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    DIOXATHION                       JMPR 1972

    Explanation

    Dioxathion was evaluated at the Joint Meeting in 1968 and further
    information was required by 30 June 1972 (FAO/WHO, 1969b). Since the
    previous evaluation, some new experimental work on residues in food
    has been reported and the information filed with FAO in 1968 was
    reviewed.

    IDENTITY

    Other information on identity and properties

    Technical dioxathion contains a minimum of 68% of the cis and
    trans isomers of 2,3-p-dioxanedithiol-S, S-bis (O,O-diethyl
    phosphorodithioate). The remainder consists of related compounds
    described by Arthur and Casida (1959) as:

         1.   10% ethyl phosphorothioates and ethyl phosphorodithioates.

         2.   1% bis (diethoxyphosphinothioyl) disulfide.

         3.   5% 2-p-dioxenethiol-S-(O,O-diethylphosphorodithioate).

         4.   Diethylphosphorothioic acid, diethylphosphorodithioic acid
              and their salts and oxygen analogues of the cis and
              trans isomers of the principal component and of (3) above.

    O,O,O-triethyl phosphorothioate and O,O,S-triethyl
    phosphorodithioate have been identified as the specific compounds
    occurring in (1) above (Hercules Inc., 1968).

    An effort has been made to synthesize, isolate and identify the oxygen
    analogues of dioxathion and of the dioxene component (3 above).
    Initial attempts to isolate these compounds in pure form using various
    chromatographic techniques were not successful because of their
    relative instability. Recently, a new approach employing column
    chromatography on silica gel packing has been successfully used to
    isolate the four possible oxygen analogues of dioxathion and the
    oxygen analogue of 2-p-dioxenethiol S-(O,O-diethyl
    phosphorodithioate). These are shown in Figure 1.

    The identities of these products have been confirmed by phosphorus NMR
    and by infrared and mass spectroscopy. Each of the four isolated
    oxygen analogues of dioxathion yield glyoxal osazone in the
    cleavage-hydrolysis step of the dioxathion residual method, and hence
    would be measured by that procedure provided they were not removed or
    destroyed by the clean-up technique. It has been shown that the
    isolated oxygen analogues of dioxathion do not pass through the
    alumina column used for clean-up in the current residue method.

    FIGURE 1


    Because of their instability, it is probable that the oxygen analogues
    occur in technical dioxathion in very small amounts, if at all. NMR
    measurements have demonstrated that the oxygen analogue content of
    technical dioxathion is less than 1-2%, which is the limit of
    detection. A more precise measurement is planned using more sensitive
    pulsed Fourier transform NMR techniques. Additional work is also
    underway to determine whether amounts of oxygen analogues are present
    in dioxathion residues on plants.

    RESIDUES IN FOOD AND THEIR EVALUATION

    USE PATTERNS

    Dioxathion is registered and used in many countries principally for
    treating livestock, citrus fruit, pome fruit, grapes and stone fruit.
    Dioxathion products are used on livestock principally cattle in the
    U.S.A., Australia, East and South Africa, South and Central America,
    France and Italy. Countries using these products on citrus fruit
    include the U.S.A., Africa, Japan, Turkey and Italy. There is
    significant use on pome fruit in the U.S.A., France, United Kingdom,
    South America and Italy. Use on grapes extends to the U.S.A., Germany,
    France and Italy.

    In some countries use on cattle precludes application to dairy cattle.
    However, in countries where ticks are a serious problem and frequent
    dipping is needed, dairy cows must be treated as well as beef cattle.

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    In animals

    Hurwood (1966) as part of a study of the excretion of pesticides in
    milk following dermal application of several organophosphorus
    acaricides to dairy cattle studied the uptake and excretion of
    dioxathion. When cows were sprayed with the officially recommended
    concentration (0.075%) of dioxathion emulsion, the maximum level of
    residues in milk were found at the third milking (29 hours) after
    spraying. The level of residue in milk fell rapidly and was not
    detectable (>0.005 ppm) 70 hours after spraying.

    Three dairy cows were sprayed with commercial dioxathion cattle spray,
    9 litres of spray (0.075%) being applied to each. Samples of milk were
    taken before treatment and twice daily for 5 days thereafter.
    Dioxathion was determined by the method of Dunn (1958). The results
    are given in Table 1.

    Studies reported by Watts (1968) showed that cows sprayed with 0.075%
    dioxathion emulsion gave milk containing a maximum (mean of six cows)
    of 2.25 ppm in fat of milk three hours after treatment. The range of
    residue levels reported was 1.13 to 3.33 ppm. The level of dioxathion
    residues in the milk of three treated animals did not decline very
    rapidly. At 45 hours post treatment (the fourth milking) the mean
    residue level was 1.27 ppm (with a range of 0.92 to 1.53 ppm) in the
    fat of milk.


    
    TABLE 1  Residues of dioxathion in butterfat and milk following spray
             treatment of daily cattle with 0.075% dioxathion

                                                                                                                                 

    Time after                Dioxathion in butterfat and total excretion at each milking
    treatment               COW 7                       COW 8                       COW 9                       MEAN
    (h)               In fat     Excretion        In fat     Excretion        In fat     Excretion        In fat      Excretion
                      (ppm)      per              (ppm)      per              (ppm)       per             (ppm)       per
                                 milking                     milking                     milking                      milking
                                 (mg)                        (mg)                        (mg)                         (mg)
                                                                                                                                 

    Pre               -1         -                -          -                -          -                -           -

    5                 3.33       534              2.30       204              1.13       261              2.25        358

    21                1.00       669              1.21       363              1.61       599              1.24        544

    29                1.29       797              2.22       612              3.18       982              2.23        797

    45                0.92       508              1.37       472              1.53       805              1.27        600

    53                0.08       33               -          -                -          -                -           -

    69                -          -                -          -                -          -                -           -

    77                -          -                -          -                -          -                -           -
                                                                                                                                 

    1  Represents a value less than the minimum detectable residue.
        In plants

    For a number of years dioxathion has been used as a dormant spray on
    apricots, cherries, peaches, plums and prunes when the material is
    applied at the rate of 4 kg/ha. It has been shown that these uses do
    not give rise to detectable residues of dioxathion in the fruit at
    harvest, when using analytical procedures specific to dioxathion and
    its metabolites, which are capable of determining levels of less than
    0.1 ppm (Hercules Inc., 1970).

    FATE OF RESIDUES

    General comments

    Dioxathion residues are confined to peel of citrus fruit, the skin of
    apples and the fat of meat. It is believed that the residue on grapes
    is also confined to the skin. The cis and trans isomers of
    dioxathion, the most biologically active major components, are also
    the most stable components of residues. Only drastic conditions will
    significantly alter the nature or quantity of the residues originally
    present. Therefore, under storage conditions normal for fresh fruit
    and meat, residues will remain relatively constant in amount and
    composition. Removal of the peel of citrus fruit and the skin of
    apples in commercial processing or for culinary purposes in the home
    will remove all of the dioxathion residue present on the whole fruit.
    No significant amount passes into citrus fruit juice. There is
    evidence that when grapes are pressed only trace amounts will occur in
    the juice. Similarly, the removal of fat from meat cuts by trimming
    prior to sale and the loss of fat during cooking will materially
    reduce dioxathion residues in the meat. The amount consumed will be
    low in comparison with the amount in raw products.

    Distribution of dioxathion residues

    Apples

    Dioxathion residues are confined to the skin of apples. The pulp
    contained 0.3 ppm dioxathion with a residue concentration in the peel
    of 36.8 and 77.2 ppm dioxathion (Hercules Inc., 1961).

    Citrus fruit

    Dioxathion residues are confined to the peel of the fruit; no more
    than an apparent 0.03 ppm was found in the edible portion. No
    significant cholinesterase inhibiting materials can be extracted from
    the pulp with hexane or chloroform (Hercules Inc., 1958; Gunther
    et al., 1958).

    Any conversion of dioxathion, by oxidation or other means, to a
    metabolite not responding to the specific analytical method must occur
    rather slowly, since dioxathion disappears from the peel at a slow
    rate. Testing of the pulp from lemons sampled 71 days after the
    application of the highest approved dosage (1.5 lb/100 gal) showed a
    barely detectable inhibition of cholinesterase by a test which would
    have detected less than 0.01 ppm dioxathion-oxon.

    Grape

    Because of solubility characteristics, it is believed that the residue
    on grapes is also confined to the skin (Hercules Inc., 1960). Trials
    in California demonstrated the persistence of dioxathion residues on
    grapes and the relationship between rate of application, stage of
    growth and residue level. Residues declined slowly after the first
    week, and were only about half the original level after 8 weeks.
    Allowance for dilution by growth indicated a very slow loss.

    Meat

    Dioxathion residues are confined to the fat of meat of animals sprayed
    or dipped in dioxathion (Hercules Inc., 1960). Cattle, sheep, pigs and
    goats all showed the same distribution pattern. Studies using
    dioxathion labelled with 32P showed that cattle treated with
    dioxathion eliminate considerable quantities in faeces and in urine.
    Much of the applied dose is, however, first transferred to fatty
    tissues. These studies showed that the material concentrated in fat is
    only dioxathion (Chamberlain et al., 1960). In another study in
    which 32P-labelled dioxathion was applied to the skin of a steer it
    was shown that fatty tissues accumulated small amounts of the
    insecticide. No detectable residues were found in meat samples (Plapp
    et al., 1960).

    Claborn et al., (1960) showed that when dioxathion was applied to
    cattle, sheep, goats and pigs the residue is found only in fatty
    tissue. No residues were found in any muscular tissue.

    Nature and stability of dioxathion residues

    Studies of dioxathion residues on fruit show a slow rate of decline
    under natural conditions. The average half-life of dioxathion residues
    on citrus fruit from three different tests was 84 days, for California
    grapes 45 days and for apples 56 days (Gunther et al., 1958;
    Hercules Inc., 1961). Casida and Ahmed (1959) established that the
    cis and trans isomers are the most persistent components of
    dioxathion residues on plant surfaces. Loss by volatilization was
    least for the cis and trans isomers with half-lives of 19-27 days.
    Hydrolysis does not occur readily on plant surfaces and is primarily
    confined to absorbed materials. The cis and trans isomers
    hydrolyse more slowly than other components both on plant surfaces and
    when subjected to strong alkali in vitro. Low volatility and
    resistance to hydrolysis appear to account for their long residual
    persistence.

    The work of Casida and Ahmed (1959) also shows that, after application
    to the surface of cotton leaves, the dioxene fraction and the cis
    and trans isomer fractions of dioxathion form more polar and more
    potent anticholinesterase agents; those formed from the dioxene
    fraction are very rapidly dissipated (0.2 day); those from the cis
    and trans isomers are somewhat more stable but decline to 10-20% of
    initial activity within 3 days. In other work, using radioactive
    dioxathion, it was established that the amount of unhydrolysed, but
    more polar materials, in aged plant residues, was a small fraction
    (10% on cabbage; 1% on beans) of the unchanged cis and trans
    isomers. This work indicates that only relatively small amounts of
    more polar metalbolites are formed and that they are subject to rapid
    hydrolysis once formed.

    Casida and Ahmed (1959) also established that the ratio of cis and
    trans isomers to each other is unchanged after application to
    plants. Therefore, no conversion of one isomer to the other occurs.

    Information on the effect of processing on dioxathion residues was
    obtained in connection with the production of dried citrus pulp and
    apple pomace. In the manufacture of dried citrus pulp for cattle feed
    from the peel, rag and seed remaining after the extraction of juice
    from citrus fruit, the dioxathion residue is reduced 63-80%.
    Destruction of dioxathion occurs in both the liming-filtration steps
    and the drying operation in which the limed material is processed in a
    rotary kiln at a gas temperature of about 310F for 13 minutes. Drying
    moist apple pomace in a rotary kiln using an inlet air temperature of
    500F caused a 60% loss of dioxathion residue.

    Pyrolytic experiments by Diveley et al. (1959) showed that, when
    dioxathion was slowly heated to 135 - 140C in vacuo, the trans
    isomer pyrolyzed completely, whereas the cis isomer remained intact.
    The products formed from the trans isomer were O,O-diethyl
    hydrogen phosphorodithioate and 2-p-dioxenethiol S(O,O-diethyl
    phosphorodithioate). Continued pyrolysis of the trans and cis
    isomers at 160 - 165C resulted in the decomposition of both isomers
    to O,O-diethyl hydrogen phosphorodithioate and 2-p-dioxenethiol
    S(O,O-diethyl phosphorodithioate).

    Evidence of residues in food in commerce or at consumption

    Dioxathion residues were not reported to have been found in any of the
    wide range of commodities examined by the U.S. Food and Drug
    Administration during the six years 1963-69 (Duggan et al., 1971).
    Neither was the presence of dioxathion reported in total diet samples
    in U.S.A. (Corneliussen, 1970).

    The most intensive use of dioxathion on plants occurs in California
    and Florida. Advice from the Departments of Agriculture in both states
    indicates practically no incidence of dioxathion residues in fruit in
    either state. In 1970, 150 samples of citrus were analysed in
    California but only one of these was found to contain dioxathion. No
    residue was reported on 329 samples of other fruit on which the use of
    dioxathion is permitted. In 1970, 357 citrus samples and in 1971, 394
    samples were screened in Florida by analytical methods which would
    detect dioxathion. No dioxathion residues were detected.

    During 1971, the New South Wales Department of Agriculture analysed
    1437 samples of internal fat from cattle slaughtered within the cattle
    tick quarantine area (Snelson, 1972). It was found that 320 (23%)
    contained dioxathion at levels ranging from 0.01 to 2.14 ppm, 4
    samples having residues above 1 ppm. Thus the incidence of dioxathion
    residues in fat from cattle had increased from the 13.8% reported
    during 1970.

    Of the 1439 cattle dips maintained by the New South Wales Government,
    713 (50%) were charged with dioxathion in 1971. A total of 1063
    samples of butter were collected from commercial butter factories in
    the cattle tick quarantine areas during 1971 and analysed by the
    laboratories of the Board of Tick Control. Of these, 382 (36%)
    contained dioxathion residues at levels ranging from 0.01 to 1.02 ppm.
    In the previous year (1970) the incidence was 18.6%.

    METHODS OF RESIDUE ANALYSIS

    The colorimetric method of Dunn (1958) is still regarded as specific
    and sensitive for the determination of dioxathion residues in plant
    and animal products. The multi-residue detection methods (Storherr
    et al., 1971; Abbott et al., 1970) have been used to determine
    dioxathion residues in plant and animal products and appear entirely
    satisfactory for regulatory purposes.

    APPRAISAL

    The 1968 Joint Meeting (FAO/WHO, 1969a and 1969b) recommended an ADI
    of 0.0015 mg/kg body-weight. Temporary tolerances were recommended for
    residues in citrus fruits, pome fruits, grapes and meat. Further
    information was required on (a) the composition of technical
    dioxathion, (b) disappearance of residues in storage and processing
    and (c) residue levels in products in commerce.

    Technical dioxathion contains a minimum of 68% of the cis and
    trans isomers of 2,3-p-dioxanedithiol S,S-bis (O,O-diethyl
    phosphorodithioate). The remaining related compounds include 10% ethyl
    phosphorothioates and ethyl phosphorodithioates. Results of studies
    confirm the identity and relative instability of the oxygen analogues.

    Studies of dioxathion residues on fruit show a slow rate of decline
    under natural conditions. The average half-life of residues on citrus
    fruits, grapes and apples was determined to be 84 days, 45 days and 56
    days, respectively. The cis and trans isomers have been shown to
    be the most persistent components. Loss by volatilization was least
    for these isomers. Hydrolysis does not take place readily on plant
    surfaces but does occur with those fractions which are absorbed into
    plant tissues.

    The ratio of cis and trans isomers to each other is unchanged
    after application to plants.

    Information derived from the processing of citrus pulp and apple
    pomace shows that 60-80% of the residues are lost during the drying
    operation.

    Data available from Australia showed the incidence and level of
    dioxathion residues in the fat of meat of cattle and in dairy produce.
    These indicate that the tolerance in the fat of meat of cattle does
    not require amendment. The occurrence of dioxathion residues in milk
    and milk products as a result of the dipping of cattle for tick
    control indicates the need for a tolerance for dioxathion residues in
    milk and milk products.

    Reports from the California Department of Agriculture indicated that
    only 1 of 150 citrus samples examined in 1970 contained dioxathion
    residues. No dioxathion residues were found on 124 samples of apples,
    81 samples of pears or 124 samples of grapes. Dioxathion was not
    reported to be found in any commodities analysed in the U.S.A. over
    the period 1963 - 1969. Neither does it appear in the results of total
    diet studies reported from U.S.A.

    Due to the stability of dioxathion residues, no appreciable decline in
    levels is to be expected during normal storage of any of the
    commodities mentioned above after harvest, slaughter, etc.

    Questions referred by the Sixth Session of the Codex Committee on
    Pesticide Residues were considered. In the light of the available
    information there was little likelihood that dioxathion residues could
    occur in the juice of apples and grapes. The strong affinity of the
    residue for the skin and the fact that residues in plant juices are
    readily degraded were noted.

    Examination of original data showed that the class "pome fruits"
    included apples, pears and quinces. Since the residues in animal
    tissues and milk, resulting from the direct treatment of animals, is
    partitioned preferentially into fatty tissues and milk fat,
    opportunity has been taken to clarify this fact in the tolerance
    previously recommended for "meat".

    RECOMMENDATIONS

    TOLERANCES

    The tolerances recommended in 1968 have been confirmed as no longer
    temporary. The following tolerances are based on residues likely to be
    found at harvest in the case of plant products and at slaughter in the
    case of meat. The limit proposed for milk and milk products are given
    on the assumption that blending will take place before milk enters
    commercial channels.

                                                      ppm

         Apples, pears, quinces                       5

         Grapes                                       2

         Citrus fruit                                 3

         Fat of meat of cattle,
         sheep, goats and pigs                        1

         Milk and milk products
         (fat basis)                                  0.2

         Apricots, cherries,
         peaches, plums and prunes                    0.1*

         * at or about the limit of determination

    FURTHER WORK OR INFORMATION

         None

    REFERENCES

    Abbott, D.C., Crisp, S., Tarrant, K.R. and Tatton. J.O'G. (1970)
    Pesticide residues in the total diet in England and Wales, 1966-1967.
    III. Organophosphorus pesticide residues in the total diet. Pest.
    Sci., 1: 10-13.

    Arthur, B.W. and Casida, J.E. (1959) Biological activity of Hercules
    AC-528 components in rats and cockroaches. J. Econ. Entomol., 52(1):
    20-27.

    Casida, J.E. and Ahmed, M.K. (1959) Mechanism of residue loss of
    Hercules AC-528 components on plant foliage. J. Econ. Entomol., 52(1):
    111-116.

    Chamberlain, W.F., Gatterdam, P.E. and Hopkins, D.E. (1960) Metabolism
    of P32 Delnar in cattle. J. Econ. Entomol., 53: 672-675.

    Claborn, H.V., Radeleff, R.D. and Busland, R.C. (1960) Pesticide
    residues in meat and milk. ARS 33 - 63 ARS-USDA.

    Corneliussen, P.E. (1970) Pesticide residues in total diet samples.
    Pesticides Monitoring J., 4(3): 89-105.

    Diveley, W.R., Hanbein, A.H., Lohr, A.D. and Mosely, P.B. (1959) Two
    new organophosphorus derivatives of p-dioxane with excellent
    insecticidal and acaricidal activity. J. Am. Chem. Soc., 81: 139-144.

    Dunn, C.L. (1958) Determination of 2,3-p-dioxanedithiol S,S-bis
    (O,O-diethyl phosphorodithioate). J. Agr. Fd. Chem., 6: 203-209.

    Duggan, R.E., Lipscomb, G.Q., Cox, E.L., Heatwole, R.E. and Kling,
    R.C. (1971) Pesticide residue levels in food in the United States
    1963-1969. Pesticides Monitoring J., 5(2) 73-212.

    FAO/WHO. (1969a) Report of the 1968 Joint Meeting of the FAO Working
    Party of Experts on Pesticide Residues and the WHO Expert Committee on
    Pesticide Residues. FAO Ag. Studies No. 78: WHO Tech. Report Series
    No. 417.

    FAO/WHO. (1969b) 1968 Evaluations of some pesticide residues in food.
    FAO/PL:1968/M/9/1; WHO/Food Add./69.35.

    Gunther, F.A., Jeppson, L.R., Barkley, J.H., Elliott, L.M. and Blinn,
    R.C. (1958) Persistence of residues of 2,3-p-dioxane-dithiol
    S,S-bis(O,O-diethyl phosphorodithioate) as an acaricide on and in
    mature lemons and oranges. J. Agr. Fd. Chem., 6: 210-211.

    Hercules Inc. (1958) Dioxathion residues in citrus fruit. Submission
    to U.S. Food and Drug Administration.

    Hercules Inc. (1960) Dioxathion residues in grapes. Submission to U.S.
    Food and Drug Administration.

    Hercules Inc. (1961) Dioxathion residues resulting from application to
    apples. Submission to U.S. Food and Drug Administration.

    Hercules Inc. (1968) Reports filed with FAO. (unpublished)

    Hercules Inc. (1970) Submission to U.S. Environmental Protection
    Agency.

    Hurwood, I.S. (1966) Excretion of pesticides in milk following dermal
    treatment of dairy cattle with coumaphos and dioxathion. Queensland
    Department of Primary Industries Bulletin No. 120.

    Plapp, F.W., Bigley, W.S. and Darrow, D.I. (1960) Studies on the
    metabolism and residues of P32 labelled Delnow in the Hereford steer.
    J. Econ. Entomol., 53 : 60-64

    Snelson, J.T. (1972) Results of residue studies with dioxathion in
    Australia. Information submitted to FAO.

    Storherr, R.W., Ott, P. and Watts, R.R. (1971) A general method for
    organophosphorus pesticide residues J. Ass. off. analyt. Chem., 54:
    513-516.

    Watts, R.M. (1968) Report to Co-ordinating Committee on Pesticides
    (Australia) from New South Wales Department of Agriculture.
    Information submitted to FAO.
    


    See Also:
       Toxicological Abbreviations
       Dioxathion (FAO/PL:1968/M/9/1)