-, [1R, cis;1S]-, [1S, trans;1R]-, 
[1S, trans;1S]-, [1S, cis;1R]-, and [1S, cis;1S]-isomer.  The ratio 
of the above isomers in the technical material is approximately 
1:1:1:1:1:1:1:1.  Among the isomers, the [1R, trans;1S]-isomer is 
the most biologically active followed by the [1R, cis;1S]-isomer.  
d-Allethrin consists of [1R, trans;1R]-, [1R, trans;1S]-, 
[1R, cis;1R]-, and [1R, cis;1S]-isomers in an approximate ratio of 
4:4:1:1.  Bioallethrin and esbiothrin consist of [1R, trans;1R]- 
and [1R, trans;1S]-isomers.  The isomeric composition of the former 
is approximately 1:1 and that of the latter, 1:3.  S-Bioallethrin 
is the [1R, trans;1S]-isomer. 

    Allethrin is a clear, pale-yellow oil with a boiling point of 
140 C at a pressure of 0.1 mmHg; it is 75 - 95% pure.  The 
specific gravity is 1.005 at 25 C.  Allethrin is practically 
insoluble in water, but soluble in organic solvents, such as 
methanol, hexane, and xylene.  It is unstable in light, air, and 
under alkaline conditions.  It is decomposed by rapid pyrolysis at 
over 400 C, but vaporizes without decomposing, when heated at 
150 C.  It is fairly volatile. 

    d-Allethrin is an oily liquid (specific gravity of 1.005 - 
1.015 at 20 C). 

    Bioallethrin is an amber-coloured, viscous liquid.

    Esbiothrin is a yellow, viscous liquid.

    S-Bioallethrin is a yellow liquid.

    Allethrin residues and levels in environmental samples are 
determined by dual-wavelength densitometry (370 or 230 nm), or by 
derivatisation and colorimetric measurement at levels as low as 
0.1 mg/litre.  A gas chromatograph with flame ionization detector 
is used for analysis of the technical product. 

1.2   Production and Uses

    It is estimated that several hundred tonnes of allethrin, 
d-allethrin, bioallethrin, esbiothrin, and S-Bioallethrin are 
manufactured and used yearly throughout the world, mainly for the 
control of household insects.  Formulations include concentrates, 
aerosol sprays, smoke coils, electric mats, and emulsifiable with 
or without synergists or other insecticides. 

1.3  Residues in Food

    No information is available on the levels of allethrin residues 
in treated crops.  Allethrin was not detected in the milk of dairy 
cows or in the meat of a female goat, which had been sprayed daily 
for 3 and 5 weeks, respectively (limit of detection of method used 
- 0.1 mg/kg). 

1.4  Environmental Fate

    The photodegradation rate was measured of a thin film of 
allethrin on glass under a sun lamp.  Approximately 8 h of exposure 
were needed for 90% degradation.  S-Bioallethrin was rapidly 
decomposed, when similarly exposed to sunlight.  The major 
photoreactions were ester cleavage, di-pi-methane rearrangement, 
oxidation at the isobutenyl methyl group, epoxidation at the 
isobutenyl double bond, and  cis/trans-isomerization.  The major 
degradation products formed were CA, the 3-(2-hydroxymethyl) or the 
3-(1-epoxy) derivative of allethrin, and cyclopropylrethronyl 
chrysanthemate.  Sunlight photolysis of allethrin in solution 
yielded similar products.  Allethrin was decomposed by rapid 
pyrolysis at over 400 C.  When kept at 150 C for 9 h in an 
aluminum foil vessel in air, it vaporized (28 - 35%), polymerized 
(24 - 45%), and decomposed (18 - 40%).  CA, allethrolone, pyrocin, 
and  cis-dihydrochrysanthemo-delta-lactone were the degradation 
products formed. 

1.5  Kinetics and metabolism

    When 14C-acid- or 3H-alcohol-labelled allethrin was 
administered orally to rats at a rate of 1 - 5 mg/kg body weight, 
the radiocarbon and tritium were eliminated in the urine (30% and 
20.7%, respectively) and faeces (29% and 27%, respectively) within 
48 h.  The major metabolic reactions were ester hydrolysis, 
oxidation at the  trans-methyl of the isobutenyl group,  gem-dimethyl 
of the cyclopropane ring, and the methylene of the allyl group, and 
2,3-diol formation at the allylic group.  The major urinary 
metabolites were chrysanthemum dicarboxylic acid, allethrolone, and 
some oxidized forms of allethrin. 

1.6  Effects on Experimental Animals and  In Vitro Test Systems

    The acute oral toxicities of all the allethrins are weak to 
moderate with LD50 values ranging from 210 mg/kg body weight 
(mouse) to 4290 mg/kg (rabbit).  On the basis of limited data, the 
dermal toxicity appears to be very low (LD50 > 2000 for the 
rabbit).  The inhalation toxicity values (LC50 values) for the 
allethrins were found to be > 1500 mg/m3 (in the mouse and rat). 

    Allethrin is a Type I pyrethroid.  The Type I syndrome involves 
hyperactivity, tremors, convulsion, and paralysis in mammals and 
insects (see Appendix). 

    Bioallethrin and esbiothrin are classified as compounds 
producing mild primary irritation of the skin of New Zealand White 
rabbits and slight irritation of the eyes. 

    When a 10% olive oil solution of allethrin was applied to the 
eyes of rabbits, slight hyperaemia of the conjunctiva and eye 
discharge were observed 10 min and 2 h after application, 
respectively. 

    When a 5% olive oil solution of allethrin was applied to the 
skin of guinea-pigs, every other day, 10 times in all, and animals 
were challenged with an intradermal injection 2 weeks after the 
last application, there was no sensitization reaction, but slight 
lymphocytic and monocytic infiltration of the dermis was noted. 

    No adverse reactions were observed when the primary dermal 
irritancy of S-Bioallethrin was evaluated in Wistar rats and Nagano 
white rabbits. 

    When rats were fed allethrin in the diet at dose levels of up 
to 10 000 mg/kg for 16 weeks, tremor and convulsions were noted at 
10 000 mg/kg, but no gross effects were seen at 5000 mg/kg. 

    Allethrin  was administered orally, using a syringe, to rats at 
dose levels of up to 1000 mg/kg body weight per day, once a day, 6 
days a week for 12 weeks.  Half of the rats died following a single 
administration of 1000 mg/kg.  Higher relative weights of the 
liver, thyroid, and kidney were noted at lower doses. 

    Inhalation of allethrin by mice at a level of 3 g/m3 for 4 h a 
day, 6 days a week, over 4 weeks, resulted in eye discharge in all 
animals.  Histopathological examination of the lungs revealed 
bronchopneumonia. 

    S-Bioallethrin was also tested via the inhalation route in 
several studies conducted on mice and rats at a range of dose 
levels (10, 20, or 25 times the normal concentration used) for 
exposure periods of up to 5 weeks.  The results of these studies 
indicated that the short-term toxicity of S-Bioallethrin is low. 

    Bioallethrin was administered in the diet to rats for 90 days 
at levels of 500, 1500, 5000, or 10 000 mg/kg.  Slight or moderate 
decreases in body weight gain and slight liver dysfunction were 
found at the 5000 and 10 000 mg/kg levels.  A no-observed-adverse-
effect level of 1500 mg/kg was determined. 

    When the same compound was administered in the diet of dogs, 
for 6 months, at levels of 200, 1000, or 5000 mg/kg, general body 
trembling, irregular heart rhythm, and increases in the mean levels 
of alkaline phosphatase and SGPT were noted at the 5000 mg/kg 
level.  Hepatocellular degeneration was found at both the 1000 and 
5000 mg/kg levels.  A no-observed-adverse-effect level of 200 mg/kg 
was established. 

    F344 rats were administered d-allethrin at levels of 0, 125, 
500, or 2000 mg/kg diet for 123 weeks.  Decreased body weight and 
hepatotoxic effects were observed at levels exceeding 500 mg/kg 
diet (i.e., 24.5 mg/kg body weight per day).  However, no oncogenic 
effects were observed at any dose and the no-observed-adverse-
effect level was 5.9 mg/kg body weight per day. 

    Dogs were fed allethrin at a rate of 50 mg/kg body weight per 
day for 2 years.  There were no compound-related gross or 
microscopic changes at this level. 

    Allethrin, bioallethrin, esbiothrin, and S-Bioallethrin have 
been evaluated in a variety of mutagenicity tests, including  in 
 vitro/in vivo gene mutation, DNA damage and repair, and  in vitro/in 
 vivo chromosomal aberrations.  The results of all studies were 
assessed as negative. 

    Allethrin, bioallethrin, and S-Bioallethrin were tested for 
embryotoxicity and teratogenicity in rats, mice, and rabbits.  No 
compound-related embryo toxicity or teratogenicity were observed in 
these studies, though some variations were observed in some 
studies. 

    S-Bioallethrin did not seem to induce any disorders in the 
fetuses of pregnant Wistar rats at doses of 100 mg/kg per day, or 
less.  Furthermore, S-Bioallethrin did not induce any teratogenic 
effects in the pregnant TVCS mice at the maximum tolerated dose of 
100 mg/kg per day. 

    Allethrin was administered daily in corn oil, by gavage, at 
doses of 0, 215, or 350 mg/kg body weight to pregnant albino 
rabbits from day 6 to day 18 of gestation.  No fetotoxic or 
teratogenic effects were observed. 

1.7  Effects on Organisms in the Environment

    Allethrin, bioallethrin, and S-Bioallethrin are all toxic for 
fish with LC50 values of 9 - 90 g/litre, S-Bioallethrin being the 
most toxic.  Allethrin is generally less toxic for  Daphnia and 
aquatic insect larvae with LC50 values of 150 - 50 000 g/litre. 

    The toxicity of allethrin is low for birds (LD50 > 2000 
mg/kg), but high for honey-bees (LD50 3 - 9 g/bee).

2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS

2.1  Identity

             CH3   CH3       CH3
                \ /          |
                 C           C
                / \        /   \\
    (CH3)-C=CH-CH-CH-COO-CH     C-CH2-CH=CH2
                          |     |
                          CH2 - C
                                 \\
                                   O

    Allethrin, the first of the synthetic pyrethroids, was 
discovered by Schechter et al. (1949), when simplifying the chemical 
structures of natural pyrethrins.  It is a mixture of 8 stereo 
isomers (Fig. 1) and is less volatile and more stable to heat and 
light than the natural pyrethrins. 

FIGURE 1

    The 3S:3R or  cis:trans ratio is reported to be 1:1 and the 
optical ratio of 1R:1S in the acid and allethronyl moiety is also 
1:1 (racemic).  Technical grade material contains 75 - 95% 
allethrin.  d-Allethrin is the ester of the (1R,  cis, trans)-acid 
with racemic allethrolone.  Bioallethrin and esbiothrin are the 
(1R, trans)-acid ester of racemic allethrolone.  S-Bioallethrin is 
the ester of the (1R, trans)-acid with (1S)-allethrolone.  The 
compositions of these isomers are shown in Table 1. 


Table 1.  Chemical identity of allethrins of various stereoisomeric compositions
---------------------------------------------------------------------------------------------------------------------
Common name/CAS     CA Index name (9CI)                      Stereoisomeric    Synonyms and
Registry No./NIOSH                                           compositiond      trade names
Accession No.a      Stereospecific nameb,c      
---------------------------------------------------------------------------------------------------------------------
Allethrine          2-methyl-4-oxo-3-(2-propenyl)-2-cyclo-   (1):(2):(3):(4)   Pallethrin, Pynamin, Allycinerin, 
584-79-2f           penten-1-yl 2,2-dimethyl 3-(2-methyl-1-  :(5):(6):(7):(8)  Pyresin, Pyresyn, Necarboxylic acid,
GZ1476000           propenyl) cyclopropanecarboxylate (9CL)  =1:1:1:1:1:1:1:1  ENT17, 510, FDA1446, FMC249, NIA249,
                                                                               RU 28173 
                    (RS)-3-Allyl-2-methyl-4-oxocyclopent-                      Allethrin concentrate MGK      
                    2-enyl (1RS,  cis, trans)-2,2-dimethyl-                               
                    3-(2,2-dimethylvinyl)cyclopropane-                         
                    carboxylate                                                           
                                  or                                                      
                    (RS)-Allethronyl (1RS,  cis, trans)-
                    chrysanthemate                     
                                                                    
d-Allethrin         same as allethrin                        (1):(2):(3):(4)   d-cis, trans-Allethrin 
                                                             =4:4:1:1          Pynamin Forte 
                                        
                    (RS)-Allethronyl [1R,  cis, trans]- 
                    chrysanthemate                     
                                    
Bioallethrin        same as allethrin                        (1):(2)=1:1       d-trans-allethrin
584-79-2f           (S)-Allethronyl[1R,trans]                                     (+)-trans-allethrin,
GZ1950000           chrysanthemate                                                depallethrine;
                                                                                  trans-allethrin
                                                                               Bioallethrin(e)R;
                                                                               D-TransR
                                    
Bioallethrin S-     same as allethrin                        (1):(2)=1:3       sinbioallethrin;
cyclopentenyl       (RS)-Allethronyl                                           espedallethrine;
isomer              [1R, trans]                                                S-bioallethrin,
28434-00-6          chrysanthemate                                             EsbiolR;
                                                                               Esbiothrin(e)R
                                            
S-Bioallethrin      same as allethrin                        (2)               Esbiol, Esdepallethrin 
28434-00-6                                                                     d-Allethronyl                    
GZ1472000           (S)-Allethronyl [1R,  trans]-                               d- trans allethrin
                    chrysanthemate                                             (+)-Allethronyl     
                                                                               (+)- trans-allethrin
                                                                               RU 16121           
---------------------------------------------------------------------------------------------------------------------

Table 1.  (contd.)
---------------------------------------------------------------------------------------------------------------------
Common name/CAS     CA Index name (9CI)                      Stereoisomeric    Synonyms and
Registry No./NIOSH                                           compositiond      trade names
Accession No.a      Stereospecific nameb,c      
---------------------------------------------------------------------------------------------------------------------
-                   same as allethrin                        -                 d- cis-Allethrin
-                                                                              (+)- cis-Allethrin
GZ1460000           (RS)-Allethronyl [1R,  cis]-
                    chrysanthemate             

-                   same as allethrin                        -                 -
-
GZ1925000           (S)-Allethronyl [1R,  cis, trans]-
                    chrysanthemate                
---------------------------------------------------------------------------------------------------------------------
a NIOSH (1983).
b (1R), d, (+) or (1S), 1, (-) in the acid part of allethrin signifies the same stereospecific conformation, 
  respectively.  (S), d, (+) or (R), 1, (-) in the alcohol part of allethrin signify the same stereospecific 
  conformation, respectively.
c Allethronyl radical is a name of the radical that forms the alcohol part of allethrin.  Chrysanthemic acid is a 
  name of the acid that forms the acid part of allethrin.
d Numbers in parentheses identify the structures shown in the figures of stereoisomers.
e ISO common name: common names for pesticides and other agrochemicals approved by the Technical Committee of the 
  International Organization for Standardization.
f CAS Registry No. 584-79-2 is assigned to both allethrin and bioallethrin.
    The technical product (Esbiol) contains 90% S-Bioallethrin. 

2.2  Physical and Chemical Properties

    Some physical and chemical properties of allethrins are given 
in Table 2. 

    Data on melting points were not available.  Allethrin is 
unstable to light and air and under alkaline conditions.  However, 
it is more stable on exposure to heat and light than pyrethrins.  
Allethrin is decomposed by rapid pyrolysis at over 400 C, but 
vaporizes without decomposition (28 - 35%) when heated at 150 C.  
d-Allethrin is soluble in most organic solvents.  d-Allethrin, 
bioallethrin, and S-Bioallethrin are also unstable to light, in 
air, and under alkaline conditions.  S-Bioallethrin is miscible 
with most organic solvents (FAO/ WHO, 1965; Martin & Worthing, 
1977; Meister et al., 1983; Worthing & Walker, 1983; Devaux & 
Bolla, 1986a,b; Devaux & Tillier, 1986). 
Table 2.  Physical and chemical properties of allethrins
------------------------------------------------------------------------------------------
                          Allethrin     d-Allethrin  Bio-          Esbiothrin  S-Bio-
                                                     allethrin                 allethrin
------------------------------------------------------------------------------------------
Physical state            oil           oily         viscous       viscous     liquid
                                        liquid       liquid        liquid 

Colour                    pale          -            amber         yellow      yellow
                          yellow

Odour                     -             -            aromatic      -           -

Relative molecular mass   302.45        302.45       302.45        302.45      302.45

Boiling point (C)        140           -            153           -           -
                          (0.1 mmHg)                 (0.4mmHg)  

Flash point (C)          -             130          65.6          -           -

Solubility in water       low           low          lowa          low         low

Solubility in organic     solubleb      soluble      solublec      soluble     soluble
solvents
                                     
Density                   d251.005      d201.005 -   d200.997      -           d200.980
                           4             4 1.015      4                         4

Vapour pressure           1.2 x 10-4    -            3.3 x 10-4    -           -
                          mmHg (30 C)               mmHg (25 C) 

 n-Octanol/water           -             -            4.8 x 104     -           -
partition coefficient                                (25 C)
------------------------------------------------------------------------------------------
a 4.6 mg/litre at 25 C.
b Methanol (> 1 kg/kg), hexane (> 1 kg/kg), xylene (> 1 kg/kg), acetone, carbon 
  tetrachloride, kerosene, petroleum.
c Acetone, ethanol, hexane, methylene chloride, kerosene.
2.3  Analytical Methods

    A limited number of publications is available on methods of 
analysis for allethrin residues and analysis of environmental 
media.  Analytical procedures listed in Table 3 include (a) 
extraction with solvent, (b) partition, (c) clean up, (d) suitable 
analytical instruments and conditions, and (e) minimum detectable 
concentration and recovery for each method. 

    The stereoselectivity of a radioimmunoassay (RIA) system using 
an S-Bioallethrin-specific antiserum was studied by observing the 
abilities of the 8 allethrin isomers and other selected compounds 
to compete with a radiolabelled S-Bioallethrin tyramine derivative 
for antibody-binding sites (Wing & Hammock, 1979).  The results 
demonstrate the feasibility of RIA as a rapid, sensitive, and 
stereoselective residue technique for compounds difficult to 
analyse using classical methods. 


Table 3.  Analytical methods for allethrina
-----------------------------------------------------------------------------------------------------------------------------
Sample     Sample preparation                      Determination              Limit of    % Recovery        Reference
           Extraction  Partition  Clean-up method  Derivatization  Detection  detection   (fortification)
           solvent                                                 method     (mg/litre)  (mg/litre)
-----------------------------------------------------------------------------------------------------------------------------
 Analysis for Residues

Milk       petroleum                               mercuric        colori-    0.1                           McClellan & Moore
                                                   oxide/          metric                                   (1958)
Meat       ether                                   sulfuric
                                                   acid

Wheat      petroleum                               modified        colori-                                  Desmarchelier
           spirit                                  Deniges         metric                                   (1976)
                                                   reagent         (584 nm)

 Analysis for total content

Dish        n-hexane     n-hexane/  HPTLC benzene/                   dual-wave-             91-104% (300 g)  Uno et al. (1982)
                       CH3CN      CCl4 (1 + 1)                     length 
Apple                              n-hexane/ether/                  densitometry           98% (300 g)
Spinach                           formic acid                      (1 = 370 nm;           92% (300 g)
(dis-                             (70/30/1)                        2 = 230 nm) 
lodgeable 
residue)

Mosquito   toluene                                                 FID-GC                 94-102%           Sakaue et al. 
coil       +99%                                                                                             (1985)
           formic 
           acid (5:1)

 Product analysis

Technical  acetone                                                 FID-GC, N2                               Murano (1972)
grade                                                              40 ml/min,
                                                                   1 m; 5% DEGS,
                                                                   180 C, 8.4 
                                                                   min                                                       
-----------------------------------------------------------------------------------------------------------------------------
a FID = Flame ionization detector; GC = gas chromatography; UV = ultraviolet; HPTLC = high-performance thin-layer 
  chromatography.
 
3.  SOURCES IN THE ENVIRONMENT, ENVIRONMENTAL TRANSPORT, DISTRIBUTION 
AND TRANSFORMATION, ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

3.1  Industrial Production

    Allethrin is prepared by the esterification of [1RS, 3RS 
or  cis, trans]-2,2-dimethyl-3-(2,2-dimethylvinyl) 
cyclopropanecarboxylic acid or chrysanthemic acid with (1RS)-3-
allyl-2-methyl-4-oxocyclopent-2-ene-1-ol or allethrolone (Sanders & 
Taff, 1954). 

    It was first marketed in 1952, in Japan and the USA (Yoshioka, 
1980).  At present, several hundred tonnes are thought to be 
manufactured annually throughout the world, mainly for the control 
of household insect pests.  Bioallethrin was first marketed in 
early 1970 and is now used at a rate of 10 - 30 tonnes per year.  
Formulations of allethrin combined with organophosphorus 
insecticides, such as tetrachlorvinphos and fenitrothion, are 
produced for agricultural use (Japan Plant Protection Association, 
1984). 

3.2  Use Patterns

    Allethrin is used mainly for the control of flies and 
mosquitoes in the home, flying and crawling insects on farm 
animals, and fleas and ticks on dogs and cats.  It is formulated as 
aerosols (1 - 6 g/litre), sprays, dusts (1%), smoke coils, and 
mats.  It is used alone or combined with synergists (e.g., 
piperonyl butoxide and  N-octylbicycloheptene dicarboximide) or 
other insecticides (e.g., fenitrothion).  It is also available in 
the form of emulsifiable concentrates (810 g/kg) and wettable 
powders.  Synergistic formulations (aerosols or dips) have been 
used on fruits and berries, post-harvest, in storage, and in 
processing plants.  Post-harvest use on stored grain (surface 
treatment) has also been approved in some countries (FAO/WHO 1965).  
No information is available on recent post-harvest treatment with 
allethrin. 

    Bioallethrin is more than twice as effective as allethrin and 
is mainly used to control household insects.  It is formulated as 
aerosols and sprays with synergists and/or other insecticides 
(e.g., d-phenothrin or deltamethrin).  A few tonnes of bioallethrin 
have been used in Spain for this purpose, according to Battelle 
(1982).  Since 1982, this aerosol formulation has been used in many 
other countries.  The use of mosquito coils and electric mats has 
also increased considerably. 

    S-Bioallethrin is several times as effective as allethrin 
against flying and crawling insects and is mainly used in industry 
and in the home.  It is formulated as aerosols and sprays with 
synergists for use as a knock-down or flushing agent.  Several 
tonnes of S-Bioallethrin were used for this purpose in 1980 in 
France, together with bioallethrin and allethrin (Battelle, 1982). 

3.3  Environmental Transport, Distribution, and Transformation

    Degradation pathways of allethrin are summarized in Fig. 2. 

FIGURE 2

    When exposed as a thin film or coating on glass (2.6 g/cm2) to 
a sunlamp for 8 h, [14C]- trans-allethrin was rapidly decomposed to 
give at least 14 products.  The photoproducts derived from the 
carboxy (acid) - and allethrolone (alcohol) - labelled compounds 
showed a similar TLC pattern, indicating that most, if not all, of 
the products were esters.  Saponification of the mixture of esters 
liberated 16 acids including  trans-carbonic acid and keto 
derivatives arising from the oxidative attack at the double bond of 
the isobutenyl moiety, and chrysanthemic acid derivatives having 
the  trans-methyl in the isobutenyl side chain oxidized to the 
alcohol, aldehyde and carboxylic acid.  There was no  cis/trans- 
isomerization, even after extended irradiation for up to 24 h (Chen 
& Casida, 1969). 

    The photodegradation rates of a thin film (54 g/cm2) under a 
sunlamp were compared for  trans-allethrin, pyrethrin-I, 
tetramethrin, and dimethrin.  The rates of transformation varied 
dramatically with variation in the alcohol moieties, and the 
exposure times needed for 90% loss of the original compound were 
approximately 0.2, 4, 8, and 16 h, for pyrethrin-I, tetramethrin, 
allethrin, and dimethrin, respectively.  The chemical reactions 
involved in the alcohol moieties were not clarified (Chen & Casida, 
1969). 

    The photostability under sunlight of bioallethrin included in, 
or mixed with, beta-cyclodextrin was studied.  Inclusion slowed 
down the decomposition of allethrin, the half-life extending from 

3 days for the free state to about 35 days for the included form.  
Inclusion retarded the photochemical decomposition of the acid 
moiety, compared with the alcohol moiety (Yamamoto et al., 1976). 

    Irradiation of a diastereomer mixture of bioallethrin in 
hexane or kerosene, using a medium or high pressure mercury arc 
lamp, resulted in the formation of the cyclopropylrethronyl 
chrysanthemates (13,15 in Fig. 2) (approx. 90%) via di-pi-methane 
rearrangement at the allyl substituent in the alcohol moiety 
(Fig. 2).  The same product was formed in kerosene and in sunlight.  
The reaction was completely quenched by 2,5-dimethylhexa-2,4-diene.  
No evidence was obtained of the accompanying formation of either 
 cis-cyclopropane- or 3,3-dimethylacrylic esters (Bullivalent & 
Pattenden, 1973; Kawano et al., 1980). 

    S-[14C]-Bioallethrin labelled in the acid moiety was rapidly 
decomposed, when exposed to sunlight as a thin film (25 g/cm2) on 
glass.  After 3 h, with 56% of the compound converted, the major 
products identified resulted from ester cleavage (18) (14.7%), 
oxidation at the isobutenyl methyl group (14) (7.9%), di-pi-methane 
rearrangement (15) (9.9%), epoxidation at the isobutenyl double 
bond (16,17) (16%), and  cis/trans-isomerization (10) (1.2%).  Many 
minor photoproducts, totalling 55% of the reaction mixture, were 
not identified.  Sunlight  photolysis in solution (1.8 - 7.2 x 
10-3 mol/litre) for 3 h yielded most of the products observed in 
the solid phase.  More epoxides (17) were formed in benzene (33%) 
than in hexane (12%), and in aerated solutions than in solutions 
saturated with argon or nitrogen.  In acetonitrile-water (4:1), 
S-Bioallethrin reacted to form cyclopropylrethronyl chrysanthemate 
(15) (70%), a  cis/trans-isomerization product (10) (14%), and 
epoxides (17) (8%) in the acid moiety.  Formation of chrysanthemic 
acid (18) by ester bond cleavage was comparable in all solvents 
(4 - 6%) but was increased in the presence of a benzil radical 
(Ruzo et al., 1980). 

    Direct photolysis of S-Bioallethrin in benzene under UV 
radiation (360 nm) yielded the products observed under sunlight, 
together with trace amounts of the decarboxylated derivative (11), 
the  cis-epoxides, and more than twenty-five other minor products.  
Triplet intermediates were involved in the cyclopropane 
isomerization and the di-pi-methane rearrangement, since the 
reactions were enhanced by a sensitizer benzophenone, especially 
at a high concentration (0.1 mol/litre), and were blocked by 
1,3-cyclohexadiene.  The epoxides formed by triplet oxygen were 
considerably enhanced by the addition of a benzil radical, and were 
the only major products in the presence of 1,3-cyclohexadiene.  
Oxidation at the  trans-methyl group in the chrysanthemate moiety 
resulted from radical reactions of ground-state oxygen.  Singlet 
oxygen was not involved in these oxidation reactions since the 
sensitizer, Rose Bengal, gave a totally different product 
distribution under UV radiation.  Under comparable conditions, the 
cyclopropylrethronyl chrysanthemate (15), formed via di-pi-methane 
rearrangement, reacted in benzene under UVR (360 nm) more slowly 
than the parent compound, yielding the corresponding epoxides (16) 
(15%) and allethrin (9) (70%) (Ruzo et al., 1980). 

    The rapid pyrolysis of allethrin and other chrysanthemic esters 
was examined by gas-liquid chromatography (GLC) with a less stable 
sample injection port heated at 250 - 550 C.  Allethrin was than 
any of the other compounds, including tetramethrin, at temperatures 
of over 400 C, because of the instability of the allethrolone 
moiety (Kyogoku et al., 1970). 

    Allethrin in a pyrex glass tube heated at 400 C, under 
nitrogen, gave chrysanthemic acid, 2,6-dimethylhepta-2,4-diene (21) 
and pyrocin (22) as pyrolysis products from the acid moiety, and 
2,7-diallyl-3,6-dimethyl-1-indanone (25) and 2,4-diallyl-3,5-
dimethyl-1-indanone (26) from the alcohol moiety (Nakada et al., 
1971). 

    Baba & Ohno (1972) studied the vaporization and degradation of 
allethrin (100 mg) in an aluminum foil vessel in air at 150 C for 
9 h.  Under these conditions, 28 - 35% of allethrin vaporized 
without undergoing any changes, 24 - 45% polymerized, and 18 - 40% 
decomposed.  The thermal degradation products formed were  trans-
chrysanthemic acid (18) and allethrolone (20), together with 
2-allyl-3-methylcyclopenta-2-ene-1,4-dione (24), which was formed 
by subsequent pyrolysis of allethrolone.  In addition,  cis-
chrysanthemic acid (19), pyrocin (22), and  cis-dihydrochrysanthemo-
delta-lactone (23) were formed under the same conditions from the 
mixture of 8 isomers of allethrin;  cis-dihydroxy-chrysanthemo-
delta-lactone (23) was produced from  cis-allethrin. 

3.4  Environmental Levels and Human Exposure

    No information is available on levels of allethrins in the 
environment or on general population or occupational levels of 
exposure. 

3.4.1  Residues in food

    No information is available on the levels of allethrin residues 
in treated crops.  Allethrin was not detected (detection limit 
0.1 mg/kg) in the milk of dairy cows that had been sprayed daily 
for 3 weeks or in the meat tissue of a female goat that had been 
sprayed daily for 5 weeks, all animals receiving a large overdose 
of spray.  No information is available on the chemical nature of 
the terminal residues in treated crops (FAO/WHO, 1965). 

4.  KINETICS AND METABOLISM

4.1  Metabolism in Mammals

    Metabolic pathways of allethrin in mammals are summarized in 
Fig. 3. 

FIGURE 3

    When allethrin (9) labelled with 14C in the acid moiety or with 
3H in the alcohol moiety was administered orally to male Sprague 
Dawley rats at levels ranging from 1 to 5 mg/kg body weight, the 
radiocarbon and tritium from the acid- and alcohol-labellings were 
eliminated in the urine (30% and 20.7%, respectively) and faeces 
(29% and 27%, respectively) in 48 h.  The tissue residues were not 
determined.  Most of the metabolites excreted in the urine were 
ester-form metabolites together with two hydrolysed products, 
chrysanthemum dicarboxylic acid (29) (CDCA) and allethrolone (20).  
The faecal metabolites were not identified.  Allethrin could have 
been metabolized via any of the following 5 biotransformation 
pathways; hydrolysis to allethrolone and to a smaller extent CDCA, 
formation of the 2,3-diol (30) from the allyl moiety, hydroxylation 
at the methylene position of the allyl grouping (31), hydroxylation 
at one of the  geminal dimethyl groups (32), and oxidation at the 
 trans methyl group of the isobutenyl moiety to carboxylic acid (28) 
(Elliott et al., 1972a,b; Yamamoto, 1970). 

4.2   Enzymatic Systems for Biotransformation

    The microsome or microsome-plus-soluble fraction prepared from 
rat or mouse liver homogenate was incubated in a phosphate buffer 
(0.1 mol/litre, pH 7.4) for 30 min at 37 C with 7 or 70 g 
allethrin, in the presence or absence of NADPH.  Allethrin yielded 
neutral metabolites (ex. 14, 27), several acidic metabolites 
(ex. 28, 29), and some other polar metabolites, when examined using 
two-dimensional thin-layer chromatography (Elliot et al., 1972a,b). 

5.  EFFECTS ON ORGANISMS IN THE ENVIRONMENT

    Acute toxicity data on allethrin in aquatic and terrestrial 
non-target organisms are summarized in Tables 4 and 5, 
respectively. 

5.1  Aquatic Organisms

    Allethrin, bioallethrin, and S-Bioallethrin are all toxic 
for fish, with LC50 values ranging from 9 to 90 g/litre, as 
shown in Table 4.

    The biological activity in fish is affected by temperature.  
The toxicity of 1R or (+)- trans-allethrin for the bluegill was 
about 1.5 times higher at 22 C than at 12 C (Mauck et al., 1976).  
Water hardness and pH did not have any significant effects on the 
toxicity for fish (Mauck et al., 1976). 

    Allethrin is generally less toxic in arthropods than in fish, 
with the exception of the stonefly, which is the most susceptible 
insect, having a 96-h LC50 of 2 g/litre, as shown in Table 4. 

5.2  Terrestrial Organisms

    Only a few data on terrestrial organisms are available.  The 
toxicity of allethrin is low for birds and high for honey-bees, as 
has been observed for other pyrethroids (Table 5). 


Table 4.  Acute toxicity of allethrin for non-target aquatic organisms
--------------------------------------------------------------------------------------------------------------------------------------
Species                Size      Parameter  Concentra-  Formula-   System   Tempera-   pH   Hardness (mg     Reference
                                            tion (g/   tiona               ture (C)       CaCO3/litre)
                                            litre)                                          or salinity (%)
--------------------------------------------------------------------------------------------------------------------------------------
Fish

Salmon ( Salmo salar)   10 cm;    96-h LC50  16.5        technical  renewal  10                               Zitko et al. (1977)
                       11.07 g                                                                               

Coho salmon                      96-h LC50   22.2       (+)-trans   static   12                               Mauck et al. (1976)
( Oncorhynchus                    96-h LC50  9.40       (+)-trans   flow-    12                               Mauck et al. (1976)
 kisutch)                                                           through                                                      
                                                                                                                                
Killifish ( Oryzias     adult     48-h LC50  87         technical   static   25                               Miyamoto (1976)
 latipes)               adult     48-h LC50  50         (+)- trans  static   25                               Miyamoto (1976)
                       adult     48-h LC50  42          (+)- cis    static   25                               Miyamoto (1976)
                       adult     48-h LC50  32          (+),(+)-t   static   25                               Miyamoto (1976)

Rainbow trout ( Salmo             24-h LC50  20          technical   static                                    Cope (1965)
 gairdneri)                       48-h LC50  19          technical   static                                    Anon. (1968)

Steelhead trout                  96-h LC50  17.5        (+)-trans   static   12                               Mauck et al. (1976)
( Salmo gairdneri)                96-h LC50  9.70       (+)-trans   flow-    12                               Mauck et al. (1976)
                                                                    through                                                      
                                                                                                                                
Channel catfish                  96-h LC50  >30.1       (+)-trans   static   12                               Mauck et al. (1976)
( Ictalurus panctatus)            96-h LC50  27.0       (+)-trans   flow-    12                               Mauck et al. (1976)
                                                                    through                                                      
                                 96-h LC50  14.6        (+),(+)-t   flow-    12                               Mauck et al. (1976)
                                                                    through                                                      
                                                                                                                                
Yellow perch ( Perca              96-h LC50  9.90       (+)-trans    flow-    12                               Mauck et al. (1976)
 flavescens)                                                         through                  
                                 96-h LC50  7.80        (+),(+)-t   static   12                               Mauck et al. (1976)

Fathead minnow                   96-h LC50  80.0        (+),(+)-t   static   12                               Mauck et al. (1976)
( Pimephales promelas)            96-h LC50  53.0       (+),(+)-t   flow-    12                               Mauck et al. (1976)
                                                                    through                                                      
--------------------------------------------------------------------------------------------------------------------------------------                                                                                           

Table 4.  (contd.)
--------------------------------------------------------------------------------------------------------------------------------------
Species                Size      Parameter  Concentra-  Formula-   System   Tempera-   pH   Hardness (mg     Reference
                                            tion (g/   tiona               ture (C)       CaCO3/litre)
                                            litre)                                          or salinity (%)
--------------------------------------------------------------------------------------------------------------------------------------
Fish (contd.)               

Bluegill ( Lepomis      0.8 g     96-h LC50  35.0       (+)-trans  static   22         7.5  40 - 80          Mauck et al. (1976)
 macrochirus)           0.8 g     96-h LC50  47.0       (+)-trans  static   17         7.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  56.0        (+)-trans  static   12         7.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  49.0        (+)-trans  static   12         6.6  10 - 13          Mauck et al. (1976)
                       0.8 g     96-h LC50  49.0        (+)-trans  static   12         7.8  160 - 180        Mauck et al. (1976)
                       0.8 g     96-h LC50  42.5        (+)-trans  static   12         8.2  280 - 320        Mauck et al. (1976)
                       0.8 g     96-h LC50  56.0        (+)-trans static    12         6.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  60.0        (+)-trans  static   12         9.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  27.6        (+),(+)-t  static   17         7.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  33.2        (+),(+)-t  static   12         7.5  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  39.0        (+),(+)-t  static   12         6.6  10 - 13          Mauck et al. (1976)
                       0.8 g     96-h LC50  30.0        (+),(+)-t  static   12         7.8  160 - 180        Mauck et al. (1976)
                       0.8 g     96-h LC50  36.0        (+),(+)-t  static   12         8.2  280 - 320        Mauck et al. (1976)
                       0.8 g     96-h LC50  >25.0       (+),(+)-t  static   12         6.6  40 - 48          Mauck et al. (1976)
                       0.8 g     96-h LC50  >25.0       (+),(+)-t  static   12         9.5  40 - 48          Mauck et al. (1976)
                                                                                            
Arthropods

 Sigara substriata      0.59 cm;  48-h LC50  150         technical  static   25                               Nishiuchi (1981)
                       6.1 mg

 Micronecta sedula      0.32 cm;  48-h LC50  420         technical  static   25                               Nishiuchi (1981)
                       1.8 mg
                                                                   
 Cloeon dipterum        0.93 cm;  48-h LC50  350         technical  static   25                               Nishiuchi (1981)
                       5.6 mg

 Orthetrum albistylum   2.3 cm;   48-h LC50  1500        technical  static   25                               Nishiuchi (1981)
 speciosum              0.62 g

 Eretes sticticus       1.5 cm;   48-h LC50  380         technical  static   25                               Nishiuchi (1981)
                       0.2 g
--------------------------------------------------------------------------------------------------------------------------------------

Table 4.  (contd.)
--------------------------------------------------------------------------------------------------------------------------------------
Species                Size      Parameter  Concentra-  Formula-   System   Tempera-   pH   Hardness (mg     Reference
                                            tion (g/   tiona               ture (C)       CaCO3/litre)
                                            litre)                                          or salinity (%)
--------------------------------------------------------------------------------------------------------------------------------------
 Sympetrum frequens     2.1 cm;   48-h LC50  1300        technical  static   25                               Nishiuchi (1981)
                       0.56 g
                       2.1 cm;   48-h LC50  2000        technical  static   15                               Nishiuchi (1981)
                       0.56 g                                                              

 Sympetrum frequens     2.1 cm;   48-h LC50  2000        technical  static   20                                Nishiuchi (1981)
(contd.)               0.56 g
                       2.1 cm;   48-h LC50  850         technical  static   30                                Nishiuchi (1981)
                       0.56 g

 Daphnia pulex                    3-h LC50   > 50 000    technical  static   25                               Miyamoto (1976)
                                 3-h LC50   > 50 000    (+)- cis    static   25                               Miyamoto (1976)
                                 3-h LC50   25 000 -    (+)- trans  static   25                               Miyamoto (1976)
                                            50 000
                                 3-h LC50   5 000 -     (+),(+)-t  static   25                               Miyamoto (1976)
                                            10 000
                                 48-h EC50  21                                                               Sanders & Cope (1966)
                                                                                            
Stonefly ( Pteronarcys            48-h LC50  28          technical                                            Anon. (1968)
 californica)           3-3.5 cm  96-h LC50  2.1         technical  static   15.5       7.1                   Sanders & Cope (1968)
                                                                                            
 Gammarus lacustris               48-h LC50  20                                                               Anon. (1968)
                                 24-h LC50  38                                                               Sanders (1969)

 Simocephalus                     48-h EC50  56                                                               Sanders & Cope (1966)
 serrulatus                                                                                  
--------------------------------------------------------------------------------------------------------------------------------------
a (+),(+)-t = (+)-allethronyl (+)- trans allethrin = S-Bioallethrin.
  (+)- trans = (+)- trans-allethrin = bioallethrin.
  (+)- cis = (+)- cis-allethrin.
Table 5.  Acute toxicity of allethrin for non-target terrestrial organisms
-----------------------------------------------------------------------------------------
Species          Size   Application  Toxicity      Temperature  Reference
                                                   (C)
-----------------------------------------------------------------------------------------
Birds

Mallard          young  oral (in     LD50 > 2000                Tucker & Crabtree (1970)
( Anas                   capsule)     (mg/kg)  
 platyrhynchos) 

Arthropods

Honey-bee ( Apis         contact      LD50 3.4      26 - 27      Stevenson et al. (1978)
 mellifera)                           (g/bee)  

                        oral         LD50 4.6-9.1               Stevenson et al. (1978)
                                     (g/bee)  
-----------------------------------------------------------------------------------------                                                                           
6.  EFFECTS ON EXPERIMENTAL ANIMALS AND  IN VITRO TEST SYSTEMS

6.1   Acute Toxicity

    The acute oral toxicity of allethrin isomers for rats is 
moderate to weak (378 - 2430 mg/kg) (Table 6).  However, allethrin 
injected intravenously in rats or intracerebrally in mice caused 
severe poisoning syndrome with tremors. 

Table 6.  Acute oral toxicity of allethrin isomers
-------------------------------------------------------------------
Compound         Animal  Sex  LD50 (mg/kg  Reference
                              body weight)
-------------------------------------------------------------------
Allethrin        rat     M    2430         Miyamoto (1976)
                 rat     F    720          Miyamoto (1976)
                 rat     M    920          Carpenter et al. (1950)
                 rat     F    900          Carpenter et al. (1950)
                 mouse   M    500          Miyamoto (1976)
                 mouse   F    630          Miyamoto (1976)
                 mouse   M    480a         Carpenter et al. (1950)
                 mouse   F    1580b        Carpenter et al. (1950)
                 rabbit  M    4290         Carpenter et al. (1950)

Bioallethrin     mouse   M    330          Miyamoto (1976)
                 mouse   F    350          Miyamoto (1976)
                 rat     M    709          Audegond et al. (1979a)
                 rat     F    1041         Audegond et al. (1979a)

S-Bioallethrin   rat     M    1290         Miyamoto (1976)
                 rat     F    430          Miyamoto (1976)
                 rat     M    574          Audegond et al. (1979c)
                 rat     F    412          Audegond et al. (1979c)
                 mouse   M    285          Miyamoto (1976)
                 mouse   F    250          Miyamoto (1976)

d- cis-Allethrin  mouse   M    210          Miyamoto (1976)
                 mouse   F    270          Miyamoto (1976)

Esbiothrin       rat     M    432          Audegond et al. (1979b)
                 rat     F    378          Audegond et al. (1979b)
-------------------------------------------------------------------
a  20% in deodorized kerosene.
b  5% in deodorized kerosene.

    When allethrin was applied to shaved skin on the backs of 
Wistar rats (8 females and 6 males/group) or ddY mice (10 females 
and 10 males/group) at dose levels of 2 g/kg body weight or 5 g/kg 
body weight, 8 out of 16 mice treated with 5 g/kg died, but none of 
the rats (Nakanishi et al., 1970). 

    Esbiothrin was applied to the shaved skin of New Zealand white 
male and female rabbits at a level of 2000 mg/kg body weight.  All 
the animals showed erythema and, in some cases, an oedematous 
reaction, but behaviour and body weight gain remained normal.  
There were no compound-related deaths (Kaysen & Sales,1984). 

    The minimum toxic doses of d-allethrin (2-h exposure) and 
S-Bioallethrin (3-h exposure) for rats and mice, exposed to each 
compound in the form of a mist, were:  d-allethrin, rats - 260 
mg/m3, mice - 260 mg/m3, S-Bioallethrin, rats - 24 mg/m3, and mice 
- 91 mg/m3 (Miyamoto, 1976). 

    Wistar male rats were exposed to atmospheres containing 
bioallethrin at 500, 1000, or 2000 mg/m3 for 24 h.  No deaths 
occurred throughout the  trial.  The  no-observed-adverse-effect 
level via inhalation was 1000 mg/m3, which is about 3000 times 
higher than the expected concentration under normal conditions of 
use (Chesher & Malone, 1972a). 

    Wistar male and female rats were exposed to respirable droplets 
of esbiothrin for a period of 4 h.  There was no treatment-related 
change in the number of survivors, but congestion of the lungs was 
found in dead animals.  The LC50 was 2630 mg/m3 (Hardy et al., 
1984). 

    Male and female ICR-JCL mice and Sprague-Dawley rats were 
exposed to S-Bioallethrin in deotomisol via the inhalation route 
for 2 h.  The LC50 was approximately 1500 mg/m3 for mice and more 
than 1650 mg/m3 for rats (Sakamoto et al., 1975c). 

    The acute inhalation toxicity (8 h/day for 3 consecutive days) 
of the smoke from S-Bioallethrin mosquite coils was extremely low 
for ICR mice and Sprague Dawley rats (Ogami et al., 1975).  A smoke 
concentration 60 times that normally found did not induce toxic 
symptoms or death in either the mouse or the rat. 

6.2  Short-Term Studies

6.2.1  Allethrin

    Rats showed a slight decrease in growth rate when fed 
commercial allethrin at a dietary level of 5000 mg/kg, while growth 
rate was nearly normal when the same concentration of purified 
allethrin was administered.  It appeared that a dietary level of 
2500 mg/kg did not produce any clinical effects.  Examination of 
the liver was not reported (Ambrose & Robbins, 1951).  Rats fed 
allethrin for 16 weeks did not show any gross effects at 
5000 mg/kg, but showed tremors and convulsions at 10 000 mg/kg 
(Lehman, 1952). 

    When allethrin was given to Wistar rats at dietary levels of 
1000, 5000, and 15 000 mg/kg for 12 weeks, a decrease in body-
weight gain, an increase in liver or kidney weight ratio, and bile 
ductule proliferation were seen at levels of 5000 mg/kg or more.  
Similar observations were seen when 5000 mg 12 weeks S-Bioallethrin/
kg was administered to Sprague-Dawley rats for (Miyamoto, 1976). 

    Allethrin was administered via gastric intubation to male rats 
(10 animals in each group) at dose levels of 0, 250, 500, or 
1000 mg/kg body weight per day, for 6 days a week over 12 weeks.  

At 1000 mg/kg, half the rats died following the first dose.  No 
abnormal signs were observed in the remaining dosage groups.  
Higher relative weights of liver, thyroid (at 250 and 500 mg/kg), 
and kidney (at 500 mg/kg) were observed.  Histopathological 
examination revealed papillary changes in the epithelium and 
hypertrophy of epithelial cells in the thyroids of rats at both 
250 and 500 mg/kg (Nakanishi et al., 1970). 

    Four male and four female dogs fed allethrin at a rate of 
50 mg/kg per day over 2 years did not show any gross or microscopic 
effects.  Animals in other groups receiving higher doses suffered 
convulsions, survival time was progressively shortened, and non-
specific pathological changes were observed (Lehman, 1965). 

    Rats (and dogs) withstood repeated inhalation of allethrin 
aerosols in air at a concentration several times higher than levels 
normally used.  However, because of the method of administration, 
it was not possible to measure intake as mg/kg body weight 
(Carpenter et al., 1950). 

    Eight female mice inhaled allethrin at a level of 3 g/m3 for 
4 h/day, 6 days a week, over 4 weeks.  No deaths were observed.  
Eye discharge was seen in all animals after each exposure 
throughout the 4-week period.  A slight, sporadic decrease in 
activity was found from the third week.  Histopathological 
examination of the lungs of 5 mice showed bronchopneumonia 
(Nakanishi et al., 1970). 

6.2.2  d-Allethrin

    A 90-day toxicity study was conducted on Wistar rats (male and 
female) fed diets containing d-allethrin at 0, 750, 2000, or 
4000 mg/kg.  Increased liver weight was observed in animals 
receiving 2000 mg/kg or more and glutamine-oxaloacetic- and 
glutamine-pyruvic acid transaminase activities were raised in those 
receiving 4000 mg/kg. 

    The no-observed-adverse-effect dietary level for d-allethrin 
was 750 mg/kg diet (49.6 mg/kg body weight per day for male mice 
and 59.2 mg/kg per day for females) (Kadota, 1972). 

    ICR mice and Sprague-Dawley rats (both male and female) were 
exposed to a mist (particle diameter 1 - 2 m, generated by means 
of atomizer) of d-allethrin (123 mg/m3) or S-Bioallethrin (6.1, 
16.9, or 61.3 mg/m3) for 3 h per day, 5 days per week, over 4 weeks 
(Miyamoto, 1976).  Mortality rates, behaviour, body and organ 
weights, haematology, clinical biochemistry, and histopathology of 
the organs were examined.  Toxic symptoms, such as salivation and 
tremors, were found only in groups administered d-allethrin at 
123 mg/m3 and S-Bioallethrin at 61.3 mg/m3. 

    In a study by Kadota et al. (1974), ICR mice and Sprague- 
Dawley rats were exposed to the smoke of mosquito coils containing 
0.3% d-allethrin, at 20 times the conventional rate of application 

(10 coils/24 m3), in a closed room for 8 h/day, 6 days/week over 
5 weeks.  There were no effects on body and organ weights, food 
consumption, haematology, blood biochemistry, or histopathology. 

6.2.3  Bioallethrin

    Bioallethrin was given to groups of Wistar rats (16 males and 
16 females) for 90 consecutive days at concentrations of 500, 1500, 
5000, or 10 000 mg/kg diet (Wallwork et al., 1972).  No marked 
adverse effects were observed, except for a slight to moderate 
decrease in body weight gain and slight liver dysfunction,  
observed in the groups receiving 5000 and 10 000 mg/kg, 
respectively.  No dose-related macroscopic or microscopic changes 
were observed.  The no-observed-adverse-effect level for 
bioallethrin in rats, after 90 days of treatment, was 1500 mg/kg 
diet  (equivalent to an intake of about 135 mg/kg body weight per 
day). 

    Dogs were administered bioallethrin in the diet at 
concentrations of 200, 1000, or 5000 mg/kg for 6 months (Griggs et 
al., 1982).  No animals died during the study.  General body 
trembling and irregular heart rhythm were noted at the highest dose 
level.  Body-weight gain was slightly reduced in males receiving 
1000 mg/kg diet and in both sexes receiving 5000 mg/kg.  Consistent 
elevation in the mean levels of alkaline phosphatase was noted at 
1000 and 5000 mg/kg in males, at 5000 mg/kg in females, and an 
elevated SGPT at 5000 mg/kg was observed in both males and 
females.  No compound-related macroscopic changes were observed.  
Histological investigation revealed hepatocellular degeneration in 
both males and females in the groups receiving 1000 and 5000 mg/kg.  
This was associated with intracanalicular and hepatocellular 
pigmentation.  Similar pigmentation was seen within the tubular 
epithelium of the renal cortex.  The no-observed-adverse-effect 
level in this study was 200 mg/kg diet (equivalent to an intake of 
6.1 and 7.2 mg/kg (1.6 ml) per day for males and females, 
respectively). 

    No marked drug-related changes were observed in Wistar male 
rats exposed through continuous inhalation to a concentration of 
125 mg bioallethrin/m3 air, for 10 consecutive days (Chesher & 
Malone, 1972b). 

6.2.4  S-Bioallethrin

    Groups of 10 Wistar rats (5 males and 5 females) were given 
S-Bioallethrin in the diet for 90 days; groups of 20 animals 
(10 males and 10 females) received S-Bioallethrin for 180 days 
(Motoyama et al., 1975a).  Males received S-Bioallethrin at dietary 
levels of 3, 1, 0.3, or 0.1 g/kg, and females, at 1.5, 0.3, 0.1, or 
0.05 g/kg.  The differences in the doses between the sexes were due 
to the results of an acute toxicity study in which the LD50 for 
males was about 300 mg/kg and that for females, about 170 mg/kg.  
Abnormal symptoms were not observed, and deaths did not occur in 
either study.  No macroscopic abnormal changes were observed.  
Histological investigation did not show any compound-related 

lesions, only scattered changes, which also occurred in the 
untreated groups and did not show any regular tendency.  
S-Bioallethrin did not induce any toxic effects in the males 
receiving the highest dose (3 g/kg) or in the females receiving the 
highest dose of 1.5 g/kg.  The calculated doses of S-Bioallethrin 
for the males were about 330 mg/kg body weight in the early stages 
of the study and 200 mg/kg body weight in the later stages; the 
females received about 120 and 100 mg/kg body weight. 

    JLC-ICR mice and Sprague-Dawley rats were exposed for 2 h/day, 
6 days a week, for a month to concentrations of S-Bioallethrin in 
deotomisol of 20 mg/m3, 80 mg/m3, or 160 mg/m3.  The lowest 
concentration was well tolerated.  At 80 mg/m3 and 160 mg/m3, toxic 
signs, such as excitation, tail raising, jumping, salivation, and 
slight trembling occurred in the mice and slight salivation and 
nasal haemorrhage, in the rats.  No changes were observed in 
haematological and biochemical tests or microscopically.  
S-Bioallethrin seemed to be more toxic in the mouse (1 death/24 at 
80 mg/m3 and 4 deaths/24 at 160 mg/m3) than in the rat (no deaths) 
(Sakamoto et al., 1975d). 

    In a further study by Sakamoto et al. (1975b), JCL-ICR mice and 
JCL Sprague-Dawley rats were exposed for 8 h/day, 6 days a week, 
for 5 weeks to the smoke containing S-Bioallethrin emitted from  
5 or 10 mosquito coils per 9.9 m2 room area.  The atmospheric 
concentrations produced were more than 10 or 20 times greater than 
would be found under normal conditions of use.  Toxic effects were 
not observed in either the mouse or the rat and there were no 
deaths.  The results indicate that the short-term inhalation 
toxicity of the fumes from S-Bioallethrin mosquito coils is 
extremely low (Sakamoto et al., 1975b). 

    Two studies with an S-Bioallethrin electric mosquito mat were 
performed on mice.  Animals were exposed for 8 h per day, 6 days a 
week over 4 weeks, to fumes that were 25 or 10 times  the 
concentration normally used.  As treated animals in the first study 
showed encephalitis, a second study was performed to check whether 
the pathological changes were a specific effect of the product or a 
viral infection.  Encephalitis did not occur in any of the treated 
animals (160 animals treated instead of 40) in the second study.  
Slight circulatory disorders in the brain and lungs and slight 
inflammation of the lungs were observed only in animals exposed to 
25 times the normal concentration.  The possibility that 
encephalitis was a specific effect of S-Bioallethrin was therefore 
dismissed (Tsuchiyama et al., 1975). 

6.3  Primary Irritation

6.3.1  Eye irritation

    Two solutions of allethrin dissolved in olive oil (10% and 50%) 
were prepared.  One tenth ml of solution was applied to one eye of 
each test rabbit.  Both dosages of allethrin produced eyelid-
closure, slight conjunctival hyperaemia at 10 and 30 min, 
respectively, after application, and eye discharge 2 h after 

application.  Lachrymation was also observed in the group treated 
with the 50% solution from 0.5 to 2 h after application (Nakanishi 
et al., 1970). 

    The effects of 0.1 ml undiluted esbiothrin were evaluated in 9 
male albino New Zealand rabbits using the Draize test method and 
classified according to irritation potential by the Kay and 
Calandra scale, as modified by Guillot (Audegond et al., 1984b).  
The compound was classified as slightly irritant in both rinsed and 
unrinsed eyes. 

    When 0.1 ml undiluted S-Bioallethrin and 0.1 ml 50% solution of 
S-Bioallethrin in corn oil were applied to the eyes of male 
Japanese white rabbits, only slight eye irritation occurred 
(Sakamoto et al., 1975a).  Symptoms included nictitation, 
hyperaemia of the conjunctiva, and tears.  No abnormalities of the 
iris or cornea were observed. 

6.3.2  Skin irritation

    Undiluted technical allethrin (0.5 ml) or a 20% solution in 
olive oil (2.5 ml) were applied to the dorsal skin of rabbits.  No 
differences were observed between allethrin-treated rabbits and the 
untreated controls (Nakanishi et al., 1970). 

    The dermal irritancy of a mixture of 4% bioallethrin and 20% 
piperonyl butoxide in an odourless petroleum distillate was 
evaluated on the intact and abraded skin of 3 California female 
rabbits, using the Draise test method.  Virtually no reaction was 
produced on the intact skin, but increases in the degree of 
erythema and the duration of reaction were observed on the abraded 
skin.  However, by 6 days, all treated sites were normal.  Thus, 
bioallethrin was classified as mildly irritating on abraded skin 
(Vercoe & Malone, 1969). 

    In a similar study, the dermal irritancies of bioallethrin and 
of esbiothrin were determined on the intact and abraded skin of the 
rabbit, according to the Draize method (Motoyama et al., 1975b).  
Both compounds were found to be slightly irritant. 

    The primary dermal irritancy of a 5 ml dose of esbiothrin was 
evaluated over a 7-day test period on the intact and abraded skin 
of 6 male, albino New Zealand rabbits using the Draise test method.  
An increase in the degree of erythema was observed in both the 
intact and abraded skin, but by 7 days all treated sites were 
normal.  Thus, esbiothrin was classified as slightly irritant 
(Audegond et al., 1984a). 

    In a study by Motoyama et al. (1975b), the primary dermal 
irritancy of S-Bioallethrin was evaluated for 72 h on the intact 
skin of 5 male and 5 female Wistar rats and 3 groups of 3 male and 
3 female Nagano white rabbits.  The doses administered to the rats 
included undiluted S-Bioallethrin and dilutions of 5 or 25 times in 
corn oil.  The doses administered to the rabbits included undiluted 

S-Bioallethrin and dilutions of 10 or 100 times in corn oil.  No 
changes were observed in the dermis of either the rat or the 
rabbit, at any dose level. 

    S-Bioallethrin produced mild primary irritation of the intact 
skin and the skin surrounding an abrasion in New Zealand white 
rabbits (details of the study not given in the report) (Fisch, 
1974). 

6.4  Sensitization

    One half ml of a 5% olive oil solution of allethrin was applied 
topically to the backs of male guinea-pigs, every other day, 10 
times.  Two weeks after the last application, the animals were 
challenged with a similar application of allethrin.  Only a 
sporadic pinkish colour was observed (same degree as vehicle 
control) at the site of application.  Histopathological examination 
revealed slight lymphocytic and monocytic infiltration of the 
dermis in the allethrin-treated group (Nakanishi et al., 1970). 

    The sensitizing properties of a 10% solution of bioallethrin in 
petroleum distillate were evaluated in the Stevens ear-flank test 
in 2 groups of 10 male albino guinea-pigs (Saunders & Vercoe, 
1970).  Bioallethrin did not produce any irritation, but produced 
slight sensitization. 

6.5  Long-term Studies and Carcinogenicity

    When Wistar rats were exposed to racemic allethrin (dietary 
levels of 500, 1000, or 2000 mg/kg) for 80 weeks, bile duct 
proliferation was seen at levels of 1000 mg/kg or more and a 
decrease in glutamine-oxaloacetic acid transaminase activity was 
seen at 2000 mg/kg.  However, no oncogenic effects were observed at 
any dose level (Miyamoto, 1976). 

    F344  rats  (male and female) were fed diets containing 
d-allethrin at 0, 125, 500, or 2000 mg/kg for 123 weeks.  Reduced 
body weight and increased liver and kidney weights were observed at 
levels exceeding 500 mg/kg and the activities of glutamine-
oxaloacetic- and glutamine-pyruvic acid transaminase and alkaline 
phosphatase decreased at these levels.  Histopathological 
examination showed histiocytes phagocyting crystals in the liver of 
animals fed levels of 500 mg/kg or more, but no oncogenic effects 
were observed at any dose level.  The no-observed-adverse-effect 
level was 125 mg/kg, i.e., 5.9 mg/kg body weight per day (male) and 
6.6 mg/kg per day (female) (Sato et al., 1985). 

6.6  Mutagenicity and Related End-Points

    The mutagenic potential of allethrin has been examined in a 
wide range of tests including  in vitro/in vivo gene mutation, DNA 
damage and repair, and  in vitro/in vivo structural chromosomal 
aberration (Suzuki, 1975; Miyamoto, 1976; Suzuki, 1979; Kawachi et 
al., 1979; Kishida & Suzuki, 1979; Matsuoka et al., 1979; Hara & 
Suzuki, 1980; Sasaki et al., 1980; Kimmel et al., 1982; Garret et 

al., 1986).  The results of all tests were negative with the 
exception of a gene mutation  Salmonella typhimurium study with 
metabolic activation and a chromosomal aberration study on Chinese 
hamster cells (Matsuoka, et al., 1979; Kimmel et al., 1982).  Both 
studies are considered inadequate because, in the gene mutation 
study the results were found to be attributable to photoproducts in 
improperly stored samples and, in the second study, the purity of 
the test material was not identified (Isobe et al., 1982, 1984). 

    Bioallethrin and esbiothrin were also tested for mutagenicity 
in both  in vitro mammalian test systems, the micronucleus test 
system, and microbial assays and found to be negative (Peyre et 
al., 1979; Chantot & Vannier, 1984; Richold et al., 1984; Vannier & 
Fournex, 1984). 

6.7  Reproductive Effects, Embryotoxicity, and Teratogenicity

    When allethrins were administered to ICR mice during gestation 
to examine maternal and embryotoxic effects (Table 7),  no 
significant adverse effects, such as abortion or resorption of the 
fetus or embryo, external or skeletal abnormalities of pups, or 
abnormalities in growth and organ differentiation, were observed at 
the doses tested (Miyamoto, 1976). 

Table 7.  Teratological studies on allethrins isomers
-------------------------------------------------------------------
Compound        Animalsa  Dose mg/kg   Route  Administration
                          body weight         (days of gestation)
                          per day  
-------------------------------------------------------------------
d-Allethrin     mouse     15,50,150    oral   7-12
S-Bioallethrin  mouse     10,30,100    oral   7-12
-------------------------------------------------------------------
a Includes breeding of naturally delivered offspring.

    Allethrin in corn oil was administered daily, by oral 
intubation, to pregnant albino rabbits from day 6 to day 18 of 
gestation at levels of 0 mg/kg (controls - corn oil only), 215 
mg/kg (low level), and 350 mg/kg (high level).  There were no 
indications of compound related effects among the test animals, 
which were similar to the controls in appearance, behaviour, body 
weight gain, and food consumption; necropsy findings were also 
similar. 

    The number of implantation sites compared with the number of 
ovarian corpora lutea observed was similar in the pregnant animals 
in control, low-dose, and high-dose groups.  The number and 
placement of implantation sites, the resorption sites, the numbers 
of live and dead fetuses, and the fetal weights and lengths were 
also similar in the control and test animals.  Fetal skeletal 
evaluations did not reveal any compound-related abnormalities or 
trends towards lesser or greater development in the test fetuses 
compared with the controls.  Pups, of low- and high-dose animals, 
delivered naturally, were similar in appearance, external 

morphology, and behaviour.  No compound-related observations were 
found during the post-delivery period (40 days) or at necropsy of 
the pups (Weatherholtz, 1972). 

    Bioallethrin was administered orally to pregnant Sprague- 
Dawley rats from day 6 to day 15 of gestation at levels of 50, 125, 
or 195 mg/kg body weight per day (Knickerbocker & Thomas, 1979).  
At 195 mg/kg, maternal mortality was increased, but there were no 
effects on dam body weight or weight gain during gestation.  The 
compound did not have any effects on pregnancy, implantations, 
number of live fetuses, number of dead fetuses, or number of 
resorption sites per dam.  Skeletal examination of fetuses revealed 
a significant increase in the number of litters with rudimentary 
14 ribs at 50, 125, and  195 mg/kg as well as missing sternebrae at 
50 mg/kg.  However, these abnormalities were generally variations 
rather than malformations.  No soft-tissue abnormalities were 
ascribed to treatment. 

    S-Bioallethrin was administered to pregnant Wistar rats from 
day 9 to day 14 of gestation at the following doses:  0.025, 0.05, 
0.1, or 0.2 ml/kg body weight (Shinoda et al., 1975).  The 
mortality rate at the dose of 0.2 ml/kg was 55%; at 0.01 and 0.05 
ml/kg, the mortality rates were 4 and 5%, respectively.  There were 
no differences between the control and treated groups in the 
numbers of implantations and live fetuses, and the frequency of 
fetal death.  The weights of live fetuses and the placenta from the 
group administered 0.2 ml/kg were lower than those of the control 
group.  Fetal and placental weights in the groups receiving 0.1, 
0.05, or 0.025 ml/kg were almost the same as those in the control 
group.  External abnormalities consisted of a cleft palate in one 
fetus and a decreased number of digits in 7 fetuses from the same 
pregnant dam (0.2 ml/kg).  Skeletal abnormalities included lumbar 
transforming into thoracic vertebrae and insufficient ossification 
of the 5th sternebra; they were frequently observed in all groups 
but appeared to be dose-related.  Some other abnormalities observed 
in a small number of fetuses from the treated groups included 
partial fusion of the cervical vertebrae or of vertebrae arches and 
ribs in the same fetuses in the 0.2 ml/kg group.  Because of their 
low frequency, these abnormalities could not be attributed to 
treatment.  In conclusion, S-Bioallethrin did not seem to induce 
any disorders in the fetuses of pregnant rats administered doses 
equal to or lower than 0.1 ml/kg, although some variations were 
observed at the 0.2 mg/kg level. 

    Shinoda et al. (1975) also administered S-Bioallethrin orally 
at 0.05, 0.1, or 0.2 ml/kg to pregnant TVCS mice from day 7 to day 
12 of gestation.  The mortality rate at 0.2 ml/kg was 40% and 
pregnancy was maintained in only one dam.  Some toxic symptoms were 
observed at 0.1 ml/kg, and the mortality rate was 7%.  The numbers 
of implantations and of viable fetuses, the sex ratio, placental 
and fetal weights in groups treated with 0.1 or 0.05 ml/kg, did not 
differ from those of the control group.  External examination 
revealed that 2 fetuses from the 0.1 ml/kg treated group had cleft 
palates; one of them had hydrocephaly.  These abnormalities could 
not be attributed to treatment because of their very low incidence 

and the presence in the control group of one fetus with an 
abdominal hernia and one with a cleft palate.  There were not any 
skeletal abnormalities that could be related to treatment.  In 
conclusion, at the maximum tolerated doses of S-Bioallethrin of 0.1 
ml/kg and 0.05 ml/kg, no lethal effects occurred in the embryos or 
fetuses and no teratogenic effects were observed. 

6.8  Potentiation

    Potentiation of toxicity between bioallethrin and piperonyl 
butoxide was studied by the intraperitoneal route in the rat 
(Wallwork & Malone, 1969).  The degree of potentiation between the 
2 compounds was very low. 

6.9  Mechanism of Toxicity - Mode of Action

    The toxic effects of allethrin result from its action on the 
nervous system.  After intravenous injection with a lethal dose of 
bioallethrin (4 mg/kg body weight), initial tremors were followed 
by death within 20 min.  Hyperexcitation and tremors usually 
developed a few minutes after application (Verschoyle & Barnes, 
1972; Carlton, 1977; Wouters & Van den Bercken, 1978; Verschoyle & 
Aldridge, 1980; Lawrence & Casida, 1982).  Signs of poisoning in 
vertebrates, including mammals, are similar to those in insects 
(see Appendix). 

    Signs of poisoning in insects generally include 
hyperexcitation, tremors, and convulsions, followed later by 
paralysis and death.  Narahashi (1969, 1971) examined signs of 
poisoning electrophysiologically using the giant axon of the 
cockroach.  Allethrin caused an increase in negative after- 
potential, repetitive discharge (or repetitive firing) following 
electrical stimulation, and a conduction block, presumably by 
allethrin binding to sodium channels.  Good correlations existed in 
cockroaches between the signs induced by allethrin and effects on 
the nervous system.  Restless behaviour, without a loss of 
coordination, was correlated with repetitive discharge of cercal 
sensory neurons, whereas the onset of uncoordinated behaviour 
coincided with the appearance of abnormal discharges, not only in 
cercal sensory neurons but also in motor neurons and the central 
nervous system (CNS) (Gammon, 1979).  Temperature had a profound 
effect on allethrin-induced repetitive discharges and its nerve-
blocking action.  In the giant axon of the cockroach treated with 
allethrin, repetitive discharges appeared at over 26.5 C and 
increased with rise in temperature.  Conversely, allethrin blocked 
the action potential of the squid and cockroach giant axons more 
strongly at 8 C than at 23 C (Wang et al., 1972).  The negative 
temperature coefficient of the nerve-blocking action of allethrin 
appears to be responsible for a greater killing effect on insects, 
and is in sharp contrast with the positive temperature coefficient 
discharges, which may be responsible for knock-down of repetitive 
(Wang et al., 1972; Starkus & Narahashi, 1978).  When the 
temperature was reduced from 23 to 8 C in the voltage clamp 
analysis, the inhibition of the transient sodium conductance and 

the shift of the sodium conductance curve along the potential axis 
in the direction of hyperpolarization were both increased, causing 
a greater blocking of action potential (Narahashi, 1976). 

    However, it has been reported that the peripheral nerves of the 
rat and the frog were fairly insensitive to the blocking action of 
allethrin, and it was tentatively suggested that the nerve 
membranes of vertebrates were less susceptible to the neurotoxic 
action of allethrin than those of invertebrates.  Allethrin causes 
a depolarizing after-potential following the action potential and 
induces pronounced repetitive firing in myelinated nerve fibres and 
in the sense organs of frogs.  In the frog peripheral nervous 
system, virtually no blocking effect of allethrin occurs, except at 
very high concentrations (Van den Bercken et al., 1979). 

    The sodium channel gating model was proposed by Van den Bercken 
& Vijverberg (1980).  The state of the sodium channel is controlled 
by 2 independent gates called the activation gate (or m-gate) and 
the inactivation gate (or h-gate), both of which are dependent on 
the membrane potential, but in opposite ways.  The action of 
allethrin has been thought to stabilize the m-gate in its open 
position. 

    Pyrethroids were classified into 2 classes based on the signs 
and symptoms produced by acutely-toxic doses in mammals (Verschoyle 
& Aldridge, 1980; Lawrence & Casida, 1982) and on the 
neurophysiological responses in cockroaches (Gammon et al., 1981).  
Type I syndrome involves hyperactivity and tremor in both insects 
and mammals.  Type II syndrome involves hyperactivity, 
incoordination, and convulsions in insects, and clonic seizures 
with sinuous writhing (choreoathetosis) in mammals.  Allethrin is 
classified as a Type I compound. 

    Interactions of allethrin with the nicotinic acetylcholine 
(ACh) receptor channel were studied in membranes from the  Torpedo 
electric organ (Abbassy et al., 1982).  Allethrin did not inhibit 
binding of [3H]-ACh to the receptor sites, but noncompetitively 
inhibited binding of [3H] perhydrohistrionico-toxin ([3H]H12-HTX) 
to the ionic channel sites in a dose-dependent manner.  The 
inhibition constant (Ki) of [3H]H12-HTX binding in the absence of 
receptor agonists was 30 mol/litre while, in the presence of 
100 mol carbamylcholine/litre, it was 4 mol/litre.  This 
inhibitory effect of allethrin had a negative temperature 
coefficient.  The high affinity binding of allethrin to the channel 
sites of the nicotinic ACh-receptor may be indicative of a 
postsynaptic site of action for allethrin, in addition to the known 
action on the sodium channel. 

    The mechanism of interaction of the 2 pyrethroids, allethrin 
and fluvalinate, with the nicotinic acetylcholine (ACh) receptor 
was investigated by means of their effects on the binding of 
radioligands to the  Torpedo electric organ receptor and tracer ion 
flux.  The data suggest that allethrin and fluvalinate bind to 
sites on the nicotinic ACh-receptor that are quite distinct from 
the receptor site and the ionic channel sites where noncompetitive 

blockers (e.g., [3H]H12HTX) bind.  Such pyrethroids may be binding 
to sites that normally bind Ca2+ and induce receptor 
desensitization.  The data imply that modulation of the nicotinic 
ACh-receptor in insect ganglia may be involved in the mode of 
action of pyrethroids (Sherby et al., 1986). 

7.  EFFECTS ON MAN

    No data were available to the Task Group on the effects of 
allethrins on man.  However, allethrins have been used for many 
years and no toxic effects on human beings have been reported. 

8.  EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT

8.1  Evaluation of Human Health Risks

    Allethrin, consisting of 8 stereo-isomers, is an effective 
insecticide mainly used to control household insects. 

    d-Allethrin, bioallethrin, esbiothrin, and S-Bioallethrin are 
also available as selected stereo-isomers or mixtures thereof.  It 
is anticipated that human exposure will be mainly through the 
inhalation of mists from aerosol sprays and from other household 
uses, such as the electric mat and mosquito coil.  The air level 
following conventional household aerosol spraying of allethrin is 
not expected to exceed 0.5 mg/m3.  Air levels of individual isomers 
are expected to be lower under similar conditions of use. 

    Although the levels of allethrins in food have not been 
determined, on the basis of current use patterns, it is unlikely 
that such dietary exposure will be significant. 

    No data are available on occupational exposure to the 
allethrins.  In fact, though they have been used for many years, no 
data have been reported on their toxicity for human beings.  Thus, 
extrapolation of data from experimental animals and  in vitro 
studies must be relied on. 

    The results of short-term studies on experimental animals 
suggest that allethrins are weakly to moderately toxic (oral or 
dermal LD50 values of 210 - 4290 mg/kg; inhalation LC50 value 
of > 1500 mg/m3). 

    Allethrins induce mild primary eye and skin irritation in 
rabbits, but no skin sensitization. 

    The short-term toxicities of S-Bioallethrin and d-allethrin 
appear to be low, according to several inhalation studies (mosquito 
coil and mat) on mice and rats at a range of dose levels (10, 20, 
or 25 times normal concentration used). 

    The allethrins are not mutagenic in a variety of test systems 
including gene mutations, DNA damage and repair, and chromosomal 
effects. 

    d-Allethrin was not carcinogenic for rats fed diets containing 
2000 mg/kg over 2 years. 

    Relatively high doses of allethrin, bioallethrin, or 
S-Bioallethrin were neither embryotoxic nor teratogenic for 
rabbits, rats, or mice.  No adequate reproduction studies have been 
reported. 

    At near lethal doses, allethrins are likely to cause 
hyperactivity, tremors, and convulsions and have been classified as 
Type I pyrethroids. 

    No-observed-adverse-effect levels were established for 
bioallethrin in a 90-day rat study and a 6-month study on dogs 
(1500 mg/kg diet, 200 mg/kg diet, respectively, corresponding to 
135 mg/kg body weight and 6.1 - 7.2 mg/kg body weight, 
respectively).  In a 2-year study on rats, the no-observed- 
adverse-effect level for dietary administration of allethrin was 
125 mg/kg, i.e., 5.9 and 6.6 mg/kg body weight per day for male and 
female rats, respectively. 

8.2  Evaluation of Effects on the Environment

    Allethrins are primarily used indoors, but no information is 
available on levels in the environment.  They are rapidly 
decomposed when exposed to sunlight and at temperatures exceeding 
400 C, but vaporize with slow heating at 150 C. 

    Allethrins  are  toxic  for  fish  with  LC50 values of 9 - 90 
g/litre, but less toxic for  Daphnia and aquatic insect larvae 
(150 - 50 000 g/litre).  Toxicity is low for birds (LD50 > 2000 
mg/kg),  but  high  for  honey-bees  (LD50 3 - 9 g/bee). 

9.  CONCLUSIONS

 General population:  Under recommended conditions of use, the 
exposure of the general population to allethrins is negligible and 
is unlikely to present a hazard. 

 Occupational exposure:  With reasonable work practices, hygiene 
measures, and safety precautions, the use of allethrins is unlikely 
to present a hazard to those occupationally exposed to them. 

 Environment:  Under recommended conditions of use and application 
rates, it is unlikely that allethrins or their degradation products 
will attain significant levels in the environment.  In spite of the 
high toxicity of these compounds for fish and honey-bees, they are 
only likely to cause a problem in the case of spillage or misuse. 

10.  RECOMMENDATIONS

-    Over 25 years of use, no adverse effects have been reported to 
     arise from human exposure to allethrins, but it is still 
     necessary to continue observations on human exposure. 

-    To improve the overall assessment of the potential 
     reproductive effects and potential carcinogenic effects of the 
     allethrins, it is suggested that consideration should be given 
     to conducting an appropriate multigeneration study and another 
     carcinogenicity study on a second species. 

-    The label for the household use of allethrins should include 
     adequate instructions for use and storage and, where 
     appropriate, warning of flammability. 

-    Efforts should be made to obtain a more precise estimate of 
     the total global usage of allethrins. 


 
11.  PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

    The Joint FAO/WHO Meeting on Pesticide Residues (JMPR) 
discussed and evaluated allethrin in 1965 (FAO/WHO, 1965).  It did 
not establish an ADI for allethrin, because data from long-term 
studies were not available. 

    The Pesticide Development and Safe Use Unit, Division of Vector 
Biology and Control, WHO, classified the acute hazard to health for 
technical allethrin as slight and for technical bioallethrin as 
moderate (WHO, 1986). 

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APPENDIX

    On the basis of electrophysiological studies with peripheral 
nerve preparations of frogs  (Xenopus laevis; Rana temporaria, and 
 Rana esculenta), it is possible to distinguish between 2 classes of 
pyrethroid insecticides: (Type I and Type II).  A similar 
distinction between these 2 classes of pyrethroids has been made on 
the basis of the symptoms of toxicity in mammals and insects (Van 
den Bercken et al., 1979; WHO, 1979; Verschoyle & Aldridge, 1980; 
Glickman & Casida, 1982; Lawrence & Casida, 1982).  The same 
distinction was found in studies on cockroaches by Gammon et al. 
(1981). 

    Based on the binding assay on the gamma-aminobutyric acid 
(GABA) receptor-ionophore complex, synthetic pyrethroids can also 
be classified into two types:  the alpha-cyano-3-phenoxy-benzyl 
pyrethroids and the non-cyano pyrethroids (Gammon et al., 1982; 
Gammon & Casida, 1983; Lawrence & Casida, 1983; Lawrence et al., 
1985). 

 Pyrethroids that do not contain an alpha-cyano group (allethrin, 
 d-phenothrin, permethrin, tetramethrin, cismethrin, and 
 bioresmethrin)  (Type I: T-syndrome) 

    The pyrethroids that do not contain an alpha-cyano group give 
rise to pronounced repetitive activity in sense organs and in 
sensory nerve fibres (Van den Bercken et al., 1973).  At room 
temperature, this repetitive activity usually consists of trains of 
3 - 10 impulses and occasionally up to 25 impulses.  Train duration 
is between 10 and 5 milliseconds. 

    These compounds also induce pronounced repetitive firing of the 
presynaptic motor nerve terminal in the neuromuscular junction (Van 
den Bercken, 1977).  There was no significant effect of the 
insecticide on neurotransmitter release or on the sensitivity of 
the subsynaptic membrane or the muscle fibre membrane.  Presynaptic 
repetitive firing was also observed in the sympathetic ganglion 
treated with these pyrethroids. 

    In the lateral-line sense organ and in the motor nerve 
terminal, but not in the cutaneous touch receptor or in sensory 
nerve fibres, the pyrethroid-induced repetitive activity increases 
dramatically as the temperature is lowered, and a decrease of 5 C 
in temperature may cause a more than 3-fold increase in the number 
of repetitive impulses per train.  This effect is easily reversed 
by raising the temperature.  The origin of this "negative 
temperature coefficient" is not clear (Vijverberg et al., 1983). 

    Synthetic pyrethroids act directly on the axon through 
interference with the sodium channel gating mechanism that 
underlies the generation and conduction of each nerve impulse.  
The transitional state of the sodium channel is controlled by 2 
separately acting gating mechanisms, referred to as the activation 
gate and the inactivation gate.  Since pyrethroids only appear to 
affect the sodium current during depolarization, the rapid opening 

of the activation gate and the slow closing of the inactivation 
gate proceed normally.  However, once the sodium channel is open, 
the activation gate is restrained in the open position by the 
pyrethroid molecule.  While all pyrethroids have essentially the 
same basic mechanism of action, the rate of relaxation differs 
substantially for the various pyrethroids (Flannigan & Tucker, 
1985). 

    In the isolated node of Ranvier, allethrin causes prolongation 
of the transient increase in sodium permeability of the nerve 
membrane during excitation (Van den Bercken & Vijverberg, 1980).  
Evidence so far available indicates that allethrin selectively 
slows down the closing of the activation gate of a fraction of the 
sodium channels that open during depolarization of the membrane.  
The time constant of closing of the activation gate in the 
allethrin-affected channels is about 100 milliseconds compared with 
less than 100 microseconds in the normal sodium channel, i.e., it 
is slowed down by a factor of more than 100.  This results in a 
marked prolongation of the sodium current across the nerve membrane 
during excitation, and this prolonged sodium current is directly 
responsible for the repetitive activity induced by allethrin 
(Vijverberg et al., 1983). 

    The effects of cismethrin on synaptic transmission in the frog 
neuromuscular junction, as reported by Evans (1976), are almost 
identical to those of allethrin, i.e., presynaptic repetitive 
firing, and no significant effects on transmitter release or on the 
subsynaptic membrane. 

    Interestingly, the action of these pyrethroids closely 
resembles that of the insecticide DDT in the peripheral nervous 
system of the frog.  DDT also causes pronounced repetitive activity 
in sense organs, in sensory nerve fibres, and in motor nerve 
terminals, due to a prolongation of the transient increase in 
sodium permeability of the nerve membrane during excitation.  
Recently, it was demonstrated that allethrin and DDT have 
essentially the same effect on sodium channels in frog myelinated 
nerve membrane.  Both compounds slow down the rate of closing of a 
fraction of the sodium channels that open on depolarization of the 
membrane (Van den Bercken et al., 1973, 1979; Vijverberg et al., 
1982b). 

    In the electrophysiological experiments using giant axons of 
crayfish, the Type I pyrethroids and DDT analogues retain sodium 
channels in a modified open state only intermittantly, cause large 
depolarizing after-potentials, and evoke repetitive firing with 
minimal effect on the resting potential (Lund & Narahashi, 1983). 

    These results strongly suggest that permethrin and cismethrin, 
like allethrin, primarily affect the sodium channels in the nerve 
membrane and cause a prolongation of the transient increase in 
sodium permeability of the membrane during excitation. 

    The effects of pyrethroids on end-plate and muscle action 
potentials were studied in the pectoralis nerve-muscle preparation 
of the clawed frog  (Xenopus laevis).  Type I pyrethroids 
(allethrin, cismethrin, bioresmethrin, and 1R,  cis-phenothrin) 
caused moderate presynaptic repetitive activity, resulting in the 
occurrence of multiple end-plate potentials (Ruigt & Van den 
Bercken, 1986). 

 Pyrethroids with an alpha-cyano group on the 3-phenoxybenzyl 
 alcohol (deltamethrin, cypermethrin, fenvalerate, and fenpropanate) 
 (Type II: CS-syndrome) 

    The pyrethroids with an alpha-cyano group cause an intense 
repetitive activity in the lateral-line organ in the form of long-
lasting trains of impulses (Vijverberg et al., 1982a).  Such a 
train may last for up to 1 min and contains thousands of impulses.  
The duration of the trains and the number of impulses per train 
increase markedly on lowering the temperature.  Cypermethrin does 
not cause repetitive activity in myelinated nerve fibres.  Instead, 
this pyrethroid causes a frequency-dependent depression of the 
nervous impulse, brought about by a progressive depolarization of 
the nerve membrane as a result of the summation of depolarizing 
after-potentials during train stimulation (Vijverberg & Van den 
Bercken, 1979; Vijverberg et al., 1983). 

    In the isolated node of Ranvier, cypermethrin, like allethrin, 
specifically affects the sodium channels of the nerve membrane and 
causes a long-lasting prolongation of the transient increase in 
sodium permeability during excitation, presumably by slowing down 
the closing of the activation gate of the sodium channel 
(Vijverberg & Van den Bercken, 1979; Vijverberg et al., 1983).  The 
time constant of closing of the activation gate in the 
cypermethrin-affected channels is prolonged to more than 100 
milliseconds.  Apparently, the amplitude of the prolonged sodium 
current after cypermethrin is too small to induce repetitive 
activity in nerve fibres, but is sufficient to cause the long-
lasting repetitive firing in the lateral-line sense organ. 

    These results suggest that alpha-cyano pyrethroids primarily 
affect the sodium channels in the nerve membrane and cause a long-
lasting prolongation of the transient increase in sodium 
permeability of the membrane during excitation. 

    In the electrophysiological experiments using giant axons of 
crayfish, the Type II pyrethroids retain sodium channels in a 
modified continuous open state persistently, depolarize the 
membrane, and block the action potential without causing repetitive 
firing (Lund & Narahashi, 1983). 

    Diazepam, which facilitates GABA reaction, delayed the onset of 
action of deltamethrin and fenvalerate, but not permethrin and 
allethrin, in both the mouse and cockroach.  Possible mechanisms of 
the Type II pyrethroid syndrome include action at the GABA receptor 
complex or a closely linked class of neuroreceptor (Gammon et al., 
1982). 

    The Type II syndrome of intracerebrally administered 
pyrethroids closely approximates that of the convulsant picrotoxin 
(PTX).  Deltamethrin inhibits the binding of [3H]-dihydropicrotoxin 
to rat brain synaptic membranes, whereas the non-toxic R epimer of 
deltamethrin is inactive.  These findings suggest a possible 
relation between the Type II pyrethroid action and the GABA 
receptor complex.  The stereospecific correlation between the 
toxicity of Type II pyrethroids and their potency to inhibit the 
[35S]-TBPS binding was established using a radioligand, [35S]- t-
butyl-bicyclophosphoro-thionate [35S]-TBPS.  Studies with 37 
pyrethroids revealed an absolute correlation, without any false 
positive or negative, between mouse intracerebral toxicity and  in 
 vitro inhibition:  all toxic cyano compounds including 
deltamethrin, [1R, cis]-cypermethrin, [1R, trans]-cypermethrin, and 
[2S, alphaS]-fenvalerate were inhibitors, but their non-toxic 
stereoisomers were not; non-cyano pyrethroids were much less potent 
or were inactive (Lawrence & Casida, 1983). 

    In the [35S]-TBPS and [3H]-Ro 5-4864 (a convulsant 
benzodiazepine radioligand) binding assay, the inhibitory potencies 
of pyrethroids were closely related to their mammalian toxicities.  
The most toxic pyrethroids of Type II were the most potent 
inhibitors of [3H]-Ro 5-4864 specific binding to rat brain 
membranes.  The [3H]-dihydropicrotoxin and [35S]-TBPS binding 
studies with pyrethroids strongly indicated that Type II effects of 
pyrethroids are mediated, at least in part, through an interaction 
with a GABA-regulated chloride ionophore-associated binding site.  
Moreover, studies with [3H]-Ro 5-4864 support this hypothesis and, 
in addition, indicate that the pyrethroid-binding site may be very 
closely related to the convulsant benzodiazepine site of action 
(Lawrence et al., 1985). 

    The Type II pyrethroids (deltamethrin, [1R, cis]-cypermethrin 
and [2S,alphaS]-fenvalerate) increased the input resistance of 
crayfish claw opener muscle fibres bathed in GABA.  In contrast, 
two non-insecticidal stereoisomers and Type I pyrethroids 
(permethrin, resmethrin, allethrin) were inactive.  Therefore, 
cyanophenoxybenzyl pyrethroids appear to act on the GABA receptor-
ionophore complex (Gammon & Casida, 1983). 

    The effects of pyrethroids on end-plate and muscle action 
potentials were studied in the pectoralis nerve-muscle preparation 
of the clawed frog  (Xenopus laevis).  Type II pyrethroids 
(cypermethrin and deltamethrin) induced trains of repetitive muscle 
action potentials without presynaptic repetitive activity.  
However, an intermediate group of pyrethroids (1R-permethrin, 
cyphenothrin, and fenvalerate) caused both types of effect.  Thus, 
in muscle or nerve membrane, the pyrethroid induced repetitive 
activities due to a prolongation of the sodium current.  But no 
clear distinction was observed between non-cyano and alpha-cyano 
pyrethroids (Ruigt & Van den Bercken, 1986). 

 Appraisal

    In summary, the results strongly suggest that the primary 
target site of pyrethroid insecticides in the vertebrate nervous 
system is the sodium channel in the nerve membrane.  Pyrethroids 
without an alpha-cyano group (allethrin, d-phenothrin, permethrin, 
and cismethrin) cause a moderate prolongation of the transient 
increase in sodium permeability of the nerve membrane during 
excitation.  This results in relatively short trains of repetitive 
nerve impulses in sense organs, sensory (afferent) nerve fibres, 
and, in effect, nerve terminals.  On the other hand, the alpha-
cyano pyrethroids cause a long-lasting prolongation of the 
transient increase in sodium permeability of the nerve membrane 
during excitation.  This results in long-lasting trains of 
repetitive impulses in sense organs and a frequency-dependent 
depression of the nerve impulse in nerve fibres.  The difference in 
effects between permethrin and cypermethrin, which have identical 
molecular structures except for the presence of an alpha-cyano 
group on the phenoxybenzyl alcohol, indicates that it is this 
alpha-cyano group that is responsible for the long-lasting 
prolongation of the sodium permeability. 

    Since the mechanisms responsible for nerve impulse generation 
and conduction are basically the same throughout the entire nervous 
system, pyrethroids may also induce repetitive activity in various 
parts of the brain.  The difference in symptoms of poisoning by 
alpha-cyano pyrethroids, compared with the classical pyrethroids, 
is not necessarily due to an exclusive central site of action.  It 
may be related to the long-lasting repetitive activity in sense 
organs and possibly in other parts of the nervous system, which, in 
a more advance state of poisoning, may be accompanied by a 
frequency-dependent depression of the nervous impulse.

    Pyrethroids also cause pronounced repetitive activity and a 
prolongation of the transient increase in sodium permeability of 
the nerve membrane in insects and other invertebrates.  Available 
information indicates that the sodium channel in the nerve membrane 
is also the most important target site of pyrethroids in the 
invertebrate nervous system (Wouters & Van den Bercken, 1978; WHO, 
1979). 

    Because of the universal character of the processes underlying 
nerve excitability, the action of pyrethroids should not be 
considered restricted to particular animal species, or to a certain 
region of the nervous system.  Although it has been established 
that sense organs and nerve endings are the most vulnerable to the 
action of pyrethroids, the ultimate lesion that causes death will 
depend on the animal species, environmental conditions, and on the 
chemical structure and physical characteristics of the pyrethroid 
molecule (Vijverberg & Van den Bercken, 1982). 







    See Also:
       Toxicological Abbreviations
       Allethrins (HSG 24, 1989)