FOLPET JMPR 1974
This monograph addendum should be read in conjunction with the
monograph from the 1973 Meeting (FAO/WHO, 1974, p. 278-280).
Explanation
Arising out of the list of requirements published in the report
of the 1969 Joint Meeting (FAO/WHO, 1970) some information on the
degradation of folpet, methods of analysis, use patterns in several
countries and residues resulting from supervised trials therein was
referred to the FAO Working Party of Experts.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Data on the use pattern in countries other than the U.S.A. was
required. Information was obtained on the current use patterns of
folpet in several countries, which is summarized in Table 1.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Residue data from supervised trials carried out in countries
other than U.S.A. was required. New data was obtained from supervised
trials on apples, peaches, grapes and strawberries (outdoor and
glasshouse, Table 2).
FATE OF RESIDUES
The main degradation mechanisms of folpet are postulated to be
the same as those for captan (FAO/WHO, 1970). Further information has
been obtained since then. The IUPAC commission on Terminal Residues
reviewed these data in its sixth Meeting in 1971. The dicarbonyl
portion of captan forms imides, phthalamic acids and dicarboxylic
acids (Lukens, 1966).
The degradation pattern of the -SCCl3 moiety is more complex. A
wide range of products containing sulphur in several oxidation states
have been found (Lukens, 1966). It was shown that volatile products
are formed such as COS (carbonyl sulfide) and CSCl2 (thiophosgene)
(Somers, 1967; Lukens and Sisler, 1958b).
The parent molecule on the CSCl2 moiety reacts with cysteine
(Lukens and Sisler, 1958a), and/or with various thiols occurring in
the plant (Richmond and Somers, 1966; Siegel, 1970).
TABLE 1. Current use patterns of folpet in several countries
Application rate
Recommended
pre-harvest
Country Crops g/100l kg/ha intervals (days)
Canada Apples 45-60 1
Blueberries, cherries 60 1.25 1
Black, red and white
currants 120 1.5 7
Gooseberries 60 1 7
Cranberries 2.25 30
Strawberries 60 1 1
France Apples, pears 100 nil
Grapes 100-175 15
Vegetables 100-125
Potatoes 150 nil
Netherlands Apples, pears -
Blackberries, raspberries,
strawberries (outdoors) 125 4
Strawberries (glasshouse) 125 14
Red and black currants 125 10
Lettuce (glasshouse) 1.6 21 period March/
November
42 period November/
March
South Africa Pome fruits, stone fruits,
citrus fruits, potatoes,
tomatoes 60 nil
TABLE 2. Supervised trials with folpet in several crops (Part A: 0-10 days)
Application
Country Rate kg Pre-harvest interval in days
Crop No a.i./ha Formulation 0-1 2-4 5-7 8-10
Netherlands3
Apples 1 2.0 w.p. 50% 1.48-1.60 1.41-1.57 1.39-1.47 1.07-1.47
Netherlands3
Red currants 5 2.251 w.p. 50% 17-4-33.6 9.0-33.6 8.1-13.2 5.1-16.3
Netherlands3
Raspberries 5 125g/100 l w.p. 50% 10.5-24.3 7.3-25.3 6.2-12.6 7.7-9.6
2 125g/100 l w.p. 50% 12.7-19.6 5.8-10.9 2.5-7.0 0.2-
Netherlands3
Strawberries 5 125g/100 l w.p. 50% 0.6-1.1 0.8-1.7
(outdoor) 2 125g/100 l w.p. 50% 0.3-0.5 0.1-0.4
Netherlands3
Strawberries 1 2 w.p. 75% 1.8-3.1
(glasshouse) 2 2 w.p. 75% 1.8-2.8
1 1.5 x normal rate
2 After 49 days
3 Food Inspection service of the Netherlands (1965 and 1967).
4 Chevron Chemical Company (undated)
TABLE 2. Supervised trials with folpet in several crops (Part B: 11-35 days)
Application
Country Rate kg Pre-harvest interval in days
Crop No a.i./ha Formulation 11-14 16-21 22-28 29-35
Netherlands3
Red currants 5 2.251 w.p. 50% 1.8-8.1 n.d.-1.5
France4
Grapes 4 1.5 w.p. 50% n.d.
(crushed) 4 1.5 w.p. 50% n.d.
4 1.65-1.75 w.p. 50% 2.1
8 0.9-2.1 w.p. 50% 0.31
4 1.2 w.p. 50%. 0.83
4 0.8-1.2 w.p. 50% n.d.
Netherlands3
Lettuce 3 1.6 dust 8% 8.5-14.1 0.3-1.4
(glasshouse) 3 1.6 dust 8% 10-0-17.3 4.3-6.5
France4
Peaches 2 1.85 w.p. 50% n.d.-0.28
Netherlands3
Strawberries 5 125g/100 l w.p. 50% 0.1-0.3
(outdoor) 2 125g/100 l w.p. 50% 0.1-0.2
Netherlands3
Strawberries 1 2 w.p. 75% 1.2-1.3 1.8-2.2
(glasshouse) 2 2 w.p. 75% 1.6-2.4 2.0-3.0
3 2.1 w.p. 83% 7.8-12.6 0.5-5.62
3 2.1 w.p. 83% 4.2-10.6 1.6-5.0
1 1.5 x normal rate
2 After 49 days
3 Food inspection service of the Netherlands (1965 and 1967).
4 Chevron Chemical Company (undated).
METHODS OF RESIDUE ANALYSIS
Kilgore et al. (1967) developed a gas liquid chromatography
method of analysis for folpet and captan. Since then the GLC method
has been modified and improved (Pomerantz and Ross, 1968; Archer and
Corbin, 1969). The limit of detection is about 0.01 mg/kg.
The above mentioned methods are suitable or can be adapted for
regulatory purposes.
TLC methods are also available, but these are less sensitive
(Engst and Schnaak, 1967).
NATIONAL TOLERANCES
Examples of national tolerances of folpet residues are reported
in Table 3.
TABLE 3. Examples of national tolerances reported to the Meeting
Tolerance
Country Commodities mg/kg
Canada Celery 30
Apples, avocados, blackberries,
blueberries, boysenberries,
cherries, crab apple, cranberries,
black, red and white currants,
dewberries, gooseberries,
grapes, huckleberries, leeks,
lettuce, loganberries, onions,
raspberries, strawberries, tomatoes 25
Citrus fruit, cucumbers, garlic,
melons, pumpkins, squash 15
Belgium Fruit and vegetables 15
France Fruit and vegetables 15
Democratic Pome fruits (apples and pears),
Republic of bananas, citrus fruit, black, red
Germany and white currants, gooseberries,
stone fruits, strawberries 5
Brassicas, fruits of vegetables,
green beans, leafy vegetables, peas,
potatoes 0.1
TABLE 3. (Cont'd.)
Tolerance
Country Commodities mg/kg
Cereals, onions, meat, fat of meat,
fish, milk, eggs, vegetable oils
and fats 0
Federal Rep. Fruit and vegetables 15
of Germany
Other agricultural crops 0.1
Hungary Fruit, including grapes, vegetables 15
Switzerland Fruit, including grapes 15
United States Celery, Cherries, leeks, lettuce,
onions (green), shallots 50
Apples, avocados, blackberries,
blueberries, boysenberries,
crab apple, cranberries, red and
white currants, dewberries,
gooseberries, grapes, huckleberries,
loganberries, raspberries,
strawberries, tomatoes 25
Citrus fruit, cucumbers, garlic,
melons, onions (dry bulb), pumpkins,
summer squash, winter squash 15
Yugoslavia Fruit, vegetables, other agricultural
crops 15
APPRAISAL
In the light of present information about the nature and fate of
terminal residues and the knowledge that the available analytical
procedures are adequate for regulatory purposes the meeting agreed
that the requirement for collaborative studies on analytical methods
was no longer necessary.
The Meeting was advised that results of further metabolism
studies should be available in 1975.
RECOMMENDATIONS
TOLERANCES
The tolerances recommended in 1969 have been confirmed as no
longer necessary.
The tolerance previously proposed for strawberries has been
amended and additional tolerances are recommended. These are based on
residues likely to be found at harvest following currently approved
use patterns.
Interval on which
recommendations
Crop ppm are based (days)
Strawberries 20 14
Lettuce 15 14
FURTHER WORK OR INFORMATION
DESIRABLE
1. Information on the nature, level and fate of residues following
washing, blanching, storage and thermal processing of treated
crops.
2. Residue data obtained by newer methods of analysis on the main
commodities for which tolerances have been recommended.
3. Information on the fate of residues in soil.
4. Further data on the quantities of degradation products in
relation to residues of the parent compound.
5. Results of metabolism studies currently planned.
REFERENCES
Archer, T.E., and Corbin, J.B. (1969) The site and fate of captan
residues from dipping prunes prior to commercial dehydration. Food
Technol. 23:235-238.
Chevron Chemical Company. Data provided to Joint Meeting.
Engst, R. and Schnaak, W. (1967) Dünnschichtchromatographische
Bestimmung von Rückständen der Fungizide Captan und Phaltan. Nahrung,
11:95-100.
FAO/WHO. (1970) 1969 Evaluations of some pesticide residues in food.
FAO/PL/1969/M/17/1; WHO/Food Add./70/38.
FAO/WHO. (1974) 1973 Evaluations of some pesticide residues in food.
FAO/AGP/1973/M/9/1; WHO Pesticide Residues Series, No. 3.
Food Inspection Service of the Netherlands, Amsterdam, (1965, 1967)
Reports 47, 68, 76, 88, 101, 106 and 122. (Unpublished).
IUPAC. (1971) Minutes of the sixth Meeting of the IUPAC Commission on
Terminal Residues, Washington, D.C., July 1971.
Kilgore, W.W., Winterlin, W. and White, R. (1967) Gas chromatographic
determination of captan residues. J. agr. Food Chem., 15(6):1035-1037.
Lukens, R.J. (1966) The fungitoxicity of compounds containing a
trichloromethyl-thio-group. J. agr. Food Chem., 14(4):365-367.
Lukens, R.J. and Sisler, H.D. (1958a)
2-Thiazolidinethione-4-carboxylic acid from the reaction of captan
with cysteine. Science, 127:650.
Lukens, R.J. and Sisler, H.D. (1958b) Chemical reactions involved in
the fungitoxicity of captan. Phytopathology, 48:235-244.
Pomerantz, I.H., Miller, L.J. and Kava, G. (1970) Extraction, cleanup,
and gas-liquid chromatographic method for the analysis of captan,
folpet and Difolatan in crops. J. Ass. off. Analyt. Chem.,
53(1):154-157.
Pomerantz, I.H., and Rose, R. (1968) Captan and structurally related
compounds: thin layer and gas-liquid chromatography. J. Ass. off.
analyt. Chem., 51(5):1058-1062.
Richmond, D.V., and Somers, E. (1966) Studies on the fungitoxicity of
captan. IV. Reactions of captan with cell thiols. Ann. Appl. Biol.,
57:231-240.
Siegel, M.R. (1970) Reactions of certain trichloromethyl sulfenyl
fungicides with low molecular weight thiols. J. agr. Food Chem.,
18(5):819-822, 823-826.
Siegel, M.R., and Sisler, H.D. (1968) Fate of the phthalimide and
trichloromethylthio (SCCl3) moieties of folpet in toxic action on
cells of Saccharomyces pastorianus. Phytopathology, 58:1123-1128.
Siegel, M.R. and Sisler, H.D. (1968) Reactions of folpet with purified
enzymes, nucleic acids, and subcellular components of Saccharomyces
pastorianus. Phytopathology, 58:1129-1133.
Somers, E., Richmond, D.V. and Pickard, J.A. (1967) Carbonyl sulphide
from the decomposition of captan. Nature, 215:214.