AGP:1970/M/12/1
WHO/FOOD ADD/71.42
1970 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
THE MONOGRAPHS
Issued jointly by FAO and WHO
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
Group on Pesticide Residues, which met in Rome, 9-16 November, 1970.
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
WORLD HEALTH ORGANIZATION
Rome, 1971
DIMETHOATE
Explanation
This pesticide was evaluated by joint meetings in 1965, 1966 and 1967
(FAO/WHO 1966b, 1967b and 1968b).
On the latter occasion temporary tolerances for three classes of
fruits and vegetables were recommended, the latter being for a
combination of dimethoate and its oxygen analog, now known as
omethoate. Further work was required before 30 June 1970 on the fate
of the compound during processing and preparation for consumption and
on residues appearing in total diet studies.
RESIDUES IN FOOD AND THEIR EVALUATION
Analysis of fresh fruit and vegetables, obtained from field trials in
northern Italy and flown with due precautions to Helsinki, were made
at the Institute of Food Chemistry and Technology (Koivistoinen,
1970). Information concerning rates and dates of application of
dimethoate, and of harvest dates, is given in Table 1. The samples
were stored at -20°C and analysed within five days by a method
employing gas chromatography with a phosphorous sensitive detector.
The lowest level detectable (LLD) was 0.02 ppm for either dimethoate
or omethoate, recovery at such levels being 90 percent. Other samples
taken at harvest were processed in Italy by normal commercial
procedures, and later analysed in a similar way. The processing
treatment(s), and the residues of dimethoate and omethoate found both
for the fresh and the processed commodities, are given in Table II.
All forms of processing reduce the level of dimethoate and omethoate;
the latter is always present at a much lower level than the parent
pesticide.
It is worth noting that Lee (1968) has published data showing that
residues of dimethoate on commercially sprayed green peas and lettuce
did not exceed 0.24 and 0.8 ppm at 2 and 9 days harvest intervals,
respectively.
Total diet samples, each consisting of 7 sub-samples (cereals, meat
and fish, fats, fruit and preserves, root vegetables, green
vegetables, milk), were collected over a 12 month period in England
and Wales, and analysed for organophosphorous pesticide residues by a
gas chromatographic procedure using a phosphous-sensitive detector
(Abbott et al., 1970). Neither dimethoate nor omethoate was detected
in any sample. Duggan and Lipscomb (1969) did not find dimethoate or
omethoate in any class of food during four years' studies of total
diets in the U.S.A.
TABLE I
Data on dimethoate application
Interval between
Concn.a.i. No. of times final application
Crop % sprayed and harvest (days)
Tomatoes 0.04 2 7
Peas, garden 0.04 2 6
Beans, green 0.04 2 6
Carrots 0.04 2 7
Peppers 0.04 2 7
Cherries 0.02 1 10
Oranges 0.05 3 10
Pears 0.04 3 10
Peaches 0.04 2 10
Spinach 0.04 2 6
Cabbage, Savoy 0.05 2 7
Artichokes 0.04 2 7
TABLE II
Dimethoate and omethoate residues in fresh and processed commodities
Commodity Dimethoate Omethoate Total
(ppm) (ppm) (ppm)
Tomatoes, fresh
washed 2 min. <LLD <LLD <LLD
juice/purée
(egg-shaped) peeled
Peas, fresh <LLD-0.1 <LLD <LLD-0.1
canned <LLD <LLD <LLD
TABLE II (cont'd)
Dimethoate and omethoate residues in fresh and processed commodities
Commodity Dimethoate Omethoate Total
(ppm) (ppm) (ppm)
Beans, fresh 0.2-0.3 0.04-0.1 0.24-0.4
canned <LLD <LLD <LLD
Carrots, fresh <LLD <LLD <LLD
canned <LLD <LLD <LLD
Peppers, fresh 0.38-0.58 0.16-0.26 0.58-0.84
canned <LLD-0.04 <LLD <LLD-0.06
Cherries, fresh 0.55-0.85 0.2 0.8-1
canned (with syrup) 0.36-0.5 0.07-0.13 0.45-0.63
Oranges, fresh(unpeeled) 1.2-1.5 <LLD 1.2-1.5
canned juice 0.24-0.32 <LLD 0.24-0.32
marmalade 0.02-0.04 <LLD 0.02-0.04
Pears, fresh 0.44-0.70 0.1-0.2 0.55-0.9
canned 0.17-0.23 0.02-0.04 0.2-0.24
Peaches, fresh 0.23-0.4 <LLD 0.23-0.4
canned halves(in syrup) 0.07-0.33 <LLD 0.08-0.33
jam 0.05-0.06 <LLD 0.05-0.06
Spinach, fresh 2.24-3.08 0.1-0.16 2.34-3.24
Cabbage (savoy), fresh 0.57-0.84 <LLD 0.57-0.84
Artichoke, fresh 0.48-1.05 0.1-0.3 0.62-1.36
NOTE: Lowest level detectable (LLD) was 0.02 ppm.
The report from Storherr and Watts (1969) that the initial ratio of
1:20 for dimethoate and omethoate, following the spraying of
dimethoate on kale, changed after fourteen days to 4:1 must be taken
to indicate a different pattern of metabolism in this crop from that
leading to the results quoted above for other vegetables and for
fruit.
Beck et al. (1968) fed silage made from dimethoate-treated corn to
cows and found no trace of dimethoate or omethoate in the milk. But
when capsules containing 1 mg/kg dimethoate and 0.1 mg/kg omethoate
were fed to three cows for fourteen days, the level of omethoate in
the milk varied from 0.004 to 0.125 ppm, although no dimethoate was
detected.
METHODS OF RESIDUE ANALYSIS
Among new methods of residue analysis using gas chromatography, that
described by Abbott et al. (1970) should be adequate for regulatory
purposes for the tolerances recommended.
APPRAISAL
Analyses of vegetables and fruits treated with dimethoate according to
recommended practice in northern Italy have shown that fresh tomatoes
and tomato products and fresh or canned carrots contained no
detectable residues of dimethoate or its oxygen analogue, omethoate.
Residues of dimethoate present at harvest in garden peas, green beans,
peppers, spinach, cabbage, artichokes, cherries, pears, peaches and
oranges were reduced by processing to levels well below those
recommended in the '1967 Evaluations of some pesticide residues in
food'.
Total diet studies in the U.S.A. and in England and Wales have shown
that neither dimethoate nor omethoate were detected. The two items of
further work required by 1970 have therefore been adequately met.
As the A.D.I. set in 1967 (FAO/WHO, 1968) was not temporary, and as
the total diet studies show that this A.D.I. is not being exceeded,
the tolerances recommended in 1967 on a temporary basis can now be
regarded as acceptable tolerances for dimethoate and omethoate
combined. The tolerances are:
Tree fruits (including citrus) 2 ppm
Tomatoes and peppers 1 ppm
Other vegetables 2 ppm
The only commodity with a significantly higher residue than that
reported in the earlier monograph (FAO/WHO, 1968b) is spinach, and in
this case the harvest interval was much shorter than before.
Other samples of the spinach, savoy cabbage, and artichokes were
subjected to cooking in salt water for suitable periods and analysed
for dimethoate only (Table III).
TABLE III
Dimethoate residues in cooked vegetables
Dimethoate Dimethoate
Vegetable (ppm) Vegetable (ppm)
Spinach, fresh = 2.23-2.92 cooked 10 min. = 0.52-0.70
Savoy cabbage, = 0.23-0.31 cooked 30 min. = 0.11-0.14
fresh
Artichokes, fresh = 0.3-0.48 cooked 30 min. = 0.27-0.32
REFERENCES
Abbott, D.C., Crisp, S., Tarrant, K.R. and Tatton, J.O'G. (1970)
Pesticide residues in the total diet in England and Wales, 1966-1967.
III. Organophosphorous pesticide residues in the total diet. Pestic.
Sci., 1: 10-13
Beck, E.W., Johnson, J.C., Jnr., Getz, M.E., Skinner, F.B., Dawsey,
L.H., Woodham, D.W., and Derbyshire, J.C. (1968) Effects of feeding
dimethoate, its oxygen analog, and dimethoate treated silage to
cattle. J. econ. Ent., 61: 605-610
Duggan, R.E., and Lipscomb, G.Q. (1969) Dietary intake of pesticide
chemicals in the United States (II), June 1966 - April 1968.
Pesticides Monit. J., 2 (4): 153-162
Koivistoinen, P. (1970) Report on dimethoate and dimethoxon residues
in fresh and processed fruits and vegetables. Institute of Food
Chemistry and Technology, Helsinki, Finland. 15 p.
Lee, D.F. (1968) Pesticide residues in foodstuffs in Great Britain.
VII. Demeton-methyl and dimethoate residues in Brussels sprouts,
lettuce, green peas and French beans, potatoes and strawberries. J.
Sci. Fd Agric., 19: 451-453
Storherr, R.W., and Watts, R.R. (1969) Gas chromatographic
determination of residues of dimethoate and its oxygen analog in
field-sprayed kale. J.A.O.A.C., 52: 511-513
See Also:
Toxicological Abbreviations
Dimethoate (EHC 90, 1989)
Dimethoate (HSG 20, 1988)
Dimethoate (ICSC)
Dimethoate (FAO Meeting Report PL/1965/10/1)
Dimethoate (FAO/PL:CP/15)
Dimethoate (FAO/PL:1967/M/11/1)
Dimethoate (JMPR Evaluations 2003 Part II Toxicological)
Dimethoate (Pesticide residues in food: 1983 evaluations)
Dimethoate (Pesticide residues in food: 1984 evaluations)
Dimethoate (Pesticide residues in food: 1984 evaluations)
Dimethoate (Pesticide residues in food: 1987 evaluations Part II Toxicology)
Dimethoate (Pesticide residues in food: 1996 evaluations Part II Toxicological)