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 PARATHION Explanation The CCPR at its fourteenth Session asked the JMPR to reconsider the definition of the residue, currently "sum of parathion and its oxygen analogue". RESIDUES IN FOOD AND THEIR EVALUATION In most of the data supplied for evaluation, residue analysis was by a method which does not differentiate between parathion and its oxygen analogue, or the oxygen analogue was not determined. Separate determinations of the thion and oxon on lettuce, however, showed that the half-life of paraoxon was much shorter than parathion. Parathion residues decreased from 1.7 mg/kg on the day of treatment to 0.02 mg/kg 14 days later, whereas the oxon residue was 0.01 mg/kg, the limit of determination, on the day of treatment and was not detectable thereafter. In spinach the parathion residue on the day of treatment was 1.5 mg/kg while the oxon was 0.05 mg/kg. In supervised trials with cottonseed, residues of parathion and its oxon in cottonseed and cottonseed oil were mainly below the limit of determination (0.05 mg/kg). Measurable residues of parathion found in 14 samples of seed ranged from 0.05 to 0.66 mg/kg, while all the oxon residues were below the limit of determination. In cottonseed oil, measurable thion residues were 0.10-0.27 mg/kg (4 samples) and all oxon residues were below 0.05 mg/kg. Extensive monitoring data from several countries, based on analytical methods which would determine the thion and oxon separately, show that residues of parathion are occasionally found, but the oxon has never been reported. Gunther et al. (1977) reviewed studies of dislodgable residues on citrus foliage after treatment with parathion (to assess the hazards of the re-entry of workers to treated orchards) which showed that residues of paraoxon could sometimes exceed those of the parent compound and could persist for several weeks. This situation is however peculiar to desert conditions where the normally unstable oxon residues are protected from degradation by soil dust covering the leaf surfaces. Residues are largely adsorbed by the dust and are effectively removed from fruit by post-harvest washing in packing houses. The meeting concluded that these dislodgable residues were therefore not relevant in the context of residues in or on food commodities. RECOMMENDATION The oxygen analogue should be excluded from the definition without changing the numerical values of the MRLs. REFERENCES Gunther, F.A., Iwata, Y., Carman, G.E. & Smith, C.A. The Citrus 1977 re-entry problem: Research on its causes and effects, and approaches to its minimization. Res. Rev. 67: 1-132.
See Also: Toxicological Abbreviations Parathion (HSG 74, 1992) Parathion (ICSC) Parathion (FAO Meeting Report PL/1965/10/1) Parathion (FAO/PL:1967/M/11/1) Parathion (FAO/PL:1969/M/17/1) Parathion (AGP:1970/M/12/1) Parathion (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental) Parathion (IARC Summary & Evaluation, Volume 30, 1983)