WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
DATA SHEETS ON PESTICIDES No. 28
It must be noted that the issue of a Data Sheet for a
particular pesticide does not imply endorsement of the pesticide by
WHO or FAO for any particular use, or exclude its use for other
purposes not stated. While the information provided is believed to
be accurate according to data available at the time when the sheet
was compiled, neither WHO nor FAO are responsible for any errors or
omissions, or any consequences therefrom.
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Nations or of the World Health ou de l'Organisation Mondiale de
Organization. la Santé.
Primary Use: Insecticide
Secondary Use: Acaricide
Chemical Group: Organochlorine compound
1. GENERAL INFORMATION
1.1 COMMON NAME:
An organochlorine insecticide of low mammalian toxicity, chemically
similar to DDT but, being more biodegradable, much less liable to
accumulate in body tissues and environment. It is of low hazard to
1.3 SELECTED PROPERTIES
1.3.1 Physical characteristics
When pure a colourless crystalline solid m.p. 89°C. Technical
methoxychlor has a fruit-like odour, and consists of up to 12%
o,p'-isomer, the balance being the insecticidally active
p,p'-isomer. Setting point of technical material 77°C.
Virtually insoluble in water but readily soluble in most aromatic
solvents, trichloroethane 70 g/100 ml at 20°C; methylene chloride
133 g/100 ml at Moderately soluble in alcohol, petroleum oils.
Relatively stable toward heat and oxidation and less readily
dehydrochlorinated than DDT by alcoholic alkali; it is stable toward
ultra-violet light susceptible to dehydrochlorination by heavy metal
1.3.4 Vapour pressure (volatility)
1.4 AGRICULTURE, HORTICULTURE AND FORESTRY
1.4.1 Common formulations
Wettable powders 25% and 50%. Emulsifiable concentrates 2 lb per US
gall. Compatible in mixtures except with highly alkaline materials.
1.4.2 Pests mainly controlled
Wide range of larval and insects affecting fruit, vegetables, forage
crops, livestock - range similar to DDI. It is not aphicidal or
acaricidal, but effective against livestock parasites (ticks, lice,
1.4.3 Use pattern
Effective for control of susceptible flies in dairy barns.
1.4.4 Unintended effects
Phytotoxic to some curcubits.
1.5 PUBLIC HEALTH PROGRAMMES:
Used against sensitive mosquitos as a 3% space spray indoors
increased to 5% for residual activity, and applied by air by high
and low volume spray in some countries.
1.6 HOUSEHOLD USE:
Active against sensitive houseflies, mosquitos, cockroaches, lice,
2. TOXICOLOGY AND RISKS
2.1 TOXICOLOGY - MAMMALS
2.1.1 Absorption route
Absorbed from the gastrointestinal tract as well as by inhalation
or, in oily solutions, through the intact skin.
2.1.2 Mode of action
Central nervous stimulant, producing hyperactivity, tremors and
2.1.3 Excretion products
Methoxychlor is metabolised in the liver; possibly the major route
of excretion is by the bile and the faeces as water soluble
2.1.4 Toxicity, single dose
Oral: LD50 rat* 6000 mg/kg
rat (F) 5000 mg/kg
Dermal: LD50 rat (M) and rat (F) 6000 mg/kg (*sex not stated)
Dermal: LD50 rabbit* 6000 mg,/kg
Most susceptible species: cattle - maximum dose 500 mg/kg
2.1.5 Toxicity, repeated doses
Oral: Rabbits were dosed daily with 200 mg/kg of methoxychlor. All
the animals died within four to 15 days with an average of 50% for
the group at eight days. Diarrhoea and anorexia were observed prior
to death and at post-mortem there was evidence of fatty degeneration
of the liver and the heart. Dogs were unaffected at 20, 100 and
300 mg/kg/day for one year.
Inhalation: Rats exposed to 10% methoxychlor dust for two hours
daily for a period of five weeks showed evidence of toxicity.
Dermal: Repeated application of methoxychlor in rabbits as a 30%
solution in kerosene at 2000 and 3000 mg/kg for 13 weeks, five days
a week, caused no deaths at 2000 mg/kg, but reduced weight gain was
observed. At 3000 mg/kg, one out of three animals died after eight
days. One rabbit at each dose level developed foot paralysis. At
post-mortem there was evidence of diffuse fatty degeneration of the
Cumulation of compound: Methoxychlor shows a slight tendency to
accumulate in the body fat; levels reach a plateau after four weeks
exposure and the stored material is mobilized within two to four
weeks of the ending of exposure.
2.1.6 Dietary studies
Short-term: 30 000 mg methoxychlor/kg feed in the diet killed
eight out of 10 rats (male and female) in 45 days. Female rats died
within a week at 10 000 mg/kg feed in diet and 5000 mg/kg feed
produced toxic effects without deaths over a period 16 weeks.
10 000 mg/kg feed produced toxic effects in dogs in the course of
Long-term: Rats were maintained for two years on a diet containing
2.5 ppm, 200 ppm and 1600 ppm methoxychlor. The two lower doses had
no effect. At 1600 ppm there was some growth reduction, but life
span was unaffected.
2.1.7 Supplementary studies of toxicity
Carcinogenicity: Methoxychlor was tested by the oral route in the
rat. Three experiments, including one employing dietary levels of up
to 1600 ppm, provided no evidence of carcinogenicity. No tumours
were reported in limited skin application and subcutaneous injection
(single dose) studies.
Teratogenicity: No information available.
Mutagenicity: No information available.
2.1.8 Modification of toxicity
Liver damage prior to exposure interferes with the metabolism of
methoxychlor and increases its toxicity. Pre-treatment of rats with
carbon tetrachloride increased toxicity and the resultant tremors
and convulsions were more apparent than with non-pretreated animals;
under these conditions deposition of methoxychlor in liver and fat
is increased 10 to 100 times.
2.2 TOXICOLOGY - MAN
Methoxychlor may be absorbed from the gastrointestinal tract, by
inhalation, or, in oily solutions, through the skin.
2.2.2 Dangerous doses
Single: No information.
Repeated: No information but see 2.2.5 below.
2.2.3 Observations of occupationally exposed workers
Investigations were carried out on a group of 51 persons employed in
producing chlorinated insecticides (DDT, HCH, dieldrin,
methoxychlor) to detect changes in enzyme activity in the blood. The
results of enzymatic determinations in the group show that the
activity of red blood cell acetylcholinesterase, serum aldolase and
alkaline phosphatase was significantly higher in this group than in
the control group. No significant differences were observed [n the
activity of serum aminotransferases cholinesterase and lactate
2.2.4 Observations on exposure of the general population
No information available.
2.2.5 Observations of volunteers
Male volunteers were fed 0.5, 1.0 and 2.0 mg/kg day for eight weeks.
Haematology, biochemistry and urinanalysis and biopsies of fat,
testis, bone marrow, liver and small intestine were all normal.
2.2.6 Reported mishaps
2.3 TOXICITY TO NON-MAMMALIAN SPECIES
96 hour TL50 for yellow perch: 30 µg/l. Half life in water varies
Slightly toxic (greater than 2000 mgms/kilo)
2.3.3 Other species
3. FOR REGULATORY AUTHORITIES - RECOMMENDATIONS ON REGULATIONS
3.1 RECOMMENDED RESTRICTIONS ON AVAILABILITY
(for definition of categories, see introduction)
All formulations above 10%, Category 4
All formulations 10% or less, Category 5
3.2 TRANSPORTATION AND STORAGE
All formulations in Category 4 - Should be transported or stored in
clearly labelled, rigid and leakproof containers. No food or drink
should be transported or stored in the same compartment. Storage
should be under lock and key and secure from access by unauthorized
persons and children.
Formulations in Category 5 - Should be transported in clearly
labelled, leakproof containers, out of reach of children and away
from food and drink.
All formulations in Category 4 - Protective clothing should be used
by those handling concentrates (see part 4). Adequate washing
facilities should be available close at hand. Eating, drinking and
smoking should be prohibited during handling and before washing
Formulations in Category 5
No special facilities other than those needed for handling of any
chemical need to be required during handling.
3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINER
Decontamination of containers is probably not practical. Container
must either be burned or crushed and buried below the topsoil. Care
must be taken to avoid subsequent contamination of water sources.
3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS
Formulations in Category 4 - Pre-employment medical examination for
workers desirable. Workers suffering from active hepatic or renal
disease should be excluded from contact. Training of workers in
techniques to avoid contact essential.
Formulation in Category 5 - Warning of workers to minimize contact
3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT
All formulations - Pilot and loaders should have special training
in application methods and early symptoms of poisoning. Flagmen, if
used, should wear overalls and be located well away from the
Formulations in Category 4 - Minimum cautionary statement
"Methoxychlor is an organochlorine insecticide. It is poisonous if
swallowed. Keep the material out of the reach of children and well
away from foodstuffs, animal feed and their containers."
Formulations in Category 5 - Minimum cautionary statement
"This formulation contains methoxychlor, an organochlorine
insecticide which is poisonous if swallowed. Keep the material out
of the reach of children and well away from foodstuffs, animal feed
and their containers."
3.8 RESIDUES IN FOOD
Maximum residue levels have not yet been recommended by the joint
FAO/WHO Meeting on Pesticide Residues.
4. PREVENTION AND POISONING IN MAN AND EMERGENCY AID
4.1 PRECAUTIONS IN USE
Methoxychlor is an organochlorine insecticide of low toxicity which
is moderately accumulative and can act as both an acute and chronic
poison. It can be absorbed by mouth, by inhalation and in liquid
formulations through the intact skin. It is important that
concentrated formulations be washed immediately from the skin and
4.1.2 Manufacture and formulation
TLV: (ACGIH) 10 mg/m3. Although volatility is vapour and dusts
should be controlled, preferably by mechanical means. Protective
equipment for the skin and respiratory protection is usually
4.1.3 Mixers and applicators
When opening the container and when mixing, care should be taken to
avoid contact with the mouth and eyes. If necessary a facial visor
and gloves should be worn. Mixing, if not mechanical, should always
be carried out with a paddle of appropriate length. The applicator
should avoid working in spray mist and avoid contact with the mouth.
Splashes must be washed immediately from the skin or eyes with large
quantities of water. Before eating, drinking or smoking, hands and
other exposed skin should be washed.
4.1.4 Other associated workers (including flagmen in aerial
Persons exposed methoxychlor and associated with its application
should observe the precautions described above in 4.1.3 under
"mixers and applicators".
4.1.5 Other populations likely to be affected
With good agricultural practice subject to 4.2 below, other
populations should not be exposed to hazardous amounts of
4.2 ENTRY OF PERSONS INTO TREATED AREAS
The general population should be kept out of treated areas for at
least one day.
4.3 DECONTAMINATION OF SPILLAGE AND CONTAINERS
Residues in containers should be emptied in a diluted form into a
deep pit taking care to avoid contamination of ground water.
Decontamination of containers in order to use them for other
purposes should not permitted. Spillage should be removed by washing
with large quantities of water.
4.4 EMERGENCY AID
4.4.1 Early symptoms of poisoning
No reported cases, but would probably include headache, nausea,
vomiting, dizziness, diarrhoea and weakness and possibly also
disturbances equilibrium, tremor and convulsions.
4.4.2 Treatment before person is seen by a physician, if these
symptoms appear following exposure
The person should stop work immediately, remove contaminated
clothing, wash the affected area with soap and water, if available,
and flush the area with large quantities of water. If swallowed,
vomiting should be induced if the person is conscious. Patient
should be removed to a shaded area and kept in conditions as quiet
as possible until medical help arrives.
5. FOR MEDICAL AND LABORATORY PERSONNEL
5.1 MEDICAL DIAGNOSIS AND TREATMENT IN CASES OF POISONING
5.1.1 General information
Methoxychlor is an organochlorine insecticide of low toxicity. It is
absorbed from the gastrointestinal tract and by inhalation. To a
lesser extent it may be absorbed by the intact skin, especially
liquid formulations. Its mode of action is as a CNS stimulant
causing tremors and convulsions. The toxic dose from repeated
exposure is well below the dangerous acutely toxic dose.
5.1.2 Symptoms and signs
No cases of human poisoning recorded, however the symptoms would
probably include headache, nausea, diarrhoea, and weakness, vomiting
and possibly disturbances of equilibrium, tremor and convulsions.
Direct measurement of methoxychlor in blood and favour or its
metabolites in urine and faeces confirms exposure.
Rapid gastric lavage should be performed using 5% sodium bicarbonate
if available. In case of skin contamination, the exposed area should
be washed with soap and water. If the compound has entered the eyes
they should be washed with isotonic saline or water.
Treatment is mainly symptomatic and there is no specific antidote.
Soluble barbiturates, diazepam or paraldehyde should be used if
tremors or convulsions are evident.
5.1 5 Prognosis
If the acute toxic effect is survived the chances of complete
recovery are good.
5.1.6 References of previously reported cases
No information of cases available.
5.2 SURVEILLANCE TESTS
There are no readily available field techniques to determine the
degree of exposure.
5.3 LABORATORY METHODS
5.3.1 Detection and assay of compounds
Suitable methods for the analysis of methoxychlor will be found in:
Analytical Methods for Pesticides. Plant Growth Regulators and Food
Additives, Zweig, vol. II, Insecticides, p. 303-312. Methoxychlor,
W. K. Lowen et al., 1964, Academic Press, New York and London. The
method of choice is by dehydrohalogenation and sulfonation as
described by Fairing and Warrington, 1950, Advances in Chem. Ser.,
1, 260. General notes on clean-up procedures and analytical
techniques can be found in: General Analytical Information,
Pesticide Residues, History Alternatives and Analysis J. Thomson and
Chemistry, Lecture Series, 1966, No. 3. For analysis in the presence
of fat see Claborn H. V and Beckman, H. F. Anal Chem., 1952, 24,
5.3.2 Other tests in cases of poisoning
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