CHINOMETHIONAT
EXPLANATION
Chinomethionat was evaluated by the JMPR in 1968 (as
oxythioquinox), 1974, 1977, and 1981 (Annex 1, FAO/WHO 1969a, 1975a,
1978a, and 1982a). At the 1974 and 1977 JMPR the following
investigations were requested:
1. Studies on the identity and relative toxicity of
metabolites.
2. An additional carcinogenicity study in another species, in
view of hepatic toxicity observed in rodents.
In 1981 new studies regarding mutagenicity, teratogenicity and
eye and dermal irritation were received. The mutagenicity and
teratogenicity studies are included and evaluated in the present
monograph addendum.
The 1984 JMPR decided to withdraw the temporary ADI (established
at the meeting of 1977) of 0.003 mg/kg bw because requested studies
had not been submitted.
The outstanding study requirements and some additional studies
have become available now and are summarized and discusses in this
monograph addendum.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOLOGICAL DATA
Toxicological Studies
Special studies on carcinogenicity
See under long-term studies.
Special studies on teratogenicity
Rats
Groups of 25 female Wistar rats received 0, 10, 25, or 62.5 mg
chinomethionat (purity, 95.1%)/kg bw by gavage from days 6-15 of
gestation. The fetuses where delivered by caesarian section on day 20
of pregnancy. The dams were observed daily ofr mortality and body
weight. The number of implantations, live and dead fetuses, early and
late resorptions and placenta weight were recorded. The fetuses were
counted, sexed and weighed and studied for visceral and skeletal
malformations.
There were no effects observed on the dams and offspring except
for a significantly decreased body weight gain in high dosed dams and
a decrease in fetal and placental weight at all dose levels (not
clearly and not significant at the highest dose (Renhof, 1986).
Rabbits
Groups of 15 rabbits (Himalayan strain) received 13 daily oral
doses of either 0, 10, 30 and 100 mg chinomethionat (Purity, 91.5%)/kg
bw from day 6-18 of gestation. The fetuses were delivered by caesarian
section on day 29 of pregnancy. Maternal toxicity was observed in high
dosed dams (e.g. diarrhoea, reduced feed intake, loss of weight) and
in the same dose group a significant decrease in both the number and
size of fetuses was found.
Examination of the offspring by standard methods and the
evaluation of the results gave no indication of teratogenicity
(Schlülter, 1981).
Special studies on mutagenicity
Chinomethionat gave no mutagenic response in test with Bacillus
subtilis, Escherichia coli and Salmonella typhimurium and the
CHO/HGPRT cell mutation assay as well as in the micronucleus test with
mice (see table 1.).
Table 1. Special studies on the mutagenicity of chinomethionat
Type of test Test object Concentration of Purity Results References
chinomethionat
In vitro
Ames test (with Salmonella 1 µg up to 91% negative Shirasu et al., 1979
and without typhimurium 5000 µg/plate
metabolic TA98, TA100
activation) TA1535, TA
1537 & 1538
Reverse mutation Escherichia 1 µg up to 91% negative Shirasu et al., 1979
assay (with and coli 5000 g/plate
without metabolic WP2 hcr
activation)
Recombination Bacillus 20 µg up to 91% negative Shirasu et al., 1979
assay subtilis 2000 µg/plate
M45 & H17
CHO/HGPRT Chinese Non activated: 94.4% negative Yang, 1986
mutation assay hamster ovary 0.1, 0.5, 1.0, (1)
(with and without cells 1.5 and 2.0/µg/ml
metabolic (CHO-K1-BH4) Activated: 0.1, negative
activation) 0.5, 1.0, 3.0 (1)
and 5.0 µg/ml
dissolved in
acetone
Table 1. (cont'd).
Type of test Test object Concentration of Purity Results References
chinomethionat
In vivo
Micronucleus NMRI mice 500 and 1000 mg/kg 95.2% negative Herbold, 1982
test (administered (1)
orally twice,
24 hr apart)
(1) Positive control yielded positive results.
Special studies on reproduction
Rats
Groups of 10 male and 20 female SPF/Cpb rats were fed diets
containing 0, 15, 60 and 240 ppm chinomethionat (purity 94.6%) in a
two generation (two litters/generation) study. Diets were maintained
during mating, gestation and lactation. Observations were made on
general condition and behaviour, food consumption and body weight.
Indices for fertility, gestation, viability, lactation and
insemination as well as litter-and pupweight and abnormalities were
recorded. Organ weights (liver, kidneys and gonads) were measured for
the F1b parents only. All parental rats and pups of the highest dose
group had yellow coats. Maternal toxicity was observed at 240 ppm and
sometimes at 60 ppm as indicated by a lower body weight gain. F0
females, F1b parents and F1b, F2a and F2b pups had decreased body
weight gain at 240 ppm and F0 females and F2b pups also at 60 ppm. F2a
mean littersize was significantly reduced in the highest dose group.
Viability was significantly reduced in F1a, F2a and F2b pups at 240
ppm. Fib females had increased relative liver and kidney weights at
240 ppm. No effects were observed at 15 ppm (Eiben, 1984).
Dogs
The effect of chinomethionat on semen quality was evaluated in
groups of beagle dogs (6/group) fed diets containing 0, 25, 75 and
225 ppm chinomethionat (purity 91.5%). The study was part of the one
year feeding study in dogs (see under short-term studies).
Semen samples were obtained at 4 month intervals throughout the
one-year study. Clinical abnormalities were not observed in the dogs
before each semen collection. Semen samples were observed for volume,
motility, status, sperm count, total viable sperm, color, viscosity,
morphology and cellular debris. Evaluations of the three collections
gives no evidence of reduced semen quality and quantity (Dahlgren,
1981; Hayes, 1983).
Special studies on thyroid function
Groups of 100 male SPF/Cpb rats were fed diets containing 0, 10,
25, 60, 150, and 500 ppm chinomethionat (purity 95.2%) for 8 weeks,
surviving animals were observed for another 4 weeks. Besides growth
and food intake, clinical chemical examinations, including T3 and T4,
were measured on day 7, 21, 63, 70 and 84. At the same times
radioiodine uptake by the thyroid was measured in 10 animals which
were killed 24 hours after 131I administration.
The fur of the animals of the 500 ppm group was yellow colored.
In the highest dose group decreased body weight gain (also at 150 ppm)
and increased relative liver weight were observed to occur in a
dose-related manner. Thyroid function tests (T3 and T4, and iodine
uptake) did not provide any indications of a dose- or time-related
effect on functioning. No consistent differences were observed in
these parameters nor in other clinical chemical parameters. No effects
on weight or histopathology of the thyroid were found (Krötlinger
et al., 1984).
Short-term studies
Rats
Groups of SPF/Cpb rats (20/sex/group) were orally administered
0, 10, 25, 60, 150, and 500 ppm chinomethionat (purity 95.2%) in the
diet for three months. All animals were observed daily for mortality
and clinical signs while body weight and food consumption were
observed weekly. Hematology, blood chemistry and urinalysis
examinations were recorded on 10 rats/group after one month and at
termination of the study. After three months all animals were killed,
selected organs weighed and complete gross and histopathological
examinations were performed.
There were no effects on appearance, behaviour and mortality
except for high dosed rats which showed a yellow fur. Reduced body
weight gain and food intake was observed in rats receiving 150 and
500 ppm. At the highest dose level Hb, Ht, RBC and MCH were
significantly decreased in both sexes. At the same dose level, females
had a lower WBC count and males a higher thrombocyte count. In females
Hb, Ht, RBC and MCH were also significantly decreased at 150 ppm. At
60 ppm MCH values were still decreased in females after 3 months.
Decreased protein levels in the urine were found in males and females
(only after 3 months) at 500 ppm. Relative brain weight was
significantly increased at 60 (males only), 150 and 500 ppm in both
sexes. Relative liver and kidney weight were significantly increased
in females at 150 and 500 ppm and relative lung and relative testes
weight in males at the same dose levels. At 60 ppm, equal to 4 (males)
- 4.6 (females) mg/kg bw, only marginal effects were observed
(Krötlinger & Kaliner, 1983).
Dogs
Beagle dogs (6/sex/group) were orally administered 0, 25, 75, or
225 ppm chinomethionat (purity 95.8%) in the diet for 52 weeks.
No compound related effects were observed on clinical signs,
mortality, urinalysis or ophthalmoscopy. Body weight was decreased in
males and females at 225 ppm (sometimes significantly). Food
consumption was significantly reduced in males at 225 ppm from week 36
onwards. Hb, Ht, and RBC were reduced sometimes significantly in males
and females at 225 ppm and sometimes also at 75 ppm. Alkaline
phosphatase and alanine amino transferase values were increased in
males and females receiving 225 ppm. In males absolute heart weight
was significantly decreased at all dose levels and absolute liver and
absolute adrenal weight decreased and relative spleen weight increased
at 225 ppm. In females relative liver and kidney weight were increased
at 225 ppm At histopathology, marked hepatopathy with early cirrhosis
at 225 ppm and an increased severity of centrilobular hepatocellular
pigmentation at 75 and 225 ppm were observed in both male and female
dogs. Increased splenic hemosiderosis was noted in dogs fed 225 ppm.
The NOAEL in this study is 25 ppm in the diet, equivalent to
0.6 mg/kg bw (Hayes, 1983).
Long-term studies
Groups of 70 male and 70 female mice (NMRI) were fed diets
containing 0, 90, 270 and 800 ppm chinomethionat (purity 95.2%) for 21
months. Twenty male and 20 female mice per group were used for interim
kill after 12 months. Observations included clinical signs, mortality,
body weight, food consumption, hematology and clinical chemistry.
Surviving mice were sacrificed after 21 months. Organs were weighed
and comprehensive histopathological examinations were made.
The mortality of males was significantly lower at 800 and
270 ppm, whereas females showed a higher mortality at 800 ppm
throughout the study and, at some examination times, also at 270 ppm.
At 800 ppm growth rate was significantly reduced throughout the study
in male mice and from week 75 onwards in female mice. At 800 ppm
significantly decreased values for Hb, Ht and RBC and number of
leucocytes (a nonsignificant decrease in Hb and Ht was also observed
at 270 and 90 ppm) were observed in males after 52 weeks. At the end
of the study males and females showed a nonsignificant decrease in Hb,
Ht and RBC and a significant increase in MCH and MCV (males).
Reticulocyte count was increased in females at both times. No
consistent effects were found on clinical chemistry parameters with
the possible exception of significantly increased urea values in
females at 270 and 800 ppm after 21 months. Relative adrenal weight
was not increased in a dose-related manner in males after 52 weeks.
Relative testes and brain weight were significantly increased in males
at 800 ppm. Relative spleen weight was significantly increased in
females at all dose levels and in males at 270 and 800 ppm (only after
52 weeks). Relative kidney weight was significantly increased in males
and females (only after 52 weeks) at 800 ppm. Relative liver weight
was increased in females at 270 and 800 ppm after 52 weeks. Relative
heart weight was significantly increased in females at 800 ppm.
At macroscopy an increased incidence of pale kidneys and a rough
kidney surface was observed in females at 270 and 800 ppm. The
incidence of progressive nephropathy was increased at 800 ppm.
No enhanced tumor incidence was observed. At 90 ppm, equal to 16
(males) - 21 (females) mg/kg bw, only marginal effects on the red
blood cells were observed (Krötlinger, 1986).
COMMENTS
The 1984 JMPR withdrew the temporary ADI of chinomethionat
because the required data, sufficient to carry out a new toxicological
evaluation, had not been supplied. The data supplied to this meeting
included studies on reproduction, teratogenicity, mutagenicity,
carcinogenicity, a short-term study in rats and a 1-year study in
dogs.
In reproduction studies, chinomethionat caused decreased
litter-size, pup weight and viability at maternally toxic dose levels.
No adverse effects were found at 15 ppm. In teratogenicity studies
with rats and rabbits, fetotoxicity and maternal toxicity were
observed but no teratogenic effects were seen. The semen of dogs was
not affected by chinomethionat administration.
Chinomethionat was not mutagenic in a battery of tests.
In a short-term study in the rat, the main effects were reduced
body weight gain, reduced food intake, and anaemia. Marginal effects
on red cells were observed at 60 ppm. In a special study with rats,
changes in thyroid function were not observed. In a one-year study
with dogs, growth inhibition, anaemia, an increase in serum alkaline
phosphatase and in alanine amino transferase, as well as
histopathological changes in the liver and spleen were found. In this
study the NOAEL was 25 ppm.
In a long-term toxicity/carcinogenicity study in mice, the same
effects were found on body weight and hematological parameters.
Relative organ weights were increased, especially those of the spleen.
The kidneys showed histopathological changes (progressive
nephropathy). With the lowest dose level tested (90 ppm) only marginal
hematological changes were observed. The tumor incidence was not
enhanced.
The meeting considered these data together with the data
previously evaluated in 1974 (acute toxicity and chronic toxicity in
rats) and 1977 (biotransformation and acute toxicity of chinomethionat
and its main metabolite) sufficient to allocate an ADI. The NOAEL for
the rat was based on the long-term study evaluated at the 1974
Meeting, showing no adverse effects at 12 ppm, the highest dose level
tested.
TOXICOLOGICAL EVALUATION
LEVEL CAUSING NO TOXICOLOGICAL EFFECT
Rat: 12 ppm in the diet, equivalent to 0.6 mg/kg bw/day
Dog: 25 ppm in the diet, equivalent to 0.6 mg/kg bw/day
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN
0-0.006 mg/kg bw.
STUDIES WHICH WILL PROVIDE INFORMATION VALUABLE IN THE CONTINUED
EVALUATION OF THE COMPOUND
1. Observations in man.
2. Ongoing studies to identify metabolites in rats and plants.
REFERENCES
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the semen quality in Canines. Unpublished report no. 222 d.d.
11-11-1981 from Raltech Scientific Services. Submitted to WHO by Bayer
AG, Bayerwerk, 5090 Leverkusen, FRG.
Eiben, R., 1984. SS 2074 (new designation SAS 2074)
(c.n. chinomethionat). Two generation study with rats. Unpublished
report no. 12794 d.d July, 6 1984 from Institute of Toxicology, Bayer
AG. Submitted to WHO by Bayer AG, Bayerwerk, 5090 Leverkusen, FRG.
Hayes, R.H., 1983. Chronic dietary toxicity of oxythioquinox
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Bayerwerk, 5090 Leverkusen, FRG.
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Submitted to WHO by Bayer AG, Bayerwerk, 5090 Leverkusen, FRG.