CHINOMETHIONAT JMPR 1977
Explanation
Chinomethionat was last reviewed by the 1974 Meeting (FAO/WHO 1975)
and the following further information was required by 1977.
1. Studies to identify and evaluate the toxicity of metabolites.
2. A method of analysis that determines the
2,3-dithiolo-6-methylquinoxaline metabolite.
The 1974 Meeting also considered the following information desirable:
1. Studies on the relationships between observed liver enlargements
and reduced microsomal enzyme activity.
2. Studies of metabolism in non-rodent species of animal.
3. Observation in humans.
4. Information on the lower limit of determination of chinomethionat
in various crops with the use of Vogeler's method.
The Codex Committee on Pesticide Residues at the ninth session (1977,
Alinorm 78/24) requested governments to make residue data available to
the 1977 Joint Meeting and also requested the Joint Meeting to
reconsider the basis for the data on which its recommendation for a
temporary maximum residue limit of 0.5 mg/kg in apples was set. This
was because some delegations believed that a limit of 0.2 mg/kg would
suffice.
No information was received from governments but the principal
manufacturer provided data on residues and analytical methods in
response to the request of the Joint Meeting. These and some data on
evaluation for ADI are reviewed below.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Biotransformation
Chinomethionat was given to rats orally as a suspension or an an
emulsion, labelled with 14C either at the carbonyl carbon or in the
ring, the dose being 10 mg/kg (Gaines, 1969; Carlson and duBois,
1970). The animals were immediately placed in all-glass Roth
metabolism cages. It was found that 97% of the dose of the
carbonyl-labelled compound was recovered as CO2, and the conversion
was so rapid (75% in 7 hr) to suggest that some was lost before the
animals were placed securely in their cages. This method of labelling,
therefore, was of no value in the further study of chinomethionat
metabolism. However, when the compound was given in the ring-labelled
form, 75% of the radioactivity was recovered from the excreta in 72
hr, and 83% in 382 hr (partition between urine and faeces not given).
Residues of 14C were found mainly in the lower G.I. tract, liver,
kidney and stomach at 12 and 24 hr. in the kidneys and lower G.I.
tract at 72 hr. Chinomethionat was not detected as such in urine or
faeces; therefore, all of the radio-activity present therein (as
suggested by the experience with the carbonyl-labelled compound) had
to be present in the form of degradation products. One of these
products, 2,3-dithiol-6 methylquinoxaline (QDSH) was found in both
urine and faeces. It was believed by the authors that the hydrolysis
ChQDSH occurs in the G.I. tract. Two metabolites, identified only as
"unconjugated compounds", accounted for 48% of the radioactivity in
the urine. Glucuronides accounted for 8% and other water-soluble
compounds for 44%. At least 6 metabolites were found in the urine, of
which one was QDSH, free and/or bound.
The metabolism of chinomethionat (35S-labelled) following single oral
doses of 40 mg/kg dissolved in olive oil, to male rats, has been
studied. These doses were very rapidly absorbed, with 35S appearing
in the plasma within 20 minutes and peaking at about 90 minutes. This
peak concentration was followed by a very slow decline, at a
regression rate indicating a half-life of about 26. The radioactive
compound in the plasma was very firmly bound to proteins, in the
approximate ratio albumin-globulin = 4/1. In animals sacrificed 24
after dosage the distribution of radioactivity was as follows: stomach
and contents, 3.5%; intestine and contents, 8.65%; caecum and
contents, 1.1%; liver, 1.05% (0.095% of dose/g); kidneys, 0.21%
(0.082% of dose/g); epididymal fat 12.4% (4.14% of dose/g); urine,
20.1%; faeces, 7.7%. On i.v. administration as a previously prepared
plasma protein complex, the 35S of chinomethionat was excreted
rapidly in the bile, peaking at about 50 minutes and then decreasing
rather rapidly to 1/6 the rate 180 minutes. The plasma regression rate
following i.v. administration of the protein complex suggested a
two-compartment model of volumes 10.4 (central) and 12.9 (peripheral),
and a plasma half-life for the comples of 7.9 hr. The peripheral
compartment as so conceived would include the adipose tissue (Carrera
et al., 1976).
EFFECTS ON ENZYMES AND OTHER BIOCHEMICAL PARAMETERS
The LD50 of chinomethionat in adult male rats is increased by the
prior administration of phenobarbital but not by the administration of
estradiol or by castration. In contrast, the LD50 in adult female
rats is decreased by the prior administration of phenobarbital, but
is not affected by the administration of testosterone (Carlson and
duBois, 1970).
TOXICOLOGICAL STUDIES
ACUTE TOXICITY
TABLE 1. Acute toxicity of chinomethionat
Route of
Animal Sex Administration LD50, mg/kg Reference
Rat Oral 1100 - 3000 Jones, 1968
Rat Dermal >1000 " "
Rat M Oral 1800(1513-2142) Gaines, 1969
Rat F Oral 1100(917-1320) " "
Rat M Dermal >2000 " "
Rat F Dermal >2000 " "
Rat (adult) M I.P. 192 ± 4.5 Carlson, 1970
Rat (adult) F I.P. 95 ± 14 " "
Rat (weanling) M I.P. 325 ± 16 " "
Rat (weanling) F I.P. 320 ± 19 " "
Rat (adult) M I.P. 458 ± 14 " "
Rat (adult) F I.P. 473 ± 6.6 " "
Acutely toxic doses cause diarrhoea, increased haematocrits, decreased
urine volume and lower blood pressure.
Relative toxicities of chinomethionat and its primary metabolite.
Carlson and duBois (1970) had available for test authentic samples of
chinomethionat and of its primary metabolite
(2,3-dithiol-6-methoxyquinoxaline). Both were evaluated for toxicity
in rats and mice, with these results (as i.p. LD50, mg/kg):
Test QDSH
Animal Sex Chinomethionat Metabolite
Adult rat M 192 ± 4.5 38 ± 5
Adult rat F 95 ± 14 86 ± 9
Weanling Rat M 325 ± 16 115 ± 12
Weanling Rat F 320 ± 19 124 ± 6
Adult Mouse M 458 ± 14 249 ± 43
Adult Mouse F 473 ± 6.6 263 ± 40
These data indicate that the metabolite was in all cases more toxic
than the parent compound although in the adult female rat the
difference found was not significant. By and large the LD50 of
chinomethionat appears to be higher than that of the QDSH metabolite.
SHORT TERM STUDIES
Rat
In female rats the MTD without mortality in a 2-month test was 25
mg/kg. Dietary levels of 500 ppm were fed to male rats in both 3- and
6-month experiments without producing excessive mortality in the
treated animals. Rather minor effects were observed, namely lower body
weights, some hepatomegaly and minor hepatic histopathology. The no-
effect level, therefore, would be somewhat less than 500 ppm. Rather
similar effects on body weight and hepatic morphology were obtained by
applying an aqueous suspension of chinomethionat to the clipped backs
of the animals 5 days/week for 3 weeks, at dose levels of 125
mg/kg/day. At lower doses no effects were seen (Carlson and duBois,
1970).
COMMENTS
A temporary ADI for humans was previously established.
A request was made for further metabolic studies in a non-rodent
species, explanation of the liver cell hyperplasia, loss of liver
microsomal enzyme activity, and, where possible, observation in
humans. Although some new metabolic data have been supplied, in
general no other information was provided. Therefore, it was decided
to extend the temporary ADI for humans.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 12 mg/kg in the diet, equivalent to 0.6 mg/kg bw.
ESTIMATE OF TEMPORARY ACCEPTABLE DAILY INTAKE FOR HUMANS
0-0.003 mg/kg bw
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Use of the compound have been summarized in the previous evaluations
(FAO/WHO 1969, 1975). Additional use patterns are summarized in Table
2.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Supervised trials were carried out on oranges and apples (United
States), strawberries (Japan), cucurbits and grapes. The results are
summarized in Table 3. It is seen that low residue levels were
observed, and in most fruits covered with peel penetration into the
pulp appears to be negligible.
FATE OF RESIDUES
In Animals
To determine whether or not chinomethionat residues in cattle feed
prepared from citrus peel could be transferred to milk or meat, a
dairy cow was given doses of 14C-labelled chinomethionat, twice daily
for 24 days, equivalent to a rate of 0.0675 mg/kg body weight/day, the
dosage expected to be normally consumed by the cow when feeding on dry
citrus peel prepared from fresh orange peel containing a residue of
1.5 mg/kg. The only tissue residue detected after the 25th day was
0.05 mg/kg in liver and the highest milk residue was 0.002 mg/kg.
Minimum limits of detection were 0.001 mg/kg for milk and 0.02 mg/kg
for meat. The experiment showed that residues of chinomethionat in
cattle feed at the level used were not likely to result in residues in
meat or milk, especially when one considers the data in Table 3 as
well as the 93% destruction of chinomethionat when fresh citrus peel
is converted to dry cattle feed (Everett and Olson, 1968).
Almond hulls are also used for cattle feed and a study was conducted
to determine whether or not residues would be detected in the tissues
and milk of two dairy cows. Almond hulls containing approximately 0.08
mg/kg chinomethionat, 14C-labelled, and 1.14 mg/kg equivalent of
total radioactive residue comprised about 20% of the ration.
Radioactive residues in milk are shown in Table 4 while Table 5 shows
the residue levels in meat. Tissue residues could be detected only in
liver and kidney and residues in milk never exceeded 0.008 mg/kg with
maximum residues being reached about 10 days after the start of
feeding. The highest level in plasma was about 0.007 mg/kg at about 14
days, declining to about 0.005 mg/kg at day 21 (Murphy et al., 1977).
In Plants
When 14C-chinomethionat was applied to apples and oranges, slow
hydrolysis to 2,3-dithiol-6-methylquinoxaline (QDSH) was observed,
reaching a maximum at 7-14 days after application. QDSH was reported
as the total of free and bound QDSH and the residue levels in the
peels are shown in Table 6. One or more unidentified bound metabolites
were also reported; their residue levels are also summarized in Table
6.
In pre-bloom application to apple trees, only chinomethionat was
detected in fruits, possibly owing to the low residues observed.
Residues in fruits were 0.002 mg/kg or less.
TABLE 2. Summary of additional uses of chinomethionat
Crop Pest Application rate Pre-harvest
(% a.i.) interval
(days)
Apples ) Mites 0.0125 21
Peaches ) Powdery mildew 0.0125 21
Cucurbits ) 7
(3 under glass)
Citrus ) Mites 0.0125 21
Grapes )
Cereals Powdery mildew 0.13 kg a.i./ ----
100-200 liters/ha.
TABLE 3. Summary of additional residues data from supervised trials with chinomethionat
Fruit Application rate Days after Residues,
% a.i. No. of applications application mg/kg
Curcurbits 0.0125% 1 1 0.12
2 0.08
4 0.12
7 0.10
Grapes 0.0125% 2 1 0.38
7 0.06
14 0.02
21 ND1
Oranges (peel) 0.22 1 7 0.38
(controlled 14 0.37
application) 28 0.16
36 0.08
Oranges (pulp) <0.01
Apples (peel) 0.145 1 0 1.8
(controlled
application) 7 0.58
14 0.32
28 0.05
36 0.03
Apples (pulp) <0.01
Apples prebloom application 35
79 <0.01
157 ND1-0.002
Strawberry 0.01 6 1 0.5
3 0.35
7 0.2
14 0.05
1 Not detectable.
TABLE 4. Residues of 14C-chinomethionat in milk from dairy cows fed daily
with almond hull ration containing chinomethionat residues
Days after first feeding Residues, mg/kg chinomethionat equivalents
Cow A Cow B
0 0.0002 -
1 - 0.0002
2 0.002 0.001
5 0.0035 0.0018
8 0.0036 0.0025
10 0.007 0.005
11 0.0054 0.0039
14 0.005 0.0033
16 0.0042 -
17 - 0.0032
21 0.0026 0.0022
TABLE 5. Residues of C14-chinomethionat in tissues taken
from dairy cows fed an almond hull ration for 21 days
Tissue Residue, mg/kg chinomethionat equivalents
Cow A Cow B
Liver 0.02 0.03
Kidney 0.03 0.02
Heart <0.02 <0.02
Brain <0.02 <0.02
Muscle <0.02 <0.02
Fat <0.02 <0.02
TABLE 6. Summary of reported residue levels of QDSH and unidentified bound
metabolites in orange and apple peels from chinomethionat application.
Application rate
Crop chinomethionat Days after Residues, mg/kg
% a.i. Number Application QDSH unidentified
Oranges 0.22 1 7 0.2 0.09
(C14labelled cpd., 14 0.2 0.09
controlled appln.) 28 0.13 0.14
36 0.14 0.18
Apples 0.145 1 0 0.6 0.01
7 0.25 0.64
14 0.11 0.55
21 0.1 0.62
28 0.03 0.5
36 0.01 0.4
METHODS OF RESIDUE ANALYSIS
A method suitable for the analysis of QDSH was submitted by the
manufacturer. It is based on chelation with an ammoniacal nickel
reagent to give a red colour which can be measured at 540 nm (Havens
et al., 1964). The method can detect about 0.1 mg/kg chinomethionat or
QDSH.
NATIONAL TOLERANCES REPORTED TO MEETING
Additional national tolerances and safety intervals reported to the
Meeting are listed in Table 7.
APPRAISAL
Chinomethionat is a widely used fungicide/acaricide used mainly in
fruits with some uses in vegetable production. In apples, if
recommended application rates (e.g. 0.0125%) and application intervals
of 7-21 days are observed, residue levels under field conditions
appear to be less than 0.2 mg/kg. Thus the proposed temporary maximum
residue limit can be lowered from 0.5 mg/kg to 0.2 mg/kg.
Chinomethionat residues are generally low 14 days after application
(about 0.37 mg/kg in orange peel and 0.32 mg/kg in apple peel) and
penetration into the flesh of fruits covered with peel appears
negligible (< 0.01 mg/kg). Residues of 2,3-dithio-6-methyl
quinoxaline (QDSH) and unidentified metabolites arising from
chinomethionat application are confined to the peel.
TABLE 7. Additional national tolerances and safety intervals for chinomethionat.
Country Crop(s) Tolerance Safety intervals
mg/kg (days)
Argentina Pome and stone fruit, citrus, grapes, - 14
tobacco, vegetables
Australia general - 14
Pome and stone fruit 0.5
Cucurbits 0.5
Austria Vegetables, fruits, cucumbers, tomatoes, 0.1 4
paprikas
All other registered crops - 14
Belgium Fruits, vegetables, except potatoes & citrus 0.3 -
Cucumbers - 3
All other registered crops - 21
Brazil General - 14
Cucurbitaceae - 7
Bulgaria General - 20
Denmark General - 7
Cucumbers - 4
Finland Cucumbers - 4
General - 14
German Democratic Fruit and vegetables - 14
Republic Leaf vegetables - 28
Cucumbers (field grown and under glass) - 4
Food crops, pasture - 14
TABLE 7. (Continued)
Country Crop(s) Tolerance Safety intervals
mg/kg (days)
Germany (FRG) Vegetables, fruits 0.3 -
Cucumbers, pumpkins (field grown) - 4
Cucumbers, melons (under glass) - 4
Pipfruit, currants, gooseberry (field grown) - 14
Hungary General 0.1 -
Vegetables - 7
Fruits - 14
Israel Apples, apricots, peaches - 10
Grapes - 14
Carrots - 7
Tomatoes, paprikas, aubergines, cucumbers, melons - 2
Italy General - 21
Japan Fruits and vegetables 0.5 -
Citrus - 7
Cucumbers, strawberries, aubergines - 1
Watermelon, melon, sweet melon, pumpkin - 3
green pepper
Mexico Fruits - 14
Vegetables and other crops - 7
New Zeland Apples, pears, peaches, grapes, citrus - 21
Cucurbits (under glass) - 3
Cucurbits (field grown) - 7
Netherlands Apples, pears 0.3 21
Cucumbers (augurk, konkommer),melons 0.3 3
TABLE 7. (Continued)
Country Crop(s) Tolerance Safety intervals
mg/kg (days)
Norway As wettable powder: cucumber under glass - 4
All other registered crops - 7
As fumigant: All registered crops - 4
Poland Fruit, vegetables - 21
Cucumbers - 4
Vegetables 0.3 -
(proposed)
Portugal General - 28
South Africa General 0.5 -
Apples, pears, cape gooseberries, citrus,
peaches, cucurbits - 14
Tomatoes - 3
cotton (for feeding) - 14
Spain Melons, cucumbers - 14
All other registered crops - 15
Sweden Cucumbers - 4
All other registered crops - 7
Switzerland Fruit, cucumbers 0.1 -
Fruit - 21
Cucumbers (field grown and under glass) - 3
United Kingdom Cereals - 60
Apples, pears - 21
Gooseberries, black, white and red currants,
strawberries - 14
Cucumbers, tomatoes - 2
Vegetables, marrows grown outdoors - 7
TABLE 7. (Continued)
Country Crop(s) Tolerance Safety intervals
mg/kg (days)
USA Apples, pears 0.05 -
Citrus fruits, papayas 0.5 60
Macadamia nuts, walnuts 0.6 0/30
Meat, fat, meat byproducts of cattle, goats,
hogs, horses, sheep 0.05 -
Milk 0.01 -
Yugoslavia Fruit 0.05 -
Cucumbers - 7
All other registered crops 14
About 93% of the compound in fresh citrus peel is destroyed in the
preparation of dry cattle feed. When dairy cows were fed with a ration
containing 0.0675 mg/kg body weight chinomethionat in dry citrus pulp,
no residues in meat and milk could be determined (< 0.001 mg/kg).
Very low residues (<0.007 mg/kg) were also observed in milk when cows
were fed almond hulls containing approximately 0.08 mg/kg
chinomethionat; the almond hulls comprised about 20% of the ration. On
the other hand, residues were observed in the liver and kidneys at
0.02-0.03 mg/kg levels.
The manufacturer submitted a colorimetric procedure for the detection
of free QDSH at concentrations about 0.1 mg/kg.
The information available indicated that the lower limit of
determination of parent chinomethionat using the Vogeler method is
0.02 mg/kg in cucumbers and pome and berry fruits.
The Meeting agreed that the information required for the evaluation of
residues in food by the 1974 Meeting had been provided.
RECOMMENDATIONS
The previously recommended temporary maximum residue limit for apples
is amended as follows.
Commodity Limit, mg/kg
Apples 0.2
FURTHER WORK OR INFORMATION
Require, (before July 1981)
1. Studies on the identity and relative toxicity of metabolites.
2. An additional carcinogenicity study in another species, in view of
the hepatic toxicity observed in rodents.
Desirable
1. Observations in humans.
REFERENCES
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biochemical mechanisms of action of 6-methyl-2,3-quinoxalinedithiol
cyclic carbonate (Morestan) J. Pharmacol. Exp. Therap. 173:60-70.
Carrera, G., Mitjavila, S., Lacombe, C. and Derache, R. (1976)
Toxicokinetics of a pesticide of the thioquinoxaline group:
oxythioquinox. Toxicology 5:161-171.
Everett, L.J. and Olson, T.J. (1968) Chemagro Corp., Research Dept.,
Report no. 23565, 18 October 1968 (unpublished).
FAO/WHO (1969) 1968 evaluations of some pesticide residues in food.
FAO/PL:1968/M/9/1: WHO/Food. Add./69.35.
FAO/WHO (1975) 1974 evaluations of some pesticide residues in food.
AGP:1974/M/11; WHO Pesticide Residues Series, No. 4.
Gaines T.B. (1969) Acute toxicity of pesticides. Toxicol. Appl.
Pharmacol. 14:515-534.
Havens R., Adams J.M. and Anderson, C.A. (1964) Colorimetric
determination of 6-methyl-2,3-quinoxalinedithion cyclic carbonate
(Morestan) residues in apples and pears. J. Agr. Food Chem. 12(3),
247-248.
Jones, K.H., Sanderson, D.M. and Noakes, D.N. (1968) Acute toxicity
data for pesticides (1968). World Rev. Pest Control 7:135.
Murphy, J.J., Minor, R.G., Strankowski, K.J., Guerrero, F.P., Peoples,
S.A. and Siegel, D. (1977) Chemagro Corp., Research Dept., Report No.
53619, 27 June 1977 (unpublished).