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

    CHINOMETHIONAT

    Explanation

         Chinomethionat was evaluated by the JMPR in 1968 (as
    oxythioquinox), 1974, 1977 and 1981 and a number of maximum residue
    limits were recommended (Temporary MRLs, as the AID is temporary).
    Information on use patterns on tomatoes and additional residue data
    derived from supervised trials were considered desirable by the 1981
    JMPR. At the 1983 JMPR limited new data together with those available
    to the 1981 meeting were reviewed but the meeting was again unable to
    estimate a maximum residue level for tomatoes owing to deficiencies in
    the data. The meeting reaffirmed that further data were desirable.

         The meeting was informed by the manufacturer that the use of
    chinomethionat on tomatoes has generally decreased, with the exception
    of two countries from which, however, practically no tomatoes are
    exported.

         New data on the penetration and metabolism of chinomethionat in
    cucumber seedlings, and on its biotransformation by a green alga were
    made available by the manufacturer.

    FATE OF RESIDUES

    In plants.

         The biodegradation of chinomethionat by cucumber seedlings
    confirms that the thiocarbonate linkage is disrupted during metabolism
    of the fungicide by plants (Metche and Piffaut 1982). The sulphur
    liberated is principally incorporated into sulphates and sulphur
    amino-acids, while the labelled (2,4-14C)-quinoxaline nucleus is
    catabolized to 14CO2. Comparison of the results obtained in
    sterilized and non-sterilized conditions suggests that micro-organisms
    play a large part in the biodegradation.

         The metabolites of chinomethionat such as 6-methyl-
    2,3-dimercapto-quinoxaline can penetrate more easily through the
    roots. This penetration causes the inhibition of some plant metabolic
    activities, while there is no inhibitory effect due to chinomethionat
    itself.

         The biotransformation of chinomethionat by a green alga
    (Ankistrodesmus falcatus) has been studied by Piffaut and Metche.
    One of the metabolic pathways leads to the transformation of
    chinomethionat into an aminochlorinated compound identified as
    6-methyl-2 amino-3-chloroquinoxaline. This compound is particularly
    phytotoxic to cucumber plants.

    APPRAISAL

         Chinomethionat was evaluated by the JMPR in 1968, 1974, 1977 and
    1981 and a number of temporary MRLs were recommended. Information on
    use patterns on tomatoes and additional residue data derived from
    supervised trials were considered desirable by the 1981 and 1983
    JMPRs.

         As a consequence of the withdrawal of the ADI, the existing
    temporary MRLs were replaced by guideline levels (GLs).

    REFERENCES

    Metche, M. and Piffaut, B. Study of the toxicity of chinomethionat.
    1983      I. Penetration and metabolism of chinomethionat in cucumber
              (Cocumis Sativus) Agric. Biol. Chem. 47, 1725-1732.

    Piffaut, B. and Metche, M. Study of the toxicity of chinomethionat.
    1983      II. Biotransformation of chinomethionat into toxic derivates
              by a green alga (Ankistrodesmus falcatus) Agric. Biol.
              Chem. 47, 1733-1740.

    See Also:
       Toxicological Abbreviations
       Chinomethionat (WHO Pesticide Residues Series 4)
       Chinomethionat (Pesticide residues in food: 1977 evaluations)
       Chinomethionat (Pesticide residues in food: 1981 evaluations)
       Chinomethionat (Pesticide residues in food: 1983 evaluations)
       Chinomethionat (Pesticide residues in food: 1987 evaluations Part II Toxicology)