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

    ISOFENPHOS

    Explanation

         The CCPR, at its sixteenth Session, asked the JMPR to consider
    whether the residue definition, currently "sum of isofenphos and its
    oxygen analogue" should be extended to include the metabolites
    des-N-isopropyl-isofenphos (DNI) and its oxygen analogue (DNIOA).
    It was pointed out that crop rotation metabolism studies had suggested
    that residues of DNIOA sometimes exceeded those of isofenphos and its
    oxygen analogue in some crops.

    RESIDUES IN FOOD AND THEIR EVALUATION

         Many of the data supporting the 1981 and 1982 evaluations were
    based on analyses for isofenphos and its oxon only. When DNI and DNIOA
    were also determined, the levels of all four compounds were often
    below the limit of determination. Data from supervised trials in which
    at least one of them was at a measurable level were available for
    maize and sweet corn grain, husks, cobs and forage, wheat, sorghum,
    soybeans and onions. Of a total of 93 samples, only one (onion)
    contained a measurable level of DNI: it was at the limit of
    determination (0.01 mg/kg) and represented about 1 percent of the
    residue. DNIOA was measured in 24 samples of corn forage, husks and
    kernels at levels ranging from 0.01 to 0.1 mg/kg. It represented 10
    percent of the residue or less in 4 samples, and 10-25 percent in 14
    samples of forage with total residues of 0.06-0.4 mg/kg. It was found
    in forage at 0.02 and 0.08 mg/kg in total residues of 0.07 and
    0.17 mg/kg, and was the only residue measured in the remaining
    four samples (maize husk, kernels and forage), at levels of
    0.01-0.03 mg/kg.

         In metabolism studies on sweet corn, onions and cabbage, DNIOA
    was a minor metabolite reaching a maximum of 10 percent of the sum of
    isofenphos, its oxon and DNIOA in sweet corn, 4 percent in onions and
    5 percent in cabbage. DNI was not detected. In feeding studies with
    hens and a pig, the main intact ester residue was isofenphos. DNI
    accounted for a maximum of about 5 percent of the total
    organophosphorus residue in tissues and eggs. DNIOA was not found. In
    a cow feeding study, the only identified organophosphorus residue was
    isofenphos oxon in liver and kidney.

         In metabolism studies with beans, sugar beet and wheat as
    rotational crops, isofenphos, its oxon, DNI and DNIOA were determined
    by GLC. Isofenphos oxon was the main component of the residue in most
    samples. DNIOA accounted for 11 percent, 18 percent and 17 percent of
    the total residue in wheat heads, stems and leaves respectively, and
    for 75 percent of a total residue of 0.08 mg/kg in sugar beet tops. It
    was below the limit of determination in sugar beet roots and bean
    forage. DNI was below the limit of determination in all samples.

         It is clear that inclusion of DNI in the residue definition is
    unnecessary. DNIOA occasionally forms a substantial proportion of the
    residue, but only apparently when the total residue is low. It occurs
    mainly in forage, for which the JMPR has not proposed an MRL. (There
    is a proposed TMRL of 0.5 mg/kg for maize fodder and sweet corn
    fodder.)

    RECOMMENDATION

         The definition of the residue should not be changed.

    See Also:
       Toxicological Abbreviations
       Isofenphos (Pesticide residues in food: 1981 evaluations)
       Isofenphos (Pesticide residues in food: 1982 evaluations)
       Isofenphos (Pesticide residues in food: 1986 evaluations Part II Toxicology)