PESTICIDE RESIDUES IN FOOD - 1981
Sponsored jointly by FAO and WHO
EVALUATIONS 1981
Food and Agriculture Organization of the United Nations
Rome
FAO PLANT PRODUCTION AND PROTECTION PAPER 42
pesticide residues in food:
1981 evaluations
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
Geneva, 23 November-2 December 1981
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome 1982
METHAMIDOPHOS
Explanation
Because of the special relation of methamidophos and acephate,
the Thirteenth Session of the Codex Committee on Pesticide Residues
requested the Joint Meeting to re-examine the limits for both
compounds to determine if they are still adequate. Governments were
requested to provide good agricultural practice information to
facilitate this review.
Methamidophos was previously reviewed in 1976 when maximum
residue levels were estimated for a variety of commodities. In 1979,
some levels were revised and new ones estimated, partly to allow for
residues resulting from the use of acephate.*
Some additional residue data, good agricultural practice
information, and information on the fate of residues have been
received and are reviewed in this addendum. However, the limited
amount of information that has been provided to this Meeting is not
adequate to fully address the issues that have been raised by the
Codex Committee. To the extent new data are available, residues
resulting from the use of acephate are considered, and this addendum
should be read in conjunction with the one on acephate elsewhere in
these evaluations.
RESIDUES IN FOOD
USE PATTERN
Some good agricultural practice information has been provided to
this Meeting and are summarized below:
* See Annex II for FAO and WHO documentation.
Country Formulation Commodity Application Pre-harvest
Rate (kg a.i./ha) Interval (days)
Australia - tomato - 4
US Monitor 4 spray, cabbage 0.56-1.12 35
Monitor 4 liquid, broccoli 0.56 14
and 1.12 21
Monitor 6 spray Brussels 14
sprouts
cauliflower 28
potato 14
New Zealand 60% E.C. Brussels 1.1-1.5 l/ha -
sprouts
broccoli 1.5 l/ha -
potato 0.8 l/ha -
Germany 600 g a.i./ha cauliflower 0.36 kg/ha 21
red and white
and savoy cabbage,
kohlrabi
RESIDUES RESULTING FROM SUPERVISED TRIALS
Additional residue data were available from six countries on a
total of 12 commodities. However, little information was provided as
to whether there are approved good agricultural practices for the
formulations used in the residue trials or what rates and pre-harvest
intervals are recommended. Results of the field trials are summarized
in Table 1.
Brussels sprouts
Minimal data were available from one country, with maximum
residues of 0.04 mg/kg at application rates and pre-harvest interval
(7 to 8 days) approximating that used as a basis for the current
1 mg/kg Codex limit. There is no need to change the previous estimate,
which should be adequate to cover residues resulting from the use of
methamidophos or acephate on the same crop, but not necessarily both.
TABLE 1. Residues of methamidophos from supervised trials
Application Residues (mg/kg) at intervals (days) after application2
Country
Crop (Year) Rate
No. (kg a.i./ha) Formulation 0 1 3 5-6 7-8 10 14-15 21 Control
Brussels
sprouts New Zealand 4 1.1 l/ha1 60% E.C. 0.78 0.17 0.09 0.02 <0.007 <0.007
(1977) broadcast
(proposed use)
New Zealand 4 1.3 l/ha.1 60% E.C. 1.7 0.1 0.04 0.01 <0.007 <0.007
(1977)
(1973) 4 1.5 l/ha.1 60% E.C. no residues (<0.007 mg/kg) 6 week post-treatm. <0.007
Broccoli New Zealand 4 1.5 l/ha1 60% E.C. <0.007 <0.007
(1973)
Broccoli USA 5 0.28 6E3 4.8 2.1 0.64 0.11
(head) (1968) 4.2 2.5 0.77 0.11
CA 7 1.7
1.4
8 1.3
1.4
5.0 2.7
9 5.7 1.1
(1967- 5 0.56 6E 6.7 5.2 1.5 0.27
1968) 7.3 5.1 1.3 0.23
CA 7 3.1
2.8
8 4.0
2.7
9 1.3 5.3
11.0 5.3
TABLE 1. (con't)
Application Residues (mg/kg) at intervals (days) after application
Country
Crop (Year) Rate
No. (kg a.i./ha) Formulation 0 1 3 5-6 7-8 10 14-15
Broccoli USA
(head) (1967- 4-5 1.1 6E3 3.1 1.4
1968) 3.4 1.4
(CA, NY, 6.4 1.6
FL,NJ) 5.4 1.3
17 2.1
15 2.1
5.3 2.1
2.8 2.5
8.7
12
1.6
1.2
7-9
8.8 7.0
4.7 3.0
9.1
1.1
8.8
9.9
14 3.0 2.1 1.3 0.27
3.3 2.4 1.3 0.17
CA
(1969) 4 2.24 6S 0.28 0.21 0.03
0.65 0.36 0.01
TABLE 1. (con't)
Application Residues (mg/kg) at intervals (days) after application
Country
Crop (Year) Rate
No. (kg a.i./ha) Formulation 0 1 3 7 14
Potato New Zealand 1 1.54/ha1 Tamaron 0.13,0.08 0.35,0.26 0.13,0.44 0.07 0.005,0.03
(1972) 600g/L 0.19
No. of
0 1 2-3 6-7 9-10 13-14 15 20-21 24 Samples
Cabbage Australia
* (1976) (2- 0.24% to run 580 g/l 0.61 0.18 0.07 0.02 1 each
4)5 off interval
* (1976) (2- 0.12% to run 580 g/l 0.43 0.12 0.03 <0.01
4)5 off 1
* (1976) (2- 0.06% 580 g/l 0.19 0.08 0.02 <0.01
4)5
* (1976) 6 0.036% 580 g/l 0.16 0.11 0.04 0.04 0.02
a.i. or
163-509 g/ha
(1973) 4 1.5 l/ha 6E 0.05 0.002 0.0007
(3 (6
day) day)
TABLE 1. (con't)
Application Residues (mg/kg) at intervals (days) after application2
Country
Crop (Year) Rate No. of
No. (kg a.i./ha) Formulation 0 1 2-3 6-7 9-10 13-14 15 20-21 24 Samples
Cauliflower Australia 1 1.3 580 g/l 11.1 4-7 3 2 Duplicate
leaves * (1970) analysis
head 0.2 0.12 0.06
Cauliflower * (1977) 4 58 g/100 l 58% E.C. 0.34
(0.06%) (38
days)
No. of
0 1 3 7 14 21 28 samples
Cauliflower Germany 1976 3 0.36 0.1% 0.55 0.02 <0.01 <0.01 N.D.7
1976 3 0.36 0.1% 0.7 0.1 0.04 0.01 <0.01
1976 3 0.36 0.1% 0.55 0.07 0.01 <0.01 <0.01
1978 2 0.36 600g/L
flower 2.0 0.9 0.55 0.34 0.04 N.D.7
2.3 1.2 0.56 0.27
leaf 1.62
1.62
TABLE 1. (con't)
Application Residues (mg/kg) at intervals (days) after application2
Country
Crop (Year) Rate No. of
No. (kg a.i./ha) Formulation 0 1 3 7 14 21 28 samples
1978 2 0.36 600 g/L
flower 0.37 0.17 0.07 0.02 0.01 N.D.7
0.36 0.32 0.07 0.02 0.01
1.3
1.3
1978 2 0.36 600g/L 0.53 0.01 N.D.7 N.D.7 N.D.7
0.56
Crop Country No. Rate Formulation Days after Residues (mg/kg)
(year) last application fruit peel whole6
Citrus Egypt
(1970- 2 0.15%
Tangerine 1971) (10.6g/tree) 5546 0 0.02 4 1.2
(Clementine) 111 0.01 0.02
Lemon Egypt 6 0.2% 600 g/L
(Italian (1971) (12g/tree) 18 0.13 1.7
seedless)
32 0.01 0.35
47 0.01 0.09
62 N.D.7 0.05
76-90 N.D. <0.01
TABLE 1. (con't)
Application Residues (mg/kg)
Country
Crop (Year) Rate Days after last
No. (kg a.i./ha) Formulation application fruit peel whole6
Lemon Egypt 2 0.15% 5546 0 0.2 8.6 2.7
(Italian (1970- (196g/tree)
seedless) 1971) 111 0.02 0.2 0.07
Lemon Egypt 7 0.2% 600g/L 1 0.17 5.2 1.7
(Eureka) (1971) (12g/tree) 18 0.1 2.0 0.7
32 0.01 0.6
47 ND7 0.09
62 ND 0.05
76 ND 0.01
90 ND -
pulp peel whole6
Lemon U.S.A. 2 1.1 4WM 0 0.0 3.2 1
FL (1974) foliar 7 0.06 0.9 0.3
spray 14 0.15 0.8 0.3
22 0.08 0.14 0.1
TABLE 1. (con't)
Application Residues (mg/kg)
Country
Crop (Year) Rate Days after last
No. (kg a.i./ha) Formulation application pulp peel whole6
38 0.05 0.03 0.04
58 0.1 0.0
control 0.0 0.0
FL (1974) 2 1.1 4WM 0 0.04 2.1
foliar 7 0.06 0.38
spray 14 0.03 0.13
30 <0.01 0.01
60 0.0 0.01
90 0.0 <0.01
control <0.01 0.0
CA (1974) 2 1.1 4WM 0 0.08 12.5 3.8
foliar 7 0.17 11.3 3.5
spray 14 0.06 5.5 1.7
28 0.19 3.2 1.2
60 0.03 0.7 0.23
TABLE 1. (con't)
Application Residues (mg/kg)
Country
Crop (Year) Rate Days after last
No. (kg a.i./ha) Formulation application pulp peel whole6
Lime U. S .A. 2 1.1 4WM 0 0.03 2.9
FL (1974) foliar 7 0.0 0.13
spray 14 0.01 0.03
30 0.0 0.01
60 0.0 0.1
90 0.0 0.0
control 0.00
Oranges U.S.A. 2 1.1 4WM 0 0.21 14.9 4.6
(FL) foliar 7 0.14 4.8 1.5
(1974) spray 14 0.12 2.2 0.74
30 0.08 0.43 0.19
60 0.03 0.04 0.03
91 0.02 0.03 0.02
control 0.00 0.00
Lettuce U.S.A.
(head) (NJ, CA) 7 1.1 6S 7 0.08-0.5
(1969) (0.25)
10 0.03-0.14
(0.1)
TABLE 1. (con't)
Application Residues (mg/kg)
Country
Crop (Year) Rate Days after last
No. (kg a.i./ha) Formulation application pulp peel whole6
14 0.01-0.13
(0.08)
N.J. 7 2.2 6S 7 0.5,0.4
(1969) 10 0.4,0.4
14 0.3,0.3
U.S.A. 0.5 6E 0 0.4-5
(NJ, CA) 4-8 (1.4)
(1968-
1969) 3 0.1-0.4
(1.1)
7 0.06-4.5
(0.93)
14 0.01-0.7
(0.3)
TABLE 1. (con't)
Application Residues (mg/kg)
Country
Crop (Year) Rate Days after last Threshed Dry Control
No. (kg a.i./ha) Formulation application beans vines beans vines
Soybean U.S.A.
All 2 1.1 aerial 57 <0.01 <0.01 <0.01 <0.01
(1978) spray
4
TX 2 1.1 foliar 66 <0.01 <0.01 <0.01 <0.01
(1977) spray
4
TX 1.1 foliar 66 <0.01 <0.01 <0.01 <0.01
(1977) spray
4
NC 2 1.1 foliar 77 <0.01 <0.01 <0.01 <0.01
(1977) spray
4
GA 1.1 foliar 161-162 0.02 <0.01 <0.01 <0.01
(1977) spray
4
Tomato New Zealand 1 1.5 l/ha1 1 0.13
(1974) 600 g/L 4 0.02
7 0.005
14 Nil
New Zealand 1.5 l/ha1 600 g/L 1 0.13
1 3 0.05
7 0.004
(1974- 10 0.002
1975)
TABLE 1. (con't)
Country Application Residues (mg/kg) at intervals (days) after application
Crop (Year) Rate
No. (kg a.i./ha) Formulation 4h 3 7 10 14
Tomato South Africa 7 0.6 0.53 0.45 0.3 0.14 0.25
(1978)
Notes: Data in Table are based on reports submitted to the 1981 JMPR by Bayer, including reports from Mobay and Chevron.
Data provided by the Australian Government indicated by *
1 Litres of product (proposed use);
2 Mean in parentheses;
3 E = emulsion;
4 Proposed label rate is 0.56-1.1 kg a.i./ha;
5 2 applications at 20 days preharvest test, 3 applications at 13 days preharvest test, 4 applications at 2 and 0 days
preharvest tests;
6 Based on assumption of 70:30 pulp: peel weight ratio.;
7 Limit of sensitivity: 0.01 mg/kg;
8 Average of two analyses where single values are given.
Broccoli
Several delegations to the Codex Committee on Pesticide Residues
(CCPR) at the 12th and 13th sessions expressed concern that limits for
methamidophos on some commodities are too high and specifically (at
the 12th session) that the 2 mg/kg limit on broccoli was too high.
Additional residue data have been provided.
The current 2 mg/kg limit is based on 3 to 5 applications at
0.56 - 1.12 kg a.i./ha and a seven-day pre-harvest interval. Most of
the data submitted to this Meeting do not fall into those constraints.
Those that do confirm the need for the current 2 mg/kg limit are based
on the above criteria for the formulations used. No information was
provided as to whether the formulations used in the trials are
approved for use on broccoli and, if they are, what rates or pre-
harvest intervals are considered good agricultural practice. The
application rates are consistent with those used as the basis for the
existing limit.
The new data do suggest that a 1.0 mg/kg limit would be supported
if no more than five applications are made at the 0.56 - 1.12 kg
a.i./ha application rate and a pre-harvest interval of 14 days is
observed. However, data previously reviewed (1976) indicate that a
21-day pre-harvest interval would be required. A 1.0 mg/kg limit would
also be consistent with methamidophos data on other brassica,
methamidophos residues on broccoli resulting from uses of acephate
(assuming both methamidophos and acephate are not used on the same
crop) and national tolerances reported to the Meeting.
Cabbage
The new residue data are within the current 1.0 mg/kg limit.
Furthermore, if residues of methamidophos on cabbage resulting from
the use of acephate (see acephate addendum) are assumed to be
approximately 15% of total acephate + methamidophos residues, the
1.0 mg/kg limit is sufficient to cover methamidophos residues in
cabbage resulting from the use of acephate, if the 5 mg/kg acephate
limit is not exceeded. It would not necessarily be adequate if both
acephate and methamidophos were used on the same crop.
Cauliflower
The new residue data are consistent with the 1.0 mg/kg level
estimated by the 1979 JMPR. No additional data have been provided on
which to base estimates of residues of methamidophos in cauliflower
resulting from the use of acephate. However, based on the same
assumptions and data for cabbage, the 1.0 mg/kg limit would probably
suffice for the use of methamidophos or acephate on cauliflower, but
not necessarily both.
Citrus
The current 0.5 mg/kg residue level for methamidophos on citrus
was estimated by the 1979 Meeting to allow for residues of
methamidophos resulting from the use of acephate, for which a maximum
level of 5 mg/kg was estimated. Residue data reflecting the use of
methamidophos on citrus in two countries were submitted to this
Meeting, although no information on national use patterns was
provided.
The data indicate that residues in the pulp would be well under
the current 1.0 mg/kg limit, even at day of application. Peel
residues, however, were as high at 15 mg/kg at day of application. If
a pulp:peel ratio of 70:30 is assumed, it can be estimated that a
pre-harvest interval of approximately 35 days would be required to
assure whole-fruit residues no greater than 1.0 mg/kg, and
approximately 50 days to assure residues less than the current
0.5 mg/kg level estimate. In the absence of information on approved
national use patterns for methamidophos on citrus, there is no basis
to change the current 0.5 mg/kg limit, which covers residues of
methamidophos resulting from the use of acephate.
Lettuce
Lettuce, with a current limit of 2 mg/kg, is one commodity for
which concern has been expressed that the limit is higher than
necessary. It is not clear what pre-harvest interval the 1976 Meeting
used for the 2 mg/kg limit, but it was presumably two weeks, based on
the data. However, based on the 'recommended' uses (1976 Evaluations)
a 21-day interval could be used, and based on the 1976 summary data
(head + wrapper leaves <0.4 mg/kg at 21 days) a lowering of the limit
to 1.0 mg/kg could be supported if a 21-day interval were observed.
Additional data from residue trials in one country were submitted
to this Meeting, although it could not be confirmed that the trials
represent approved good agricultural practices in that country. The
application rates are similar to the rates 'recommended' in the 1976
Evaluations. At 14 days from application and with rates approximately
0.5 × the maximum 'recommended' rate, maximum residues are 0.7 mg/kg.
These data are consistent with a 1.0 mg/kg limit based on a 21-day
pre-harvest interval.
No additional data were provided to this Meeting to permit
estimation of methamidophos residue levels in lettuce resulting from
the use of acephate. Based on results in other brassica, a 1.0 mg/kg
methamidophos limit would probably be adequate to include residues of
methamidophos resulting from the use of acephate, but probably not for
the use of acephate and methamidophos on the same crop.
On the basis of data and uses previously reviewed and data
submitted to this Meeting, a 1.0 mg/kg limit after a 21-day pre-
harvest interval, could be supported.
Potato
Residue data from trials reflecting two times the recommended
national application rate were available from one country. Although
the pre-harvest interval basis for the current 0.1 mg/kg limit for
methamidophos on potatoes was not specified, it was probably 2 to 3
weeks. If the uses utilized in the trials submitted to this Meeting
become nationally approved uses, a 14-day pre-harvest interval would
be required to assure that residues would not exceed the current
0.1 mg/kg limit.
No data were available to estimate possible methamidophos
residues resulting from the use of acephate (1.0 mg/kg limit) on
potatoes. In the absence of such data, the current 0.1 mg/kg limit for
methamidophos should also apply to residues resulting from the use of
acephate. It may not be adequate to cover residues of methamidophos
resulting from the use of methamidophos and acephate on the same crop.
There is insufficient information to warrant a revision of the current
0.1 mg/kg limit.
Soybean
The 1979 Meeting estimated the current 0.05 mg/kg level for
methamidophos residues on soybeans to include residues resulting from
the use of acephate, for which residues were estimated at 0.5 mg/kg
with a 14 day pre-harvest interval.
Residue data reflecting experimental trials of a foliar spray 4
formulation were available to this Meeting from one country. As
residues in beans at 57 to 162 days after treatment were below the
current 0.05 mg/kg limit, there is no basis for revising the current
limit even if the uses were approved ones.
Tomato
Tomato is a commodity for which concern has been expressed at the
CCPR as having a limit higher than necessary. It is currently 2 mg/kg
as estimated by the 1976 Meeting, which apparently used a one-week
pre-harvest interval as a basis. One government has informed this
Meeting that their good agricultural practice requires a four-day pre-
harvest interval, presumably at application rates comparable to those
submitted to the 1976 Meeting.
Additional residue data were available to this Meeting resulting
from residue trials in two countries. It could not be determined
whether the trials represent nationally approved good agricultural
practices. However, all residues were <1.0 mg/kg, even after a four-
hour pre-harvest interval.
No additional data were provided to the Meeting for use in
estimating methamidophos residues in tomatoes resulting from the use
of acephate. However, based on data provided to the 1976 Meeting, the
current 2 mg/kg methamidophos limit should be more than adequate for
such use, if both acephate and methamidophos are not used on the same
crop.
On the basis of the new data, summary data in the 1976 Evaluation
(residues up to 1.8 mg/kg at one week), and a national good
agricultural practice allowing a four-day pre-harvest interval, a
lowering of the 2 mg/kg limit on tomatoes cannot be justified with
current uses.
FATE OF RESIDUES
In animals
Sixteen hens were given a single dose of methyl-carbon C-14
labelled methamidophos at 1 mg (14.15 µCi/mg) per kilogram body weight
and the tissues, eggs and faecal matter analysed at different
intervals up to 96 hours (Bayer 1975). Results for methanol
extractable and unextracted (bound) residues in individual tissues and
eggs are given in Table 2. It can be seen that more of the residue
becomes bound at the longer interval and that the binding at six hours
was more rapid in the enzymatically active liver and kidney than in
other tissues.
Faeces were analysed in a similar 3, 24 and 96 hours post-
treatment. Bound and methanol extractable methamidophos were as
follows:
Hours Extractable (%) Bound (%)
3 36.5 53
24 18.2 69
96 30.2 66
Investigations were made into the nature of the residues in the
liver and in the breast and thigh muscle, with only limited success.
The residues in all cases were found to be very polar and could not be
separated from impurities, although a number of purification and
separative techniques were used. In muscle tissue, approximately 80%
TABLE 2. Methanol extraction of Carbon-14 labelled residues of methamidophos from the organs
and tissues of hens sacrificed at 6 and 96 hours and eggs at 72 hours post-treatment.1
Extractable Bound Recovery from Extration
Sample Residue (TER) Residue (TBR) (sum TER and TBR)
6 h. 96 h 6 h 96 h 6 h 96 h
Liver 66.22 25.83 36.42 72.13 102.6 97.9
Kidney 60.6 46.4 31.0 50.1 91.6 96.5
Gizzard 84.2 66.4 17.7 27.2 101.5 93.6
Heart 78.7 48.1 21.7 40.4 100.4 88.5
Skin 85.2 23.7 16.3 57.8 101.5 81.5
Fat 81.2 11.7 16.8 7.0 98.0 18.74
Thigh 82.2 33.3 11.6 58.1 93.8 91.4
Breast 81.5 37.9 14.3 52.6 95.8 90.5
72 h 72 h 72 h
Eggs 50.45 44.35 94.7
1 All figures are percent of total residues;
2 Average of three samples;
3 Average of 4 samples;
4 Remainder of residue was in methanol insoluble liquid fat;
5 Average residue of eggs collected from two hens.
of the residue was found to be in the polar lipid fractions where
methamidophos, O, S-dimethyl-phosphorothioate and some methyl
dihydrogen phosphate would be found, if present. However, the residues
could not be identified because of impurities.
In a poultry feeding study, three groups of eight hens were fed
respectively, ad libitum, rations containing approximately 2, 6 and
20 mg/kg methamidophos for 28 consecutive days (Bayer 1975a). Eggs
were collected daily. After 28 days the animals were sacrificed and
samples of heart, gizzard (emptied and stripped of lining), liver,
kidneys, muscle, subcutaneous and visceral fat and skin were sampled
for analysis by a gas chromatographic procedure (Stanley 1971), which
was modified to use pentane extraction, a carbowax 20 M liquid phase
and a flame photometric detector. Other slight modifications were made
for eggs, and in both cases analytical standards were prepared in
extracts of control samples.
At the 20 mg/kg feeding level composites of like tissues
(including heart and gizzard) were analysed after 28 days. Four-egg
composites were analysed at 3, 7, 14 and 28 days at the 20 mg/kg
feeding level and at the 2 and 6 mg/kg level at 28 days. As tissue
residues were low at the 20 mg/kg feeding level, tissues were not
analysed at the lower feeding levels. Residues in tissues and eggs
corrected for average overall recoveries of 86% and 60% respectively
are summarized in Table 3, which also gives a relative comparison of
results from the feeding study with total residues from the metabolism
study.
It can be seen in Table 3 that residues in eggs had reached
equilibrium by the third day. Although not shown in Table 3, residues
in eggs at 28 days at the 2 and 6 mg/kg feeding levels were 0.008 and
0.032 mg/kg respectively (corrected for 64% recovery).
In the feeding study, liver and kidney contained the lowest
residues of methamidophos and muscle and eggs the highest. This
contrasts to local residues in the metabolism study, which indicates
the highest total radioactive tissue residues in kidney and liver.
This comparison suggests that residues are distributed to the
respective tissues before substantial metabolism occurs, resulting in
greater metabolism and bound residues in the enzymatically active
tissues and more unmetabolized residue in tissues of less enzymatic
activity.
TABLE 3. Residues in tissues and eggs of hens fed methamidophos
at 20 ppm in the diet for 28 days compared with total
carbon-14 methamidophos residues from the metabolism study.
Methamidophos (mg/kg) Total Carbon-14
Tissue from feed study residue(mg/kg)at 6 hours
corrected for recovery from metabolism study
Liver 0.003 1.070
Kidney 0.005 0.700
Skin 0.022 0.146
Fat 0.003 0.024
Heart and gizzard 0.026 0.2341
Muscle 0.033 0.1842
Eggs
28(day of collection) 0.198 -
14 0.178 -
7 0.142 -
3 0.181 0.3213
1 Average of values for breast and thigh muscles;
2 Average of values for heart and gizzard;
3 Average of four separate determinations.
In plants (rotational crops)
Wheat, soybeans, turnips and cauliflower were grown in plastic
containers containing 800 g of soil previously treated 11 times with
[S.methyl-14C] methamidophos at a rate equivalent to 227 g a.i./a
(McNamara 1976). The soil was previously used to grow cabbage plants
for three weeks. Mature soybeans, wheat, turnips and cauliflower were
harvested after 124, 124, 201 and 275 days respectively.
Except for 0.31 mg/kg methamidophos equivalent residues in
immature whole turnip plants, residues in turnips and all parts of
cauliflower were < 0.08 mg/kg and were not further characterized.
Residues in all immature and mature wheat and soybeans (whole or
parts) were > 0.1 mg/kg, with maximum methamidophos equivalents of
1.3 and 1.1 mg/kg in wheat stems and soybean leaves respectively.
Residues in wheat heads and soybean pods were 0.27 and 0.14 mg/kg
respectively. Further characterization of the radioactive residues in
parts of wheat and soybeans indicated that residues of intact
methamidophos was < 0.08 mg/kg.
Another rotational crop residue study was carried out by applying
methamidophos to soil plots in Kansas and Florida (US) at rates of
1.7, 3.4 (normal seasonal rate), 6.8 and 13.6 kg a.i./A and planting
sorghum, wheat, snapbeans, peas, carrots, radishes, maize black-eyed
peas and turnips at 30, 60, 90, 120 and 365 days post-treatment
(Murphy and Morris 1979).
In all mature crops (or parts), except maize green forage at 365
days post soil treatment, residues were < 0.03 mg/kg. At 365 days
at the 60-240 oz./A rates on green maize forage residues were
0.09-0.15 mg/kg. These values are inconsistent with the < 0.03 mg/kg
residue in an earlier post soil treatment.
Apparent residues in green maize forage controls were < 0.01 and
0.06 mg/kg. Therefore, there is reason to suspect that the high values
in green maize may be aberrant. Even at the 0.1 mg/kg level, residues
of methamidophos would not be expected in animal products as a result
of residues in rotational crops from normal usage.
In soils
Sandy loam soil (2.8% organic matter and pH 5.1) was fortified at
10 mg/kg with [S-methyl-14C] methamidophos, aged at room temperature
for 30 days, then packed and eluted from 4.8 cm i.d.x30 cm long
columns with oxygen-saturated water at a rate of 1.25 cm/day for 45
days (Obrist 1979). Approximately 80% of the radioactivity was lost
during the ageing process, presumably due to volatilization. Over 80%
of the aged residue was found in the upper 1.25 cm, approximately 5%
in the leachate and an additional 11% was lost during the leaching
period, presumably due to volatilization. None of the residue in the
leachate or organosoluble soil fractions was intact methamidophos.
Residues were unidentified.
Methamidophos adsorption experiments were carried out on three
soil types (Shaw 1979). One-gram soil samples were added to 10-ml
solutions of [S-methyl-14C] methamidophos at concentrations of 0.5
to 10 µg/ml and equilibrated for three hours at 15 and 30°C. The
highest adsorption was 5% on high organic silty clay loam at 15°C.
Freundlich adsorption constants were 1.28 (l/n) and 0.12 (ka).
Essentially no adsorption occurred on any soil at 30°C.
In storage and processing
An 11.34 kg samples of shelled peanuts was fortified with
345 mg/kg methamidophos by dipping (473 ml Monitor 4 in 38 litres of
water) then processed into meal, crude oil, refined oil, refined
deodorized oil and soapstock (Morris et al 1981). Concentration
factors were shelled peanuts (1.0), pressed and extracted peanut meal
(0.59), crude peanut oil (0.07 screw pressed; 0.2 solvent extract),
and < 0.01 in all other fractions. Controls were < 0.01 mg/kg except
for 0.03 mg/kg in the meal and recoveries in all fraction > 73% at
the 0.1 mg/kg fortification level.
Tomatoes and savoy cabbage, previously sprayed with a
600 g a.i./l formulation, were cooked in open and closed vessels with
an equal amount of water for 20 minutes (Möllhoff 1978). Residues in
uncooked cabbages were 0.77 and 0.57 mg/kg and in tomatoes 0.067 and
0.055 mg/kg. Recoveries of methamidophos were 84% and 86% in the
cabbage cooked in open and closed vessels respectively and 100 and 87%
in tomatoes cooked in open and closed vessels respectively.
NATIONAL MAXIMUM RESIDUE LIMITS REPORTED TO THE MEETING
MRL Pre-harvest interval
Country Crop (mg/kg) (days)
Australia tomato 2 4
USA1 broccoli, Brussels 1 (see use patterns)
sprouts, cabbage
cauliflower, cucumber,
eggplant, lettuce,
pepper and tomato
melon 0.5
cottonseed and potato 0.1
1 These tolerances replace those reported to the 1976 Meeting.
EVALUATION
APPRAISAL
The Meeting took note of the request of the Thirteenth Session of
the Codex Committee on Pesticide Residues (CCPR) to re-examine maximum
residue limits (MRLs) for methamidophos and acephate, taking into
account their relationship. The Committee requested governments to
provide good agricultural practice information to facilitate this
review.
The Meeting has not received sufficient information to address
fully the questions raised by the CCPR. It did receive a very limited
amount of good agricultural practice information and was informed that
at least two countries were planning to provide additional
information. The Meeting also received additional residue data on
several crops and information on the fate of methamidophos residues.
On the basis of these new data, the Meeting was able to confirm the
1 mg/kg limit for Brussels sprouts, cabbage and cauliflower; 0.5 mg/kg
for citrus; 0.1 mg/kg for potato; 0.05 mg/kg for soybean and 2 mg/kg
limit for tomato. New good agricultural practice information and
residue data for broccoli (head) and residue data for lettuce indicate
that the current 2 mg/kg limits could be lowered if longer pre-harvest
intervals were observed.
Although the Thirteenth Session of the CCPR also discussed limits
for eggplant and cucumber, no additional information was available for
these crops.
Metabolism and feeding studies in poultry supplement that
previously reviewed for rats and lactating goats. In the poultry
metabolism study, binding of radioactive residues increased with time
from dosing and was more predominant in enzymatically active tissues.
Analytical difficulties prevented identification of the metabolites,
although the majority of the radioactivity was found in polar lipid
fractions, as was the case for one rat study previously examined by
the Meeting.
Comparison of methamidophos residues from the poultry feeding
study with total active residues from the metabolism study suggests
that residues are rapidly distributed to the various tissues, where
they are metabolized. Metabolism is more rapid, with more rapid
conjugation in enzymatically active tissues and conversely, more
methamidophos is found in less enzymatically active tissues.
Radioactive rotational crop studies in containers indicate
considerable uptake of residues in a variety of crops. This was not
confirmed from field tests with unlabelled material applied at
exaggerated rates.
In leaching studies, most of the residue was found in the upper
1.3 cm of soil, although laboratory adsorption studies indicate very
low adsorption of methamidophos from aqueous solutions by soil.
Residues were found not to concentrate in processed fractions of
peanuts fortified with methamidophos. Residue losses of 0-16% were
observed when methamidophos fortified cabbage or tomatoes were cooked
in open or covered vessels.
RECOMMENDATIONS OF RESIDUE LIMITS
The Meeting examined residue data from supervised trials on a
number of crops. From these data, the Meeting was able to confirm or
estimate revised MRLs that are likely to occur when methamidophos (or
acephate) are used in practice and when the reported intervals are
observed. These levels refer to methamidophos alone and are intended
to cover residues of methamidophos resulting from the use of either
acephate or methamidophos on a crop (but not both), except where
indicated otherwise. The Meeting concluded that the revised maximum
residue levels given below are suitable for establishing MRLs.
Pre-harvest interval on
Previous residue Revised which the revised estimates
Crop estimate (mg/kg) estimate(mg/kg) are based (days)
Broccoli 2 1 21
Lettuce 2 1 21
REFERENCES
Bayer AG An investigation of the extractable residues of Carbon-14
1975 labeled Monitor in tissues, organs, eggs and faeces
following oral administration of the pesticide to laying
hens. Report No. 44069 and No. 3 of ADC Project No. 124.
2 April 1975. Submitted by Bayer. (Unpublished)
Bayer AG. Residues of Monitor in tissues and eggs and the effect upon
1975a serum acetylcholinesterase activity following oral
administration of the pesticide to poultry for twenty-eight
consecutive days. Bayer Report No. 43737 (Report No. 2 of
ADC Project No. 124), 11 February 1975. (Unpublished)
McNamara, F.T. Radioactive residues of [14C] - Monitor in rotational
1976 crops. Mobay Report No. 49656. 1 September 1976.
(Unpublished)
Morris, R.A., Delphia, L.M. and Murphy, J.J. The effect of processing
1981 on residues of Monitor in peanuts. Mobay Report No. 68649,
2 March 1981. (Unpublished)
Möllhof, Dr., Kochversuche mit Tameron-behandeten Wirsing and Tomaten;
1978 Leverkusen, Bayerwerk, Dr. Mö/Kuj., RA-857, Bayer Ag
Pflanzenschultz-Anwendungstechnik, Biologische Forschung,
Institut Für Ruckstandsanalytik, 12 December 1978.
(Unpublished)
Murphy, J.J. and Morris, R.A. Residues of Monitor in rotational crops.
1979 Mobay Report No. 68476, 3 August 1979. (Unpublished)
Obrist, J.J. Leaching characteristics of aged monitor soil residues.
1979 Mobay Report No. 68005, 5 July 1979. (Unpublished)
Shaw II, H.R. Adsorption of Monitor by soils. Mobay Report No. 6849,
1979 31 July 1981. (Unpublished)
Stanley, C.W. A gas chromatographic method for the determination of
1971 residues of Monitor in animal tissues and milk. Chemagro
Report No. 31093. (Unpublished)
See Also:
Toxicological Abbreviations
Methamidophos (HSG 79, 1993)
Methamidophos (ICSC)
Methamidophos (JMPR Evaluations 2002 Part II Toxicological)
Methamidophos (Pesticide residues in food: 1976 evaluations)
Methamidophos (Pesticide residues in food: 1979 evaluations)
Methamidophos (Pesticide residues in food: 1982 evaluations)
Methamidophos (Pesticide residues in food: 1984 evaluations)
Methamidophos (Pesticide residues in food: 1985 evaluations Part II Toxicology)
Methamidophos (Pesticide residues in food: 1990 evaluations Toxicology)