Sponsored jointly by FAO and WHO


    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, 23 November - 2 December 1982

    Food and Agriculture Organization of the United Nations
    Rome 1983




         Cyhexatin was evaluated in 1970, 1973, 1974, 1978 and 1981
    (FAO/WHO 1971, 1974, 1975, 1979 and 1982)1/. A temporary ADI was
    recommended in 1978 and converted to an ADI in 1981. Azocyclotin was
    evaluated in 1979 and 1981 (FAO/WHO 1980, 1982). An ADI was
    recommended in 1981. The 1979 evaluation of azocyclotin resulted in
    some recommended temporary MRL's, which were at variance (lower) with
    those already proposed for cyhexatin for the same commodities. The
    1979 Meeting noted that residues from these two compounds cannot be
    distinguished shortly after application, and therefore required
    additional information on use patterns and residue data to resolve
    this problem and harmonize residue limits.

         Information was received on analytical methodology and on the
    results of a joint residue study by the manufacturers.



         Parallel trials were carried out by Dow in England (Dow 1982) and
    by Bayer in the Federal Republic of Germany (Bayer 1982) in which
    apples (James Grieve in England and Golden Delicious in FRG) were
    treated with Plictran 25W and Peropal WP, each at the rate of 375 g
    a.i./ha in a spray volume of 1 500 litres of water. Similar mist
    blower applications were used in both countries. Samples from each
    trial were collected at 0, 7, 14, 28 and 35 days after the last
    application and divided into two sets. One set was exchanged between
    labs in the respective countries. One set from each country was
    analysed for total organotin residues, using the colorimetric method
    by Dow in England, and the other two sets were analysed by Bayer,
    using their gas chromatographic method, which determines azocyclotin,
    cyhexatin and dicyclohexyl tin oxide.  The results of the Dow analyses
    are summarized in Table 1 and the results of the Bayer analyses are
    summarized in Table 2.


    1/  See Annex 2 for FAO and WHO documentation.

        Table 1.  Residues in Apples Determined by Colorimetric Analysis

                                         Residues (mg/kg) at interval post-treatment (days)1/
    Location                     0              7              14             28             35
    of           Product         mean           mean           me an          mean           mean
    treatment    used            (range)        (range)        (range)        (range)        (range)

    UK 1         Plictran 25W    0.46           0.90           0.31           0.12           0.08
                                 (0.33-0.63)    (0.71-1.03)    (0.21-0.44)    (0.11-0.13)    (0.05-0.12)

                 Peropal WP      0.49           0.73           0.28           0.11           0.04
                                 (0.42-0.58)    (0.54-1.10)    (0.19-0.37)    (0.09-0.16)    (0.02-0.05)

    UK 2         Plictran 25W    1.04           0.46           0.39           0.14           0.08
                                 (0.69-1.18)    (0.27-0.54)    (0.31-0.48)    (0.10-0.16)    (0.07-0.09)

                 Peropal WP      0.90           0.39           0-29           0.14           0.14
                                 (0.66-0.99)    (0.28-0.53)    (0.18-0.42)    (0.09-0.23)    (0.09-0.19)

    FRG 1        Plictran 25W    0.39           0.15           0.14           0.07           0.13
                                 (0.37-0.41)    (0.13-0.18)    (1.10-0.19)    (0.06-0.08)    (0.07-0.19)

                 Peropal WP      0.54           0.37           0.31           0.09           0.14
                                 (0.53-0.54)    (0.26-0.48)    (0.31-0.32)    (0.05-0.12)    (0.12-0.16)

    FRG 2        Plictran 25W    0.50           0.59           0.53           0.28           0.29
                                 (0.49-0.52)    (0.58-0.60)    (0.51-0.56)    (0.25-0.31)    (0.29-0.30)

                 Peropal WP      0.32           0.49           0.31           0.19           0.14
                                 (0.24-0.40)    (0.45-0.52)    (0.28-0.34)    (0.11-0.26)    (0.10-0.18)

    1/   Residues not corrected for recovery or control, but corrected for reagent blanks. Average
         recovery = 93.7%.
    Table 2.  Residues in Apples Determined by Gas Chromatographic

    Location                          Residues (mg/kg) at interval
    of            Product                 post-treatment (days)1/
    treatment     used             0      7      14      28     35

    UK 1          Plictran 25W     0.35   0.72   0.25    0.18   0.10
                  Peropal WP       0.44   0.54   0.31    0.16   0.06

    UK 2          Plictran 25W     1.20   0.51   0.51    0.21   0.21
                  Peropal WP       1.06   0.33   0.58    0.24   0.23

    FRG 1         Plictran 25W     0.97   1.06   0.68    0.37   0.40
                  Peropal WP       0.42   0.60   0.53    0.37   0.34

    FRG 2         Plictran         0.50   0.23   0.30    0.11   0.15
                  Peropal WP       0.50   0.25   0.23    0.13   0.14

    1/   Plictran values reported as the sum of cyhexatin and
         dicyclohexyltin oxide. Peropal values reported as the sum of
         azocyclotin + cyhexatin and dicyclohexyltin oxide.

         It is evident from a comparison of the values both within the
    tables and between the tables, that there is no significant difference
    in residues on apples from the use of either azocyclotin or cyhexatin.
    Therefore, the discrepancies noted by the 1979 Joint Meeting are
    mainly due to the use of different application methods and not to any
    differences in the analytical methods or in the degradation chemistry.


    Definition of residue

         In order to better conform to current analytical practice, the
    Meeting proposes that the definitions of the residues of azocyclotin
    and cyhexatin be changed to read as follows:

    azocyclotin -     sum of azocyclotin, cyhexatin and dicyclohexyltin
                        oxide, expressed as cyhexatin.

    cyhexatin   -     the sum of cyhexatin and dicyclohexyltin oxide,
                        expressed as cyhexatin.

         These redefinitions have no effect on recommended maximum residue
    limits for either product.


         The 1979 evaluation of azocyclotin resulted in a discrepancy in
    certain recommended maximum residue limits for commodities for which
    limits had already been recommended, based on data from the use of
    cyhexatin, which is also a degradation product of azocyclotin. In
    response to this problem, the manufacturers conducted a joint project
    on apples in England and the Federal Republic of Germany. The results
    of these tests clearly indicate that the discrepancy was due to
    different application technologies and that no significant differences
    in residues would result under identical treatment, climate and
    analytical conditions. Inasmuch as these new data support the existing
    recommendations for apples and pears associated with cyhexatin, no
    changes in any of the cyhexatin maximum residue levels are needed.

         Residues resulting from the use of either of these products
    cannot be distinguished analytically because they are principally
    surface residues and the degradation products are determined by
    environmental rather than metabolic processes. In addition, the
    analytical method converts both azocyclotin and cyhexatin to
    tricyclohexylmethyl tin. Therefore, it is necessary to revise the
    recommended limit for azocyclotin on apples, beans and strawberries to
    the same limits recommended for cyhexatin on those commodities. In the
    case of grapes and eggplant for which supervised trial data are
    available only for azocyclotin, the recommended limits for azocyclotin
    remain unchanged.

         New definitions of the residues are proposed for both products to
    conform more with current analytical practice.


    Cyhexatin:   Recommended maximum residue limits, all commodities -
                   no change. Residues to which the limits apply are the
                   sum of cyhexatin and dicyclohexyltin oxide expressed as

    Azocyclotin: The previously recommended maximum residue limits are
                   increased to the values listed below. The limits for
                   azocyclotin represent the sum of azocyclotin, cyhexatin
                   and dicyclohexyltin oxide, expressed as cyhexatin.

                  Commodity                Limit (mg/kg)
                  Apples                   2 (increased from 0.1)
                  Beans                    0.5 (increased from 0.2)
                  Strawberries             2 (increased from 0.1)


    Bayer AG Residue trials on apples with Peropal and Plictran.
    1982     RA-643181B (Plus covering letter). (Unpublished)

    Dow Ltd. Organotin residues in apples following treatments with
    1982     Plictran 25W and Peropal WP acaricides in England and the
             Federal Republic of Germany - 1981. (Plus covering letter)

    See Also:
       Toxicological Abbreviations