1967 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
THE MONOGRAPHS
The content of this document is the result of the deliberations of the
Joint Meeting of the FAO Working Party of Experts and the WHO Expert
Committee on Pesticide Residues, which met in Rome, 4 - 11 December,
1967. (FAO/WHO, 1968)
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
WORLD HEALTH ORGANIZATION
Rome, 1968
ZINEB
This pesticide was evaluated toxicologically by the 1965 Joint Meeting
of the FAO Committee on Pesticides in Agriculture and the WHO Expert
Committee on Pesticide Residues (FAO/WHO, 1965). Additional
toxicological information, together with information for evaluation
for tolerances, is summarized and discussed in the following monograph
addendum.
IDENTITY
Other relevant chemical properties
There are various proprietary formulations of zineb, including
Parzate, Dithane Z-78, Siaprit and Polyram (also known as Metiram, a
zinc-activated polyethylene thiuramdisulfide).
Parzate and Dithane Z-78 contain 65 per cent of active ingredient and
are formulated for use as dusts or water suspensions. Siaprit, on the
other hand, contains 45 per cent zineb plus 5 per cent ethylene
thiuram monosulfide (ETM), together with the usual inert diluents,
dispersants, stickers, etc. Polyram (Metiram) is formulated as an 80
per cent wettable powder, a 53.5 per cent seed protectant for cereals
and flax and a 7 per cent duct for foliar dusting and potato seed
treatment.
EVALUATION FOR ACCEPTABLE DAILY INTAKES
Short-term studies
Rat. In a reproduction study, rats were given ziram in doses of 10
and 50 mg/kg/day and zineb in doses of 50 and 100 mg/kg/day orally for
2-6 months. Sterility, resorption of fetuses and anomalous tails in
new born rats were observed at the high levels. The lower doses did
not cause any significant changes, compared with a control group
(Ryazanova, 1967).
Comments on experimental studies reported
The lowest level used in the long-term study in the rat, 500 ppm,
produced a goitrogenic effect. This was the only effect seen at this
level.
In the one-year study in the dog a level of 2000 ppm (50 mg/kg) was
associated with normal thyroid, and no toxicological effects were
observed at this level.
Apart from the goitrogenic effect in the rat, zineb is less toxic than
ziram in both rat and dog. A temporary ADI may be estimated using the
no-effect level in the rat for ziram (250 ppm), until data containing
a level that is non-goitrogenic in rats are provided.
TOXICOLOGICAL EVALUATION
Estimate of temporary acceptable daily intake for man
0 - 0.025 mg/kg body-weight (alone or in combination with other
ethylene bisdithiocarbamates).
This value is based on experiments carried out with zineb and does not
take account of chemical alterations after application.
Further work required
Studies in the rat, using levels below 500 ppm, to establish a level
that is non-goitrogenic.
Studies of the compound in plants to determine the chemical nature of
the residues, followed by appropriate toxicological studies.
Results of the above work should be made available not later than 30
June 1971 after which a re-evaluation of this compound will be made.
The re-evaluation may be made at an earlier meeting should relevant
information become available.
EVALUATION FOR TOLERANCES
USE PATTERN
Pre-harvest treatments
Zineb is primarily used as a pre-harvest spray or dust to protect
agricultural crops, both fruit and plants, from invasion by fungal
plant pathogens. Since the material is insoluble and non-systemic,
spraying involves the whole plant.
RESIDUES IN FOOD AT TIME OF CONSUMPTION
A recent survey of five composite basic 2-week diets for males, 14 to
19 years, showed the presence of six dithiocarbamates, ferbam, maneb,
metiram, thiram, zineb and ziram with values ranging from 0.4 to 0.8
ppm (Duggan, Barry and Johnson, 1966).
FATE OF RESIDUES
General considerations
Residues are reduced by a variety of factors such as weathering,
metabolism, physical removal by washing and trimming or brushing the
food product. During weathering, moisture, air and the plant may
participate in the production of a number of products such as
ethylenethiuram monosulfide, ethylene thiourea and ethylene
thiuramdisulfide.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Rate of Number Pre-harvest
application of interval
Crop (lb/acre) applications (days) Residue (ppm) Reference
apples 3.1 Rohm + Haas (1956)
apples 2 6 49 0.15 du Pont (1957)
celery 1 12 7 11 (unwashed) Rohm + Haas (1956)
3.4 (washed) "
cherries 2 4 30 3.6 "
cranberries 2 2 82 0.3 "
cucumbers 2 6 3 0.1 du Pont (1957)
lettuce 1 7 3.6 Rohm + Haas (1956)
oats 2 2 nil "
peppers 2 7 15 0.27 du Pont (1957)
potatoes 13 9 25 nil "
snapbeans 1.5 1 0 5.6 "
3 7.6 "
6 6.2 "
squash 2 7 30 0.05 "
tomatoes 1.5 1 0 1.7 "
Although the zinc salt is relatively inert and insoluble, degradation
slowly occurs when exposed to the atmosphere. Ethylene thiuram
disulfide (ETD) and ETM were identified (Morehart and Crossan, 1965)
as well as ethylene thiourea (ETU) and an unknown (Fishbein and
Fawkes, 1965) by chromatography. The former authors suggested, from
their metabolism studies with fungal spores, that toxicity is due
mainly to ETD. However others (Kovacs and Caumo, 1966) showed that a
formulation (Siaprit) gradually releases ETM which is immediately
effective in the control of the fungal pathogen. Zineb is insoluble
while ETM, although water solubility is only 200 ppm, exhibits
systemic activity (Kovacs and Caumo, 1966).
The decomposition of radioactive labelled zineb when applied to plants
has also been studied (Sato and Tomizawa, 1960). Chloroform extracts
contained ETU and at least one other decomposition product.
Accelerated decomposition by incubation with leaf washings was also
shown (Kovacs and Cucchi, 1964).
METHODS OF RESIDUE ANALYSIS
To date the usual method of analysis is based on a colorimetric
measurement of the carbon disulfide released on acid treatment of the
residue with modifications for particular crops to get improved
quantitative recovery (Gordon, Schuckert and Bornak, 1967).
RECOMMENDATIONS FOR TOLERANCES
Although some progress has been reported, neither the chemical nature
nor the mode of action of the residues of zineb in or on the plant
have been ascertained and there is no specific method of analysis
available. Accordingly, no tolerance figures can be recommended.
FURTHER WORK
Further work required before recommendations for tolerances can be
made
Further work is required on the metabolism of zineb in or on the plant
to include the identification and mode of action of any critical
intermediates, and on the development of specific methods of analysis.
The data on this subject is required prior to 30 June 1971.
NATIONAL TOLERANCES
Country Tolerance, ppm Crop Reference
Canada 1 wheat FDD, Canada (1967)
7 apples, apricots, beans, beets,
blackberries, black-eyed peas,
broccoli, Brussels sprouts,
cabbage, carrots, cauliflower,
celery, cherries, citrus fruits,
collards, corn, cranberries,
cucumbers, currants, eggplant,
endive (escarole), gooseberries,
grapes, guavas, kale, kohlrabi,
lettuce, loganberries, melons,
mushrooms, mustard greens,
nectarines, onions, parsley,
peaches, peanuts, pears, peas,
peppers, plums (fresh prunes),
pumpkins, quinces, radishes,
raspberries, rutabagas, salsify,
spinach, squash, strawberries,
summer squash, Swiss chard,
tomatoes, turnips.
U.S.A. 1 wheat * USDA, 1967
7 ** apples, apricots, beans, beets, USDA, 1967
blackberries, broccoli, Brussels
sprouts, cabbage, cantaloupes,
carrots, cauliflower, celery,
cherries, grapefruit, lemons, corn,
cranberries, cucumbers, grapes,
onions, peaches, peppers, radishes,
strawberries, turnips.
Country Tolerance, ppm Crop Reference
U.S.A. 25 Swiss chard, *** lettuce **** USDA, 1967
West Germany 3 leafy vegetables, fruits, pulses
* 3-4 week pre-harvest after application at 2.1 lb/acre
** various pre-harvest intervals following specific application rates
*** pre-harvest interval, 7 days
**** pre-harvest interval, head lettuce, 5 days.
REFERENCES PERTINENT TO EVALUATION FOR ACCEPTABLE DAILY INTAKES
Ryazanova, R.A. (1967) Gigiena i sanitaria, 2, 26.
REFERENCES PERTINENT TO EVALUATION FOR TOLERANCES
Duggan, R.E., Berry, H.C., Johnson, L.Y. (1966) Pesticide residues in
total diet samples. Science 151 : 101-104.
du Pont. (1957) Submission to Food and Drug Directorate, Canada Dept.
of Health and Welfare
FDD/Canada. (1967) Food and Drug Directorate, Canada. T.I.L. 290, 15
September
Fishbein, L., Fawkes, J. (1965) Thin layer chromatography of metallic
derivatives of etheylenebis(dithiocarbamic acid) and their degradation
products. J. Chromatog. 19 : 364-369.
Gordon, C.F., Schuckert, R.J., Bornak, W.E. (1967) Improved method for
the determination of ethylenebisdithiocarbamate residues in plants,
fruits and vegetables. J. Assoc. Off. Anal. Chem. 50 : 1102-1108.
Kovacs, A., Cucchi, N.J.A. (1964) Influence of excreted substance from
leaves on decomposition of zineb, a dithiocarbamate fungicide. Nature
204 : 1090.
Kovacs, A., Caumo, B. (1966) Systemicity of zinc
ethylene-bisdithiocarbamate. Atti. Simp. Int. Agrochim. 6 : 263-269.
Morehart, A.L., Crossan, D.F. (1965) Studies on the
ethylenebisdithiocarbamate fungicides. Exp. Sta. Bull. 357, Agric.
Exp. Stn. Univ. Delaware, Newark, Del. 26 p.
Rohm and Haas. (1956) Submission to Food and Drug Directorate, Canada
Dept. of Health and Welfare.
Sato, T. and Tomizawa, C. (1960) Decomposition of zineb applied to
plants. Bull. Natl. Inst. Agr. Sci., Ser. C, No. 12 : 181-187.
USDA. (1967) Summary of registered agricultural chemical pesticide
uses. 2nd ed. Suppl.III.
See Also:
Toxicological Abbreviations
Zineb (ICSC)
Zineb (FAO Meeting Report PL/1965/10/1)
Zineb (Pesticide residues in food: 1993 evaluations Part II Toxicology)
Zineb (IARC Summary & Evaluation, Volume 12, 1976)