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
See Also: Toxicological Abbreviations Phosmet (ICSC) Phosmet (JMPR Evaluations 2003 Part II Toxicological) Phosmet (Pesticide residues in food: 1976 evaluations) Phosmet (Pesticide residues in food: 1978 evaluations) Phosmet (Pesticide residues in food: 1979 evaluations) Phosmet (Pesticide residues in food: 1981 evaluations) Phosmet (Pesticide residues in food: 1994 evaluations Part II Toxicology)