OMETHOATE JMPR 1978
Explanation
Omethoate was evaluated by the Meetings in 1971 and 1975
(FAO/WHO, 1972b, 1976b). A temporary ADI was established and
further toxicological information required (1978); also information
on residues occurring in food in commerce was listed as desirable.
The Tenth Session of the Codex Committee on Pesticide Residues
(1978) raised some questions regarding this compound. Information
received is reviewed in this monograph addendum.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Omethoate is a direct inhibitor of cholinesterase activity. In
a study evaluating the reversibility of cholinesterase depression
following oral acute intoxication, cholinesterase activity of
plasma, RBC and brain was evaluated at various times up to 14 days
after treatment. Groups of female rats were administered omethoate
at dose levels ranging from 0 to 17.8 mg/kg. Plasma cholinesterase
was rapidly depressed (within 2 hours) and was more sensitive than
RBC cholinesterase.
Recovery of plasma activity was essentially complete within 7
days. RBC cholinesterase was not substantially depressed at any
dose level tested. In contrast, brain cholinesterase was
substantially depressed at 1.3 mg/kg. Brain cholinesterase was
recovered completely at this level within 24 hours while at the
highest dose level recovery occurred some time between 3 and 7 days
(Flucke and Kimmerle, 1978).
Acute toxicity
Species Sex Route LD50 Reference
mg/kg
Rat M Oral 27.3 (25.5-29.6) Flucke & Kimmerle, 1978
F Oral 25.6 (23.8-27.6) Flucke & Kimmerle, 1978
M Dermal 1018 (937-1118) Flucke & Kimmerle, 1978
F Dermal 865 (774-943) Flucke & Kimmerle, 1978
COMMENTS
Acute toxicity and cholinesterase depression and recovery data
were received and reviewed in this monograph addendum. The data on
brain cholinesterase depression suggest this enzyme to be the most
sensitive parameter for evaluating the anticholinesterase effects
of omethoate. The recovery of cholinesterase activity was
essentially complete in 7 days after poisoning attesting to the
rapid reversibility of enzyme depression. Assurances were presented
to the Meeting that the data required for the long-term studies which
were in progress since 1975, would be available in the near future.
The temporary ADI was maintained until the next meeting.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 1.0 ppm in the diet equivalent to 0.05 mg/kg bw.
Dog: 1.6 ppm in the diet equivalent to 0.12 mg/kg bw.
Estimation of temporary ADI for man
0 - 0.0005 mg/kg body weight.
RESIDUES IN FOOD AND THEIR EVALUATION
RESIDUES RESULTING FROM SUPERVISED TRIALS
In written comments to the 10th Session of CCPR (1978) the
delegation of the Netherlands had questioned the usefulness of
limits for omethoate in sugar beet in the absence of MRLs for milk
and meat. No information on this subject was received by the
Meeting, but review of the data from animal feeding trials reported
by the 1971 Meeting (FAO/WHO, 1972b) showed that it could be
possible for omethoate to occur in the milk of cows fed on
material, such as sugar beet leaves, containing omethoate at the
recommended MRL of 1 mg/kg. Data would be required to clarify this
matter and to provide information on any occurrence in meat.
RESIDUES IN FOOD IN COMMERCE
Data received from New Zealand (1978) showed that of 16 random
retail samples of apples examined in 1975, 10 contained residues of
omethoate in the range 0-0.2 mg/kg with a mean of 0.14 mg/kg. One
sample of 16 of canned fruit (unspecified) contained 0.02 mg/kg of
omethoate. Apples known to have been treated with omethoate were
also examined. In 1975, levels in 8 samples ranged up to 0.4 mg/kg
with a mean of 0.13 mg/kg in 1977, levels in 10 samples reached 1.9
mg/kg with a mean value of 0.66 mg/kg. These are all within the MRL
of 2 mg/kg recommended in 1971 (FAO/WHO, 1972a, b).
Samples of raw produce examined continuously in routine
national surveys (Australia, 1978) had led to no reports of
omethoate residues in meat, grain, dairy products, fruit or
vegetables. This report indicated that omethoate was used in
Australia on pome fruits, citrus, potatoes, onions and cotton.
APPRAISAL
Some information was made available concerning residues of
omethoate occurring in food in commerce, this confirmed the
applicability of the previously recommended MRLs.
Data on omethoate residues occurring in milk and meat from
feeding animals with treated crops such as sugar beet leaves was
not available. The limited evidence showed that such data were
desirable.
RECOMMENDATIONS
No change in suggested in the MRLs previously recommended.
FURTHER WORK OR INFORMATION
Required (by 1979)
Submission of the long-term studies on rats currently in
progress.
Desirable
Data on omethoate residues in meat and milk following feeding
of animals with treated forage such as sugar beet leaves.
REFERENCES
Australia Data on use patterns and residues of omethoate in food
(1978) in Australia. Unpublished report.
CCPR Report of the 1977 Meeting of the Codex Committee on
(1978) Pesticide Residues. ALINORM 78/24, Para. 115.
Flucke W. and G. Kimmerle Folimat-Wirkstoff (S-6876) Untersuchungen
(1978) zur akuten toxiaitat bei ratten mit bestimmung der
activitat der cholinesterasen in blutplasma,
erythrozyten und gehirn. Unpublished report from
the Institute for Toxicologie, Bayer AG submitted
by Bayer AG to the WHO.
New Zealand Data on residues of omethoate in food. Unpublished
(1978) report.
See Also:
Toxicological Abbreviations
Omethoate (WHO Pesticide Residues Series 1)
Omethoate (WHO Pesticide Residues Series 5)
Omethoate (Pesticide residues in food: 1979 evaluations)
Omethoate (Pesticide residues in food: 1980 evaluations)
Omethoate (Pesticide residues in food: 1981 evaluations)
Omethoate (Pesticide residues in food: 1984 evaluations)
Omethoate (Pesticide residues in food: 1985 evaluations Part II Toxicology)