Sponsored jointly by FAO and WHO


    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Expert Group on Pesticide Residues
    Geneva, 3-12 December 1979



    Fenbutatin oxide was evaluated by the meeting in 1977 and an ADI was
    established.  MRLs on a range of fruits and vegetables were
    recommended and the fate when feeding food wastes to livestock was

    The 11th Session of the CCPR (ALINORM 79/24) considered these
    recommendations and requested that the Joint Meetings should:

    a)  review the MRL proposed for peaches (paragraph 154)
    b)  reduce the MRL for apples and pears (paragraph 155)
    c)  define the residue resulting from the use of fenbutatin oxide
        (paragraph 155)
    d)  propose an MRL for grapes (paragraph 165).


    The summary of residue data on peaches in the 1977 monographs reflects
    a cross section of data from supervised trials considered by the
    Meeting.  Whilst many of the data indicate that the residues on fruit
    harvested 14 days after the last application range from 0.5 to 3.5
    mg/kg, 60% of the residue levels are above 2 mg/kg and 22% are above 4
    mg/kg.  The meeting recognized that since the data from trials in
    three distinctly different regions, California, South Carolina, and
    South Africa, indicate residues ranging from 4 to 8 mg/kg it was not
    unlikely that good agricultural practice in many other regions would
    yield residues near to 7 mg/kg, the figure chosen for the MRL.

    The meeting notes that in several trials, heavy rain (up to 75 mm) had
    fallen only a few days before harvest, and this would have had a
    tendency to lower the residue level.  It also recognized that some
    national governments had established MRLs in the range of 1.5 to 3.0
    mg/kg.  This raised the question as to whether the same data had been
    available to all authorities.  On the strength of the data available,
    the meeting agreed that the MRL recommended in 1977 should not be

    So far as apples are concerned, the meeting confirmed the observations
    of the 1977 Meeting that "in most instances residues in whole fruit
    were below 3 mg/kg following a pre-harvest interval of 14 days.  In a
    few instances however, residues at harvest exceeded this figure, but
    were essentially below 5 mg/kg".  In fact, 33% of the residue trials
    yielded residue levels above 2.0 mg/kg at harvest, 14 days after the
    last application.  Of these, 15% were above 3 mg/kg.  There was little
    or no reduction whether the apples were treated 28 days or 14 before
    harvest.  In the data presented in the 1977 monographs, over 20% of
    the trials yielded residues above 2 mg/kg 28 days after application. 
    Residue levels 28 days after application ranged up to 5.7 mg/kg. 
    Recognizing the many varieties of apples, the widely differing
    cultural practices and the wide range of climatic conditions in

    apple-growing areas of the world, the meeting agreed that there was no
    justification for reducing the MRL below the 5 mg/kg recommended in

    In reviewing the data on pears, it was recognized that although the
    number of trial results indicating residues above 2 mg/kg was less
    than with apples, there were a number of cases recorded in the data
    from the U.S.A. Since a significant proportion of the results from
    trials harvested 28 days after application ranged well above 3 mg/kg
    the meeting recommended to retain the MRL of 5 mg/kg.

    As with other fruits, fenbutatin oxide residues on grapes decline only
    slowly.  A number of the trials considered in 1976 show residues at
    30-56 days not significantly lower than the residues found 3 and 7
    days after application.  The pre-harvest intervals approved in various
    countries range from 7 to 42 days.  On the strength of these data, the
    meeting recommended a MRL for grapes of 5 mg/kg.

    Definition of Residue

    The residue was defined in 1977 as fenbutatin oxide, excluding any
    metabolites.  This recommendation is supported by studies with
    radio-labelled compounds an well as regular chemical analysis.  It has
    been shown that less than 5% of the total radioactivity originates
    from the principal metabolites with less than 0.7% due to other
    organo-tin metabolites.  Inorganic tin represents approximately 10% of
    the total tin in the residue.  Studies on apples have shown that the
    metabolites are degraded more rapidly than the parent, and thus
    disappear from the residue.  With citrus, the metabolites represent
    approximately 3% of the residue, whereas on many different crops the
    residue of metabolites is generally below the limit of determination
    (0.04 mg/kg).

    All of the residue data considered in support of the recommendations
    made by the 1977 meeting were generated by sensitive analytical
    methods designed to measure the parent compound, fenbutatin oxide,

    The main additional relevant data relate to residue levels of the
    degradation products 1,1,3,3 tetrakis
    (,-dimethylphenethyl)-1,3-dihydroxydistannoxane (SD31723) and
    ,-dimethylphenethylstannoic acid polymer (SD 33608) in crops and
    their significance in relation to the incidental residues in products
    of animal origin.  As a result of studies carried out on methods for
    the analysis of these compounds, a method was developed by Shell (see
    later) using glc and having a normally-achievable limit of
    determination of 0.02 mg/kg for both degradation products. This method
    was used in most of the new studies reported here.

    Data obtained with this method and a few additional data obtained with
    the previous method are given below.  The crops include apples,
    peaches and grapes which were included in the original review and also
    a series of nuts which were not covered previously. These latter data

    are included here since it is considered that they assist the
    evaluation of the significance of degradation products in the total
    residue present in treated crops.  The data are summarised in Table 1.

    With fruit samples the overall picture is the same as suggested by
    data presented to the 1977 JMPR.  For apples, where the method of
    analysis employed was similar to that given in the 1977 submission, a
    positive residue, at the limit of determination of 0.1 mg/kg, was
    reported in only one of 21 treated samples examined.

    The more sensitive method used for the grape and peach samples showed
    the presence of small residues in several samples.  These amounted to
    a total of 0.11 mg/kg in a dried peach sample 15 days after the second
    of two treatments and 0.08 mg/kg in the corresponding fresh material. 
    Grape samples harvested 14 days after three applications at the
    recommended rate contained no measurable residues of either
    degradation product, but a sample treated at an excessive rate under
    similar conditions contained 0.21 mg/kg SD 31723 and 0.06 mg/kg SD
    33608 against a content of 5.5 mg/kg fenbutatin oxide itself.  In
    dried grape pomace prepared from the same samples, residues were
    correspondingly higher, but residue levels of the degradation products
    were in total below 5% of the fenbutatin oxide level.

    Data for nuts show that residues of parent acaricide in the non-edible
    parts of the nuts are in some instances considerably higher than have
    generally been reported in the edible parts of crops analysed.  In
    these nut samples easily measurable levels of SD 31723 and SD 33608
    were also found.  However, these did not exceed 5% of the level of
    fenbutatin oxide present.  Hence, the current residue situation for
    crops in respect of degradation products indicates that the levels of
    these products are small in relation to those of the parent product
    and unlikely to exceed 5% of the fenbutatin oxide level.  There is no
    evidence from these data that these degradation products may exceed
    the levels of parent acaricide.

        Table 1.  Residues of Fenbutatin Oxide breakdown products in Fruits and Nuts (Additional Data)

                                                 Interval between                                           Ref.
      Crop           Dose Rate       No. of       last treatment    Fenbutatin    SD 31723     SD 33608    (Shell)
    (Location)                     treatments      and harvest        Oxide

    Apples           0.025%            3              0 days           1.8           0.1          -         (A)
    (Germany)                                         7 days           1.3          <0.1          -
                                                     14 days           1.8          <0.1          -
                                                     21 days           1.2          <0.1          -
                                                     28 days           1.0          <0.1          -

                     0.025%            3              0 days           1.7          <0.1          -         (B)
                                                      7 days           1.2          <0.1          -
                                                     14 days           1.1          <0.1          -
                                                     21 days           0.95         <0.1          -

                     0.025%            3              0 days           2.6          <0.1          -
                     (SC formn.)                      7 days           1.5          <0.1          -
                                                     14 days           0.65         <0.1          -
                                                     21 days           0.5          <0.1          -

                     0.025%            3              0 days           1.3          <0.1          -
                                                      7 days           1.1          <0.1          -
                                                     14 days           1.0          <0.1          -
                                                     21 days           0.5          <0.1          -

                     0.025%            3              0 days           2.3          <0.1          -
                     (SC form.)                       7 days           1.5          <0.1          -
                                                     14 days           1.3          <0.1          -
                                                     21 days           1.0          <0.1          -

    Peaches          0.0625%           2             15 days           1.1 (fresh)  0.08          <0.02     (D)
    (California)                                                       8.2 (dried)  0.08           0.03

    Grapes           0.0625%           3             14 days           0.7          <0.02         <0.02     (E)
    (California)     0:125%                                            5.5           0.2           0.06

    Table 1.  Continued...

                                                 Interval between                                           Ref.
      Crop           Dose Rate       No. of       last treatment    Fenbutatin    SD 31723     SD 33608    (Shell)
    (Location)                     treatments      and harvest        Oxide

    Dried grape      0.0625%           3             14 days            5.3         0.1          0.05
    pomace           0.125%                                             3.9         1.4          0.40

    Walnut Hulls     0.03%             2             14 days            5.8         0.16         0.09        (F)
    (California)     0.06%             2             14 days            6.0         0.12         0.05

                     0.03%             2             14 days           12.0         0.32         0.13        (G)
                     0.06%             2             14 days            5.1         0.15         0.07

    Walnut Shells    0.03%             2             14 days            1.5         0.06         <0.02       (F)
    (California)     0.06%             2             14 days            0.9         0.03         <0.02

                     0.03%             2             14 days            1.0          0.05        <0.02       (G)
                     0.06%             2             14 days            0.05        <0.02        <0.02

    Walnut Meats     0.03%             2             14 days            0.05        <0.02        <0.02       (F)
    (California)     0.06%             2             14 days            0.05        <0.02        <0.02

                     0.03%             2             14 days            0.04        <0.02        <0.02       (G)
                     0.06%             2             14 days           <0.02        <0.02        <0.02

    Almond Hulls     0.03%             2             14 days            24          1.1          0.34        (H)
    (California)     0.06%             2             14 days            39          1.7          0.58

                     0.03              2             14 days            56          2.7          0.78        (I)
                     0.06              2             14 days           170          7.1          1.3

                     0.06%             2             14 days            29          1.5          0.25        (C)
                     0.125%            2             14 days            36          1.7          0.26

    Almond Shells    0.03%             2             14 days            8.3         0.31         0.15        (H)
    (California)     0.06%             2             14 days            3.5         0.10         0.07

    Table 1.  Continued...

                                                 Interval between                                           Ref.
      Crop           Dose Rate       No. of       last treatment    Fenbutatin    SD 31723     SD 33608    (Shell)
    (Location)                     treatments      and harvest        Oxide

    Almond Shells    0.03%             2             14 days            13          0.3          0.12       (I)
    (cont'd)         0.06%             2             14 days            36          1.3          0.30

                     0.06%             2             14 days            40          1.9          0.27       (C)
                     0.125%            2             14 days            45          2.2          0.35

    Almond Meats     0.03%             2             14 days           0.16         <0.02        <0.02      (H)
    (California)     0.06%             2             14 days           0.12         <0.02        <0.02

                     0.03%             2             14 days           0.13         <0.02        <0.02      (I)
                     0.06%             2             14 days           0.58         <0.02        <0.02

                     0.06%             2             14 days           0.16         <0.02        <0.02      (C)
                     0.125%            2             14 days           0.23         <0.02        <0.02

    Pecan Shells     1.4 kg/ha         1             14 days           1.6          0.03         <0.02      (J)
    (S.Carolina)     2.8 kg/ha         1             14 days           1.4          0.03         <0.02

    Pecan Nut Meat   1.4 kg/ha         1             14 days           0.03         <0.02        <0.02
                     2.8 kg/ha         1             14 days           0.03         <0.02        <0.02

    Residues in Products of Animal Origin

    Additional experiments have been carried out in which cattle and hens
    were fed high levels of fenbutatin oxide in their diet in order to
    obtain further information on the residue consequences of using
    treated crops as feed.  For these experiments radio-labelled material
    was not used and fenbutatin oxide and its degradation products were
    determined using a sensitive recently developed glc procedure.

    Cattle (ref. M)

    In this experiment fenbutatin oxide was added to dairy concentrate at
    two levels; 85.7 mg/kg and 857.5 mg/kg.  This concentrate was then fed
    daily to two batches of lactating Guernsey cows so that they either
    received a total feed containing 11 mg/kg or 96 mg/kg. The experiment
    was carried out over a period of three weeks during which levels of
    fenbutatin oxide, SD 31723 and SD 33608 in the milk were monitored. 
    No residues of any of the three compounds were found in samples of
    cream or skim milk of cows fed at 11 mg/kg or in skim milk from
    animals receiving 96 mg/kg in their diet.  Cream from the latter group
    of cows was, however, reported to contain residues up to a maximum of
    0.11 mg/kg fenbutatin oxide, but no SD 31723 or SD 33608 were found. 
    The limit of determination in this study was 0.02 mg/kg for each
    compound (See Table 2).

    At the end of the three-week experimental feeding period, the animals
    were slaughtered and tissue samples (liver, kidney, muscle, fat, bone
    and brain) taken for analysis.  No residues of SD 33608 were found in
    any sample.  Similarly no SD 31723 was found in any tissue from cattle
    given feed treated at the 11 mg/kg rate, nor in muscle, fat, bone or
    brain at the 96 mg/kg intake level.  Again the limits of determination
    were 0.02 mg/kg.  Only in liver and kidney from animals at the higher
    feeding level were small residues of SD 31723 reported - up to a
    maxima of 0.12 and 0.04 mg/kg respectively.

    Fenbutatin oxide itself was found in kidney (0.08 mg/kg max.), liver
    (0.07 mg/kg max.) and fat (0.06 mg/kg max.) at the higher level of
    feeding, but was absent from samples from the lower rate animals (see
    Table 2).

    Grape pomace is not fed to cattle, but nut hulls are occasionally fed
    at levels up to 15-20% in the diet.  Hence, on the basis that cattle
    will be given feed with hulls containing the highest residue so far
    observed following recommended treatments, residue levels on feed are
    unlikely to exceed 11 mg/kg on a whole feed basis.  Thus, it is
    unlikely that measurable levels of fenbutatin oxide or its two
    degradation products would occur in milk, milk products or in meat.

        Table 2.  Maximum residue levels of fenbutatin oxide, SD31723 and SD33608 in milk and tissues of cattle
    receiving fenbutatin oxide in the daily ration (values in mg/kg)

    Sample                Cream          Skim milk          Liver            Kidney            Fat
    Feeding Level       11     96       11       96       11      96       11      96       11      96

    Fenbutatin oxide  <0.02    0.11    <0.02   <0.02    <0.02    0.07     <0.02   0.18    <0.02    0.06
    SD 31723          <0.02   <0.02    <0.02   <0.02    <0.02    0.12    <0.02    0.04    <0.02   <0.02
    SD 33608          <0.02   <0.02    <0.02   <0.02    <0.02   <0.02    <0.02   <0.02    <0.02   <0.02

    The results on bone, brain and muscle samples were all <0.02

    Poultry (Ref. L)

    White Leghorn laying hens were given fenbutatin oxide at 5 or 25 mg/kg
    in their daily ration for up to 28 days.  At the end of this period
    some of the birds were given untreated feed for a short period. 
    Throughout the experiment, samples of eggs were taken. Birds were also
    sacrificed at intervals and tissue samples taken for analysis.

    None of the samples of light or dark meat, or fat were found to
    contain fenbutatin oxide, SD 31723 or SD 33608 at a limit of
    determination of 0.02 mg/kg.  In the remaining tissue samples and in
    eggs, maximum levels were found as shown in Table 3.

    Hence, following use of grape pomace in poultry feed, residues of SD
    31723 and SD 33608, but not fenbutatin oxide, may occur at measurable
    levels in liver and kidney, but are unlikely to be present in other
    tissues.  Eggs may conversely contain small levels of fenbutatin
    oxide, but not its degradation products.  Nut hulls are not fed to

    Table 3.  Residues in poultry tissues and eggs

    Sample                  Eggs              Liver           Kidney
    Feeding level        5       25         5       25       2       25

    Fenbutatin oxide    0.02+   0.12++    <0.02    0.04    <0.02    0.03
    SD 31723           <0.02   <0.02       0.03    0.12    <0.02   
    SD 33608           <0.02   <0.02      <0.02    0.04    <0.02  

    Levels in meat and fat all <0.02.
    + 0.17 in yolk; ++ 0.25 in yolk.


    The new evidence presented confirms earlier data showing that residues
    of the two degradation products of fenbutatin oxide, SD 31723 and SD
    33608, are unlikely to exceed 10% of the residue of fenbutatin oxide
    in crops.  When treated crops are fed to cattle residue levels of the
    degradation products are unlikely to rise above the limit of
    determination of the analytical method in milk or tissues.  However,
    in experiments where residues have been found in milk, they have
    occurred entirely as fenbutatin oxide.  In animal tissues, residues
    have also been found following feeding at an excessive rate.  These
    residues have been shown to consist of fenbutatin oxide and SD 31723. 
    SD 33608 has not been found.

    With poultry, the experiments have shown that small residues may occur
    in eggs and that these will consist entirely of fenbutatin oxide. 
    Poultry meat, apart from liver and kidney, are unlikely to contain
    measurable levels.  In the two tissues mentioned, however, small
    residues consisting of fenbutatin oxide and SD 31723 may occur.

    It is thus only in some animal tissues that appreciable amounts of
    degradation products of fenbutatin oxide may be found.  Apart from
    liver and kidney, these are unlikely to be at measurable levels and
    where they do occur they are likely to consist of SD 31723 with
    fenbutatin oxide at roughly the same order of magnitude.


    The method previously used to obtain data on SD 31723 submitted to the
    1977 JMPR, was based on thin-layer chromatography and was capable of
    achieving a limit of detection between 0.1 and 0.4 mg/kg, depending on
    the nature of the sample.

    Recently, a technique for determining residues of SD 31723 and SD
    33608 together with fenbutatin oxide, by gas-liquid chromatography
    using a tin sensitive flame photometric detector, has been developed
    (Ref. K).  The samples are extracted with chloroform and HCl, and the
    chloroform extract evaporated to dryness.  The residue is dissolved in
    hexane and partitioned repeatedly into acetonitrile and finally into
    ether.  The ether solution is then methylated with methyl lithium. 
    Excess of the latter is destroyed with isopropanol and water and the
    aqueous phase is extracted with hexane.  Clean-up is effected by
    chromatography on Florisil and the appropriate fractions of eluate
    analysed by glc.  A limit of determination of 0.02 mg/kg for each
    product is normally achievable with this method.


    The following limits, additional to those recorded in 1977, were
    reported to the meeting:

    Canada           mg/kg

    Apples, pears      3
    Citrus fruit       3

    New Zealand      mg/kg

    Pome fruit         1
    Stone fruit        1


    Fenbutatin oxide has been reviewed at the request of the 11th Session
    of the CCPR.  The meeting examined new residue data together with that
    considered previously and confirmed the maximum residue limit for
    peaches, apples and pears.

    It was noted that metabolites of fenbutatin oxide disappeared from
    treated fruit and vegetables at a more rapid rate than the parent
    compound and were generally present only in insignificant
    concentrations.  Though these metabolites could be found in liver and
    kidney of experimental animals fed excessive concentrations of the
    pesticide, they did not occur after feeding levels likely to be
    encountered in practice.  The determination of metabolites requires
    separate analytical procedures and the meeting confirmed that the
    definition of the residue included only the parent fenbutatin oxide.

    On the strength of the residue data published in the 1977 monograph,
    the meeting recommended a MRL for fenbutatin oxide on grapes.  Because
    the residue level is not significantly influenced by the interval
    between application and harvest, the meeting recommended that the MRL
    for grapes not be linked with a preharvest interval.


    The following additional maximum residue limit for fenbutatin oxide is
    recommended.  It refers to fenbutatin oxide, excluding any

    Commodity    Limit, mg/kg

    Grapes         5



    The further information listed in 1977.


    The references in the Tables are to a series of unpublished Reports
    received from the Shell International Chemical Co. and indexed from A
    to M.

    See Also:
       Toxicological Abbreviations
       Fenbutatin oxide (Pesticide residues in food: 1977 evaluations)
       Fenbutatin oxide (Pesticide residues in food: 1992 evaluations Part II Toxicology)