WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANIZATION
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
ET L'AGRICULTURE
VBC/DS/83.54
ORIGINAL: ENGLISH
DATA SHEETS ON PESTICIDES No. 54
1983
OXAMYL
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.
The issue of this document does Ce document ne constitue pas une
not constitute formal publication. Il ne doit faire
publication. It should not be l'objet d'aucun compte rendu ou
reviewed, abstracted or quoted résumé ni d'aucune citation sans
without the agreement of the l'autorisation de l'Organisation
Food and Agriculture des Nations Unies pour
Organization of the United l'Alimentation et l'Agriculture
Nations or of the World Health ou de l'Organisation Mondiale de
Organization. la Santé.
CLASSIFICATION:
Primary use: Insecticide
Secondary use: Nematicide, Acaricide
Chemical group: Carbamate
Date issued: March 1983
1. GENERAL INFORMATION
1.1 COMMON NAME:
Oxamyl (BSI, ISO, ANSI, JMAF)
1.1.1 Identity:
IUPAC: N, N-dimethyl-2-methyl-carbamoyloximino-2-
(dimethylthio) acetamide
CAS#1: methyl N', N'-dimethyl-N-((methylcarbamoyl)oxy)-1-
thiooxamimidate
CAS Reg. No.: 23135-22-O
Mol. Form.: C7H13N3O3S
Mol Wt.: 219. 29
1.1.2 Synonyms:
D-1410; DPX-1410; Thioxamyl; VydateR
1.2 SYNOPSIS
Oxamyl is a broad spectrum, carbamate pesticide; a fast acting
anti-cholinesterase agent with effective direct contact and stomach
action. Highly toxic to mammals, it is rapidly metabolized and it is
non-cumulative in animal tissues. Oxamyl is an effective plant
systemic with excellent knockdown properties but poor residual
action.
1.3 SELECTED PROPERTIES
1.3.1 Physical properties
Oxamyl is a colourless crystalline solid with a melting point
of 100-102°C changing to a dimorphic form with a melting point of
108-110°C. It has a slightly sulfurous odour. Oxamyl is non-
corrosive. It has a specific gravity of 0.97 (25°/4°).
1.3.2 Solubility:
(25°c) 280 g/kg water
1440 g/kg methanol
1080 g/kg DMF
670 g/kg acetone
330 g/kg ethanol
290 g/kg cyclohexanone
110 g/kg isopropanol
10 g/kg toluene
insoluble in hexane
1.3.3 Stability
Solid oxamyl is very stable, in neutral or acid solutions it is
quite stable; in alkaline solution, natural waterbodies and soil
oxamyl decomposes readily to carbon dioxide and organosoluble
degradation products. In soil, the decomposition rate is inversely
proportional to the organic content of the soil. When in solution,
aeration, sunlight and heat hasten the degradation process.
1.3.4 Vapour pressure
3.059 x 10-5 kPa (2.3 x 10-4 mmHg) at 25°C.
1.4 AGRICULTURE, HORTICULTURE AND FORESTRY
1.4.1 Common formulations
Oxamyl is commercially available in a water soluble liquid
formula (24% a.i.), as a granule formulation (10% a.i.) and as
technical material in cyclohexanone/water (42% a.i.).
1.4.2 Susceptible pests
Oxamyl is used to control a wide variety of plant parasitic
insects, mites and nematodes on fruit, vegetable and field crops
and, ornamentals.
1.4.3 Use pattern
Used in soil applications between furrows at 1-30 kg/ha; in
soil dressing at 4.5-16.8 kg/ha; and, as a foliar spray at 0.4
kg/ha.
1.4.4 Unintended effects
Increased soil microbial population may follow soil treatment.
Phytotoxicity is not a problem when recommended application rates
are used.
1.5 PUBLIC HEALTH PROGRAMMES
No recommended usage reported.
1.6 HOUSEHOLD USE
No recommended usage reported.
2. TOXICOLOGY AND RISKS
2.1 TOXICOLOGY - MAMMALS
2.1.1 Absorption route
Oxamyl may be absorbed from the gastrointestinal tract; through
the intact skin; or, through inhalation of spray mist or fine
residue of granular formulations.
2.1.2 Mode of action
Oxamyl acts through inhibition of cholinesterase activity, this
inhibition is rapidly reversed spontaneously. The half-life of the
inhibited enzyme is approximately 30 minutes.
2.1.3 Excretion products
Oxamyl is rapidly absorbed from the gastrointestinal tract and
rapidly metabolized by liver microsome enzymes. In rats and mice the
excretion rate is 70 and 95% respectively within 72 hours of
administration, excretion is largely in the urine. The major
excretion products are oxamyl and several organosoluble metabolites
of which methyl N-hydroxy-N',N'-dimethyl-1-thiooxamimidate and N,N-
dimethyloxamate are the most prominent. Glucoronide conjugation
accompanies metabolism. The acute toxicity of these metabolites is
lower than oxamyl.
2.1.4 Toxicity, single dose
Oral LD50: Rat(M); 5.4 mg/kg bw (technical material)
37.0 mg/kg bw (24% liquid formulation)
110.0 mg/kg bw (10% granular formulation)
Dermal LD50: Rabbit(M); 740 mg/kg bw (27% liquid formulation)
2960 mg/kg bw (24% liquid formulation)
Dermal ALD*: Rabbit(M); 2250-5000 mg/kg bw, in a hydrophilic
ointment on intact skin
90-130 mg/kg bw, in a hydrophilic
ointment on abraded skin
130 mg/kg bw, in propylene glycol on
intact skin
60 mg/kg bw, in propylene glycol on
abraded skin
Inhalation LC50 (1 hour): Rat(M): 0.17 mg/l (oxamyl dust)
Rat(F): 0.12 mg/l (oxamyl dust)
Rat(M): 0.035 mg/l (27% liquid
formulation)
Eye irritation: Exposure of the rabbit eye to the solid, or
to a propylene glycol suspension of oxamyl caused marked pupillary
constriction, some iritic congestion but no corneal injury.
Insufficient information in published form to select the most
susceptible species.
2.1.5 Toxicity, repeated doses
Oral: Male rats (fed oxamyl for 2 weeks at 2.4 mg/kg bw
showed no evidence of tissue accumulation, cumulation of effect nor
lasting ill-effects.
Dermal: Groups of male and female rabbits were given dermal
applications of a 24% liquid formulation (193 mg/kg bw) or oxamyl
(50 mg/kg bw) on intact or abraded skin for 15 days. No mortalities
occurred during the 4 week study period. No treatment related
changes in body weight, organ weight or histopathology were found.
Mild erythema of the treated skin was observed on all animals. All
oxamyl treated rabbits with abraded skin showed marked signs of
cholinesterase inhibition but only slight signs were observed in
those with intact skin.
* ALD: approximate lethal dose.
Cumulation of compound: See above. In vitro biodegradation
of oxamyl by rumen fluids indicate that the rate of rumen floral
activity would preclude the absorption of moderate amounts of
dietary oxamyl into tissues of the ruminant organism.
2.1.6 Dietary studies
Short-term: In a 90-day study, groups of male and female rats
were fed oxamyl at 0, 50, 100 and 500 mg/kg of diet, the highest
dose level proved to be too toxic and was reduced to 150 mg/kg diet
after 3 days on a normal diet. At the highest dose level only, food
consumption was decreased and protein was found in the urine. At the
two highest dose levels body weights and organ weights were
decreased and, blood was observed in the urine. No treatment related
changes in haematology, clinical chemistry or histopathology were
observed at any dose level. Cholinesterase activity was not
determined.
In a 90-day dog study, males and females were fed oxamyl at 0,
50, 100 and 150 mg/kg of diet. Only marginal clinical effects were
observed at 150 mg/kg. No significant changes in body weight, organ
weight, haematology, clinical chemistry or histopathology were
observed in any animals.
Long-term: In a two year study, groups of male and female
rats were fed oxamyl at 0, 50, 100 or 150 mg/kg of diet. In the 50
mg/kg diet group only the males showed a slight decrease in body
weight at 4 weeks and continuing for the duration of the test
period. A dose dependent decrease in body weight was observed in the
100 and 150 mg/g diet group. At 150 mg/g, food consumption was
significantly decreased; cholinesterase activity decreased in the
females after 4 days of treatment, in the males after 8 days
(returning to normal after one month); relative weights of brain,
testes and adrenals increased in males and brain, heart, lungs,
kidney and adrenal weight increased in the two highest dose female
groups. No compound related changes in haematology, clinical
chemistry or histopathology was observed at any dietary dose level.
In a two year dog dietary study (0, 50, 100 and 150 mg/g of
diet), haemoglobin levels, haematocrit and erythrocyte count were
lower in the highest dose group while cholesterol levels and
alkaline phosphatase activity were increased from week 4 to the end
of the test period. No treatment related changes in organ weights,
cholinesterase activity or histopathology were observed at any dose
level.
2.1.7 Supplementary studies
Carcinogenicity: No tumours were found in the rat and dog
dietary studies described above. Mouse dietary study results are not
available at this time.
Mutagenicity: Oxamyl was not mutagenically active in two
microbial tests, or rec-assay test with B. subtilis and a reverse
mutation test with five strains of S. typhimurium and one of E.
coli.; and, in a host mediated assay in mice using the S.
typhimurium G-46 strain.
Teratogenicity: No teratogenic or embryotoxic effects were
observed when groups of pregnant rats were fed oxamyl at 50, 100,
150 or 300 mg/kg of diet from day 6-15 of the gestation period.
Reproduction: Six male and female rats from each dosage group
of a 90-day dietary study (described in 2.1.6) were used for a
three-generation reproductive performance test. At weaning the body
weight of all pups was significantly decreased. In the F1a and
F1b generation, the fertility index and letter size were
significantly decreased for the 100 and 150 mg/kg dietary dose
groups.
Neurotoxicity: Two groups of five adult hens received 20 or
40 mg/kg bw of oxamyl followed by 0.5 mg/kg bw of atropine. No
mortalities occurred in either group. All hens showed marked signs
of cholinesterase inhibition, recovery was complete after 12 hours
and there was no evidence of delayed neurotoxicity.
2.2 TOXICOLOGY - MAN
2.2.1 Absorption route
Oxamyl may be absorbed through the gastrointestinal tract; the
intact skin; and by inhalation of spray mist or fine residue of
granular preparations.
2.2.2 Dangerous doses
No published information available.
2.2.3 Observations on occupationally exposed
workers
No published information available.
2.2.4 Observations on exposure of the general
public
No information available. The public should not be exposed to
hazardous amounts of oxamyl due to its poor persistence in plant and
animal tissues and provided proper treatment precautions are
followed.
2.2.5 Observations on volunteers
No published information available.
2.2.6 Reported mishaps
No published information available.
2.3 TOXICITY TO NON-MAMMALIAN SPECIES
2.3.1 Fish
Toxic to fish.
LC50 (96 h): Bluegill: 5.6 mg/l
Goldfish: 27.6 mg/l
Rainbow trout: 4.2 mg/l
2.3.2 Birds
Birds, oral LD50: Japanese Quail: 4.2 mg/g bw (technical
cmpd.)
Bobwhite Quail: 39.2 mg/g bw (24% a.i.,
liquid)
Mallard Duck: 10.75 mg/kg bw (24% a.i.,
liquid)
Birds, 8-day dietary: Bobwhite Quail: 225 ppm/l diet (24% a.i.,
liquid)
Mallard Duck: 1536 ppm/1 diet (24% a.i.,
liquid)
2.3.3 Other species
Toxic to earthworms.
LC50: Daphnia magna 1.95 mg/l (24% a.i., liquid)
3. FOR REGULATORY AUTHORITIES - RECOMMENDATIONS ON REGULATION OF
COMPOUND
3.1 RECOMMENDED RESTRICTIONS ON AVAILABILITY
(For definitions of categories see the Introduction to Data Sheets)
Liquid formulations of 24% only available, Category 2
Solid (granular) formulations of 104 available, Category 3
3.2 TRANSPORTATION AND STORAGE
All formulations - Should be transported and stored in
clearly labelled impermeable containers under lock and key, secure
from access by unauthorized persons and children.
No food or drink should be stored in the same compartment.
3.3 HANDLING
All formulations - Full protective clothing (see paragraph
4.3, part 4) should be used by those handling the compound. Adequate
washing facilities should be available at all times during the
handling and should be close to the site of handling. Eating,
drinking and smoking should be prohibited during handling and before
washing after handling. A respirator should be worn at all times
when spraying. Oxamyl formulations should not be applied by hand
held ULV applicators.
3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINERS
All formulations - Container must be either burned or crushed
and buried below topsoil. Care must be taken to avoid subsequent
contamination of water sources. Decontamination of containers in
order to use them for other purposes should not be permitted.
3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS
All formulations - Pre-employment medical examination of
workers necessary. Workers suffering from active hepatic or renal
disease should be excluded from contact. Pre-employment and periodic
cholinesterase test for workers desirable. Special account should be
taken of the workers' mental ability to comprehend and follow
instructions. Training of workers in techniques to avoid contact
essential.
3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT
All formulations - Pilots and loaders should have special
training in application methods; and early symptoms of poisoning,
and must wear a suitable respirator. Use of flagmen not recommended.
Flagmen, if used, should wear protective clothing and be located
well away from the dropping zone.
3.7 LABELLING
All formulations, minimum cautionary statement:
"DANGER - POISON"
(Skull and cross bones insignia)
Oxamyl is a carbamate compound which inhibits cholinesterase.
It is of very high toxicity. Contact with the skin, inhalation of
dust or spray, or swallowing may be fatal. Wear protective gloves,
clean protective clothing, and a respirator of the organic vapour-
type when handling this material. Bathe immediately after work.
Ensnare that containers are stored under lock and key. Empty
containers must be disposed of in such a way as to prevent all
possibility of accidental contact with them. Keep the material out
of reach of children and well away from foodstuffs, animal feed and
their containers.
In case of contact, immediately remove contaminated clothing
and wash the skin thoroughly with soap and water; for eyes, flush
with water for 15 minutes.
If poisoning occurs, call a physician. Atropine is a specific
antidote and repeated doses may be necessary. Artificial respiration
may be needed.
3.8 RESIDUES IN FOOD
Maximum residue levels
Maximum residue levels have been recommended by the Joint
FAO/WHO Meeting on Pesticides residues.
4. PREVENTION OF POISONING IN MAN AND EMERGENCY AID
4.1 PRECAUTIONS IN USE
4.1.1 General
Oxamyl is a carbamate pesticide of very high toxicity. It
penetrates the intact skin and is also absorbed by inhalation and
from the gastrointestinal tract. Most formulations should be handled
by trained personnel wearing protective clothing.
4.1.2 Manufacture and formulation
T.L.V. - no information. Formulation should not be attempted
without advice from the manufacturer.
Although volatility is low, vapour and dusts should be
controlled preferably by mechanical means. Protective equipment for
the skin and respiratory protection is usually necessary.
4.1.3 Mixers and applicators
When opening the container and when mixing, protective
impermeable boots, clean overalls, gloves and respirator should be
worn. Mixing, if not mechanical, should always be carried out with a
paddle of appropriate length. When spraying tall crops or during
aerial application a respirator should be worn as well as an
impermeable hood, clothing, boots and gloves. The applicator should
avoid working in spray mist and avoid contact with the mouth.
Particular care is needed when equipment is being washed after use.
All protective clothing should be washed immediately after use,
including the insides of the gloves. 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
operations)
Persons exposed to oxamyl and associated with its application
should wear protective clothing and 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 oxamyl.
4.2 ENTRY OF PERSONS INTO TREATED AREAS
Unprotected persons should be kept out of treated areas for at
least one day.
4.3 SAFE DISPOSAL OF CONTAINERS AND SPILLAGE
Residues in containers should be emptied in a diluted form into
a deep pit taking care to avoid ground waters. The empty container
may be decontaminated by rinsing two or three times with water and
scrubbing the sides. An additional rinse should be carried out with
5% sodium hydroxide solution which should remain in a container
overnight. Impermeable gauntlets should be worn during this work and
a soakage pit should be provided for the rinsings. Decontaminated
containers should not be used for other purposes.
Spillage of oxamyl and its formulations should be removed by
washing with 5% sodium hydroxide solution and then rinsing with
large quantities of water.
4.4 EMERGENCY AID
4.4.1 Early symptoms of poisoning
Early symptoms of poisoning may include excessive sweating,
headache, weakness, giddiness, nausea, vomiting, stomach pains,
blurred vision, slurred speech and muscle twitching. Later there may
be convulsions, coma loss of reflexes and loss of sphincter control.
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 and wash the affected skin with water and soap, if
available, and flush the area with large quantities of water. If
swallowed, vomiting should be induced if the person is conscious. In
the event of collapse, artificial respiration should be given,
bearing in mind that if mouth to mouth respiration is used, vomit
may contain toxic amounts of oxamyl.
5. FOR MEDICAL AND LABORATORY PERSONNEL
5.1 MEDICAL DIAGNOSIS AND TREATMENT IN CASES OF POISONING
5.1.1 General information
Oxamyl is a carbamate insecticide of very high toxicity. It is
absorbed from the gastrointestinal tract and by inhalation, and only
to a limited extent through the intact skin. Its mode of action is
by reversibly inhibiting acetyl cholinesterase. Erythrocyte
cholinesterase is more inhibited than plasma cholinesterase.
Symptoms of poisoning are short lasting and in case of occupational
overexposure occur without delay and at doses well below the fatal
dose. Because of its rapid metabolism and excretion it does not
accumulate in the tissues.
5.1.2 Symptoms and signs
Symptoms and poisoning include excessive sweating, headache,
chest tightness, weakness, giddiness, nausea, vomiting, stomach
pains, salivation, blurred vision, slurred speech and muscle
twitching. Paraesthesia and mild skin reactions have also been
reported.
5.1.3 Laboratory
Because oxamyl is a reversible inhibitor of cholinesterase,
measurements of cholinesterase activity should be made by a method
which minimizes the reactivation of inhibited enzyme. Erythrocyte
cholinesterase determination is more informative than measuring
either plasma or whole blood cholinesterase, but the enzyme will
only be inhibited for a short time (few hours) after exposure. The
presence of metabolites of oxamyl in urine is also indicative of
exposure.
5.1.4 Treatment
If the pesticide has been ingested, unless the patient is
vomiting, rapid gastric lavage should be performed using 5% sodium
bicarbonate, if available. For skin contact, the skin should be
washed with soap and water. If the compound has entered the eyes
they should be washed with isotonic saline or water. Since the
symptoms of poisoning with oxamyl are of short duration, atropine
treatment is usually not necessary by the time the patient reaches a
place where this antidote is available. Where there are manifest
symptoms 1-2 mg of atropine sulfate (adult dose) may be given
intramuscularly or even intravenously and repeated as necessary.
Care should be taken to avoid overdosage of atropine, especially
when treating children. In extreme cases, if the patient is
unconscious or is in respiratory distress, oxygen may be required.
Provide patient support as required, including: suction of
secretion, maintenance of airways, intravenous fluids if needed, and
bladder catheterization. Contraindications are barbiturates and
central stimulants of all kinds. The chemical similarities between
oxamyl and aldicarb suggest that pralidoxime chloride (25-50 mg/g
bw) may be safely used in addition to atropine to counter the
nicotinic symptoms of oxamyl poisoning when it is known for certain
that contraindicating carbamates are not involved and if the
severity of the symptoms warrant.
5.1.5 Prognosis
If the acute toxic effect is survived, the chances of complete
recovery are very good.
5.1.6 References of previously reported cases
Few cases of oxamyl poisoning have been reported, very few
fatalities, see Gehlbach, S.A. & Williams, W. A. (1975) Accidental
ingestion, Arch. Environ. Contam., 30, 49.
5.2 SURVEILLANCE TESTS
Due to rapid reactivation of inhibited enzyme, determination of
blood cholinesterase levels is of little, if any, practical value in
determining when workers should be withdrawn to prevent over-
exposure. Minor complaints, such as headache and nausea, cause the
worker to stop work and thus prevent further exposure. The worker
quickly recovers, particularly if appropriate decontamination
procedures are followed.
5.3 LABORATORY METHODS
5.3.1 Detection and assay of compound and residues
Chapman, R. A. & Harris, C. R. (1979) Journal of
Chromatography, 171, 249-262
Davis, P. L. et al. (1978) J. Agric. Food Chem., 26(3),
777-778
Holt, R. F. & Pease, H. (1976) J. Agric. Food Chem., 24(2),
263-266
Holt, R. F. & Leitch, P. E. (1978) Anal. Methods Pestic. Plant
Growth Regul., 10, 111-119
Kanazawa, J. (1978) Bunseki, 6, 389-394
Krause, R. T. (1980) J. Assoc. Off. Anal. Chem., 63(5),
1114-1124
Singhal, J.P. et al. (1977) J. Agric, Food Chem., 25(2),
377-380
Singhal, J.P. et al. (1978) Analyst (London), 103, 872-875
Thean, J. E. et al. (1978) J. Assoc. Off. Anal. Chem., 61(1),
15-17
5.3.2 Other tests in cases of poisoning
Cholinesterase levels in blood are unreliable as a routine test
to detect poisoning by oxamyl. However, shortly after absorption,
inhibition of erythrocyte cholinesterase may be demonstrated by an
appropriate method.
Plasma cholinesterase activity; Ellman, G. L. et al. (1961)
Biochem. Pharmacol, 7 88095
Whole blood cholinesterase activity; Fleischer, J. et al.
(1956) Arch. Indust. Hyg., 14, 510
Bull. Wld Hlth Org., 48, 235-238 (1973)