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
Piet