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
PHOSMET
EXPLANATION
Phosmet was reviewed by the JMPR in 1976, 1978, 1979 and 1981.
1/ After reviewing current good agricultural practices the 1981 JMPR
recommended MRLs of 10 mg/kg for apples, pears and peaches based on
short (0-1 day) pre-harvest intervals. At the 15th Session of the CCPR
several countries questioned the need for such short intervals in good
agricultural practices. The present meeting re-examined the reported
GAP in the USA and Canada in relation to the residues data available
on a range of fruit and forage crops.
The CCPR at its 14th Session asked the JMPR to reconsider the
definition of the residue, currently "sum of phosmet and its oxygen
analogue", with a view to excluding the oxygen analogue. The Meeting
reviewed the definition in the light of the original data on which the
residue evaluations had been based.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
The current US labels include the following pre-harvest
intervals:
apples and pears 7 days
apricots and nectarines 14 days
grapes 7 days (Western USA)
14 days (Eastern USA)
peaches 14 days
alfalfa 7 or 14 days (depending on area)
The O-day interval reported in the 1981 evaluations for apples and
pears was an error.
In Canada the use pattern includes the following intervals:
apples, pears, ) 1 day
peaches, plums )
alfalfa, cherries, ) 7 days
grapes, potatoes )
carrots 40 days.
1/ See Annex 2 for FAO and WHO documentation
RESIDUES RESULTING FROM SUPERVISED TRIALS
The data reported in the 1976 evaluations supported the
estimation of 5 mg/kg as a maximum residue level on alfalfa following
rates up to 1.1 kg a.i./ha and allowing a 14-day interval between the
last application and harvesting or grazing. These data were reviewed
together with some new data and consideration of the current GAP in
Canada and the USA which is a maximum dose rate of 1 lb a.i./acre
(1.1 kg. a.i./ha) and a minimum pre-harvest interval of seven days (in
Canada and all states in the USA except Arizona, California and
Nevada).
The trials were carried out in California in 1980 on 2-year
alfalfa. Application was by helicopter at 0.825 kg a.i./ha in 5 and 10
gallons of water to all plots. There were eight treatments, some
including diazinon and mevinphos formulations in addition to the
standard phosmet treatment.
The fresh alfalfa was sampled at 0, 7, 11 and 14 days after
treatment. The residues of the parent compound, phosmet, are shown in
Table 1.
The maximum concentration of phosmet oxygen analogue of 0.5 mg/kg
was found at day 0. Subsequently residues were 0.05 mg/kg or less.
METHODS OF RESIDUES ANALYSIS
Phosmet and its oxygen analogue are extracted from the macerated
crop with benzene. Oils, when present, are separated from the
extracted residues by a hexane/acetonitrile partition. Further clean-
up may be by charcoal or silica column followed by GLC with an alkali
flame ionization detector (AFID).
DEFINITION OF THE RESIDUE
Most of the many residue analyses reported did not differentiate
between phosmet and its oxon or did not detect either compound above
its limit of determination. The contribution of the oxon to the total
residue could however be assessed in some cases.
Separate determinations of the thion and oxon in apples, Bermuda
grass, maize, potatoes and soybeans were reported in the 1976
evaluation. In most samples, the oxon was undetectable or represented
less than 5% of the total residue. Other data (Stauffer, 1968) showed
oxon levels below 6% of the total residue in apples, oranges, pears
and tomatoes. In alfalfa the oxon contributed 1-13%, with a mean of
5%.
In a total of 181 analyses of various fruits, vegetables and
cereals (Stauffer, 1969, 1974, 1978), when it was measurable, exceeded
10% of the total residue in only seven.
Table 1. Residues of phosmet in alfalfa
Residues of phosmet, mg/kg
0 days 7 days 11 days 14 days
fresh dry
22, 26, 62 8, 8, 10 3, 3, 4 2, 4, 3 3, 8,
6
28, 48, 41 11, 10, 16 6, 12, 7 4, 4, 5 8, 13,
14
37, 39, 28 19, 23, 13 4, 5, 7 3, 7, 7 6, 10,
9
Average 37 13 5.5 4.4 8.5
Maximum 62 23 12 7 14
Residues of phosmet in 34 samples of beef fat (Stauffer, 1970,
1973) ranged from 0.1 to 0.6 mg/kg, with oxon levels at or below the
limit of determination of 0.05 mg/kg, except in two samples containing
0.07 mg/kg. Residues in seven samples of cream showed a similar
picture. One sample contained 0.6 mg/kg of phosmet and 0.1 mg/kg of
the oxon.
Residues of phosmet in 34 samples of beef fat (Stauffer, 1970,
1973) ranged from 0.1 to 0.6 mg/kg, with oxon levels at or below the
limit of determination of 0.05 mg/kg, except in two samples containing
0.07 mg/kg. Residues in seven samples of cream showed a similar
picture. One sample contained 0.6 mg/kg of phosmet and 0.1 mg/kg of
the oxon.
The 1978 evaluation drew attention to the presence of high
proportion of the oxon in some citrus residues resulting from
supervised trials. The trials (Stauffer, 1974) yielded 61 samples of
oranges, lemons and grapefruit (whole fruit or peel) which contained
residues of phosmet between 0.1 and 6.4 mg/kg. In 16 of these the oxon
content was below 2% of the total residue or was below the limit of
determination, and in a further 27 it was less than 10% of the total.
Of the remaining 18 samples, four were lemons in which interference
had prevented reliable estimation of the oxon. Residues in the other
14 were all below one third of the MRL (5mg/kg). In eight samples the
oxon accounted for 10-20% of the total residue and in the other six it
was between 21 and 44%.
It is concluded that the oxon is unlikely to represent a high
proportion of the residue except when the total residue is low.
Nevertheless, since it has occasionally occurred as a substantial
proportion of the residue, the meeting did not feel justified in
excluding it.
APPRAISAL
The meeting reviewed the residues data on apples, pears, grapes,
peaches, apricots and nectarines considered by the 1981 meeting in the
light of the information on GAP in Canada and the USA and re-affirmed
its estimates of maximum residue levels of 10 mg/kg for apples,
grapes, peaches and pears, and 5 mg/kg for apricots and nectarines.
The meeting was informed that the use of phosmet on cranberries
is no longer GAP in the USA and, in the absence of GAP information
from other countries, agreed to withdraw its proposal for an MRL on
this commodity.
New residues data on treated alfalfa enabled the meeting to
estimate a maximum residue level of 20 mg/kg for alfalfa (7-day
interval) which the meeting recommended as suitable for establishing
an MRL. The earlier proposal of 5 mg/kg for forage crops, in the
opinion of the meeting, did not accommodate current GAP on alfalfa in
the USA and Canada. There were insufficient data to extrapolate the
new estimate to other forage crops.
Since "forage crops" is not a currently used Codex group
commodity description, the meeting recommended that the data on which
the original proposal was based should be re-examined.
The definition of the residue was reviewed as requested by the
CCPR. It appeared that the oxygen analogue was unlikely to constitute
a high proportion of the residue except when the total residue was
low. Since it occasionally occurred as a substantial proportion of the
residue however, the meeting concluded that its exclusion from the
residue definition was not justified.
RECOMMENDATIONS
The following maximum residue levels were recommended as suitable
for use as MRLs:
Commodity MRL, Pre-harvest interval on which
mg/kg recommendation is based
alfalfa 20) on a 7 days
forage crops ) dry weight
(except alfalfa) 5) basis
The MRL for phosmet on cranberries should be withdrawn. The
definition of the residue should not be changed.
REFERENCES
Stauffer. Unpublished data from Stauffer Chemical Co.
1968
Stauffer. Unpublished data from Stauffer Chemical Co.
1969
Stauffer. Unpublished data from Stauffer Chemical Co.
1970
Stauffer. Unpublished data from Stauffer Chemical Co.
1973
Stauffer. Unpublished data from Stauffer Chemical Co.
1974
Stauffer. Unpublished data from Stauffer Chemical Co.
1978