Sponsored jointly by FAO and WHO


    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



         The CCPR at its fourteenth Session asked the JMPR to reconsider
    the definition of the residue, currently "sum of parathion and its
    oxygen analogue".


         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


         The oxygen analogue should be excluded from the definition
    without changing the numerical values of the MRLs.


    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)