PESTICIDE RESIDUES IN FOOD - 1984
Sponsored jointly by FAO and WHO
EVALUATIONS 1984
The monographs
Data and recommendations of the joint meeting
of the FAO Panel of Experts on Pesticide Residues
in Food and the Environment and the
WHO Expert Group on Pesticide Residues
Rome, 24 September - 3 October 1984
Food and Agriculture Organization of the United Nations
Rome 1985
DEMETON-S-METHYL
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Absorption, Distribution and Excretion
Absorption, distribution and excretion of radioactivity were
assayed in male Sprague-Dawley rats given single oral doses of 0.1,
0.5, 5 or 10 mg/kg or intravenous doses of 0.5 or 1 mg/kg of
14C- demeton-S-methyl. Additional female rats were given a single
oral dose of 0.5 mg/kg. The test material was very rapidly and nearly
completely absorbed following oral administration. More than 50
percent of the administered radioactivity was eliminated in about
three hours and approximately 90 percent within about eight hours
following an oral dose of 0.5 or 5 mg/kg. Within 48 hours, radio-
activity excreted in the urine accounted for 98-99 percent of the
administered dose. Faeces accounted for 0.5 - 2 percent and exhaled
air for about 0.2 percent. Radioactivity remaining in the body was
about 61 percent of the administered dose at two hours (about 39
percent having been already excreted at that time), about 1.3 percent
at 24 hours, 0.5 percent at 48 hours and 0.2 percent at ten days.
Total recovered radioactivity in experiments averaged 90-100 percent.
Recovery percentages in excreta were largely independent of dose
level, route of administration and sex of the animal. Rates of
elimination were dose-proportional. In a separate experiment in which
0.5 mg/kg of 14C-demeton-S-methyl was intraduodenally administered to
male rats with bile duct fistulas, about 3 percent of the administered
radioactivity was excreted in the bile within 24 hours.
Blood levels of radioactivity peaked at about one hour following
oral administration of 5 mg/kg of the test material. From zero to six
hours following administration, the blood half-life was calculated to
be about two hours. From six to 24 hours post-dosing, the half life
was about six hours and after 24 hours it was considerably longer.
Nearly all the radioactivity in blood after 24 hours was accounted for
by a high retention in erythrocytes which had considerably higher
levels of radioactivity than other organs and tissues for up to ten
days. Serum levels after 24 hours were low compared to erythrocytes
and at ten days were negligible. Distribution of radioactivity in
various body organs and tissues was relatively uniform at two hours.
Radioactivity did not concentrate in fat tissue or in the
reticuloendothelial system (liver, spleen, bone marrow). By two days
post-administration, radioactivity in most organs and tissues, except
blood and erythrocytes, had dropped 130 fold. At ten days,
radioactivity was nearly undetectable in the majority of organs and
tissues except for blood and erythrocytes. In a separate experiment,
whole-body autoradiography confirmed previous findings regarding
distribution of radioactivity in body tissues, but also indicated some
localized accumulation or radioactivity in the pineal gland, thyroid
and in some glands of the genital tract (Cowper's gland, seminal
vescicle, accessory genital gland) (Weber, Patzschke and Wegner,
1978).
Biotransformation
Rat urine samples from the experiments performed by Weber,
Patzschke and Wegner in 1978 were collected and subjected to thin
layer chromatographic and radioactivity counting methods designed to
identify and quantitate the parent compound and metabolites.
Zero-to-eight hour and eight to 24-hour samples were collected from
male rats given a single oral dose of 5 or 10 mg/kg of
14C-demeton-S-methyl. About 92 percent of the administered
radioactivity was recovered in the urine within eight hours. The main
route of metabolism of demeton-S-methyl was oxidation of the side
chain to form the corresponding sulfoxide. Some further slight
oxidation of the same side chain to form the corresponding sulfone was
also observed. Three corresponding O-demethylated metabolites of the
sulfide, sulfoxide and sulfone moieties were also identified in the
urine, as were two additional metabolites presumably resulting from
cleavage of the O-methylphosphoric ester group and subsequent
methylation and sulfoxidation steps. The parent compound,
demeton-S-methyl, was nearly completely metabolized and was not
detected in the urine (<1 percent). Approximately 99 percent of the
radioactivity in the urine samples, equivalent to about 95 percent of
the administered oral doses, was identified and quantitated as
follows: demeton-S-methyl (unchanged parent compound), < 1 percent,
demeton-S-methyl sulfoxide, 58 percent; demeton-S-methyl sulfone, 6
percent; O-demethyl-demeton - S-methyl, 6 percent;
O-demethyl-demeton-D-methyl sulfoxide, 6 percent;
O-demethyl-demeton-S-methyl sulfone, 4 percent;
methyl sulfinyl-2-ethyl sulfinyl ethan, 8.4 percent and methyl
sulfinyl-2-ethyl sulfonyl ethane, 10.4 percent. Another metabolite
accounting for less than 1 percent of the radioactivity in the urine
was not further investigated. Treatment of urine with glucuronidase or
sulfatase did not indicate the presence of any glucuronide or sulfate
conjugates (Ecker, 1978; Ecker and Colln, 1983).
TOXICOLOGICAL STUDIES
Acute Toxicity
Buffalo Calves
Single oral doses of Metasystox, containing 25% demeton-S-methyl,
were administered to seven male buffalo calves (ten to twelve months
of age) at a dosage level of 180 mg/kg. At the first signs of
poisoning, 15 to 35 minutes later, two calves were treated repeatedly
with atropine, D-tubocurarine and glucose. Another two calves were
treated repeatedly with atropine, gallamine and glucose. Three calves
were not treated. All calves displayed typical signs of cholinesterase
poisoning. Treatments delayed but did not prevent deaths which
occurred at about 2 hours in untreated calves and in about 23 hours in
treated calves after administration of the test material (Mitra, Sud
and Bahga, 1978).
Special Study on Teratogenicity
Rabbit
E 154 (demeton-S-methyl, 52.2 percent active ingredient in
xylene) was orally administered by intubation to mated Chinchilla
Hybrid rabbits on gestation days 6 to 18 at dosage levels of 0
(control), 3, 6 and 12 mg/kg/day. Each group consisted of 16 rabbits.
The dams were observed two times daily for mortality, appearance and
behaviour. Body weights were recorded daily and feed consumption was
determined six times during the study. Caesarean sections were
performed on gestation day 28. Dams were necropsied for gross changes
and special attention was given to ovaries and particularly to uterine
contents. All foetuses were counted, weighed, sexed, inspected
externally and then subjected to thorough and comprehensive visceral
and skeletal examinations.
There were no mortalities. Appearance and behaviour were normal
in all animals at all times in the control, low- and mid-dosage
groups. In the high-dosage group, diarrhoea was observed in all
animals after four to ten days of treatment. Beginning one to two
hours after dosing, it persisted for six to 24 hours. There were no
relevant differences in mean food consumption between the control,
low- and mid-dosage animals. In the high-dosage group, mean food
consumption, compared to control group intake, decreased 7.3 percent
during gestation days 6 to 18 and 16.6 percent during gestation days
19 to 24. There were no relevant difference in mean body weight gains
during gestation between the control, low- and mid-dosage animals. In
the high-dosage group, mean body weight gain, compared to the control
gain, was decreased 6.9 percent during gestation days 6 to 18. The
diarrhoea, decreased mean food consumption and decreased mean body
weights observed in the high-dosage animals is attributed to the test
material. The numbers of litters examined were 15, 16, 15 and 16 in
the control, low- mid- and high-dosage groups respectively. One animal
in the control group and one in the 6 mg/kg/day group had no
implantations. There were no abortions. Regarding reproductive
parameters, there were no relevant differences between test and
control groups in the numbers of implantations per dam, pre-
implantation losses, post-implantation losses, resorptions, living and
dead foetuses or sex ratios. The numbers of foetuses examined were
124, 129, 126 and 138 in the control, low-, mid- and high-dosage
groups respectively. Although there were no relevant differences in
mean foetal body weights between the control, low- and mid-dosage
groups, a decrease in mean foetal body weight, compared to the mean
control weight, of 6.6 percent was observed in the high-dosage group.
This decrease may possibly be related to the maternal toxic effects
noted at this dosage level or may possibly be a foetotoxic effect
attributable to the test material.
External and visceral examinations of foetuses revealed no
findings attributable to effects of the test material. Two foetuses
(from the same dam) in the 3 mg/kg/day group and one in the
6 mg/kg/day group had external or visceral malformations. Skeletal
examinations revealed two, one and one foetuses with skeletal
malformations in the low-, mid- and high-dosage groups respectively.
In addition, isolated instances of irregular ossified sternebrae
and/or other minor skeletal variations occurred randomly across all
groups. No teratogenic potential was observed in the rabbits in this
study at dosage levels up to 12 mg/kg/day. The evidence for a possible
foetotoxic effect (reduced foetal body weights) at the highest dosage
level tested, 12 mg/kg/day, is equivocal (Becker,1983).
SPECIAL STUDIES ON MUTAGENICITY
For the results of special studies on the mutagenic potential of
Demeton-S-methyl, please see Table 1.
COMMENTS
Demeton-S-methyl was rapidly and nearly completely absorbed in
rats following oral administration. More than 50 percent of single
doses up to 5 mg/kg was excreted in about three hours and
approximately 90 percent within eight hours. By 48 hours, only 0.5
percent remained in the body. Some binding to erythrocytes occurred
for at least ten days. Excretion was almost entirely via the urine. The
parent compound was nearly completely metabolized and was not detected
in the urine (<1 percent). Compounds identified in the urine were
oxydemeton methyl (58 percent), demeton-S-methyl sulfone (6 percent),
three O-demethylated metabolites (16 percent) and two additional
metabolites (19 percent).
In a teratology study on rabbits, no teratogenicity was observed,
but a slight decrease in mean foetal body weights was noted at the
highest dose level, at which maternal toxicity occurred.
Mutagenicity studies on demeton-S-methyl were equivocal in a
number of in vitro tests but were negative in in vivo tests.
FURTHER WORK OR INFORMATION NEEDED BEFORE AN ADI CAN BE ESTABLISHED
Required:
Teratology study in a second species.
Reproduction study.
Long-term feeding study in rodents.
Six-month or longer feeding study in dogs.
Delayed neurotoxicity study in hens.
Table 1. Special studies on mutagenicity of demeton-S-methyl
TYPE OF TEST TEST SUBJECT PURITY RESULT REFERENCE
In vitro Activated Non-activated
Reverse Mutation Saccharomyces
Induction Assay cerevisiae Hoorn, 1983
Strain S138 unknown negative negative
Strain S211 " negative negative
Ames Salmonella/ Salmonella
Microsome Test typhimurium
Strain TA98 " negative negative Herbold, 1980c
Strain TA100 " positive positive
Strain TA1535 " positive positive
Strain TA1537 " negative negative
In vivo
Micronucleus Test Mouse
(in bone marrow) Strain Bor:NMRI " negative Herbold, 1980b
Dominant Lethal Mouse
Study Strain NMRI " negative Herbold, 1980a
Table 1. Special studies on mutagenicity of demeton-S-methyl sulphone
TYPE OF TEST TEST SUBJECT PURITY RESULT REFERENCE
In vitro Activated Non-activated
Reverse Mutation Saccharomyces
Induction Assay cerevisiae De Graff, 1983
Strain 8138 unknown negative negative
Strain S211 " positive positive
Ames Salmonella/ Salmonella
Microsome Test typhimurium
Strain TA98 " negative negative Herbold, 1980b
Strain TA100 " positive positive
Strain TA1535 " negative negative
Strain TA1537 " negative negative
In vivo
Micronucleus Test Mouse
(in bone marrow) Strain Bor:NMRI " negative Herbold, 1981
Dominant Lethal Mouse
Study Strain NMRI " negative Herbold, 1980a
In vitro
Primary Rat Hepatocyte Rat, male negative Myhr, 1983
Unscheduled DNA Strain Fischer 344 unknown
Synthesis Assay
Mouse Lymphoma Mouse
Forward Mutation Strain Fischer L5178Y " positive positive Witterland, 1984
Assay
Human Leucocyte Test Human " positive Vaidya & Patankar, 1980
Table 1. (continued)
TYPE OF TEST TEST SUBJECT PURITY RESULT REFERENCE
Sister Chromatid Lymphocytes,
Exchange Assay Human, male * positive Pandita, 1983
In vivo
Micronucleus Test Mouse
(in bone marrow) Strain Bor:NMRI unknown negative Herbold, 1980a
Micronucleus Test Mouse
(in bone marrow) Strain Bor:NMRI " negative Herbold, 1981
In vivo
Micronucleus Test Mouse
(in bone marrow) Strain Swiss unknown positive Vaidya & Patankar, 1980
Micronucleus Test Mouse
(in bone marrow) Strain Swiss * positive Pandita, 1983
Sister Chromatid Chinese Hamster unknown negative Herbold, 1983
Exchange (in bone marrow)
Dominant Lethal Mouse
Study Strain NMRI " negative Herbold, 1980c
* Test material was Metasystox R Insecticide
Table 1. Special studies on mutagenicity of oxydemeton-S-methyl
TYPE OF TEST TEST SUBJECT PURITY RESULT REFERENCE
In vitro Activated Non-activated
Reverse Mutation Saccharomyces
Induction Assay cerevisiae Jagannath, 1980
Strain S138 unknown negative negative
Strain S211 " negative negative
Salmonella Salmonella
typhimurium typhimurium
Microsome Test Strain TA98 * positive positive Pandita, 1983
Strain TA100 * positive positive
Ames Salmonella/ Salmonella
Microsome Test typhimurium
Strain TA98 unknown negative negative Herbold, 1980b
Strain TA100 " positive positive
Strain TA1535 " positive positive
Strain TA1537 " negative negative
Recombination Bacillus
Assay Subtilis
Strain H17 " negative negative Jagannath, 1980
Strain M45 " negative negative
Desirable:
Observations in humans.
REFERENCES
Becker, H. Embryotoxicity and teratogenicity study on E 154 in
1983 rabbits. Research and Consulting Company Ltd. Itingen,
Switzerland. Report No. R2422. Submitted by Bayer AG to WHO.
Ecker, W. Biotransformation of (ethylene-1-14C) Demeton-S-methyl in
1978 rats. Bayer AG, Institute for Pharmacokinetics. Pharma
Report No. 7458. Submitted by Bayer AG to WHO.
Ecker, W. and Colln, R. Biotransformation of Demeton-S-methyl in rats.
1983 (final report). Bayer AG, Sparte Pharma. PF Report No. 1759,
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Herbold, B. E 25/154 (Demeton-S-methyl; Metaisosystox (i) active
1980a ingredient: dominant lethal study on male mouse to test for
mutagenic effects. Bayer AG, Institute for Toxicology.
Report No. 9336. Submitted by Bayer AG to WHO.
Herbold, B. E 25/154 (Studien Nr.: E 25/154/004): Mikronucleus-Test an
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Institute for Toxicology, Report No. 8932. Submitted by
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Herbold, B. E 25/154 (Studien Nr.: E 25/154/002):
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punktmutagene Wirkung. Bayer AG, Institute for Toxicology.
Report No. 8809. Submitted by Bayer AG to WHO (in German)
Hoorn, A.J.W. Mutagenicity evaluation of E 154 50 VL (in xylene) batch
1983 no. 808 204 103, content 53.1% in the reverse mutation
induction assay with Saccharomyces cerevisiae strains S138
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2372. Submitted by Bayer AG to WHO.
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1978 Metasystox in buffalo calves. Indian J. Exp. Biol. 16(7):
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Weber, H., Patzschke, K. and Wegner, L.A. (14C)Demeton-S-methyl
1978 (Metasystox i Active Ingredient): biokinetic studies on
rats. Bayer AG, Institute for Pharmacokinetics. Pharma
Report No. 7491. Submitted by Bayer AG to WHO.