PESTICIDE RESIDUES IN FOOD - 1984
Sponsored jointly by FAO and WHO
EVALUATIONS 1984
The monographs
Data and recommendations of the joint meeting
of the FAO Panel of Experts on Pesticide Residues
in Food and the Environment and the
WHO Expert Group on Pesticide Residues
Rome, 24 September - 3 October 1984
Food and Agriculture Organization of the United Nations
Rome 1985
DIMETHOATE
Explanation
Dimethoate was evaluated by the Joint Meetings held in 1965 and
1966; a complete revision was written in 1967, with addenda in 1970
and 1977. 1/ At the 1973 Joint Meeting the related compound
formothion was reviewed. In 1978 the Joint Meeting studied dimethoate,
omethoate and formothion together and expressed the view that residues
arising from the use of dimethoate should be determined and expressed
as the sum of dimethoate and omethoate, while residues arising from
the use of omethoate should be determined and expressed as omethoate.
The CCPR at its Twelfth Session (ALINORM 81/24, para 64)
requested the JMPR to consider separating the recommendations for
these compounds in view of the wide difference between their ADIs.
Efforts were therefore made to determine whether there was an adequate
data base upon which to recommend separate MRLs for the two compounds.
In response to a request to governments, a small amount of information
was received from Australia, Canada, Denmark, The Netherlands, New
Zealand, Portugal, Sweden and the UK. An extensive search of open
scientific literature was made and the many manufacturers of technical
dimethoate and many of the major formulators of dimethoate pesticides
were contacted with variable response. A spokesman for the task force
set up by the dimethoate manufacturers to review, revise and extend
the available data on dimethoate advised that the required information
could not be provided before 1987.
From the information obtained, and reviewed below, it has been
concluded that there is no basis for proposing separate MRLs for
dimethoate and omethoate when the latter compound occurs as a
metabolite of dimethoate and formothion.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
Dimethoate was first developed as an insecticide in the mid-
1950s. Its broad spectrum of effect due to its contact and systemic
action when applied to both animals and plants has resulted in its
being adopted for use against a wide variety of pest species on
virtually every crop except a small number that show phytotoxic
reaction to some dimethoate formulations. Even in some of these
situations special formulations have been developed to eliminate or
reduce the phytotoxicity.
1/ See Annex 2 for FAO and WHO documentation.
There are currently more than 10 manufacturers of dimethoate and
there seems little doubt that dimethoate is used for some purpose in
almost every country. Detailed use patterns were available from about
10 countries. These indicate a significant degree of similarity in
application rates and preharvest intervals (Table 1).
RESIDUES RESULTING FROM SUPERVISED TRIALS
Most reports of supervised trials present the residues data as
the sum of dimethoate and omethoate. Only very few reports indicate
the two values separately. Many of the results are based on the
determination of total phosphorus measured under controlled
conditions, and therefore do not provide data on which to judge the
relative concentrations of parent and metabolite.
Tables 2 and 3, the latter from a review by Agnihothrudu and
Mithyantha (1978), summarize the results of some studies which have
reported the residues as the sum of the two compounds. (Results of
others are reported in detail by de Pietri-Tonelli et al. (1965).
Studies which present the values for the concentration of the two
compounds separately are reported in greater detail in the following
sections.
Residues in Fruit
Apples
The results of trials by de Pietri-Tonelli and Barontini (1958)
and Enos and Frear (1964) are quoted by de Pietri-Tonelli et al.
(1965). The former indicate that the insecticide penetrates from the
epicarp into the pulp and that 15 days after treatment only a
negligible amount still remains on the outside of the fruits. After
penetration, the insecticide gradually diffuses into the pulp and also
into the core and becomes metabolized at the same time, the half-life
being approximately 8 days. The trials by Enos and Frear show that the
initial concentration of the insecticide in the fruits is roughly
proportional to the concentration of dimethoate applied to the plants.
They found a lower rate of disappearance (half-life 15-16 days).
Wit (1972) reported a trial carried out in The Netherlands in
1971 with two different formulations of dimethoate applied to two
varieties of apples at the rate of 300 g a.i./1. The apples were
harvested 1, 2 and 3 weeks after spraying. No omethoate (<0.1 mg/kg)
was found. The concentration of dimethoate declined from 0.2 mg/kg at
the time of spraying to 0.14 mg/kg 3 weeks later, with intermediate
values of 0.1 and 0.3 mg/kg at 1 and 2 weeks.
Information received from Portugal (1984) gives details of a
trial in which two groups of 9 apple trees were treated 5 and 7 times
with dimethoate emulsion (50g/1001) at intervals of 14 days. Analysis
for dimethoate and omethoate was by GLC (thermionic detector) with a
limit of determination of 0.01 mg/kg dimethoate and 0.05 mg/kg
omethoate. The omethoate residues were generally less than 10 percent
of the total dimethoate and omethoate residue (Table 4).
The Danish National Food Institute (Denmark, 1984a) provided
results of trials conducted in 1980 to determine the rate of
conversion of dimethoate to omethoate in apples sprayed with
dimethoate for the control of aphids. The treatments were made at the
highest permitted rate (a) and twice the permitted rate (b). The
results are given in Table 5.
A parallel experiment was conducted in which formothion was
substituted for dimethoate at: (a) the approved rate of application,
0.5 g/l; and (b) 1.0 g/l. The results are shown in Table 6.
Apricots
De Pietri-Tonelli et al. (1965) reported studies carried out
in 1959 in which apricot fruits were collected from trees sprayed with
dimethoate at two dosage rates when the pulp of the apricots, still in
the pre-ripe stage, was beginning to soften. Bioassay indicated, for
both rates of application, substantially similar rates of
disappearance of residues having insecticidal activity. The half-life
was approximately 7 days.
Black currants
Chilwell and Beecham (1960), using a method based on the
determination of phosphorus, showed that the residues in black
currants 7 and 14 days after application of dimethoate spray (0.5 g/l)
were 0.1 and 0.4 mg/kg respectively.
Bananas
Braithwaite (1963) dipped bananas in dimethoate solution
(0.3 g/l) for the control of fruit fly. Dimethoate residues in the
bananas 8 days after dipping were 0.7 mg/kg in the peel and 0.3 mg/kg
in the pulp. Further studies (Anon. 1969) indicated that the time of
immersion of the bananas in the dip bath did not significantly alter
the concentration of dimethoate residues which were between 0.3 and
0.7 mg/kg in the whole fruit and 0.05 and 0.08 mg/kg in the pulp
irrespective of whether the time of immersion was 10, 40 or 160
seconds.
Cherries
De Pietri-Tonelli et al. (1965) reported trials carried out
in 1956 which showed that dimethoate penetrated through the skin of
sprayed cherries into the pulp within a few hours of treatment. The
results indicated that the half-life of residues having insecticidal
activity was about 5 days.
TABLE 1. Registered uses of dimethoate
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
Cereals
barley Australia 35
maize 35
oats 35
sorghum 35
wheat 35
barley New Zealand 280-320
maize 280-320
oats 280-320
rye 280-320
wheat 280-320
sorghum South Africa 150-200
wheat 200-300
cereals UK 320-680
corn USA 350-500 3 14
sorghum 250-500 3 28
soybeans 500 21
wheat 250-400 14
barley Canada 200-480 21
oats 200-480 21
rye 200-480 21
wheat 200-480 21
Field Crops
alfalfa Australia 25-150
corn fodder 25-50
cotton 200
oilseeds 300
peanuts 35
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
rapeseed 135
safflower 135
soybeans 135
cotton (Algeria, Morocco) 200-500
soybeans (Tunisia, Senegal) 200-500
alfalfa New Zealand 120-200
chou moellier 320-400
rapeseed 320-400
sugarbeet 320-400
cotton South Africa 300 14
tobacco 300 14
peanuts 200-300 14
fodder best UK 84-420 2 7
mangolds 84-420 2 7
sugarbeet 84-420 2 7
alfalfa USA 250-500 1 10
cotton 250-500 2 14
safflower 250-500 2 14
soybeans 500 21
tobacco 250-350 21
alfalfa Canada 200-675 2, 7, 28
fababean 560 7
forage crops 200-260 2
pastures 200-260 2
rapeseed 275-300 1 30
sugarbeet 560 30
sweet clover 200-260 2
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
Fruit
apple USA 60 each 10-14 days 28
citrus 1000-2000 30-60 15
melons 500 3
pears 30-60 28
watermelons 250-500 3
apples Australia 30-60 7 & 5 weeks 7
(minimum)
pre-harvest
avocados 30 7
berry fruits 30 7
bananas 30 post-harvest -
cherries 20 7
citrus 30-60 7
grapes 30 7
mangoes 30 7
melons 30 7
pears 30-60 7 & 5 weeks 7(min.)
pre-harvest
peaches 30 4 & 2 weeks 7(min.)
pre-harvest
plums 30 4 & 2 weeks 7(min.)
pre-harvest
strawberries 30 7
apples France 50 7
cherries 30 7
grapes 15 7
melons 30 7
pears 50 7
peaches 30 7
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
strawberries 30 7
pineapples Algeria, Morocco 200-500
citrus Tunisia 200-500
bananas 20-500
apples New Zealand 20-24
berry fruit 32
citrus 32
pears 20-32
plums 20-32
strawberries 32
apples South Africa 30-50 14
citrus 20-40 14
grapes 2000 28
pears 800-1100 30-50 14
peaches 400-1000 40 28
plums 720-1680 50 28
pineapples 50 14
strawberries 30 14
apples UK 336-680 2 7
berry fruit 30 7
cherries 336-680 2 7
pears 336-680 2 7
peaches 30 7
plums 336-680 2 7
strawberries 30 7
apples Canada 1 47-60 3 7-14
blueberries 28-40 2 15
cherries 25-30 2 15
loganberries 20-37 2 -
peaches 800 22 2 70
pears 47-60 3 7-14
strawberries 75 2 7
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
Miscellaneous
fodder crops Australia 35-300
pastures 35-300
olives France 30 21
coffee (Algeria, Morocco) 200-500
cocoa (Senegal, Tunisia) 200-500
tobacco 200-500
olives 200-500
tobacco South Africa 320
hops UK 30 each 3 weeks 7
alfalfa USA 250-500 1 10
cotton 250-500 2 14
safflower 250-500 2 14
soybeans 500 21
tobacco 250-500 21
Vegetables
beans Australia 320 30 1-3 7
beetroot 320 30 1-3 7
broccoli 320 30 1-3 7
Brussels sprouts 320 30 1-3 7
carrots 320 30 1-3 7
cabbage 320 30 1-3 7
cauliflower Australia 320 30 1-3 7
celery 320 30 1-3 7
cucurbits 320 30 1-3 7
leafy vegetables 320 30 1-3 7
lettuce 320 30 1-3 7
onions 320 30 1-3 7
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
parsnips 320 30 1-3 7
peas 320 30 1-3 7
peppers 320 30 1-3 7
potatoes 320 30 1-3 7
tomatoes 320 30 4 & 2 weeks 7(min.)
pre-harvest
tomatoes 30 post-harvest -
capsicums 30 post-harvest -
artichokes France 30 15
asparagus 50 15
beetroot 250 30 15
cabbage 30 15
endive 30 15
lettuce 30 15
peas 30 15
broccoli New Zealand 400 7
beetroot 320 7
Brussels sprouts 400 7
cabbage 400 7
carrots 320 7
cauliflower 400 7
peas 320 7
potatoes 320 7
sweet corn 280 7
turnips 320-400 7
beans South Africa 30 14
brassicas 30 14
broccoli 30 14
Brussels sprouts 30 14
cabbage 30 14
cauliflower 30 14
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
cucurbits 30 14
kale 30 14
mustard 30 14
potatoes 300 14
beans UK 336 7
beetroot 336 7
brassicas 336 7
carrots 336 7
peas 336 7
peppers 30 7
potatoes 336 14 day intervals 7
tomatoes 30 7
turnips 336 7
beans USA 250-500 1
broccoli 250-500 7
cabbage 250-500 3
cauliflower 250-500 7
celery 500 7
collards 250 14
endive 250 14
kale 250 14
lettuce 250 14
mustard 250 14
peas 250 1
peppers 250-350 1
potatoes 250-500 1
spinach 250 14
tomatoes 250-500 7
turnips 250 14
beans Canada 275-500 as necessary 7
broccoli 275-500 " 4
TABLE 1. (continued)
Rate
Pre-harvest
Crop Country g/ha g/1001 Frequency interval, days
Brussels sprouts 275-500 " 4
cabbage 275-500 " 4
cauliflower 275-500 " 4
Chinese cabbage 550 2 7
beetroot 275-325 as necessary 12
kale 275-325 " 7
lettuce 275-325 " 7
peas 125-200 " 3
peppers 325-675 3
potatoes 275-675 7
spinach 275-325 7
turnip 275-325 7
tomatoes 275-675 7
Table 2. Residues reported as sum of dimethoate & omethoate
Application
Residues in mg/kg, at intervals (days) after application
Crop Country Year rate
no kg ai/ha formulation 0 1-2 4 7 10 14 Reference
Beans UK 1958 1 0.1% - 0.7
(French) UK 1958 1 0.1% 0.4
Egypt 1979 2 0.476 400EC 16.1 13.7 9.8 5.3 1.8 0 (21) Belal &
days Gomaa 1979
Brussels UK 1957 1 0.750 0.7 Chilwell &
Sprouts 1957 1 0.750 0.5 0.1 Beecham 1960
1957 1 0.750 1.1
1958 1 0.12 0.2 0.2
Cabbage UK 1958 1 0.04% 0.1 0.7 0.2 Chilwell
(21 & Beecham
days) 1960
UK 1958 1 0.04% 0.3
UK 1981 1 - 0.2
0.04 0.02
India 1977 1 0.25% - 6.8 3.84 Chakraborty &
0.05% 13.0 6.9 Mutatkar 1978
0.1% 15.4 8.9
UK 1958 1 0.04% - 1.3 0.5 Chilwell &
1981 1 - 0.1 Beecham 1960
Carrots UK 1958 3 1.0 0.6 Chilwell &
Beecham 1960
Table 2. (continued)
Application
Residues in mg/kg, at intervals (days) after application
Crop Country Year rate
no kg ai/ha formulation 0 1-2 4 7 10 14 Reference
Netherlands 1965 2 13.0 40EC 11 weeks
0.04
0.02
0.02
0.04
2 13.5 40EC 11 weeks 0.02 Greve 1980
12 weeks 0.03
14 weeks 0.02
Beetroot UK 1958 1 0.09 Chilwell &
Beecham 1960
Onions UK 1958 3 1.0 0.2
Cucumber Egypt 1979 2 0.476 900EC 11.8 10.3 6.3 3.2 0.8 Belal & Gomaa
1979
Tomatoes Egypt 1979 2 0.476 400EC 27.3 22.1 10.1 4.7 Belal & Gomaa
1979
Turnips UK 1958 2 1 0.4 Chilwell &
Beecham 1960
Kale UK 1958 1 0.5 0.3 Chilwell &
Beecham 1960
Peas UK 1958 1 0.2 - 0.3 0.1 Chilwell &
(without 1958 1 0.2 Beecham 1960
pod)
Table 2. (continued)
Application
Residues in mg/kg, at intervals (days) after application
Crop Country Year rate
no kg ai/ha formulation 10 15 20 25 30 Reference
Potatoes India 1977 5 300 300EC 2.03 1.27 0.69 0.43 0.08 Misra et al.
(unwashed) 500 30EC 2.73 1.53 0.87 0.51 0.14 (1981)
1977 5 300 300EC 1.87 0.98 0.61 0.21 0.06
500 300EC 2.11 1.07 0.67 0.33 0.09
Table 3a. Residues of dimethoate on crops arising from supervised trials in India.
Total Method
Crop Variety Location Dosage of No. of
used (kg Formulation application application
a.i/ha) used
1 2 3 4 5 6 7
Dimethoate;
Cabbage Golden '' 0.40 30 EC 0.03% One, 15
acre spray days before
(winter crop) 1300 l/ha. harvest
Cabbage Golden Delhi 0.52 30 EC 0.04% One, 15
acre spray at days before
1300 l/ha harvest
Spring 0.40 ,, 0.03% One, 15
crop) spray days before
1300 l/ha. harvest
0.52 ,, 0.04% spray ,,
1300 l/ha,
Cauliflower Pusa Delhi 0.42 '' 0.03% spray ''
Kathki 1400 l/h.
Early
crop: Aug-
Dec.)
0.56 ,, 0.04% spray ,,
1400 l/ha.
Table 3a. (continued)
Total Method
Crop Variety Location Dosage of No. of
used (kg Formulation application application
a.i/ha) used
1 2 3 4 5 6 7
Cauliflower Snow Delhi 0.42 '' 0.03% spray ,,
ball (Late 1400 l/ha.
crop Oct,
Feb.)
0.56 '' 0.04% spray ,,
1400 l/ha.
Yellow sarson Delhi 0.66 '' 0.03% spray Two
2200 l/ha.
0.50 ,, 0.0225% Two
spray
2200 l/ha
Yellow Delhi 0.88 30 EC 0.04% spray Two
sarson
Brown sarson '' 0.50 '' 0.0225% Two
spray 2200
l/ha.
Cabbage 0.225 EC Spray
Cowpea Bhubaneshwar 2.0 5% Gr. Soil Two, at
application sowing
flower
initiation
Table 3a. (continued)
Total Method
Crop Variety Location Dosage of No. of
used (kg Formulation application application
a.i/ha) used
1 2 3 4 5 6 7
Grape Anab-e- Coimbatore 30 EC 0.03% Four, at
Shahi spray 15 days
intervals
Grape Muscat Coimbatore 0.35 ,, Spray ,,
Guava Ludhiana 30 g/tree ,, 0.1% spray One
Peach '' '' '' '' One
Coconut Bangalore 2.5 g/ ,, Stem injection One
Tree
5.0 g/ ,, ,, One
tree
Chillies Local Bangalore ,, 0.06% Once in
spray 10 days
Tomato Bangalore '' ,, ,, 3 sprays
once in
10 days
Table 3a. (continued)
Total Method
Crop Variety Location Dosage of No. of
used (kg Formulation application application
a.i/ha) used
1 2 3 4 5 6 7
French Prochessor ,, ,, ,, ,, Once in
beans 10 days
Blue crop ,, ,, ,, ,, ,,
Ozark ,, ,, ,, ,, ,,
Var-60 ,, ,, ,, ,, ,,
Can yon ,, ,, ,, ,, ,,
Royalty ,, ,, ,, ,, ,,
purple
Silvert ,, ,, ,, ,, ,,
Groundnut TMV-7 Palghat ,, 03% spray Two
TMV-7 Coimbatore ,, ,, ,,
Table 3b.
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Dimethoate;
Cabbage Golden Heads: 17.03(0), 4.87(1), 3.95 7.2 0.59 2.0 B Krishniah
acre 3.25(4), 1.64(7), 1.02(10), & Rattan
(winter crop) 0.59(14) Lal (1973a)
Leaves: 15.11(0), 11.03(1), 4.40 1.65 ,, ,,
7.87(4), 4.80(7), 2.63(10),
1.65(14)
Heads: 6.78(0), 5.02(1), 0.54 ,, C ,,
3.17(4), 1.23(7), 0.82(10),
0.54(14)
Leaves: 15.32(0), 10.84(1), 1.39 ,, ,, ,,
8.95(4), 4.50(7), 2.82(10),
1.39(14)
Cabbage Golden Head: 9.68(0), 5.87(1), 3.82 8.0 0.79 2.0 B ,,
acre 4.61(4),2.22(7), 1.03(10),
0.79(14)
Leaves: 18.18(0), 15.03(1), 4.35 2.14 ,, ,, ,,
10.42(4), 5.91(7), 3.09(10),
2.14(14)
Head: 9.01(0), 6.99(1), 5.40(4), 0.67 ,, C
2.14(7), 1.07(10), 0.67(14)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Leaves: 17.82(0), 14.03(1), 1.82 ,, ,,
9.55(4), 4.87(7), 2.75(10),
0.22(14)
(Spring Head: 6.99(0), 4.40(1), 2.99 5.7 0.22 ,, B
crop) 3.15(4), 1.80(7), 0.78(10)
0.22(4)
Leaves: 12.86(0), 8.33(1), 3.33 0.63 ,, ,,
4.01(4),2.5(7), 1.32(10),
0.63(14)
Heads: 9.02(0), 5.51(1), 3.23 7.0 0.39 ,, ,,
4.00(4), 1.75(7), 1.04(10),
0.92(14)
Leaves: 15.2(0), 9.07(1), 3.57 0.92 ,, ,,
5.77(4), 2.97(7), 1.71(10),
0.33(14)
Cauliflower Pusa Curds: 6.37(0), 4.85(1), 3.38 0.33 ,, ,,
Kathki 3.28(4), 1.57(7),0.97(10),
(Early 0.33(14)
crop: Aug-
Dec.) Leaves: 12.61(0), 9.50(1), 3.82 5.7 0.95 ,, ,,
5.18(4), 2.63(7), 1.7(10),
0.95(14)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Curds: 6.90(0), 4.46(1), 0.44 ,, C
2.79(4), 1.78(7), 0.96(10),
0.44(14)
Leaves: 13.54(0), 9.58(1), 1.21 ,, ,,
5.28(4), 1.93(7), 1.51(10),
1.21(14)
Curd: 8.80(0), 5.29(1), 3.23 6.9 0.35 ,, B
3.59(4), 1.69(7), 1.12(10),
0.35(14)
Leaves: 14.26(0), 10.0(1), 4.02 1.45 ,, ,,
6.70(4), 3.09(7), 1.67(10),
1.45(14)
Curd: 8.71(0), 5.65(1), 3.11(4), 0.49 ,, C
1.55(7), 0.86(10), 0.49(14)
Leaves: 14.75(0), 9.72(1), 1.15 ,, ,,
5.70(4), 2.28(7), 1.32(10),
1.15(14)
Cauliflower Snow Curd: 6.71(0), 5.66(1), 4.30 7.5 0.81 ,, B
ball(Late 2.86(4), 1.70(7), 0.94(10)
crop Oct. 0.81(14)
Feb.)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Leaves: 11.14(0), 8.33(1), 4.33 1.29 ,, ''
5.09(4), 2.20(7), 1.84(10),
1.29(14)
Curd: 6.48(0), 5.20(1), 2.75(4). 0.74 ,, C
1.27(7), 0.87(10), 0.74(14)
Leaves: 11.67(0), 8.64(1), 1.23 ,, C
5.69(4), 2.31(7), 1.60(10),
1.23(14)
Curd: 8.75(0),5.79(1), 4.13 8.8 0.92 '' B
3.04(4), 1.68(7), 0.97(10),
0.92(14)
Leaves: 13.09(0), 8.97(1) 4.36 1.51 ,, ,,
5.91(4), 2.93(7), 1.67(10),
1.51(14)
Curd: 8.21(0), 5.64(1), 2.91(4), 0.81 ,, C
1.81(7), 1.09(10), 0.81(14)
Leaves: 13.60(0); 9.15(1), - 1.27 ,, ,,
5.80(4), 3.04(7), 1.82(10),
1.27(14)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Yellow sarson Leaves: 8.27(0), 6.38(1), 3.46 8.0 Seed: ND ,, B Krishniah &
2.25(3), 1.66(5), 1.01(7), Rattan
0.60(10), 0.56(14) Lal (1973b)
Leaves: 9.15(0), 6.45(1),2.88(3) ,, C ,,
1.78(5), 0.77(7),
0.70(10), 0.61(14)
Green pods: 3.93(0), 2.40(4), 4.85 5.0 ,, B ,,
1.58(7), 0.62(14), 0.19(21)
Green pods: 4.07(0), 2.24(4), ,, C
1.41(7), 0.54(14), ND(21)
Yellow Green pods: 6.29(0), 3.71(4), 5.1 8.4 Seed:ND 2.0 B
sarson 2.55(7), 0.93(10), 0.37(21)
Green pods: 5.69(0), 2.37(4), C
2.31(7), 0.83(14), ND(21)
Brown sarson Green pods: 3.90(0),2.14(4), 5.2 5.0 Seed:ND ,, B Krishniah
1.21(7), 0.40(14), 0.10(21) & Rattan
Green pods: 3.91(0), 1.86(4), ,, C Lal (19736)
1.08(7), 0.42(14), ND(21)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Green pods: 6.45(0), 3.05(4), 5.9 10.0 Seed:ND ,, B
2.60(7), 1.37(14), 0.46(21)
Green pods: 6.30(0),3.33(4), ,, C ,,
2.72(7), 1.24(14), 0.49(21)
Cabbage 3-7 0.47-1.92 ,, Vevai
(1974a)
Cowpea Leaves: 1.437(10), 0.920(20) ,, ,, Sathpathy
0.575(30) et al. (1974)
Fruits: 1.275(10), 0.712(20),
0.300(30)
Grape Anab-e- 0.23-0.32 ,, B & C Saivaraj et
Shahi el. (1976b)
Grape Muscat 13.5(0), 5.67(1),2.70(2), 5 0.75 C Raju-
1.56(4). 0.12(5), ND(8) kkannu et
al. (1977)
Guava 2.30(0) 3.0 1 2.0 TLC&C Sohi
(1974)
Peach 2.98(0) 4-5 3 ,, ,, ,,
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Coconut Water: 0.019, 0.003(14), ,, C Anon
ND(21) (1977a)
Water: 0.024(7), 0.004(14), ,, ,, ,,
ND(21)
Copra: 0.043(14)
Chillies Local Green fruits: 7.89(1), 0.25(15) ,, ,, ,,
Tomato 1.78(1),0.62(9),0.55(11), ,, ,, ,,
0.20(25)
French Prochessor Green fruits: 2.35(2), 1.27(4)
beans 0.48(10)
Blue crop Green fruits: 2.35(2), 0.91(4) ,, ,, ,,
0.57(10)
Ozark Green fruits: 2.24(2). 1.09(4) ,, ,, ,,
0.39(10)
Var-60 Green fruits: 2.46(2), 1.00(4) ,, ,, ,,
0.65(10)
Can yon Green fruits: 2.56(2), 1.00(4) ,, ,, ,,
1.00(10)
Table 3b. (continued)
Half Waiting Residues Tolerance Method
Crop Variety Dissipation rate life period of limit of Reference
(ppm after days*) suggested harvest (ppm) analysis
(days) (days) (ppm)
1 2 8 9 10 11 12 13 14
Royalty Green fruits: 2.67(2), 1.09(4) ,, ,, ,,
purple 0.65(10)
Silvert Green fruits: 2.56(2), 1.27(4) ,, ,, ,,
0.65(10)
Groundnut TMV-7 Kernel:0.48 ,, ,, ,,
Shell: 1.72 ,,
TMV-7 Kernel:0.55
Shell: 1.94
Table 4. Residues of dimethoate and omethoate in apples resulting from multiple applications of dimethoate
(Portugal, 1984)
Number Days
of between Residues found* (mg/kg)
applications last
application Field replicate 1 Field replicate 2 Field replicate 3 Mean
and
harvest dimethoate omethoate dimethoate omethoate dimethoate omethoate dimethoate omethoate
5 1 1.7 0.12 2.1 0.14 1.7 0.14 1.8 0.13
4 1.7 0.10 1.7 0.11 1.2 0.11 1.5 0.11
7 1.5 0.10 1.3 0.10 1.2 0.12 1.3 0.11
12 1.0 0.09 1.2 0.12 1.1 0.11 1.1 0.11
14 0.79 0.09 0.93 0.09 0.86 0.09 0.86 0.09
21 0.80 0.11 0.92 0.12 0.79 0.14 0.84 0.12
28 0.74 NA 0.72 NA 0.68 NA 0.71
7 1 2.7 0.16 2.5 0.14 2.6 0.16 2.6 0.15
4 2.3 0.18 2.1 0.18 1.8 0.15 2.1 0.17
7 2.1 0.15 1.9 0.16 1.9 0.16 1.9 0.16
12 1.8 0.15 1.8 0.14 1.5 0.14 1.7 0.14
14 1.7 0.16 1.5 0.14 1.4 0.12 1.5 0.14
21 1.6 0.13 1.4 0.14 1.1 0.12 1.4 0.13
28 1.3 0.12 1.4 0.11 1.3 0.11 1.3 0.11
* Mean of 3 analyses
NA - not analysed
Table 5. Residues resulting from the treatment of apples with dimethoate (Denmark, 1984a)
Application details Treatment (a) Treatment (b)
Concentration 0.6 g/l 1.1 g/l
Rate of application 400 l/ha 400 l/ha
Rate/ha 1.1 kg/ha 2.2 kg/ha
No. of applications 4 4
Interval between sprays 7 days 7 days
P.H.I. 10 days 10 days
Residue, mg/kg
Variety Dimethoate Omethoate Dimethoate Omethoate
Golden delicious 1.56-1.61 0.17-0.23 0.17-0.23 0.31-0.40
Cox orange 1.06-1.61 0.11-0.17 2.32-2.86 0.21-0.29
Cortland 1.04-1.09 0.09-0.07 1.48-2.52 0.09-0.14
Table 6. Residues resulting from the treatment of apples with formothion (Denmark, 1984)
Treatment (a)1 Treatment (b)1
Residue, mg/kg
Variety Formothion Dimethoate Omethoate Formothion Dimethoate Omethoate
Golden
delicious n.d2-0.03 0.77-1.73 0.11-0.16 0.05-0.14 1.18-2.0 0.10-0.15
Cox orange 0.02-0.03 0.86-1.69 0.12-0.17 0.03-0.11 1.34-1.88 0.09-0.12
Cortland n.d.-n.d. 1.11-1.35 0.11-0.14 n.d.-n.d. 1.11-1.73 0.05-0.07
1 Details as in Table 4, except application rates were (a) 0.5 g/l and (b) 1.0 g/l.
2 n.d. - not detected.
In further studies by Santi and de Pietri-Tonelli (1959), the
concentration of the insecticide in the fruits significantly increased
in the first days after treatment and then diminished. The increase of
concentration was attributed to systemic migration from leaves and
twigs into the fruits.
Zwick et al. (1975) demonstrated that dimethoate was most
effective for controlling cherry fruit fly in sweet cherries in
Oregon, USA. The highest residue of dimethoate was 0.9 mg/kg on the
day of application. Omethoate residues varied between 0.10 and
0.37 mg/kg. Details are given in the original publication.
MacNeil et al. (1975) studied the persistence of dimethoate
and omethoate in cherries when two sprays of dimethoate were applied
to both sweet and sour cherries 28 and 14 days prior to harvest. Table
7 shows the results. The omethoate residue remained relatively
constant at about 0.2 mg/kg indicating that omethoate is degraded at
about the same rate as it is formed by metabolism of dimethoate.
Zwick et al. carried out an extensive study at two sites in
Oregon to obtain data on the fate of two separate formulations of
dimethoate applied at 1.35 and 2.0 kg/ha to sweet cherries by
air-carrier application. Dimethoate and omethoate were determined
separately. The analytical data (Zwick et al., 1977) indicated
that the initial deposit was similar whether wettable powder or
emulsifiable concentrate was used. The residue concentration declined
with a half-life of less than 5 days. Omethoate exceeded 0.2 mg/kg in
only one sample, and was a minor proportion of the total residue until
about 14 days after treatment or when the total residue had declined
to about 0.2 mg/kg.
Since the concentration of omethoate remained relatively constant
in spite of the steady disappearance of the parent insecticide it
would appear that omethoate was formed and degraded at about the same
rate.
Citrus
Gunther et al. studied the persistence of residues of
dimethoate on and in mature Valencia oranges and reported that the
half-life was approximately 19 days. Their results (Gunther et
al., 1965) indicate that little or no residue reaches the pulp at
any stage after application following 1 or 2 treatments.
De Pietri-Tonelli and Barontini (1960a) sprayed tangerine trees
with 0.03 percent and 0.06 percent dimethoate when the fruits started
to change colour from green to yellow and analysed the peel and pulp
separately. The results (de Pietri-Tonelli et al., 1965) show that
most of the insecticide was localized in the peel where it was
degraded. Irrespective of the dosage, the half-life of the deposit in
the peel was 13-14 days. In the pulp of the fruits sprayed with the
lower concentration the residues were below the limit of determination
(0.1 mg/kg), whereas in the pulp of those treated with the higher
concentration, residues of 0.18 mg/kg were found after 10 days. These
decreased with a half-life of over 45 days.
De Pietri-Tonelli et al. (1965) recorded that when dimethoate
(1g/l) was applied to grapefruit for the control of certain scales
(Wood, 1964) the residue was principally in the peel and diminished
very slowly. In the pulp, the residue level remained below 1 mg/kg but
the concentration steadily rose until the fruits became ripe 90 days
after spraying. It is evident, therefore, that if the total residue
determined in the pulp was dimethoate, the behaviour of the
insecticide in grapefruit differs significantly from that observed in
tangerines.
Woodham et al (1974a) determined dimethoate and omethoate on
and in citrus leaves by a GC/FPD procedure following treatment of the
trees with: (1) an ultra-low volume (ULV) concentrate; and (2) a high
volume (HV) spray, both applied by helicopter at the rate of 1 kg/ha.
The ULV treatment produced higher initial residues, probably owing to
excessive run-off of the aqueous HV spray solution from the waxy leaf
surfaces. Only 1-5 percent of the deposit from both treatments was
converted into omethoate in the first 2 days and thereafter the
concentration of dimethoate decreased rapidly with a gradual decrease
in the concentration of omethoate. After 7 days, dimethoate residues
were 0.3-3.4 mg (UV) and 0.05-1 mg/kg (HV), with corresponding
omethoate levels of 0.15-0.9 mg/kg and <0.05-0.17 mg/kg. The
omethoate had disappeared entirely by 14 days and dimethoate residues
were almost all below 0.1 mg/kg.
The same authors studied the concentration and fate of dimethoate
and omethoate in the leaves, skin and pulp of grapefruit treated with
dimethoate wettable powder applied by spray gun at a concentration of
0.625 g a.i./l with and without surfactant. The results (Woodham et
al., 1974b) showed that the residue was substantially all in the
peel and mainly (>90%) dimethoate. Two days following treatment, mean
residues of 6.28 mg/kg of dimethoate and 0.23 mg/kg of omethoate were
detected on and in the peels. After 14 days, these residues had
decreased to 3.13 and 0.16 mg/kg respectively. Residues of dimethoate
in the pulp of the fruit were 0.09, 0.12 and 0.03 mg/kg after 2, 7 and
14 days respectively. No omethoate was detectable in any of the pulp
samples.
Van Dyk (1974) using a complex mathematical approach to the study
of the persistence of some pesticides in South African citrus
concluded that the apparent persistence of dimethoate in growing fruit
was not influenced by climatic conditions. This seeming anomaly may be
explained by the predominant influence of growth dilution on the
concentration of dimethoate on and in citrus fruits, which may mask
the effects of smaller influences.
Table 7. Rate of degradation of dimethoate and omethoate on cherries
Residue, mg/kg
Sweet cherries Sour cherries
Day Dimethoate Omethoate Dimethoate Omethoate
0a 0.24 0.14 0.48 0.22
1 2.30 0.24 2.76 0.23
2 1.65 0.21 1.91 0.23
4 1.24 0.23 1.56 0.31
7 0.89 0.21 0.80 0.28
14 0.53 0.19 0.38 0.33
a Residues measured at day 0 are those remaining frcm first cover
spray applied 14 days earlier on samples taken prior to the
application of the second cover spray.
Iwata et al (1979) studied the fate of dimethoate applied to
citrus trees in California. They reported that the edible portion
(pulp) of fruit sampled about 60 days after application contained no
analytically significant residues.
Neubauer et al (1982) studied the accumulation of residues in
leaves and mature fruits of citrus when dimethoate was applied to the
soil in a citrus grove. The residue levels in the fruits were much
lower than in the leaves.
Grapes
Enos and Frear (1964) used a colorimetric method to determine
dimethoate residues in grapes sprayed at the rate of 500 g/ha. Their
data (de Pietri-Tonelli et al., 1965) indicate that the
application of the insecticide at this dosage produced high residues
(6.8 mg/kg) 1 day after treatment which declined progressively at a
rate corresponding to a half-life of 8-9 days. Analytically
significant residues persisted for more than 50 days.
Rajukkannu et al (1977) working in India and using a
colorimetric method of analysis reported similarly high residues in
muscat grapes immediately after spraying but these declined to
0.12 mg/kg after 5 days and to undetectable levels by 8 days.
Steller and Pasarella (1972) collected grapes from a study in
which three applications of dimethoate were made at a rate of
2.5 kg/ha. The samples were analysed 0, 3, 7, 14, 21 and 28 days after
the final application. The level of dimethoate decreased from 4 mg/kg
at 0 days to 2.5 mg/kg at 3 days and 0.6 mg/kg at 14 days. This latter
value remained fairly constant at 0.5 mg/kg in samples collected 21
and 28 days after application. The omethoate level increased slightly
from 0.2 mg/kg at 0 days to 0.28 mg/kg at 3 days and then decreased
gradually to 0.15 mg/kg at 28 days.
Steller and Brand studied the metabolism of dimethoate in grapes.
They too found that the initial deposit of dimethoate was converted to
a small degree into omethoate, the concentration of which remained
relatively constant at about 0.2-0.4 mg/kg over the 35 days of the
trial. The concentration of the initial deposit of dimethoate
(7-18 mg/kg) had decreased to about 1-2 mg/kg by 21 days and to
0.2-0.5 mg/kg by 35 days (Steller and Brand, 1974).
Peaches
De Pietri-Tonelli et al. (1959) conducted bioassays to
establish the rate of disappearance of dimethoate from peaches and to
investigate its relationship with the date of treatment of different
peach varieties, with the concentration of the insecticide applied to
the plants and with the growth of fruit. The concentration of residues
having insecticidal activity decreased at higher rates in the
varieties which were treated in June than in those sprayed in
September or October. The half-life values were about 4 to 5 days for
the former and about 9 to 12 days for the latter. It was demonstrated
that the weight of the pulp of the fruits increases more rapidly in
the early than in the late varieties.
Santi (1961) sprayed peach trees with P32-labelled dimethoate at
a concentration higher than that recommended for the control of fruit
flies. The results (de Pietri-Tonelli et al., 1965) indicate that
the concentration of dimethoate in peaches treated in July diminished
with a half-life of 7 to 8 days. Omethoate reached a maximum of
0.07 mg/kg after about 10 days, when the dimethoate residue was
0.83 mg/kg.
Information received from Portugal (1984) records details of a
trial in which two groups of nine peach trees were sprayed with
dimethoate emulsion (40 g/1001) 2 and 3 times respectively at
intervals of 16 days in the summer of 1982 (average air temperature
25°C). Samples were collected from each field 1, 4, 7, 11, 14 and 21
days after the last application. Dimethoate and omethoate residues
were determined on three replicate samples of whole fruit (stones
removed but included in weight of sample) by a GLC (thermionic
detector) method with a limit of determination of 0.01 mg/kg
dimethoate and 0.05 mg/kg omethoate. The omethoate residues were
always less than 10 percent of the sum of dimethoate and omethoate
residues (see Table 8).
Plums
Wit (1972) carried out trials in two districts of The Netherlands
on two varieties of plums treated at two different times with two
dimethoate formulations. Analysis for the sum of dimethoate and
omethoate showed residues immediately after application of 0.3 mg/kg.
The residues declined rapidly so that most samples showed less than
0.01 mg/kg 1 and 2 weeks after application.
Strawberries
Data from Canada quoted in the 1977 evaluation indicated the need
for an MRL of 1 mg/kg.
Ahmad et al (1984) conducted an extensive trial with
3 varieties of strawberries treated with dimethoate spray at 3
concentrations applied on 4 occasions at 7-day intervals, to determine
whether a withholding period shorter than 7 days could be approved
without risk of violating the Australian MRL of 2 mg/kg for the sum of
dimethoate and omethoate. Samples were analysed by a procedure which
gave an average recovery of 95 percent for both dimethoate and
omethoate, with a limit of determination of 0.05 mg/kg.
As shown in Tables 9-11, the dimethoate residue was independent
of the strawberry variety but roughly proportional to the
concentration of dimethoate in the spray. No omethoate was detected in
any sample. On the strength of these data it was accepted that when
Table 8. Residues of dimethoate and omethoate in peaches resulting from multiple applications with dimethoate
Number Days
of between Residues* (mg/kg)
applications last
application Field replicate 1 Field replicate 2 Field replicate 3 Mean
and
harvest dimethoate omethoate dimethoate omethoate dimethoate omethoate dimethoate omethoate
2 1 1.8 0.09 2.2 0.09 1.7 0.07 1.9 0.08
4 1.3 0.09 1.4 0.08 1.5 0.05 1.4 0.07
7 0.89 0.08 1.0 0.09 0.98 0.09 0.95 0.09
11 0.54 0.07 0.66 0.05 1.0 0.08 0.73 0.07
14 0.54 0.08 0.64 0.08 0.73 0 06 0.64 0.07
21 0.52 NA 0.61 NA 0.57 NA 0.57
1 2.4 0.19 2.5 0.20 2.0 0.18 2.3 0.19
4 1.6 0.15 1.8 0.17 1.5 0.15 1.6 0.16
7 1.3 0.16 1.5 0.17 1.4 0.15 1.4 0.16
11 1.2 0.14 1.2 0.14 1.0 0.15 1.1 0.14
14 1.1 NA 1.2 NA 0.83 NA 1.0
21 0.9 NA 0.7 NA 0.86 NA 0.82
* Mean values of 3 analyses, total weight basis
NA - not analysed
Table 9. Mean dimethoate residues in strawberry fruit following spray application at 200 mg/1.
Number of Strawberry Variety
days after Torrey Tioga Naratoga Mean
4th spray
R* SE+ R SE R SE R SE
0 2.69 .17 3.33 .21 2.40 .20 2.81 .27
1 1.98 .46 2.17 .48 1.78 .20 1.98 .11
2 1.51 .10 1.37 .24 1.83 .26 1.57 .14
3 0.99 .03 1.03 .24 1.28 .20 1.10 .09
4 0.54 .10 0.81 .33 0.95 .05 0.77 .12
7 0.36 .08 0.75 .18 0.82 .05 0.64 .14
14 0.46 .23 0.11 .02 0.33 .10 0.30 .10
21 0.34 .08 0.06 .01 0.14 .01 0.18 .08
Table 10. Mean dimethoate residues in strawberry fruit following spray application at 300 mg/l.
0 3.23 .30 3.91 .09 3.80 .81 3.65 .21
1 2.18 .44 3.25 .20 2.25 .12 2.56 .34
2 1.45 .24 2.09 .19 2.17 .07 1.90 .23
3 0.93 .13 1.42 .12 1.78 .12 1.38 .25
4 0.54 .12 1.35 .22 1.31 .21 1.07 .26
7 0.37 .49 0.82 .07 0.88 .11 0.69 .16
14 0.15 .02 0.30 .10 0.30 .10 0.25 .05
21 0.29 .02 0.29 .18 0.31 .03 0.30 .007
Table 11. Mean dimethoate residues in strawberry fruit following spray application at 500 mg/l.
0 7.25 .45 6.59 .41 5.06 .48 6.30 .65
1 5.95 .39 4.91 .39 4.67 .43 5.18 .39
2 3.25 .67 3.75 .74 3.74 .80 3.58 .16
3 1.95 .12 2.73 .21 2.39 .27 2.36 .23
4 1.68 .17 1.45 .33 1.99 .19 1.71 .16
7 1.18 .08 0.78 .09 1.00 .21 0.99 .12
14 0.57 .14 0.57 .06 0.44 .11 0.53 .04
21 0.47 .10 0.33 .14 0.33 .02 0.38 .05
R* = Dimethoate residue (mg/kg)
+SE = ± Standard Error
dimethoate spray of concentration 300 mg/l is applied on a 7-day
schedule the ripe fruit can be picked 3 days after application without
risking violation of the maximum residue limit of 2 mg/kg.
Olives
An extensive review of the early history of the use of dimethoate
for the control of olive fly was published by Alessandrini (1962). By
the mid 1950's dimethoate was widely used in most of the Mediterranean
countries and extensive monitoring by the Italian Ministry of
Agriculture during the years 1957, 1958 and 1959 showed that
commercial olive oil contained less than 0.1 mg/kg of dimethoate, the
limit of determination then available. A number of factors contribute
to keeping the level of residues low:
1. Dimethoate is applied to the crop well before harvest;
2. the deposit is degraded relatively quickly;
3. the residue is polar, particularly the omethoate metabolite;
4. the processing of olives into oil and the washing of the oil with
water as the first step in its refining results in the removal of
virtually all of the omethoate and much of the remaining
dimethoate.
Table olives are picked not less than one month after the last
treatment with dimethoate and therefore the residues in the
unprocessed olives are relatively small. Subsequent processing of the
raw olives removes more than 90 percent of the residues originally
present.
Bazzi et al (1960) sprayed olive trees with dimethoate
(0.6 g/l) at various times between August and November. Details are
given by de Pietri-Tonelli et al. (1965). Initial half-life
periods increased progressively from 3-4 days in August to about 23
days in November.
The distribution of dimethoate and of its phosphorus-containing
metabolites in olive fruits was studied by de Pietri-Tonelli and
Barontini (1961) using radio-labelled dimethoate. They showed that the
insecticide penetrated into the olives through the skin and
systemically through the stem.
Ramos and Costa (1962) found dimethoate residues of 0.7, 0.3 and
0.5 mg/kg respectively 1, 15 and 30 days after treatment.
Further studies on olives for oil were undertaken by Santi and
Giacomelli (1962) who sprayed olive trees with P32-labelled dimethoate
in July, September and October. The results (de Pietri-Tonelli et
al., 1965) indicate that the concentration of dimethoate in the
olives progressively diminishes, the amount of P=O derivative rises to
a maximum and then decreases, the concentration of water-solubles
increases and the chloroform- and water-insolubles begin to decline
about 5 weeks after treatment. The concentration of the insecticide in
the fruit was directly proportional to the concentration of the
insecticide spray, the number of applications and the variety of
olives which influences the surface to weight ratio.
Irrespective of the rate of application or the time of the year
when the spray was applied, omethoate represented less than 10 percent
of the total residue 4 to 5 days after treatment. Although the
concentration of omethoate did not increase significantly thereafter
the rapid decline of the total residue meant that by the 15th-18th day
the omethoate portion represented 50 percent and thereafter the
proportion increased until by the 45th day the omethoate represented
80 percent of the total residue (0.7 mg/kg).
The same authors determined residues in fresh eating olives.
Bearing in mind the lower ratio of surface-to-mass of eating olive
varieties and the influence of this factor on the initial
concentration of the insecticide in the fruits, the results (de
Pietri-Tonelli et al., 1965) can be considered very similar to
those obtained in the olives for oil.
Albi and Rejano (1982) reported residues of dimethoate in fresh
olives of 0.93-0.95 mg/kg 24 hours after application.
Ferriera and Tainha (1983) carried out residue dissipation
studies with a range of organophosphorus insecticides on olives in
Portugal with a view to checking the preharvest intervals established
for olives. Following the treatment of olive trees with dimethoate
spray (0.6 g a.i./l) the authors reported mean residues of 5.3, 3.1,
1.5, 0.78, 0.41, 0.28 and 0.03 mg/kg after 1, 7, 14, 21, 28, 35, and
41 days, respectively.
Residues in Vegetables
Chilwell and Beecham (1960) made an extensive study of the
residues found in many British and overseas crops 1-3 weeks after
spraying with dimethoate. This included a wide variety of vegetables.
Some results are included in Table 2. De Pietri-Tonelli et al.
(1965) reviewed much of the available information published to that
date on beans, carrots, potatoes and sugar beets.
Beans
Van Middelem and Waites (1964) analysed snap beans treated with
dimethoate at 3 dosage rates and compared colorimetric and gas-
chromatographic methods of analysis. The results (de Pietri-Tonelli
et al., 1965) showed excellent agreement between the two
procedures and demonstrated that dimethoate residues were proportional
to the dosage applied to the plants and disappeared at the same rate,
with a half-life of about six days, from all three rates of
application.
Results obtained by Belal and Gomaa (1979) are quoted in Table 2.
They calculated the residue half-life to be 4.3 days. The analytical
method used (Giang and Schecter, 1963) should also have determined any
omethoate that was present. These residue levels are much higher than
those reported by other workers.
Brussels Sprouts
Greve and Hogendoorn (1981) reported the results of field trials
carried out on Brussels sprouts in 3 districts of The Netherlands. The
crops were sprayed with a dimethoate emulsion (50 g/1001) at the rate
of 200 g/ha applied three times at approximately 12-day intervals. 1,
2 and 3 weeks following the last spraying, samples from each field
were analysed for dimethoate and omethoate residues by methods which
had a limit of determination of 0.005 and 0.01 mg/kg respectively. The
highest level of omethoate found was 0.07 mg/kg. The detailed results
are given in Table 12.
Carrots
Stobwasser (1963) sprayed two varieties of carrots with
dimethoate at two rates. The colorimetric analytical data (de
Pietri-Tonelli et al., 1965), showed that the residues in the
roots were very low a few weeks after the last treatment and slowly
diminished thereafter so that they were below the limit of
determination
(0.03 mg/kg) about 200 days after the last application. The total
residues are likely to be higher than indicated because the analytical
method used would not detect omethoate.
Chicory
Ten Broeke and Dornseiffen (197.3) studied the uptake and
degradation of dimethoate applied to Witloof chicory in forcing beds
when the shoots first began to swell. The rate of application was
equivalent to 0.5 g/m2 applied in the form of a diluted emulsion at
the rate of 1 1/m2 Two trials were carried at different temperatures
and four samples from each trial, taken 36 and 50 days after spraying,
were analysed (see Table 13). The residues of dimethoate and omethoate
together were generally less than 0.4 mg/kg, the dimethoate and
omethoate being present in equal proportions.
Cucumbers
Greenhouse cucumber plants were treated in three different
experiments with formulations of either pure or technical dimethoate
(0.05%) and the residues separated by thin-layer chromatography. The
amount and nature of the residues did not differ significantly.
Dimethoate and omethoate were the only residual compounds identified,
omethoate appearing only in very small quantities. Seven days after
application, the total residue was less than 0.5 mg/kg in all
experiments. (Kubel et al., 1966).
Table 12. Omethoate and dimethoate residues in Brussels sprouts
sprayed with dimethoate 3 times at 10 day intervals
starting 4 months after planting. (PHI = interval
between last application and harvest)
Test PHI Omethoate (mg/kg) Dimethoate (mg/kg)
site (days) mean range mean range
Tinte 7 <0.01 0.01-0.02 0.08 0.005-0.09
14 <0.01 <0.01 0.02 0.005-0.02
21 (0.01 <0.01 0.005 0.005-0.005
Breda 7 <0.01 (0.01 0.05 0.005-0.06
14 <0.01 <0.01 0.06 0.005-0.10
21 <0.01 0.01-0.07 0.03 0.005-0.04
Kirkwyk 7 (0.01 <0.01 0.01 0.005-0.01
14 (0.01 0.01-0.04 0.01 0.005-0.10
21 0.01 <0.01 0.005 0.005-0.02
Table 13. Dimethoate and Omethoate Residues in Witloof Chicory
(ten Broeke and Dornseiffen, 1973a)
residue, mg/kg, at intervals after application
Dimethoate Omethoate
Test I Test II Test I Test II
Cold conditions 36 days 50 days 36 days 50 days
Untreated <0.001 <0.001 <0.005 <0.005
<0.001 <0.001 <0.005 <0.005
Treated 0.11 0.13 0.11 0.13
0.15 0.14 0.14 0.18
0.12 0.13 0.11 0.14
0.11 0.15 0.12 0.14
Average 0.12 0.14 0.12 0.15
Average corrected
for recovery 0.14 0.15 0.15 0.19
(0.12-0.17) (0.14-0.17) (0.14-0.18) (0.16-0.23)
Warm conditions 36 days 50 days 36 days 50 days
Untreated <0.001 <0.001 0.07+ <0.005
<0.001 0.007 0.03+ 0.02
Treated 0.14 0.12 0.24 0.17
0.18 0.10 0.23 0.12
0.17 0.11 0.20 0.16
0.14 0.22 0.19 0.20
Average 0.16 0.14 0.21 0.16
Corrected for control 0.16
Average corrected for
recovery 0.18 0.15 0.20 0.20
(0.16-0.20) (0.11-0.24) (0.18-0.24) (0.15-0.25)
+ Contamination by solvent (ethyl acetate)
Tomatoes
As part of a programme of investigations into methods for
controlling fruit fly in a number of fruits and vegetables, Rigney
(1976) dipped tomatoes which had been artificially infested with
Queensland fruit fly larvae for 30 seconds in a dilute dimethoate
emulsion (3 g/l). Half of the tomatoes were rinsed with clean water 30
minutes after the dipping. Results are shown in Table 14.
Swaine et al (1984) carried out a similar experiment in which
the tomatoes were dipped for a period of 3 minutes in a diluted
dimethoate emulsion containing 0.5 g/l. The results are given in
Table 15.
Asparagus
Szeto et al (1982) studied the level and fate of dimethoate
residues in asparagus plants after foliar application. They
applied dimethoate by means of a backpack sprayer at the rate of
1.12 kg a.i./ha on two occasions approximately 6 weeks apart at 2
locations. Samples of the above-ground foliage from each treatment
were analysed for dimethoate and omethoate by GLC-AFID. The results
(Table 16) show that dimethoate is oxidized to omethoate in the
asparagus foliage and that the residues disappear rapidly. No residue
was detected (<0.002 mg/kg) in samples of the marketable spears
harvested in the spring of the following year (9 months after
treatment).
Cereals
Lee and Westcott (1981) carried out field experiments on wheat
plants sown at three different dates to ensure that at the time of
spraying with dimethoate (420 g/ha) the plants were at three stages of
development: the boot stage, second node visible, and tillering.
Samples were collected immediately after application and at several
intervals over the next three weeks. The dimethoate and omethoate
residues are recorded in Table 16a. These data indicate that the
conversion to omethoate and the subsequent degradation of the
metabolite is slightly greater in young than in mature plants and that
the concentration of omethoate is about 10 percent of the total two
days after spraying, rising to 35-50 percent seventeen days after
spraying.
Oilseed Crops
Cotton Seed
De Pietri-Tonelli and Barontini (1961) carried out radiometric
determinations of the chloroform-soluble extractives (i.e. dimethoate
and omethoate) in the seeds of potted cotton plants raised in the
glasshouse. The plants were sprayed with [32p]-dimethoate (0.2 g/l)
when the bolls were nearly ripe. The analytical data (de
Pietri-Tonelli et al., 1965) showed that systemically translocated
Table 14. Dimethoate residues in tomatoes following a 30 second
dip in dimethoate emulsion (3 g/l)
Dimethoate residues (mg/kg)
Time after dipping Dip Only Dip and Rinse
1 day 1.35 0.71
3 days 1.05 0.61
7 days 0.69 0.49
Omethoate was not detected (<0.01 mg/kg)
Table 15. Residues of dimethaote in tomatoes dipped in dimethoate (0.5 g/l)
for 3 minutes
Experiment Average Size Interval Residues (mg/kg)
No. of tomato after
(cm) dipping, (1) (2) Average
days
1 8 cm 0 0.54 0.57 0.56
2 6 cm 0 0.51 0.79 0.65
3 7 cm 0 0.59 0.50 0.55
3 0.71 0.62 0.67
7 0.26 0.25 0.26
Omethoate was not detected.
Table 16. Dimethoate and omethoate in asparagus foliage
Days after Residues, mg/kg (fresh wt)
spray Dimethoate Omethoate Total
1st spray (July 24, 1982)
2 11.0 1.00 12.00
10 1.01 1.02 2.03
17 0.21 0.43 0.64
31 Trace* 0.06 0.06
46 Trace Trace Trace
2nd spray (Sept. 8, 1982)**
2 4.43 0.45 4.88
12 0.71 0.65 1.36
21 0.17 0.52 0.69
26 0.36 0.18 0.54
33 0.12 0.38 0.50
1st spray (July 29, 1982)
5 5.14 1.62 6.76
12 0.43 0.48 0.91
20 0.08 0.29 0.37
26 0.02 0.04 0.06
39 0.10 Trace* 0.10
2nd spray (Sept. 17, 1982)
2 22.4 2.12 24.5
9 0.98 0.75 1.73
* Trace = <0.01 mg/kg.
** Rained on Sept. 9, 1982, i.e., one day after the spray.
Table 16a. Residues of dimethoate and omethoate on and in wheat plants following application of dimethoate at
420 g ai/ha
Days Residues, mg/kg at seeding dates
Sampling after May 1 May 15 June 1
Date spray Dimethoate Omethoate Dimethoate Omethoate Dimethoate Omethoate
June 28 0 17.36 ND* 41.50 ND 63.18 ND
29 1 7.08 T** 14.07 T 13.79 0.19
30 2 5.19 0.45 9.96 0.96 10.39 1.32
July 1 3 4.72 0.63 5.40 0.71 8.54 1.22
2 4 4.25 0.62 4.86 0.74 5.46 0.90
4 6 4.03 0.60 3.65 0.56 4.89 0.76
5 7 3.99 0.58 2.70 0.49 2.97 0.55
7 9 2.13 0.44 1.95 0.36 1.22 0.25
11 13 0.64 0.25 0.55 0.19 0.12 0.06
15 17 0.62 0.24 0.36 0.14 0.02 0.03
* ND = not detectable (less than 0.005 mg/kg.
** T = trace amounts (between 0.005 and 0.009 mg/kg)
dimethoate and omethoate occurred inside the bolls both in the
delinted seeds and in the lint. The residue was below 1 mg/kg 1 day
after application and diminished in the following days but changed
little between days 12 and 26, possibly owing to the competitive
effects of degradation and systemic translocation.
Llistro et al (1982) report that no residues were found in
cotton seed 10 to 30 days after the last of 10 sprays, each at
0.5-0.9 kg/ha.
Mustard
Verma (1980) in evaluating insecticides against pests of the
mustard crop reported that dimethoate persisted to a level of
0.08 mg/kg 6-29 days after spraying.
Peanuts
Studies carries out in India (Anon, 1977) indicated that
following 2 sprays with dimethoate (0.3 g/l) the residue in peanut
kernels was 0.48-0.55 mg/kg.
Soybeans
Beck et al. (1966) applied diluted dimethoate emulsion at the
rate of 125, 250 and 500 g/ha and found that residues had decreased to
0.1 mg/kg by the seventh day after treatment.
FATE OF RESIDUES
The fate of dimethoate residues was reviewed in the 1967
evaluation and in the 1971 evaluation of omethoate. These include
references and diagrams of the metabolic pathways in plants and
animals. Additional material is reviewed below.
In Animals
Kaplanis et al. (1959) studied the metabolism of
[32P]-dimethoate in cattle following oral and intra-muscular (i.m.)
administration of 10 mg/kg. About 90 percent of the oral dose was
eliminated in the urine after 24 hours. The same percentage of the
i.m. dose was excreted after 9 hours. Only 3.7 to 5 percent of the
oral dose and about 1 percent of the i.m. dose was eliminated in the
faeces. The major metabolic products were dimethylphosphate,
dimethylphosphorothioate, and several unknowns. Analysis of tissues
from an orally treated calf showed only very low levels (0.02 mg/kg)
of organo-extractable radioactive compounds present in brain, liver,
testes, and lungs.
After oral treatment with 10 mg/kg body weight, Plapp et al.
(1960) reported residues in the fat of cattle obtained by biopsy as
3 mg/kg after 3 hours and 0.1 mg/kg after 8 hours; 14 days after oral
intake the values in all tissues had dropped to less than 0.1 mg/kg.
Shortly after treatment with [32P]-dimethoate high concentrations were
observed in the blood of cattle and these reached their maximum after
1 hour for i.m. treatment and after 3 to 6 hours for oral treatment.
The absorption, distribution, metabolism and excretion of
[32P]-labelled dimethoate was studied in rats and 3 species of insects
by Brady and Arthur (1963). Phosphorothioate oxidation occurred in
rats, but degradation, rather than activation was predominant. Of the
many compounds excreted by rats, dimethoate accounted for much less
than 1 percent and omethoate for less than 5 percent. Amidase activity
was more pronounced in rats than in insects immediately following
treatment with dimethoate; this major metabolic difference may partly
explain selectivity. Phosphatase activity was also more evident in
rats than in insects.
Morikawa and Saito (1966) studied the metabolism of dimethoate in
insects, plants and mammals, in vivo and in vitro. The optimum
pH for the degradation of dimethoate was approximately 8 for rat liver
homogenate and 7 to 7.4 for insect homogenate. The hydrolysis of the
S-C bond of dimethoate was specific to the rat liver homogenate.
By means of TLC and colorimetric analysis, Mitsui et al.
(1966) showed that when dimethoate was given to rats, the content in
each organ was highest 2 hours after treatment. About 95 percent of
the administered dose was hydrolysed in 7 days.
Beck et al. (1968) studied the effect of feeding
dimethoate-treated silage, dimethoate and omethoate to cattle. The
work is reviewed in the 1970 evaluation.
Bazzi (1968) prepared a review of the metabolism of dimethoate in
animals and plants and on the analytical methods for the assay of the
insecticide and of its active and inactive metabolites, together with
data on their acute toxicities.
Menzer and Dauterman (1970) in a review of the metabolism of
some organophosphorus insecticides pointed out that dimethoate is
hydrolysed in liver by microsomal amidase and that this enzyme occurs
at high concentrations in sheep liver. Studies have shown that the
carboxyesterase responsible for the hydrolysis of malathion has no
effect on dimethoate.
Menzie (1974) reviewed the metabolism of a number of pesticides
including dimethoate.
In Plants
Santi (1961) showed that dimethoate penetrates from the skin of
peaches into the pulp, but more slowly than was observed in cherries.
5 of 8 metabolites were identified.
De Pietri-Tonelli and Barontini (1960g) showed that there is
little movement of dimethoate deposits from fruit to other parts of
the plant, but translocation from leaf to leaf may occur mainly upward
through the xylem to young leaves, and to a limited extent downward.
Treating sections of lemons with labelled dimethoate revealed little,
if any, movement of the insecticide from the treated area, laterally
or inwardly. This suggests that citrus peel from treated citrus crops
used for cattle feed might contribute significant residues to animal
fodder. Gunther et al. (1965) showed, however, that residues were
lost during processing (see "Fate in processing and cooking").
The penetration of dimethoate into plants was studied by de
Pietri-Tonelli and Barontini (1960b, 1961) by applying aqueous
solutions of labelled dimethoate to lemons, peaches and olives.
Autoradiography of sections of the lemons showed that penetration of
the phosphorus-containing metabolites was restricted to the peel; in
peaches they penetrated through the pulp to the stone, and in olives
the penetration included the stones if the olives were sprayed when
unripe, but not if the olives were sprayed after the stones had
hardened.
In a series of tests with labelled dimethoate applied to the
trunks of lemon trees, Santi (1962) found it was translocated mostly
upward and deposited in varying amounts, large in leaves, medium in
twigs and small in the skins of the fruit. Small quantities of
unidentified [32P]-substances were found in the roots.
Santi et al. (1962) found that the metabolism of dimethoate
in leaves of sugar beets followed two courses: oxidative, with the
formation of omethoate, and hydrolytic with the formation of 3
phosphoric acids and a phosphorothioate. Four other [32P]-substances
were recorded but not identified.
Bull et al. (1963) treated cotton seedlings with labelled
dimethoate. After 5 days, 60 percent of the absorbed insecticide had
been degraded to 11 metabolites, all but 4 of which were identified.
Kubel et al. (1966) studied the impurities in technical
dimethoate and prepared experimental formulations of the technical
active ingredient and the pure compound which they applied to
greenhouse cucumbers. The resulting residues differed little in
composition or residual life. Dimethoate and omethoate were the only
residual compounds identified, omethoate appearing only in very small
quantities.
Mitsui et al. (1966) used thin-layer chromatography and
spectrophotometry to study the fate of dimethoate applied to plants
cultured in various concentrations of dimethoate emulsion for 20 hours
and in plants treated with a granulated formulation. Following
systemic uptake, the maximum concentration in plant tissues was
6.59 mg/kg and this dropped below 0.1 mg/kg in less than 10 days after
the removal of the insecticide source. When the dimethoate was applied
to the plant leaf the uptake reached a maximum in approximately 10
days and persisted for less than 25 days.
Lucier and Menzer (1968) and Lucier (1967) investigated the
metabolism of dimethoate in bean plants. Results are summarized in the
1967 evaluation.
Bazzi (1968) reviewed the metabolism of dimethoate in animals and
plants and the analytical methods for the assay of the insecticide and
its active and inactive metabolites, together with data on their acute
toxicities (64 references).
Lucier and Menzer (1970) showed that dimethoate undergoes
oxidative N-demethylation with the formation of a hydroxymethyl
intermediate leading to the production of an un-substituted amide
metabolite. In this case, demethylation takes place with both
dimethoate and omethoate. These authors reported that in bean plants
the half-life of dimethoate was 1.7 days and that at harvest omethoate
was the major organo-extractable metabolite, reaching a level of 7.3
percent of the total residue after 3 days.
Ishiguro and Saito (1971) applied 32P-labelled dimethoate to the
water and soil in which rice plants were growing. They found that
under conditions where the water was saturated with insecticide,
radioactive metabolites of dimethoate moved to the aerial parts of the
plants very rapidly, and accumulated in the leaf sheath and leaf blade
in large amounts. From these results, it seems probable that
dimethoate is not only absorbed through roots but also penetrates
through the leaf sheath and is translocated in the plant tissues.
Dimethoate was decomposed in the plant tissue. Metabolism was most
active at the junction of aerial and root parts of the plants, and
metabolites accumulated.
Sauer (1972) showed that formothion, the N-formyl-N-methyl
analogue of dimethoate, was metabolized to dimethoate in bean plants,
but further oxidative demethylation did not occur.
Steller and Brand (1974) analysed field-treated grape samples
harvested 28 days after the last application of dimethoate and found
less than 0.05 mg/kg each of what appeared to be des-N-methyl
dimethoate, N-hydroxymethyl dimethoate, des-N-methyl omethoate and
N-hydroxymethyl omethoate.
Garrett (1980) studied the metabolism of N-hydroxymethyl
dimethoate and N-demethyl dimethoate in bean plants but the paper, a
111-page thesis, was not available for review.
Wagner et al examined the metabolism of omethoate in sugar
beets in greenhouse studies. A summary appears in the evaluation of
omethoate.
In soil
Getzin and Rosefield (1968) measured dimethoate residues by
gas-liquid chromatography 2 weeks after application to clay loam.
Dimethoate was degraded to about the same extent in heat-sterilized
and gamma-irradiated soil, 18 and 20 percent respectively. About
7 percent of the dimethoate had been degraded after 2 weeks in
non-sterile soil.
Graham-Bryce (1969) studied the diffusion characteristics of
dimethoate in silty loam soil. Diffusion rates changed very little as
the dimethoate concentration was increased, but increased rapidly as
the soil moisture increased. There was little movement of dimethoate
in soil, except under moist conditions.
Harris and Hitchon (1970), in laboratory tests on the biological
activity of several pesticides in soil, reported dimethoate to be
moderately persistent, its biological activity disappearing after
36 weeks. In dry sandy loam, 50 mg/kg was the lowest concentration at
which dimethoate showed biological activity when applied as a soil
treatment; in moist sandy loam the level was 10 mg/kg, and in high
organic soil 100 mg/kg. The reported increase in cholinesterase
inhibition shown by dimethoate in moist soil, as compared to dry, is
probably due to the greater production of omethoate. Dimethoate and
its metabolites rapidly disappeared from wet organic (muck) soil.
Ishiguro and Saito (1971) showed that dimethoate yielded more
chloroform- and water-extractable radioactivity than vamidothion,
disulfoton, thiometon and mecarbam 6 days after application to soil.
There was significantly less radioactive material adsorbed. The
dimethoate-treated soil produced the highest level of biological
activity against the small brown plant hopper fed on rice plants
growing in the treated soil. Larger amounts of chloroform-partitioned
metabolites of dimethoate were detected in the aerial and root parts
of rice plants as compared with other test compounds.
Kawamori et al. (1971a) studied the retention of dimethoate
in 3 soils: a loamy sand, clay loam and a silty clay loam. In each
soil, much less dimethoate was retained than disulfoton. Larger
amounts were retained in the soils having higher organic matter
content and cation exchange capacity. The amount of retained
insecticide was related to the content of organic matter rather than
clay in the soils.
Kawamori et al. (1971a) studied the changes in the retention
and metabolism of dimethoate in soils and showed that the amount of
dimethoate retained initially was very small but increased rapidly
during the first 2 days. Initially the insecticide was retained
without degradation but was decomposed gradually during the succeeding
period.
Duff and Menzer (1973) studied the persistence and degradation of
dimethoate in silty loam, loamy sand and clay loam. No major
difference in total radioactivity recovered was noted between the 3
soil types in two experiments. Moisture promoted more rapid
disappearance of the dimethoate radioactivity. Downward movement of
dimethoate was slightly more extensive in loamy sand than silty loam
or clay loam and was increased by moisture in all three soils.
In moist soils the conversion of dimethoate to omethoate was
faster, and the level of omethoate was generally greater. The only
hydrolytic metabolite identified was dimethoate carboxylic acid. Less
than 1 percent of the applied radioactivity was recovered from the
2.5-5 cm layer after 5 weeks under relatively dry conditions; however,
residues were found as far down as 10 cm after 3 weeks under wetter
conditions. Less than 0.5 percent of the applied dose was recovered
from corn and bean plants grown in the soil.
El Beit et al. (1977a) found that for a given application of
dimethoate, the loss by leaching increased with soil type in the order
clay < clay loam < sandy clay loam < sand. In general, the loss
through leaching for a single soil type increased with the amount of
dimethoate applied. Retention was greatest in the loam and least in
the sand and was thought to be affected by physical forces and
hydrogen bonding. The loss of the pesticide through evaporation,
degradation and irreversible adsorption increased with the dosage
applied. It was in the descending order clay > clay loam > sand
>sandy clay loam > loam. However, the loss due to evaporation alone
was in the order sand > sandy clay loam > clay loam > loam.
Biological degradation of dimethoate was of little importance and
depended on the type of soil as well as the type and number of
micro-organisms originally present in the soil.
The same authors (El Beit et al. 1977b) reported that the
residual accumulation of dimethoate increased with frequency of
application, even under leaching conditions. Increasing the initial
soil moisture content resulted in increased loss by leaching and a
consequent reduction in the proportion of pesticide retained in the
soil. Removal of soil organic matter reduced biodegradation of the
pesticide but accelerated the loss by leaching, evaporation or
co-distillation, so that the retention was reduced. Moist soil would
help to make the pesticide available in solution for the control of
soil pests and absorption by root crops.
El Beit et al. (1978) found that pH, temperature and the type
of medium are important factors affecting the stability of dimethoate
in soils and solutions. Within the pH range 7-11, dimethoate
degradation depends on the alkalinity of the medium rather than the
time of storage. At pH 4.2 degradation is largely dependant on the
length of time the dimethoate solution has been stored. Acid or salt
concentration has little effect on the degree of degradation when the
pH is maintained constant. Liming the soil results in a decrease in
leachability and in retention of the pesticide by the soil.
Alexander and Rosenberg (1979) were able to isolate bacteria from
soil and sewage capable of utilizing dimethoate as the sole source of
phosphorus. Extracts of 2 bacteria derived from organophosphate-grown
cultures catalysed the disappearance of 5 organophosphorus compounds
but not dimethoate.
El Beit et al. (1981) made an extensive review of the factors
affecting soil residues of dimethoate and 4 other widely used
pesticides. They drew upon most of the above-mentioned papers together
with the findings of some other workers.
In Water
Eichelberger and Lichtenberg (1971) studied the persistence of
28 common pesticides in raw river water over an 8-week period. They
found that dimethoate was much more stable in river water than other
organophosphorus compounds such as parathion, malathion,
carbophenothion and fenthion but about as persistent as ethion and
just slightly less so than monocrotophos. It was significantly more
persistent than any of the carbamate compounds tested though less
stable than most of the organochlorine compounds. Following the
addition of 10 ug/l, 50 percent of the dimethoate was recoverable at
the end of 8 weeks. By comparison, only 50 percent of parathion and 25
percent of malathion was recoverable from the same initial
concentration at the end of the first week. No reasons were advanced
for the stability of dimethoate, the molecule of which is
unsymmetrical. The symmetry of the ethion molecule was advanced as an
explanation of the stability of that compound.
Kadoum and Mock (1978) analysed water and pit bottom soil in
tailwater pits from irrigated corn and sorghum fields in Kansas, USA,
for a wide variety of herbicide and insecticide residues. Dimethoate
was one of the pesticides most likely to enter tailwater pits as a
result of aerial application to the crops. However, no trace of
dimethoate was found in 129 samples of pit bottom soil but it was
detected in 10 of the 129 samples of tailwater at levels ranging up to
0.0043 mg/l with a mean of 0.0019 mg/l. The analytical methods used
had a limit of determination for dimethoate of 0.0001 mg/l. Residues
of other pesticides occurred much more frequently and at levels up to
50 times that reported for dimethoate.
Noble (1984) studied the effect of pH and temperature on
postharvest dip solutions of dimethoate (500 mg/l) by measuring the
half-lives at pH4, 6, 8, 10 and 11.5 and at 25°C and 52°C. The
half-lives ranged from 206 days to 39 minutes at 25°C and 5.6 days to
205 seconds at 52°C. A formula was developed which gives the half-life
of the dimethoate as a function of pH and temperature.
In Processing and Cooking
Fruit
Apples
An abstract of a report by Antonovich and Vekshtein (1975)
reports that washing in cold running water removes 64 percent of the
dimethoate residue from apples whilst heating to 100°C for 15 or 30
minutes reduces the residue by more than 85 percent. Processing into
juices, jams or purees removes all trace of dimethoate residue from
peeled fruit and reduces the content of unpeeled fruit by almost 100
percent. The apples on which the studies were conducted contained
0.06 mg/kg dimethoate. The original Russian reference was not
available and the interpretation given in the abstract is questioned.
Citrus
Gunther et al. (1965) showed that no measurable amount of
dimethoate could be removed by hand washing of Valencia oranges with
dilute detergent. They also reported that most of the dimethoate
residue in citrus peel was lost during processing into citrus pulp
cattle feed (see Table 17).
Albach and Lime (1976) studied the effect of preparing whole
orange puree on the level of dimethoate in unwashed and washed Marrs
oranges. The puree incorporates from 85 to 90 percent of the entire
fruit into the final product. In the process, whole fruit are
water-blanched at 100°C for 10 minutes before grinding. This would be
expected to eliminate a considerable portion of any residue that might
be present in the fruit as picked. No residues of dimethoate were
found in the unwashed, washed or pureed fruit. In the light of
findings of other workers the validity of these results is questioned.
Grapes
Steller and Pasarella (1972) studied the level of residues in
grapes, grape pomace, wine and raisins. The results are reported in
Table 18.
Kawar et al. (1979) report a study in which dimethoate was
added to grape concentrate at the rate of 1 and 25 mg/kg prior to
fermentation with yeast. The finished wine, 56 days later, contained
0.98 and 21 mg/kg respectively of the dimethoate added to the grape
must. Residues in wine stored at 24°C were hydrolysed with a half-life
of 30 days. Residues were unchanged in wine in frozen storage for
1 year.
TABLE 17. Residues of Dimethoate Found in the Processing of Laboratory
Valencia Pulp Cattle Feed
Sample A Sample B
Moisture Moisture
% mg/kg 1 % mg/kg
FRESH GROUND PEEL
77.5 2.5 80 2.6
77.5 2.6 80 3.2
77.5 2.2 80 2.0
77.5 3.1 80 2.3
DRIED CATTLE FEED
14 2.2 1 nil
14 3.5 1 nil
14 2.7 1 nil
14 2.8 1 nil
14 2.2 1 nil
14 2.2 1 nil
1 All values were corrected for background and recovery of dimethoate
added at the time of equilibration. Recovery from four samples of
fortified ground peel (2.0 to 4.0 mg/kg) was 76 +/- 4% and from four
samples of final fortified cattle feed (4.0 to 8.0 mg/kg) was
81 +/- 10%.
nil = less than 0.3 mg/kg.
TABLE 18. Residues of Dimethoate and Omethoate in Grapes, Grape
Pomace, Wine and Raisins
Sample Treatment 1 Residue, mg/kg
Dimethoate Omethoate
Grapes A 0.23 0.16
Grapes B 0.35 0.18
Grape pomace A 0.22 0.16
Grape pomace B 0.37 0.22
Wine A 0.15 0.12
B 0.23 0.13
Raisins A 0.15 0.05
B 0.2 0.05
1 Treatment: A-3 applications at 2.5 kg/ha.
B-2 applications at 2.5 kg/ha and finally at 5 kg/ha
at intervals of 28 days and 13 days, the last 28 days
before harvest.
Miscellaneous Crops
Olives
Ramos and Costa (1960) studied residues of dimethoate in olive
oil originating from olive plantations treated with dimethoate. The
residues ranged from 0.3 mg/kg to 1 mg/kg. Analysis of preserved
olives showed residues of dimethoate between 0.07 and 0.14 mg/kg. No
reference was made in this work to the number of treatments nor to the
interval between treatments and the collection of the samples. In
another study (Ramos and Costa, 1962) olive oil made from olives
containing 0.5 mg dimethoate/kg was found to contain a maximum of
0.4 mg/kg.
Santi and Giacomelli (1962) found that the concentration of
dimethoate in olive oil represented about 1/3 to 1/4 of the
concentration in the olive. Their results, quoted in detail by de
Pietri-Tonelli et al. (1965) showed that dimethoate, omethoate and
other products of hydrolysis were largely removed during the
processing of the oil, while treatment of eating olives with NaOH as
in the normal industry process extracted 80-90 percent of the
dimethoate and metabolites present in the olives at the time of
dipping. A further soaking of the olives in water for 5 days reduced
the total radioactivity to 1-2 percent of that present in the olives
at harvest time, and the chloroform-soluble residue effectively to
zero.
Many analyses of oil samples from numerous olive-growing areas
have consistently shown the practical absence of dimethoate and
omethoate. Alessandrini (1962), in an extensive review of insecticide
residues in olive oil and table olives, reported that a large number
of samples of olive oil analysed by the Italian Ministry of
Agriculture contained no measurable dimethoate or omethoate. This was
not unexpected because the coefficient of distribution of omethoate
between water and oil is such that even when large quantities of the
metabolite are deliberately added to the oil and the latter is simply
washed with water the omethoate passes entirely into solution in the
water.
Albi and Rejano (1982) reported studies carried out in Spain
showing that residues of dimethoate in olives ranging from 0.93 to
0.95 mg/kg were completely eliminated after the initial treatment with
2.36 percent NaOH solution during pickling.
Bajra Grains (Pennisetum typhoides)
Santharam et al. (1976) found that dimethoate, applied at the
rate of 30 g/ha produced a residue at harvest of 0.65 mg/kg in the raw
grain. Cooking reduced the residue level to 0.05 mg/kg as determined
by the TLC method of Steller and Curry (1964).
Silage
Beck et al. reported a series of studies involving the
application of dimethoate sprays to corn plants destined for silage
for feeding to cattle. In one of these experiments dimethoate emulsion
was sprayed on corn plants at the rate of 1 and 2 kg/ha. Samples were
taken immediately the spray had dried and on the following day when
the corn was cut and placed in silage pits. The silage was sampled
8 times over the period when it had been in storage for 80 to 122
days. The samples were analysed by a method based on the determination
of total sulphur. It is believed that this method would not recover
residues of omethoate. The results (Beck et al., 1968) showed that
losses of residue that could be associated with 1 day of weathering in
the field and harvesting amounted to 70-90 percent of the dose
applied. Of that amount about 50 percent of the dimethoate residue
ensiled was present after 80 days. However, the levels may have been
influenced by downward translocation of residues in the silos and
subsequent losses caused by the relatively small amount of seepage:
e.g. 1 day after ensiling, dimethoate residues in seepage from the
silos containing corn treated with 1 and 2 kg/ha were 4.9 and
26.6 mg/kg respectively. In subsequent studies (same reference) corn
treated at the rate of 500 g/ha and 2 kg/ha was fermented at 30°C for
30 days before being analysed (by GLC) for dimethoate and omethoate.
Silage from corn harvested 1 day after treatment with 500 g/ha had an
average residue of 1.27 mg/kg dimethoate (0.6-2.1) and less than
0.1 mg/kg of omethoate. Samples from the 2 kg/ha treatment at 1 day
contained an average of 7 mg/kg (3.7-10.8 mg/kg) dimethoate and about
0.2 mg/kg of omethoate. Samples of silage made 7 days after treatment
at the high rate contained an average of 0.53 mg/kg dimethoate
(0.350.74) and no omethoate (less than 0.01 mg/kg).
Tea
Manchanda and Dougan (1975) studied the level and fate of
radiolabelled dimethoate applied to tea plants. The experimental
formulation was applied to 2 leaves and a leaf bud. After 2 weeks the
leaves to which the pesticide had been applied were plucked and
processed to simulate the conditions used in commercial tea
manufacture. The tea from each sample was treated with boiling water
(20 ml/g of tea) and, after standing for 10 minutes with occasional
agitation, was filtered. The residue was washed with several
quantities of boiling water and the filtrates combined. The aqueous
infusion contained 52 percent of the activity present in the processed
leaves. About 15 percent of the radioactivity was due to the presence
of dimethoate and about 25 percent to omethoate. N-demethyl dimethoate
and the acids of dimethoate and omethoate which have both been
reported as metabolites in plants were also confirmed to be present by
GCMS.
Vegetables
Beans
An abstract of a study by Bognar (1977) in the Federal Republic
of Germany into the fate of pesticide residues in vegetables following
preparation and cooking indicates that more than 82 percent of the
dimethoate present in fresh beans is removed by washing and cooking.
Agnihothrudu and Mithyantha (1978) report extensive studies carried
out in India (Anon, 1977) in which 14 separate samples of French beans
containing known amounts of dimethoate residues were cooked in the
normal manner, resulting in a loss of 87 percent (75-95.5 percent) of
the residues.
Cabbage
Kaemmerer and Buntenkotter (1973) recorded that Askew and
Mitchell (1968) found a 44-52 percent loss of dimethoate from cabbage
cooked for 30 minutes.
Krishnaiah and Rattan Lal (1973) reported that washing cabbage
heads reduced the level of dimethoate residues by an average of 40
percent (21.151.8 percent).
Cauliflower
Krishnaiah and Rattan Lal (1973) showed that washing cauliflower
curds reduced the dimethoate residue by an average of 32 percent
(18.5-48.4 percent) and Bognar (1977) found that approximately 82
percent of the dimethoate present in fresh cauliflowers was removed by
washing and steaming.
Chillies
In studies carried out in India (Anon, 1977), 91 percent of the
dimethoate residues present in green chillies were removed by washing.
Details of the interval between application and harvest and the method
of washing are not available.
Chicory
Ten Broeke and Dornseiffen (1973b) studied the effect of washing
and boiling (as practised in the kitchen) on the level of dimethoate
and omethoate in Witloof chicory. They showed that 32 percent of the
dimethoate and 22 percent of the omethoate was removed by washing and
63.4 percent of the dimethoate and 60 percent of the omethoate by
washing and boiling. (Table 19.)
TABLE 19. Dimethoate and Omethoate Residues in Chicory Before and
After Washing and Cooking
Dimethoate Omethoate
Sample Before After After Before After After
No. Washing Washing Cooking Washing Washing Cooking
1 0.11 0.07 0.04 0.11 0.09 0.04
2 0.15 0.08 0.04 0.14 0.11 0.05
3 0.12 0.08 0.04 0.11 0.09 0.05
4 0.11 0.07 0.04 0.12 0.12 0.05
5 0.13 0.11 0.07 0.13 0.14 0.09
6 0.14 0.11 0.06 0.18 0.16 0.08
7 0.13 0.09 0.05 0.14 0.11 0.06
8 0.15 0.10 0.06 0.14 0.12 0.06
9 0.14 0.09 0.05 0.19 0.13 0.07
10 0.18 0.10 0.05 0.18 0.09 0.03
11 0.17 0.11 0.05 0.15 0.09 0.04
12 0.14 0.10 0.05 0.14 0.08 0.04
13 0.12 0.10 0.05 0.17 0.14 0.11
14 0.10 0.08 0.04 0.12 0.14 0.06
15 0.11 0.08 0.04 0.16 0.09 0.05
Average 0.14 0.09 0.05 0.15 0.12 0.06
Egg plant
Khaire et al (1983) reported that following treatment in the
field with dimethoate at the rate of 0.3-0.6 g/l the residues in egg
plant (brinjal) fruit were reduced by 23.3-96.1 percent by washing and
by 52.3-95.7 percent by washing and cooking.
Potatoes
Kaemmerer and Butenkotter (1973) quoted Askew and Mitchell (1968)
as reporting that 30 minutes cooking of potatoes reduced the
dimethoate content by 22 to 39 percent.
Misra et al,(1981) reported that washing and peeling reduced
residues to about 20 percent of the concentration in the unwashed and
unpeeled potatoes. Boiling the washed, peeled potatoes apparently
destroyed all the remaining residue as none was detected in potatoes
or water in which the washed potatoes were boiled. The limit of
determination was not mentioned (Table 20).
Tomatoes
Agnihothrudu and Mithyantha (1978) reported official trials in
India (Anon, 1977) in which washing tomato fruit reduced the
dimethoate residue by 72 percent (1.8 reduced to 0.48 mg/kg).
METHODS OF RESIDUE ANALYSIS
Early methods were reviewed by de Pietri-Tonelli et al.
(1965) and/or in the 1976 evaluation.
The ad hoc Working Group on methods of analysis of the Codex
Committee on Pesticide Residues at its meeting in 1983 issued
recommendations for methods of residue analysis, which included
dimethoate and omethoate, in foods. In the references given below,
those methods which cover omethoate as well as dimethoate are marked
with an asterisk. The primary recommendations were for methods which
had been collaboratively tested. These included:
Pesticides Analytical Manual, 1979*; Manual on Analytical
Methods, 1973/1984; Anon, 1982*; Abbott et al., 1970*; Ambrus
et al., 1981; Panel, 1977*; Panel, 1980.
The Working Group also recognised that a number of other methods
which had not been collaboratively tested were probably suitable for
regulatory purposes and merited consideration. These include:
Anon., 1982*; Carson, 1981; Eichner, 1978*; Krause and Kirchoff,
1970; Mestres et al., 1977a, 1979; Specht and Tillkes, 1980*;
Steller and Pasarella 1972*; Wagner and Frehse, 1976*.
TABLE 20. Dimethoate Residues in Potatoes
Average residues (mg/kg dimethoate) 2
Sampling Unwashed and Washed and Washed, boiled Water in which
(days) 1 unpeeled potatoes peeled potatoes and peeled washed potatoes
potatoes were boiled
A B A B A B A B
Autumn Crop, 1976-77
10 20.3 2.73 0.44 0.57 nd nd nd nd
15 1.27 1.53 0.28 0.32 nd nd nd nd
20 0.69 0.87 0.08 0.08 nd nd nd nd
25 0.43 0.51 0.02 0.03 nd nd nd nd
30 3 0.08 0.14 nd nd nd nd nd nd
Spring Crop, 1977
10 1.87 2.11 0.27 0.33 nd nd nd nd
15 0.98 1.07 0.21 0.23 nd nd nd nd
20 0.61 0.67 0.95 0.06 nd nd nd nd
25 0.21 0.33 nd 0.02 nd nd nd nd
30 3 0.06 0.09 nd nd nd nd nd nd
1 After last spraying.
2 Average of three replications.
3 At harvest.
nd = Residues not detected.
A = 300 g dimethoate a.i. per ha per spray treatment.
B = 500 g dimethoate a.i. per ha per spray treatment.
The Working Group also recommended a number of methods which
could be used for confirming the identity of residues determined by
the above methods. These included:
Pesticides Analytical Manual, 1979; Safe and Hutzinger, 1979*;
Cabras et al., 1979; Greehalgh and Kovacicova, 1975; Mestres
et al., 1977b*.
Other publications include the following:
TLC: Mitsui et al, 1966; Joint Dimethoate Residues Panel,
1968; Kosmatyi et al, 1969; Zadrozinska, 1973;
Antonovich and Vekshtein, 1975; Chakrabarti et al.,
1975; Curini et al., 1980; Segovia and Hernandez, 1981b.
GLC: Bazzi 1968; Joint Dimethoate Residues Panel, 1968; Baumler
and Rippstein 1969; Steller and Brand, 1974; Laski, 1974;
Woodham et al., 1974a,b; Manchanda and Dougan, 1975;
Smart et al., 1978; Le Bel et al., 1979; Ripley et
al., 1974; Ferriera and Fernandez, 1980; Iwata et al.,
1981; Lee and Westcott, 1981; Segovia and Hernandez,
1981a,b; Holland and McGhie, 1983; United Kingdom, 1984.
Methods based on high performance liquid chromatography (HPLC)
have been included in the Pesticides Analytical Manual (1979) and in
the corresponding manual of the Federal Republic of Germany (Anon.,
1982).
Mass spectrometry, combined with gas chromatography, has been
used by Manchanda and Dougan (1975), Lee and Westcott (1979) and
Cairns et al. (1984), qualitatively and/or quantitatively.
Chakrabarti et al (1982) published a method for the
determination of dimethoate in formulations and its residues in foods
by gel electrophoresis. The tissue extracts are first subjected to
hydrolysis. It is possible that the results include both dimethoate
and omethoate. The minimum detectable limit is 0.1 mg and the method
is reported to be simple and quick.
An isotope dilution method employing [32p]-dimethoate and a
liquid scintillation counter was developed by Luther et al.
(1974). The authors reported this to show a 99.5-100.1 percent
recovery of dimethoate. Analyses performed by this method would not
record the level of omethoate.
RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
The Netherlands Government supplied comprehensive information
from surveys conducted by the Food Inspection Service on Witloof
chicory and other commodities produced in The Netherlands and
imported. These results are presented in Table 21 (Netherlands
1981a,b, 1984). It should be noted that the national MRLs were changed
during the period for which the data apply.
TABLE 21a. Dimethoate & Omethoate Residues Found in Food Monitoring in The Netherlands
Dimetholate (D)
+
Omethoate (O)
Source
Netherlands (N) 1973 1973 1974 1974 1978 1979 1980 1982 1982 1982 1982
Imported (I) Witloof Witloof Witloof Witloof Witloof Witloof Witloof Witloff Apples Apples Cherries
(N) (N) (N) (N) (N) (N) (N) (N) (N) (I) (I)
Residue D O D O D+O D+O D+O D+O D+O D+O D+O
mg/kg
0.000 - - - - 33 32 8
0.001-0.200 38 51 23 31 148 192 101 60 2 8
0.201-0.400 21 6 15 1 39 47 38 17 1
0.401-0.600 19 10 20 5
0.601-0.800 9 9 5 1
0.801-1.000 7 5 5 13 0
1.001-1.500 8 8 3 1
1.501-2.000 2 3 1
2.001-2.500 3 1
2.501-3.000 2
> 3.000 4
TOTAL 68 57 53 32 262 323 176 85 2 8 1
> National MRL 9 0 5 0 22 42 9 3
TABLE 21b.
Dimetholate (D)
+
Omethoate (O)
Source
Netherlands (N) 1982 1982 1982 1982 1982 1982 1982 1982 1982 1982
Imported (I) Currants Orange Plums Plums Raspberries Endive Lettuce Mushrooms Parsley Turnips
(I) (I) (N) (I) (N) (N) (N) (N) (N) (N)
Residue D+O D+O D+O D+O D+O D+O D+O D+O D+O D+O
mg/kg
0.000 1
0.001-0.200 1 1 1
0.201-0.400 1 1
0.401-0.600 1 1
0.601-0.800
0.801-1.000
1.001-1.500 1
1.501-2.000 1
2.001-2.500
2.501-3.000 1
> 3.000 1
(7.9)
TOTAL 1 1 1 1 1 1 3 1 1 1
> National MRL
The Swedish Government (Sweden, 1984) provided information from
the monitoring of domestic and imported foods by the National Food
Administration. Table 22, which summarizes this information, does not
indicate the total number of samples in which dimethoate or omethoate
residues were detected, but it clearly indicates that the number of
samples with residues above 0.4 mg/kg was small. Over the 3 years from
the beginning of January 1981 to the end of 1983 seven of 1017 samples
of Swedish Commodities (0.69 percent) were found to contain dimethoate
residues above 0.41 mg/kg and 19 of 2582 (0.74 percent) of imported
commodities contained dimethoate above this level. None of these
exceeded the Swedish MRL for fruit and vegetables of 2 mg/kg.
The Government of the United Kingdom (United Kingdom, 1984)
provided information about residues in lettuce gathered from food
monitoring during 1981/82 as indicated in Table 23. A significant
proportion of the samples (8.6 percent) were found to contain
dimethoate/omethoate residues. However only 2 of the 302 samples
contained combined residues exceeding the current recommended MRL of
2 mg/kg.
The levels of dimethoate and omethoate in the samples containing
determinable residues are shown in Table 24.
The samples were analysed by a multi-residue procedure.
Recoveries from spiked lettuce were 80 percent and the limit of
detection was 0.01 mg/kg. All residues reported were confirmed using
two GLC columns of different polarities as well as by the relative
responses of alkali-flame and flame photometric detectors.
The UK Ministry of Agriculture, Fisheries and Food (United
Kingdom, 1984) examined 24 samples of apples, pears and plums that had
been treated with dimethoate 11 to 126 days before harvest. Only in
one sample of pears did the combined residue exceed the limit of
determination (0.01 mg/kg dimethoate and 0.02 mg/kg omethoate). This
contained 0.13 mg/kg of omethoate. The pears in question had been
treated only 11 days before harvest.
The Government of Denmark (Denmark, 1984b) reported that in the
monitoring of pesticide residues in fruit and vegetables they
frequently find small residues of dimethoate or omethoate, mainly in
imported fruit. Seldom are dimethoate and omethoate residues present
in the same sample. Over the period 1976-1984 the only samples
containing both dimethoate and omethoate were the 14 listed in Table
25.
TABLE 22. Results of Residue Monitoring in Sweden, 1981-1984
Pesticide: Dimethoate
Number of Number of samples with residues Highest
Food Origin samples within given ranges, mg/kg residue
analysed n.d.-0.41 0.41-1.03 1.04-2.05 mg/kg
Apple Sweden 385 379 6 0.85
Import 915 914 1 0.56
Cabbage Sweden 126 125 1 0.60
Chinese Import 191 191
Cherries Sweden 9 9
Import 52 46 4 2 1.4
Chicory Import 26 19 5 2 1.4
leaves
Cucumber Sweden 312 312
Import 416 414 2 0.71
Grapes Import 452 451 1 0.47
Lettuce Sweden 185 185
Import 179 178 1 0.98
Mandarin Import 351 350 1 0.57
Total Sweden 1017 7
Import 2582 15 4
Grand Total 3599 22 4
Swedish MRL - Fruit and Vegetables: 2 mg/kg
Potatoes: 0.2 mg/kg
TABLE 23. Dimethoate/omethoate Residues in Lettuce
Total number Residue range Number in range
analysed mg/kg
Dimethoate
UK-produced 65 0.01-0.1 7
0.11-0.5 4
1.9 1
Imported 86 0.14, 1.48 2
Omethoate
UK-produced 65 0.01-0.1 7
0.16, 0.27 2
Imported 86 0.07, 0.74 2
TABLE 24. Dimethoate/omethoate Residues in Lettuce
Samples Dimethoate residue Omethoate residue
No. mg/kg mg/kg
EL1 0.15 0.04
EL2 0.09 0.04
EL8 0.50 0.09
EL9 0.10 0.04
EL36 1.90 0.27
EL37 0.08 <0.05
EL43 0.05 0.06
EL65 0.12 0.09
EL69 0.34 0.16
DL5 1.48 0.74
FL41 <0.05 0.20
SL51 0.14 0.07
SL60 0.05 <0.05
TABLE 25. Samples of Fruit and Vegetables Found to Contain both
Dimethoate and Omethoate Residues (Denmark, 1976-1948)
Commodity Dimethoate (mg/kg) Omethoate (mg/kg)
Cherries (Italy) 0.02 0.12
" " 0.19 0.22
" " 0.07 0.08
" " 0.05 0.14
" " 0.51 0.09
Apples (France) 0.09 0.05
" " 0.10 0.04
" " 0.13 0.02
" (Italy) 0.06 0.11
" " 0.41 0.15
" (Netherlands) 0.02 0.21
Grapes (Italy) 0.08 0.11
Satsumas (Spain) 0.02 0.07
Lettuce (USA) 0.04 0.04
NATIONAL MAXIMUM RESIDUE LIMITS REPORTED TO THE MEETING
The meeting was informed that the following national MRLs had been established.
Argentina dimethoate apple, pear. 1
pea, broccoli, lettuce, pepper
cabbage, savoy cabbage,
cauliflower, ruff, spinach,
chick-pea, broad bean, tomato. 2
Australia dimethoate (including tomatoes, peppers. 1
its oxygen analogue) fruits, vegetables (except
tomatoes, peppers). 2
oilseeds. 0.1
peanuts, eggs, meat, raw
cereals. 0.05
Austria dimethoate ) total
omethoate vegetables, fruit. 1.5
omethoate ) not over
0.4 ppm
) total
omethoate grains, sugarbeets. 0.2
) not over
0.05 ppm other. 0.1
omethoate vegetables, fruit,
sugarbeets. 0.4
other. 0.05
Belgium dimethoate fruit, vegetables. 1
omethoate fruit, vegetables. 0.2
artichokes, cherries, witloof,
spinach. 0.4
berries, onions, leeks,
root vegetables. 0.1
cereal grains. 0.05
Canada dimethoate (Cygon, apples, broccoli, beet greens,
Rogor) cabbages, cauliflower, kale,
O,O-dimethyl S-methyl- lettuce pears, spinach, Swiss
carbamoyl methyl chard, turnip greens. 2*
phosphorodithioate
citrus fruit. 1.5*
beans, blueberries, celery,
cherries, strawberries. 1.0*
peas, peppers, tomatoes. 0.5*
Czechoslovakia dimethoate - as tomatoes, green peppers. 1
dimethoate (including vegetables, fruits, including
the oxygen derivative) citrus fruit. 2
Denmark dimethoate - total of berries and small fruits,
dimethoate & omethoate pome and stone fruits,
vegetables. 2
omethoate berries and small fruits, pome
and stone fruits, vegetables. 0.5
potatoes. 0.05
* including the metabolite omethoate.
EEC dimethoate all products. 1
omethoate cherries, witloof chicory,
artichokes, spinach. 0.4
berries, onions, leeks,
root vegetables. 0.1
other products. 0.2
Finland dimethoate and 0.5
omethoate, total
France dimethoate all fruits & vegetables. 1.5
omethoate all fruits & vegetables. 0.4
German dimethoate - max 20% cereals. 0.05
Democratic as oxy compound pome, stone & small fruits,
Republic strawberries, citrus, root
vegetables, leaf vegetables,
cole crops, pulses. 0.5
vegetable fruit 0.5
sprout vegetables. 0.1
other foods. 0
German dimethoate vegetables, fruits. 1
Federal cereals, sugarbeets. 0.2
Republic other vegetable foodstuffs. 0.1
omethoate artichokes, chicory, cherries,
spinach. 0.4
small fruits, leeks, onions,
root vegetables. 0.1
other vegetables and fruits. 0.2
other vegetable foodstuffs. 0.05
Hungary dimethoate green pepper, tomato,
currant, strawberry. 1
apple, Brussels sprouts, cherry,
potato (unpeeled), apricot,
cabbage, kohlrabi, cauliflower,
savoy, pear, peach, parsley,
lettuce, sorrel, spinach, plum,
celery leaf. 2
omethoate apple, cherry, apricot,
pear, peach, plum, grape. 2*
India dimethoate fruit, vegetables. 2
(residues to be determined
dimethoate and its oxygen
analogue and expressed as
dimethoate)
Ireland dimethoate all products. 1
Israel dimethoate tree fruits (including citrus
fruit), eggplant, cucurbits,
peas, beans, vegetables. 2
tomatoes, peppers. 1
omethoate citrus fruit. 0.4
Italy dimethoate fruits, vegetables, sugarbeets. 1.5
cereals. 0.2
omethoate fruits, sugarbeets, vegetables. 0.4*
cereals. 0.05
Japan dimethoate persimmon, summer orange (pulp),
summer orange (peel), mandarin
orange, potato, tomato. 1
Kenya dimethoate tree fruit (including citrus). 2
maize, millets, sorghum,
tomatoes, peppers. 1
other vegetables. 2
omethoate apples, beans, broccoli,
cabbage, cauliflower, collards,
endive (escarole), kale, lemons,
lettuce, oranges, pears, peas,
peppers, spinach, Swiss chard,
tomatoes, turnips. 2
melons. 1
potatoes. 0.2
pecans. 0.1
wheat grain. 0.04
meat, fat and meat by-products
of cattle, goats, hogs, horses
and sheep. 0.02
Mexico dimethoate alfalfa, celery, broccoli, peas,
chili peppers, cabbage, citrus
fruit, spinach, string beans,
lettuce, tomato, apples, pears,
soybeans (forage and hay), wheat
(forage and straw). 2
corn (forage), melons, grapes. 1
corn (grain). 1N
potatoes, sorghum (forage). 0.2
safflower, sorghum (grain)
nuts, cottonseed. 0.1
soybeans (grain). 0.05
wheat (grain). 0.04N
Netherlands dimethoate fruit, vegetables (not
potatoes), spices. 1
omethoate fruit, vegetables (not
potatoes), spice. 0.2
Belgian endive (chicory),
spinach, cherry, artichoke. 0.4
strawberry, berry, leek,
onion, carrot greens. 0.1
New Zealand dimethoate tomatoes. 1
other fruit and vegetables. 2
Singapore dimethoate fruits. 0.5
olives. 1
South Africa dimethoate (sum of apples, beans, citrus, cruici-
dimethoate and ferae, cucurbits, grapes, peaches,
omethoate) pears, plums, sorghum and wheat. 2
cottonseed and groundnuts. 0.1
potatoes, strawberries and
pineapples. 0.5
apples, Grapes and pears. 1.5
citrus and lucerne. 2
peas. 1
Spain dimethoate fruit, vegetables. 1.5(2)
omethoate fruit, vegetables. 0.4
Sweden dimethoate including fruit and vegetables,
oxygen analogue (of except potatoes. 2
omethoate) potatoes. 0.2
omethoate citrus fruit. 0.5
fruit and vegetables,
except potatoes. 0.2
Switzerland dimethoate fruit (except cherries). 0.5
vegetables. 0.3
cherries. 0.8
beets. 0.05
milk. 0.005
Taiwan dimethoate citrus fruit. 2
USA dimethoate (Cygon, dried citrus pulp. 5*
Rogor) alfalfa, apples, beans (dry,
O,O-dimethyl S-methyl- lima, snap), broccoli, cabbage,
carbomoly methyl cauliflower, celery, collards,
phosphorodithioate endive (escarole), grapefruit,
kale, lemons, lettuce, mustard
greens, oranges, pears, peas,
peppers, soybean forage and hay,
spinach, Swiss chard, tangerines,
tomatoes, turnips (roots and tops),
wheat (green fodder and straw). 2*
corn fodder and forage,
grapes, melons. 1*
potatoes, sorghum forage. 0.2*
cottonseed, pecans, safflower
seed, sorghum grain. 0.1*
corn grain. 0.1
(negligible residues)
soybeans. 0.05*
(negligble residues)
wheat grain. 0.04*
(negligible residues)
eggs, meat, fat, and meat
by-products of cattle,
goats, hogs, horses,
poultry and sheep. 0.02*
(negligible residues)
milk. 0.002*
(negligible residues)
* including its oxygen analog O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorothioate
USSR phosphamide (Rogor, fruits, citrus fruits. 1.5
dimethoate)
Yugoslavia dimethoate edible olives, fruit, vegetables. 1
other food commodities. 0.5
omethoate vegetables and fruit. 0.5
sugarbeets and other food
commodities. 0.05
APPRAISAL
Following requests made at the 1980, 1981 and 1983 meetings of
CCPR that, if possible, separate MRLs should be proposed for
dimethoate and omethoate when the latter is used directly as an
insecticide as well as when it occurs as a metabolite of dimethoate
and formothion, a review was made of the published scientific
literature as well as limited unpublished information available to the
meeting. This included all information published since 1960 that was
accessible and which had not already been evaluated by JMPR.
Information on current uses in 11 countries indicated
considerable similarity in rates of application but important
differences in preharvest intervals. There is considerable overlap in
the use of dimethoate and omethoate when viewed world-wide though in
individual countries the uses may not coincide closely.
The convention which has been accepted from the early days of the
development of dimethoate that the residue should be expressed as the
sum of the parent and metabolite has meant that most of the residue
data has not indicated the relative proportions of dimethoate and
omethoate. Furthermore, many of the analytical methods that have been
widely used measured total phosphorus by colorimetric procedures. This
has no doubt caused authorities to wonder whether omethoate occurs as
a relatively high proportion of the total residue.
A concerted effort has therefore been made to locate and evaluate
all available reports of studies in which the concentration of both
dimethoate and omethoate have been reported. In all of these studies
it is clear that omethoate is produced within one day of treating
crops with dimethoate dusts, wettable powders, or emulsion sprays. The
concentration of omethoate remains low and relatively constant for
periods as long as 35 days. The concentration of dimethoate falls
rapidly during the first 7 days and thereafter, at a steady rate until
it eventually reaches a level comparable with the concentration of
omethoate. Thereafter the concentration of dimethoate continues to
decline whilst the omethoate remains relatively constant. Thus, the
proportion of omethoate in the total residue ranges from 1-2 percent
initially, 10-15 percent during most of the post-treatment period,
rising to approximately 50 percent after 35 days when the total
residue level is of the order of 0.1-0.2 mg/kg.
When omethoate is applied directly to these or similar crops the
initial deposit of approximately 20 mg/kg declines within a few days
to about 5 mg/kg and to between 2 mg/kg and 1 mg/kg by the 14th day
after treatment. This level is 10-50 times the level which occurs from
the metabolism of dimethoate applied to the same crops.
It is noteworthy that several investigators have failed to detect
omethoate residues in some fruits and vegetables following the
application of dimethoate. This was reported for strawberries, citrus
(edible portion), Brussels sprouts from preharvest application, and
tomatoes and bananas following postharvest treatment.
The information from residue trials made available from this
review was evaluated to determine residue levels which would be
appropriate for use in the establishment of MRLs. Data from trials on
apples, apricots, black currants, cherries, citrus, grapes, peaches,
plums, strawberries, olives, beans, Brussels sprouts, cabbage,
cauliflower, chicory, peanuts and soybeans were available. With the
exception of information on olives, all other data strongly supported
the existing recommendations for MRLs when considered in the light of
the PHI's adopted in most countries for these crops. The data from
trials on olives would suggest that the MRL could be reduced to
0.5 mg/kg if the olives were not harvested until 30 days after the
last spray.
Considerable information on the metabolism of dimethoate in
animals, plants and soil and on the fate of dimethoate in animals and
soil was available to the meeting. There appears to be only a remote
possibility of omethoate residues being excreted in milk following the
feeding of dimethoate treated fodder, silage or agricultural wastes to
dairy cows. The level in the milk is not likely to exceed 0.1 mg/kg.
It is clear that residues of dimethoate are taken up by crop
plants following the application of dimethoate to the soil but the
levels appear to be well within the limits already recommended for
dimethoate and omethoate residues in the corresponding commodities.
There was a substantial amount of information available on the
effect of processing and cooking on dimethoate residues in fruit,
vegetables, olives and grapes. The preparation of citrus juice
eliminates most, if not all, of the dimethoate from whole citrus. As
far as could be determined from the several studies available, no
omethoate is found in the juice of citrus. Dimethoate residues are
eliminated when treated apples are processed into juice, jam or puree.
Dimethoate residues on grapes find their way into grape juice and wine
without change in composition or concentration but during storage of
wine the residues completely degrade. There is a significant loss of
the omethoate component during the processing of raisins but the
dimethoate residue appears to remain at about the same concentration
in the dried fruit as in the fresh fruit if no allowance is made for
the water lost in the process.
The processing of olives for the recovery and refining of olive
oil eliminates virtually all traces of dimethoate and omethoate
residues. The process of pickling olives for eating removes and
destroys substantially all trace of residues present in the fresh
olives.
Normal domestic preparation and cooking of beans, cabbage,
cauliflowers, peppers, tomatoes and chicory removes or destroys from
60-100 percent of the dimethoate and omethoate present in the fresh
commodity.
Methods of residue analysis used to develop residue data over the
30 years since dimethoate insecticides have been available have been
reviewed. Some of these have obviously not recovered all of the
omethoate that may have been present but methods recommended since
about 1970 appear more satisfactory. The recommendations of the ad
hoc. Working Group of the CCPR on methods suitable for regulatory
purposes were confirmed.
A number of countries have provided results of monitoring studies
which indicate that the incidence of dimethoate and omethoate residues
in foods in commerce is relatively low and that these residues are
well within the recommended MRLs.
Attention is drawn to the differences between the MRLs
established in the legislation of many countries and the lack of
harmony with the recommendations of the CCPR. The variation in
preharvest intervals which apply in different countries could, in
part, explain the differences in MRLs.
RECOMMENDATIONS
The Meeting, having considered extensive information on the
occurence, level, nature and fate of residues resulting from the use
of dimethoate and omethoate agreed that it was not possible to develop
separate MRLs for dimethoate and omethoate bearing in mind that
omethoate is frequently used on exactly the same commodities that are
generally treated with dimethoate and in such cases the residues of
omethoate are considerably higher than those from dimethoate.
The MRLs previously recommended are confirmed.
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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 (AGP:1970/M/12/1)
Dimethoate (Pesticide residues in food: 1983 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)