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    PESTICIDE RESIDUES IN FOOD - 1983


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1983





    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
    Geneva, 5 - 14 December 1983

    Food and Agriculture Organization of the United Nations
    Rome 1985

    PIRIMIPHOS-METHYL

    RESIDUES

    Explanation

         Pirimiphos-methyl was evaluated in 1974, 1976, 1977 and 1979.1 
    An acceptable daily intake (ADI) was established and maximum residue
    limits (MRLs) were recommended in a range of commodities.

         A number of items of information considered desirable by these
    Meetings still appear to be outstanding:

    1.   Information on residues in fruit and vegetables following
         approved uses (1974).

    2.   Further information on the level and fate of residues in food at
         the point of consumption following the use of primiphos-methyl
         for the control of various stored product pests (1974 and 1977).

    3.   Results of studies now in progress on the residues in peanuts and
         peanut products (1976).

    4.   Results from commercial trials in other commodities (1976).

         Pirimiphos-methyl has been approved for use in the control of
    vectors of human disease and an interim specification has been issued
    by the Vector Biology and Control Division of WHO (WHO 1982). 

    RESIDUES IN FOOD AND THEIR EVALUATION

    USE PATTERN

         A limited amount of new information has been received. From the
    results of monitoring of imported fruits and vegetables provided by
    Sweden (1983) it is apparent there must be significant uses on citrus,
    sweet peppers and tomatoes, at least. Barry et al. (1981) report
    measurable residues of pirimiphos-methyl in chickpeas (Australia) -
    pigeon peas (Kenya), Moong dall (Tanzania), peanuts (South Africa),
    split peas (Kenya) and Sardo cheese (Argentina).

         The Spanish Ministry of Agriculture (Spain 1983) advised that
    pirimiphos-methyl is registered for use on fruit including citrus and
    grapes, olives, beets, potatoes and other vegetables, maize, sorghum,
    sugarcane and stored grain.


              

    1  See Annex 2 for FAO and WHO documentation.


         The use against mosquito vectors of malaria was described by
    Rishikesh et al. (1977) and Shaw et al. (1979) and against the
    blackfly vector of onchocerciasis (river blindness) by Le Berre 
    et al. (1972).

         McCallum Deighton (1978) reported that Soderstrom & Armstrong
    (1973) showed that raisins treated with pirimiphos-methyl at the rate
    of 4 mg/kg gave complete kill of several stored product pests 12
    months after treatment. An application of 2 mg/kg killed more than 95
    percent under similar conditions.

         The same author reports that Spitler & Hartsell (1975) found that
    almonds in the shell treated with an initial deposit of 1.6 mg/kg
    pirimiphos-methyl showed little damage after 10 months of storage.
    When treated at the rate of 3.6 mg/kg, the protection was excellent
    and little damage occurred at the end of 12 months.

         Similarly, it was reported that trials during 1974-75
    demonstrated that packages containing dates treated on the outside,
    with pirimiphos-methyl at the rate of 0.5 g/sq m remained free of
    insects for at least 6 mo. irrespective of the nature of the packages
    (cardboard, wood, palm leaf). The dates remained free of any
    detectable residues.

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Postharvest Cereal Grains

         The extensive world literature on the usefulness, effect and fate
    of pirimiphos-methyl when applied to cereal grains for the control of
    the whole spectrum of stored-product pests was reviewed. The
    application rate necessary to control most species adequately is of
    the order of 4 mg/kg but depends on the insect species, the
    temperature and humidity of the grain, type of storage structure, and
    anticipated period of storage. The application rate ranges from 2-6
    mg/kg. Treatment may be confined to pirimiphos-methyl alone but where
    tolerant species are a problem it is more practical to combine another
    insecticide that is specifically effective against the 
    pirimiphos-methyl tolerant species than to increase the level of
    pirimiphos-methyl sufficient to control the tolerant pests.

         In India, Chawla, & Bindra (1971) reported that the rate of
    dissipation of pirimiphos-methyl residues from grain was significantly
    slower than that of malathion, bromophos or iodofenphos. The Cyprus
    Agricultural Research Institute observed (Anonymous 1972), when
    testing a range of insecticides as grain treatments against a variety
    of stored-grain insects, that by the third mouth most of the chemicals
    had lost their effectiveness, whereas pirimiphos-methyl was still
    effective four months after application. In the United States, La Hue
    (1974) studied the patterns of degradation of a number of potential
    grain protectants compared with malathion, the standard treatment.
    Pirimiphos-methyl residues were influenced less by high moisture
    content of the grain at time of treatment than those of malathion and
    fenitrothion.


         Bowker (1974) studied the degradation of radio-labelled
    pirimiphos-methyl during eight months storage, when applied as a 2
    percent dust to wheat at 4 mg/kg. In grain with a moisture content
    below 14 percent, only 20 percent degradation was observed during
    storage, whereas 70 to 80 percent degradation was recorded, in grain
    with about 18 percent moisture. He found no significant levels of
    degradation products, other than the hydrolysis product 
    2-diethylamino-4-hydroxy-6-methyl pyrimidine. In particular, levels of
    the very unstable "oxon" and of the N-de-ethylated thionate were all
    less than 0.05 mg/kg total residue.

         Rowlands (1975) reported results of studies on the breakdown and
    recovery of radio-labelled pirimiphos-methyl in wheat treated at 4
    mg/kg in hexane solution and stored under laboratory conditions at
    21C. After eight months, 78 percent of the radioactivity was still
    recoverable as intact parent compound and 9-10 percent was bound to
    lipid and proteinaceous matter in the grain. The latter could only be
    recovered by digestion and was thought to be associated chiefly with
    the protein. The only metabolite detected was the hydroxy-pyrimidine.

         Rowlands & Wilkin (1975) applied solutions of radiolabelled
    pirimiphos-methyl and also a 2 percent dust to wheat with a moisture
    content of 14 and 18 percent to give 4 mg/kg final treatment. The
    samples were then stored in a laboratory at 20C for six months. They
    also found that approximately 10 percent of the radioactivity was
    bound to lipoprotein material and was unextractable except by
    digesting the aleurone regions of the grain. Such labelled material,
    as recovered by this means, appeared to be unchanged 
    pirimiphos-methyl, but degradation during this extraction and
    subsequent purification hampered identification. During the storage
    period, the breakdown rates were approximately the same for both
    solvent and dust treatments. After six months, 15 and 50 percent
    degradation had occurred at the 14 and 18 percent moisture levels,
    respectively.

         Bengston et al. (1975), in studying the effect of 
    pirimiphos-methyl against malathion-resistant insects and its fate in
    bulk wheat under typical semi-tropical conditions found that the
    deposit degraded rather slowly. Deposits of 2 and 4 mg/kg degraded to
    1.62 and 2.94 mg/kg after 25 weeks, respectively. The authors
    estimated the half-life of such deposits to be of the order of 45
    weeks (temperature and moisture conditions not stated).

         Weaving (1975) found pirimiphos-methyl, applied to maize and
    sorghum so as to give a deposit of 5 and 10 mg/kg, gave complete kill
    of Sitophilus zeamais for 12 months under tribal storage conditions
    in Rhodesia (now Zimbabwe).


         La Hue & Dicke (1976) found that pirimiphos-methyl applied at the
    rate of 8.4 mg/kg to high-moisture sorghum grain gave excellent
    protection against damage by six different insect pests for a period
    of 12 months.

         Morallo-Rejesus & Carino (1976) reported pirimiphos-methyl was
    more persistent on maize than on sorghum but apparently little
    allowance was made in their studies for any difference in temperature
    or moisture content.

         Desmarchelier (1977) reported that the degradation of 
    pirimiphos-methyl over a 35-week period was too slow to allow accurate
    measurements of temperature effects (experiments conducted over the
    range 20 to 30C and 11.5 to 12.5 percent moisture content).

         La Hue (1977) noted that pirimiphos-methyl degraded much more
    slowly than did malathion under similar conditions; 83 percent of the
    original deposit of pirimiphos-methyl remained on wheat 12 months
    after treatment, whereas only 16 percent of the malathion deposit
    remained under identical conditions.

         Cerna & Benes (1977) provided results of a study carried out in
    Czechoslovakia where 400 tonnes of wheat, containing 12.6-14.2 percent
    moisture at a temperature of 8-10C, was treated with 
    pirimiphos-methyl at a rate to provide 4 mg/kg. The wheat was analysed
    at the time of treatment and at intervals thereafter until discharged
    for milling at the end of 286 days. Over this period, the residue
    levels declined from 3.7 to 1.62 mg/kg.

         Bengston et al. (1978) carried out duplicate field experiments
    on the control of insect infestation in stored sorghum. Residues of
    pirimiphos-methyl declined from 3.9 to 3.0 mg/kg over a period of 24
    weeks; the average temperature was 26C and average moisture content
    was 12.4 percent.

         Banks & Desmarchelier (1978) discussed the finding that the loss
    of insecticide residues from stored grain follows pseudo first-order
    reaction kinetics and that this model applies equally well to
    pirimiphos-methyl (Desmarchelier 1977; Desmarchelier 1978). They noted
    the influence of water vapour and temperature on changes in pesticide
    residue levels with time and drew attention to the errors introduced
    in calculating the rate of degradation from a "linear" or a 
    semi-logarithmic model. Desmarchelier & Bengston (1979) further
    developed this concept and explained how the mathematical models are
    developed and used. They compared the rate of degradation of 12 grain
    protectants. The half-life of pirimiphos-methyl at 30C and 50 percent
    relative humidity was given as 70 weeks. This compared with 12 weeks
    for malathion under similar conditions. The interesting point is that
    the co-efficient of variation with respect to temperature is much
    smaller for pirimiphos-methyl than for any of the other compounds
    considered.


         Desmarchelier et al. (in press) provided extensive information
    from 21 commercial storages treated with pirimiphos-methyl at 6 mg/kg.
    Grain condition and protectant residue levels were regularly
    monitored. The residue level declined from 6 to 4 mg/kg over ten
    months on grain that remained at 30C for seven months and then cooled
    gradually to 20C. The moisture content of this grain was between 11
    and 12 percent. The mean observed and predicted residue levels of
    pirimiphos-methyl were plotted at intervals after application. Figure
    1 shows the high level of agreement with the model, based on pseudo
    first-order kinetics.

         Bengston et al. (1980b) reported the results of duplicate field
    trials carried out on bulk wheat in commercial silos, where
    pirimiphos-methyl was applied at the rate of 6 mg/kg in conjunction
    with phenothrin (2 mg/kg). The effectiveness against a range of
    stored-product pests and the residue levels were monitored throughout
    a period of nine months, during which the pirimiphos-methyl residue
    level did not change appreciably. The moisture content of the grain
    ranged from 10.7 to 11.1 percent and the temperature from 26 to 29C.

         Bengston et al. (1980a) reported the results of field trials
    with various pesticide combinations carried out on bulk wheat in
    commercial silos in Queensland, South Australia and Western Australia.
    Once again, the concentration of pirimiphos-methyl declined only
    slightly during the eight months storage period.

         Desmarchelier et al. (1980b) reported the results of an
    extensive collaborative study of residues on wheat of methacrifos, 
    chlorpyrifos-methyl, fenitrothion, malathion and pirimiphos-methyl.
    Pirimiphos-methyl degraded more slowly and to a lesser extent than the
    other compounds. The measured values of residues of pirimiphos-methyl
    on wheat at the experimental sites agreed with the values predicted
    from the calculation using first-order kinetics, grain temperature and
    interstitial relative humidity. The rate of degradation was
    surprisingly slow.

         Desmarchelier et al. (1980a) reported studies on the fate of
    pirimiphos-methyl and five other grain protectants or rice and barley
    after storage and during processing. The level of residues were
    determined on unhusked rice, husked rice, polished rice and barley
    over a storage period of six months. The observed levels were close to
    those predicted from use of a model relating rate of loss of residue
    levels to a rate constant and only two variables, temperature and
    equilibrium relative humidity. The difference between predicted and
    observed values of residues of pirimiphos-methyl on the four
    commodities was 8 percent.


    FIGURE 1


         Residue data were obtained over a year from hard winter wheat,
    shelled corn and sorghum grain treated with pirimiphos-methyl stored
    in bins in a laboratory (La Hue 1974). Table 1 shows the average
    residues of pirimiphos-methyl in the stored grain over the 
    twelve-month period at 27C. It is noticeable that the degradation
    appears to be independent of the moisture content of the grain under
    these conditions. Malathion, included in the same trial, degraded to
    about one tenth of the initial dosage within the same period. In the
    case of the high moisture sorghum, it was almost entirely destroyed
    within one month.

         Seth (1974) reported trials to evaluate pirimiphos-methyl for the
    control of pests in stored rice in South-east Asia. Rice in husk and
    polished rice were treated with emulsifiable concentrate (E.C.) and
    dust formulations at rates equivalent to 2, 4 and 8 mg/kg. The rice
    was analysed at monthly intervals throughout the four-month trial. In
    polished grains, the residue at the end of four months was
    approximately 25 percent of the residue found on the first day of the
    trial. In rice in husk, it was not possible to deduce the degradation,
    since the residue data were expressed on hull and milled grain
    separately. However, there appeared to be relatively little loss of
    pirimiphos-methyl over five months. Relatively little of the
    insecticide (generally less than 0.5 mg/kg) transferred to milled
    grain. There was no significant difference between the dust and E.C.
    formulations.

    FATE OF RESIDUES

    In Grain

         Residues of pirimiphos-methyl on wheat grain are degraded and
    detoxified by hydrolysis of the phosphorus-ester side chain to give
    principally the parent hydroxypyrimidine (Figure 2, IV), and the
    related compounds (V and VI). At a given temperature, the rate of
    breakdown increases with increasing moisture content of the grain.
    Levels of the N-desethyl phosphorus compound (II) were always
    extremely low (approximately 0.05 mg/kg over a period of 32 weeks in
    wheat grain treated at 4 mg/kg). No residue of the chemically-unstable
    oxygen analogue (III) was detected. The limit of detection was 0.01
    mg/kg (Bowker 1973).

         Radio-autograms of grain sectioned after four months showed that
    the insecticide and its degradation products were concentrated in the
    seed coat, so that residues in white flour and bread are likely to be
    lower than in bran and wholemeal products. The general pattern of
    breakdown on stored rice was similar to that found on wheat grain. The
    insecticide and its degradation products were concentrated in the
    husk, in which the rate of breakdown appeared to be unaffected by the
    moisture content of the rice (Bowker 1973; Bullock 1973).



      Table 1.  Average Residues of Pirimiphos-methyl in Stored Grain1
 
                                                                                                    
                                                        Post-treatment residues (mg/kg)
                                                                                                    
    Grain          Moisture    Intended                               months
                   Content     dosage                                                               
                   (%)         (mg/kg)      24 h     1          3        6          9        12
                                                                                                    

    Wheat          12.5        7.8          6.5      6.1        5.6      6.2        4.9      5.4

    Maize          12.5        8.4          7.9      6.3        4.5      4.1        3.4      3.0

    Sorghum        17.6        8.4          7.5      6.5        4.3      3.8        3.8      3.7
                                                                                                    


    1  Over 12 months at 27C.
    

    FIGURE 2


         Degradation was marginally more rapid in contact with the grain
    than in the isolated formulation but whether this additional breakdown
    was caused by factors within the grain, or by the associated
    microflora, was not known. At a higher moisture content (ca. 18
    percent) less pirimiphos-methyl was recovered on analysis but
    increased levels of the hydrolysis product (IV) were obtained,
    suggesting that a more rapid degradation of the insecticide occurred.
    Bowker (1973) concluded that grain may lack the enzymatic activity,
    believed to be present in plants and soil, to cleave the pyrimidine 
    N-ethyl bonds. It is likely, therefore, that following the treatment
    of wheat and brown rice with pirimiphos-methyl, the major residues
    during storage will be the parent compound and the simple hydrolysis
    product (IV). Under optimum conditions, the maximum level of compound
    (IV) following treatment at 4 mg/kg was found to be 0.17 mg/kg; under
    poor storage conditions, with high moisture content grain it was 0.62
    mg/kg.

         Solutions and also a 2 percent dust of radio-labelled 
    pirimiphos-methyl were applied in the laboratory to wheat grain of 14
    and 18 percent moisture to give levels of 4 mg/kg. Throughout a
    storage period of six months, the residues of pirimiphos-methyl were
    found almost entirely in the seed coat and aleurone layer, with only
    traces present in the germ or endosperm. It was also clear that, as
    with malathion but to a greater extent, there was transfer of
    insecticide between grains, possibly in the vapour phase. About 10
    percent of the total residual radioactivity was bound to lipoprotein
    material in the  aleurone region of the grain and could be extracted
    only by digestion of the aleurone protein. In contrast with other
    organophosphates studied, the bound material appeared to be unchanged
    pesticide rather than a metabolite. It was undoubtedly a P=S compound,
    but degradation during the liberation of the bound material
    complicated identification (Rowlands et al. 1974).

    In Animals

         The metabolism of pirimiphos-methyl was studied in the rat and
    dog. Twelve metabolites were detected, none of which showed
    anticholinesterase activity. No parent pirimiphos-methyl was detected
    in the urine. In both rats and dogs, 2-ethylamino-4-hydroxy-6-methyl
    pyrimidine was the major urinary metabolite (Bratt & Jones 1973).

         When rats were given a single oral dose of radio-labelled
    pirimiphos-methyl at 7.5 mg/kg, the uptake of radioactivity into blood
    and its subsequent disappearance from the bloodstream were both very
    rapid. More than 50 percent of the radioactivity present in the blood
    30 min. after dosing had disappeared at one hour after dosing.
    Unchanged pirimiphos-methyl usually represented less than 10 percent
    of the total residue in the blood 24 h after dosing. When 
    radio-labelled pirimiphos-methyl was administered orally to rats at
    7.5 mg/kg per day for four days, total radioactive residues in the
    liver, kidney and fat did not usually exceed 2 mg/kg pirimiphos-methyl


    equivalents. There was no evidence to show that either 
    pirimiphos-methyl or its metabolites accumulated in the liver, kidney
    or fat of rats following daily dosing with the insecticide over four
    days (Mills 1976).

         The rodioactive residues in the liver and kidney of a goat, dosed
    daily for seven consecutive days with 14C-pirimiphos-methyl at 30
    mg/kg in the diet, were examined. (Curl and Leahy 1980).

         A radioactive residue of 0.25-0.30 mg/kg of 
    14C-pirimiphos-methyl equivalents was detected in the liver, and 89
    percent of this was extracted and analysed by thin layer
    chromatography. 5.9 percent of the total radioactive residue in the
    liver was unchanged pirimiphos-methyl. The hydroxypyrimidines,
    compound (II) (2-diethylamino-6-methyl-pyrimidin-4-ol), compound (III)
    (2-ethylamino-6-methyl-pyrimidin-4-ol) and compound (IV) 
    (2-amino-6-methyl-pyrimidin-4-ol) accounted for 3.7 percent, 21.8
    percent and 17.5 percent respectively, of the total radioactive
    residue in the liver. Compounds (II), (III) and (IV) were present
    mainly as "free" metabolites. However, 13.7 percent of the
    hydroxypyrimidines detected were released from the liver by acid
    reflux.

         The remainder of the radioactivity extracted from the liver
    consisted of at least five compounds.

         A radioactive residue of 0.59-0.70 mg/kg of 
    14C-pirimiphos-methyl equivalents was found in the kidney; 91 percent
    of this was extracted and analysed by thin-layer chromatography.
    Compound (II), compound (III) and compound (IV) accounted for 7.9
    percent, 35.3 percent and 17.0 percent respectively, of the total
    radioactive residue in the kidney. Compounds (II), (III) and (IV) were
    present mainly as "free" metabolites, however, 9.0 percent of the
    hydroxypyrimidines detected were released from the kidney by acid
    reflux.

         The remainder of the radioactivity extracted from the kidney
    consisted of at least six compounds.

    In Storage and Processing

         Bullock (1973, 1974) reported several individual experiments
    which demonstrated that residue levels of pirimiphos-methyl are
    significantly reduced during the milling and baking processes. Table 2
    summarizes the results of residue trials carried out in the United
    Kingdom on wheat that had been treated to contain nominally 4 mg/kg
    pirimiphos-methyl.

         Table 3 summarizes results of a residue trial (Bullock 1973)
    carried out in the United Kingdom with wheat nominally treated to
    contain 8 mg/kg pirimiphos-methyl. These data are substantially in
    agreement with those of Bengston et al. (1975) and show that there
    is relatively little penetration beyond the seed coat, even throughout
    a storage period of nine weeks.


    Table 2.  Effect of Milling and Baking on Residue in Wheat Admixed 
              with Pirimiphos-Methyl1

                                                                       

                    Interval between
    Grain           treatment and               Residues (mg/kg)
    fraction        sampling (months)     Highest    Lowest    Mean
                                                                       

    Whole grain            0              4.2        1.9       2.9 (9)
                                          3.0        -*        3.0*

                           1              4.1        1.5       2.8 (9)

                           2              4.1        1.6       2.6 (8)
                                          2.5*       2.4*      2.5* (3)

                           3              3.6        1.3       2.3 (7)

    Whole meal             0              1.3        0.94      1.1 (3)
    flour                  1              2.1        1.1       1.7 (4)
                           2              2.2        1.2       1.7 (3)
                                          1.5*       1.4*      1.5* (3)
                           3              2.1        1.0       1.5 (4)

    White flour            0              0.88       0.30      0.52 (6)
                                          0.56*      0.53*     0.55*(3)
                           1              0.77       0.44      0.59 (5)
                           2              0.64       0.24      0.56 (6)
                                          0.29*      0.24*     0.27*(3)
                           3              0.67       0.38      0.56 (3)

    Wholemeal              0              0.72       0.53      0.64 (4)
    bread                  1              0.91       0.55      0.79 (4)
                           2              1.1        0.65      0.93 (4)
                                          0.97*      0.82*     0.88* (3)
                           3              0.54       0.21      0.49 (3)

    White bread            0              0.28       0.19      0.23 (6)
                                          0.26*      0.24*     0.25* (3)
                           1              0.36       0.22      0.30 (5)
                           2              0.45       0.31      0.36 (8)
                                          0.15*      0.13*     0.14* (3)
                           3              0.54       0.21      0.43 (3)
                                                                       

    1    Dosage of pesticide was 4 mg/kg. All results are from field 
         trials except those marked *, which are from a small-scale trial.
         Figures in parentheses are the numbers of results on which the 
         means are based.


    Table 3.  Residues of Pirimiphos-methyl in Whole Grains and in Milling
              and Baking Fractions Treated in a Laboratory Trial1

                                                                         

    Interval between                 Residues (mg/kg)
    treatment and       Whole    White    White   Wholemeal  Wholemeal
    sampling            grain    flour    bread   flour      bread
                                                                         

    0 days              6.0      0.86     0.52
                        6.0      0.91     0.56
                        6.0      1.0      0.57

    9 weeks             4.8      0.47     0.28    3.2        1.7
                        5.2      0.59     0.33    3.0        1.6
                        5.2      0.60     0.30    3.2        1.5
                                                                         

    1    Dosage of pesticide was 8 mg/kg. In all cases, no residues of the
         phosphorus-containing compounds (II) or (III) (Figure 1) were 
         detected. (Limit of detection: 0.01 mg/kg in each case.)


         Seth (1974) discussed experiments on the admixture of 
    pirimiphos-methyl with paddy rice (rice in husk) in Southeast Asia.
    Both emulsion and dust formulations were used and were applied at
    rates of 2, 4 and 8 mg/kg. A portion of the rice was milled
    immediately after treatment and further portions at the end of one,
    two, three and five months. It was found that the deposit of
    pirimiphos-methyl on both the husk and the milled grain was
    proportional to the amount applied, but the concentration on the husk
    was always about 25 times that on the milled grain. The residue on the
    husk and milled grain declined steadily over the five-month storage
    period. Although the concentration on the husk initially was as high
    as 12 mg/kg, the residue on the milled rice barely exceeded 0.5 mg/kg
    and even at the highest rate of application was always below 1 mg/kg.
    These experiments clearly showed that there is minimum transfer of
    pirimiphos-methyl from the husk to the kernel of rice, even during
    prolonged storage. The degree of penetration is comparable to that
    reported by Kadoum & La Hue (1974) for malathion on wheat, maize and
    sorghum.

         Residues of pirimiphos-methyl in flour are relatively stable
    during baking to bread and biscuits. However, because of the dilution
    which the flour undergoes during these processes, flour initially
    containing 1 mg/kg pirimiphos-methyl is likely to yield 
    bread/ biscuits containing residues of ca. 0.5 mg/kg.

         Bullock et al. (1976) studied the fate of pirimiphos-methyl
    during processing of flour into bread and biscuits. In studies with
    the radio-labelled compound, flour was dosed with 2-14C-labelled
    pirimiphos-methyl and baked to produce white bread, wholemeal bread
    and biscuits. Although pirimiphos-methyl is known to be a relatively
    volative compound, there was no significant loss of radioactivity by
    volatilization. Distribution of radioactivity throughout the bread was
    fairly uniform. Unchanged pirimiphos-methyl accounted for 75-90
    percent of the radioactivity in the baked product. The major
    degradation product formed during the baking was hydroxypyrimidine,
    which accounted for 3-10 percent of the radioactivity in the final
    product.

         Similar results were obtained by residue analysis in a second set
    of studies. After correcting for the weight increase when flour is
    converted to bread, residues of pirimiphos-methyl fell by 11-18
    percent. Likewise, residue analysis of biscuits showed average losses
    of 8 percent. However, owing to the dilution of the flour that occurs
    during baking, the residue of pirimiphos-methyl in bread will be lower
    than that in the corresponding flour. Bullock et al. (1976) found
    levels of pirimiphos-methyl in bread and biscuits to be about 50
    percent of those in the flour from which they were derived. These
    findings agreed well with the earlier work of Bullock (1973, 1974). No
    residues of the phosphorus-containing compounds (II) and (III) were
    detected in bread baked from flour treated with pirimiphos-methyl at 
    1 mg/kg or in biscuits baked from flour containing up to 5 mg/kg
    (Bullock et al. 1976)


         The hydroxypyrimidine (IV) also undergoes only slight degradation
    during the baking process. This compound constitutes only a minor part
    of the residue in stored grains (FAO/,WHO 1975).  Bullock et al
    (1976) used radio-labelled compound (IV) and found that it degraded by
    less than 10 percent during the baking of bread. It can, therefore, be
    concluded that residues of compound (IV) in baked products will never
    exceed 0.2 mg/kg and will normally be considerably lower.

         Bullock & May (1976) studied the fate of residues in wheat during
    processing to semolina and pasta. White semolina, prepared from durum
    wheat treated at 10 mg/kg, contained only 1.6 mg/kg pirimiphos-methyl.
    Pirimiphos-methyl levels in both white and wholemeal pasta were
    approximately 85-90 percent of those in the corresponding semolina; 70
    percent of the pirimiphos-methyl residue in semolina was transferred
    unchanged to cooked pasta. However, the weight of pasta increased by
    100 percent on cooking, so that the concentration of pirimiphos-methyl
    in cooked pasta is likely to be approximately 35 percent of that in
    the corresponding semolina.

         Results of experiments in Czechoslovakia (Cerna & Benes 1977)
    indicated that residues of pirimiphos-methyl in grain, which had been
    in store for nine months, were substantially removed by the milling
    process. The bulk of the residue was removed in the bran; there was no
    substantial difference in the concentration in the different bran
    fractions. When white flour was made into white bread, there was a
    further loss of approximately 50 percent so that the concentration of
    the residue in the bread was only 10-15 percent of its concentration
    in raw grain. Some residue was destroyed during milling.

         Tempone (1979) reported a series of studies on the effects of
    insecticides on barley malting and the resulting residues. In the
    first of these trials, barley treated with pirimiphos-methyl at the
    rate of 6 mg/kg or 18 mg/kg was converted into malt but no residues 
    were detected in the wort (unfermented extracts from the malted
    barley), the limit of determination being 0.004 mg/kg. Wort, prepared
    from barley malted after being in store for three, six and nine
    months, likewise showed no residues. In the second series of similar
    trials, the residue was determined in the malt (germinated grain that
    had been calcined). Residues could be found in the malt, but at a
    level of from 10 to 20 percent of that in the barley before malting.
    Barley kept in storage for three months after being treated with
    pirimiphos-methyl transferred significantly less residue to the malt
    than did the barley malted immediately after treatment, no doubt
    because there was significantly less residue on the outside of the
    kernel, where it would be protected from the enzymatic activity within
    the barley grain during germination.

         Bengston et al. (1980 a, b) arranged for wheat from bulk grain
    treated with pirimiphos-methyl and held in commercial silos to be
    processed through to wholemeal bread and white bread. The results
    obtained in these trials are reported in Tables 4 and 5. During
    processing from wheat to white bread, residues were reduced by 85-91
    percent.


        Table 4.  Mean Residues of Pirimiphos-methyl Following Milling and Baking of Stored Wheat

                                                                                                                  

    Site         Storage                                 Residues (mg/kg)
                 (weeks)                                                                                          
                             Wheat      Bran      Pollard    Wholemeal    White        Wholemeal     White
                                                             flour        flour        bread         bread
                                                                                                                  

    Site B       13          5-7        12-16     2-4        2.6          0.1-0.2      1.0-2.0       0.05-0.1

    Site D       19          2.5-3.0    6-8       1-2        1.2          0.05-0.1     0.5-1.0       0.05
                                                                                                                  



    Table 5.  Reduction in Pirimiphos-methyl Residues Following Milling and Baking of Stored Wheat

                                                                                                                  

    Site                                        Reduction in residues(%)
                                                                                                                  
                 Wheat to      Wheat to     Wholemeal flour    White Flour     Wheat to        Wheat to
                 Wholemeal     White        to Wholemeal       to White        Wholemeal       White
                 Flour         Flour        Bread              Bread           Bread           Bread
                                                                                                                  

    Site B       5             68           47                 54              50              85

    Site D       0             78           55                 58              56              91
                                                                                                                  
    
         Desmarchelier et al. (1980b), after treating bulk wheat in
    commercial silos with pirimiphos-methyl, arranged for a portion to be
    milled and for the white flour to be converted into white bread. The
    results are given in Table 6. It is of interest to note that the
    residues in flour and bread were higher in the hard wheat which was
    held for 22 weeks before milling, than in the soft wheat which was
    held of 11 weeks before milling.

         Desmarchelier et al. (1980a) studied the fate of 
    primiphos-methyl, and a number of other grain protectant insecticides,
    applied to unhusked rice, husked rice, polished rice and barley over a
    storage period of six months and subsequently during the processing
    and cooking of these grains. The results of these trials are given in
    Table 7, and show that only about 10-15 percent of the residue present
    on husked rice or polished rice was destroyed in the cooking process.
    However, if the treatment was applied to unhusked rice, approximately
    70 percent of the residue was removed with the husk and a great deal
    more when the husked rice was milled for the removal of the bran.
    Subsequent cooking of the husked rice or polished rice brought about a
    further substantial reduction in the residue level.

         These same workers found that pirimiphos-methyl, applied to
    barley destined for malting, was substantially lost during the malting
    process. Barley treated at the rate of 6 mg/kg and held in storage for
    six months was found to contain 4.9 mg/kg pirimiphos-methyl. When this
    grain was malted, the pirimiphos-methyl residue in the prepared malt
    was only 0.9 mg/kg. The work of Tempone (1979) showed that little, if
    any, of the residue in the malt is extracted into the wort.

         There have been no reports of pirimiphos-methyl being metabolized
    by attack at either of the O,O-dimethyl groups (to give a desmethyl
    derivative) as is common with certain other organophosphorus
    triesters. Morallo-Rejesus & Carino (1976) noted, but did not
    identify, breakdown products in shelled maize stored in 
    pirimiphos-methyl treated bags.

         Rowlands (1981), reporting work carried out some years previously
    using radio-labelled compound, treated small quantities (10 g) of
    wheat that were held in store for up to 6 months. Aliquots were
    removed at intervals and, after crushing, were extracted first with
    hexane, followed in turn by chloroform, methanol and acetonitrile and
    then,  after sequential digestion by three enzymes, further extraction
    by chloroform. The results are recorded in Table 8.

         It is clear from Table 8 that very soon after treatment, a
    portion of the aged pirimiphos-methyl residue is not extractable from
    wheat unless it is digested out enzymatically. It is thought that this
    is due to a complex formed by intact pirimiphos-methyl within the
    aleurone layer (Rowlands 1975).


        Table 6.  Residues of Primiphos-methyl in Wheat, Its Milling Products and Bread

                                                                                                                  

                                                   Residues (mg/kg)
    Type of     Storage                                                                                           
    Wheat       (weeks)     Initial deposit     Whole grain     bran       pollard    flour      bread
                                                                                                                  

    Soft        11          5.2                 4.2             9.1        8.3        0.2        0.1

    Hard        22          6.1                 4.5             12.4       10.4       1.3        0.35
                                                                                                                  


    Table 7.  Residues of Pirimiphos-methyl on Husked, Polished and Unhusked Rice After Storage and Processing

                                                                                                                  

    Grain         Application                    Residues (mg/kg)
                  level
                  (mg/kg)                                                                                         
                                 After       After       After         After
                                 3           6           Cooking at    Cooking at
                                 Months      Months      3 Months      6 Months
                                                                                                                  

    Husked
    rice          6              6.5         4.9         4.9           4.0

    Polished
    rice          6              6.0         6.0         4.9           4.9
                                                                                                                  

                                                         Residues (mg/kg) after
                                                         6 months storage and
                                                                                                                  
                                                         Milling                 Milling &
                                                                                 Cooking
                                                                                                                  
                                                         Husked     Polished     Husked       Polished
                                                         rice       rice         rice         rice
                                                                                                                  

    Unhusked
    rice          6.0            6.0         4.6         1.4        0.3          0.6          0.1
                                                                                                                  
            Table 8.  Recovery of Pirimiphos-methyl From Crushed Wheat (18% mo) By Sequential extraction

                                                                                                 

    Extraction by           14C activity recovered %1 at time of extraction after
                            application (0 h)

                            0 h         1 h        7 days      14 days     1 month      6 months
                                                                                                 

    Hexane                   97          89         84          78          72          67

    Chloroform              nil           1          4           7           8           8

    Methanol                trace         1          2           2           6           7

    Acetonitrile            trace         2          1           4           2           2

    Digest Sequence2
    (1)                     nil           2          1           4           2           2
    (2)                       4           5          7           7           9          12
    (3)                     nil           2          2           1           2           1
                                                                                                 

    Total extracted         101         102        101         103         101          99
                                                                                                 

    1    Average of three results  3 percent.
    2    Digest sequence: (1) = lipase pH 7.4; (2) = papain pH 4,5; (3) - cellulase pH 4.5,
         All at 37C for 24 h
    

         Studies reported by Rowlands (1981) on the uptake from dust or
    solvent application as determined by the separated tissue of the wheat
    grains after storage, showed that intact pirimiphos-methyl and free
    pyrimidinols occur chiefly in the seedcoat. These findings received
    some confirmation in the work of Mensah et al. (1979), who found
    that pirimiphos-methyl emulsion, applied to wheat that was then milled
    six months later, had accumulated in the bran and middlings fractions,
    irrespective of the moisture content of the stored wheat (12 percent
    and 16 percent). They found little or no residue in white flour.

         Rowlands (1981) found only pirimiphos-methyl (I) and the
    corresponding pirimidinol (IV) as residues in pirimiphos-methyl
    treated wheat with 12 percent moisture that was kept in sealed jars
    for up to eight months. However, in wheat with 18 percent moisture, a
    small (less than 10 percent of the total residue) quantity of the 
    N-des-ethyl pirimidinol (V) was found after six and eight months. (See
    Figure 2 for conformations of these compounds).

         Further to the work of Thomas & Rowlands (1975) on the uptake and 
    degradation of pirimiphos-methyl by Cheshire cheese, similar studies
    were carried out using Stilton cheeses, which differ in physical
    characteristics and are stored differently.

         In these studies a wooden plank was treated with 
    14C-ring-labelled pirimiphos-methyl and allowed to dry for 24 h
    before two young Stilton cheeses were placed on the treated surface.
    One of the cheeses was first covered by a layer of cheesecloth. The
    cheeses were turned every two days. Replicate core samples were taken
    with a cork borer from each face of both cheeses. The core was
    analysed for pirimiphos-methyl. Some of the cores were sectioned with
    a microtome and the concentration of pirimiphos-methyl in the cheese
    at various depths was determined by means of a scintillation counter.
    The findings are reported in Table 9.

         This experiment has shown that only a small amount of 
    pirimiphos-methyl penetrated into the cheeses under the various
    storage techniques used with Stilton cheese. No breakdown of the
    pirimiphos-methyl could be detected in the cheese or the cheesecloth
    throughout the seven weeks of storage.

         These results indicate that the MRL of 0.5 mg/kg for 
    pirimiphos-methyl in cheese would not be exceeded when the insecticide
    was used for the control of cheese mites during the making and storage
    of Stilton cheese.

         Mensah et al. (1979) reported results of small-scale trials, in
    which water-based emulsions of malathion, bromophos, iodofenphos and
    pirimiphos-methyl were applied at two dosage rates to spring wheat of
    12 percent and 15 percent moisture content, to compare the fate of the
    residues. Pirimiphos-methyl degraded at a comparatively slower rate
    than the other three compounds, but the rate of degradation was
    significantly higher on the high moisture grain. The results are given
    in Table 10. The residue levels were concentrated in the seed coat,


    resulting in high levels in bran and middlings. When applied at the
    rate of 6 mg/kg, the residues in these fractions exceeded the MRL
    recommended by the Meeting.

         Results were reported of small-scale trials in which the efficacy
    and fate of pirimiphos-methyl residue on wheat and milling fractions
    were assessed. Two rates (7.3 mg/kg and 14.6 mg/kg) were applied and
    the wheat was stored for up to 12 months. The results are reported in
    Table 11. These show that the residues in bran and middlings (shorts)
    exceeded the MRL following application at the lower rate and storage
    for less than six months. At the higher rate (which is well in excess
    of the recommended rate) the residues greatly exceeded the MRL.

    RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION

         Residues of pirimiphos-methyl were detected in the United States
    in several samples of imported foods (Barry et al. 1981) and the
    identification of these residues by GC-MS and GLC was reported. The
    level and source of residues found are reported in Table 12.

         The Swedish National Food Institute (Sweden 1983) indicated that
    during the period 1-1-80 to 30-4-83, 8 654 samples of fruit and
    vegetables were analysed for pesticide residues. From among these,
    eight samples were found to contain pirimiphos-methyl at levels up to
    1.4 mg/kg, as indicated in Table 13.

    METHODS OF RESIDUE ANALYSIS

         Barry et al. (1981) have provided details of GC-MS
    identification and analytical behaviour of pirimiphos-methyl in a
    variety of foods as part of an investigation of unknown residues
    detected in imported foods.

         Zakitis & McCray (1982), having reviewed the analytical
    methodology for residues of pirimiphos-methyl in a variety of
    substrates, concluded that none of the eight known methods met all the
    desired criteria for analysis of residues in water, fish and snails,
    viz. specificity, simplicity of sample preparation and recovery after
    clean-up. Water was simply extracted with hexane prior to
    determination by GC. Fish and snails were extracted with acetone in
    the presence of sufficient anhydrous sodium sulphate to form a dry
    powder. The acetone was filtered and the solids were extracted three
    more times with acetone. The combined, filtered extracts were
    evaporated to low volume before being transferred to de-ionized water
    for extraction with hexane as for analysis of water. Recoveries ranged
    from 93 to 101 percent. The method is being used for environmental
    studies involving the use of pirimiphos-methyl for disease vector
    control. The limit of determination in snails is 0.5 mg/kg. Below this
    concentration, some naturally occurring substance interferes with the
    determination of pirimiphos-methyl. Good recoveries were obtained from
    dechlorinated water at concentrations as low as 0.005 mg/l and in fish
    down to 0.05 mg/kg.


        Table 9.  Pirimiphos-Methyl Residues From Microtomed Sections of Two Cheeses1

                                                                                                                                 

                                                                  Residues (mg/kg)
    Storage                                                                                                                      
    period         End                                         Depth (mm) into cheese
    (days)         sampled   0-1       1-2       2-3       3-4       4-5       5-6       6-7       7-8       8-9       9-10
                                                                                                                                 

                             Cheese in direct contact with treated surface

    31             1         41.15     7.48      4.03      1.73      1.25      0.90      0.65      0.55      0.40      0.10
                   2         27.50     7.70      2.32      1.09      0.71      0.50      0.28      0.20      0.16      -

    49             1         29.57     9.26      2.87      2.04      1.52      1.13      0.82      0.71      0.51      0.27
                   2         23.73     6.54      2.82      2.71      1.52      1.07      0.74      0.55      0.51      0.37

                             Cheese on cloth barrier

    31             1         18.04     3.40      0.65      0.30      0.18      0.08      -         -         -         -
                   2         35.28     11.48     4.19      0.62      0.36      0.27      0.22      0.16      -         -

    49             1         19.58     5.69      1.72      0.72      0.45      0.28      -         -         -         -
                   2         12.26     7.13      1.84      1.11      0.84      0.66      0.46      0.31      -         -
                                                                                                                                 

    1    Dashes indicate that no pirimiphos-methyl was detected.


    Table 10.  Mean1 Pirimiphos-methyl Residues (mg/kg) on Dry and Tough Wheat and Milled Fractions After Storage
               of Treated Wheat

                                                                                                                                              

                                         12% moisture content (dry)                               16% moisture content (tough)
               Storage                                                                                                                            
    Dosage     period       Whole                                                     Whole
    (mg/kg)    (months)     wheat2        Bran           Middling3      Flour         wheat2        Bran           Middling3       Flour
                                                                                                                                              

    4          1            3.290.07     15.660.79     21.441.96     1.940.25     3.240.03     19.811.63     15.350.58      1.570.03
               3            2.980.10     13.930.26     15.101.00     1.930.12     3.040.01     13.450.80     13.510.36      1.160.06
               6            2.540.07     13.160.51     13.801.36     1.560.06     2.260.18     11.980.67     10.680.60      0.810.23

    6          1            4.930.13     20.870.82     23.151.47     2.860.14     4.920.04     27.331.41      21.831.73     1.910.07
               3            4.540.10     20.541.38     19.340.74     2.420.22     4.440.04     20.902.92      17.890.59     1.500.08
               6            3.660.23     19.320.73     16.051.35     2.230.13     3.860.26     18.600.73      16.890.56     1.330.14
                                                                                                                                              

    1    Mean of 3 replicates  SE.
    2    Ground wheat.
    3    Shorts, wheat germ and coarse particles of flour.


    Table 11. Average Pirimiphos-methyl Residue (mg/kg) on Hard Winter Wheat
              and Wheat Fractions Stored up to 12 Months

                                                                                                                       

                                                     Rate of application
                                                                                                                       
                                   7.3 mg/kg                                          14.6 mg/kg
                                                                                                                        
    Storage       Whole                                              Whole
    Period        wheat1       Bran         Shorts       Flour       wheat1       Bran        Shorts       Flour
                                                                                                                       

    24 h          7.15         25.50        18.29        0.83        14.75        50.41       36.01        2.01

    Months

    1             6.88         21.45        17.89        1.38        13.13        41.43       31.01        2.94
    3             6.60         20.11        20.82        1.47        12.98        39.97       42.97        3.15
    6             5.78         18.06        20.46        1.47        11.17        30.52       46.58        2.91
    9             5.43         17.34        17.90        1.17        10.39        34.52       31.47        2.44
    12            5.27         13.47        15.35        1.05        9.72         32.29       26.98        2.14
                                                                                                                       

    1    Before tempering to 15% for milling.
        Table 12. Pirimiphos-methyl residues in imported foods

                                                                     

    Food                  Country of Origin       Residue (mg/kg)
                                                                     

    Chickpeas             Australia               0.07
    Dried green peas      Australia               3.0
    Pigeon peas           Kenya                   0.19
    Moong dall            Tanzania                0.03
    Peanut butter         South Africa            0.23
    Split peas            Kenya                   0.1-0.171
    Sardo cheese          Argentina               0.21-1.41,2
                                                                     

    1    Represents range found in multiple samples of the same 
         commodity.
    2    Determined on fat basis.

        Table 13. Primiphos-methyl Residues Detected in Sweden1

                                                                                               

    Food       Origin     No. of      No. of samples with residues within         Maximum
                          samples     given ranges (mg/kg)                        residue
                          analysed    <0.21     0.21-0.53   0.54-1.05   >1.05     (mg/kg)
                                                                                               

    Mandarin   Import     292         291       1                                 0.21

    Orange     Import     622         621       1                                 0.41

    Pepper     Import     206         201       3           1          1          1.4
    (sweet)

    Tomato     Sweden     205         205
               Import     500         499       1                                 0.30
                                                                                               

    1    Total number of samples analysed:8 654
         Period: 81-01-01 -- 83-04-30
    

         A number of the methods reviewed by Zakitis & McCray (1982) have
    not been considered previously by the Meeting. They are briefly
    mentioned for information.

         A general review of analytical methods was published by Bullock
    (1976) including procedures suitable for animal tissues. There is also
    a TLC-UV method for residues in water, soil and plants (Krasnykh,
    1978), an HPLC method for determining pirimiphos-methyl and five
    metabolites in samples of plasma and urine (Beasley & Lawrence, 1979),
    and gas chromatographic methods for residues in stored grain (Varca 
    et al. 1975), peanuts (Redlinger & Simonaitis 1977) and milled
    fractions of wheat (Mensah et al. 1979). In addition, a 
    gas-chromatographic method has been proposed for the simultaneous
    determination of residues of pirimiphos-methyl and malathion in
    peanuts (Simonaitis et al. 1981), and GC-MS was used to identify
    residues of pirimiphos-methyl in imported foods (Barry et al. 1981).

         The residue in stored grains (barley, maize, oats, rice in husk
    and wheat) consisted mainly of the parent compound. Neither the oxygen
    analogue (O,O-dimethyl-O(2-diethylamino-6-methyl-pirimidine-4yl)
    phosphate), (metabolite III) nor the desethyl analogue 
    (O, O-dimethyl-O(2-ethylamino-6-methyl-pyrimidin-4-yl)
    phosphorothionate), (metabolite II) was detectable. No metabolite was
    detectable in milled products or in white and wholemeal breads. A
    large number of plant samples (leafy vegetables, carrots, celery,
    spring onions, potatoes, sugarbeets, cucumber, tomatoes, peppers,
    mushrooms, lettuce, blackcurrants, apples, pears, plums, lemons,
    oranges, olives) were analysed for residues of pirimiphos-methyl and
    the phosphorous-containing metabolites. However, significant amounts
    of the metabolites did not appear and so were not reported. The
    residues listed in various tables of the 1976 Evaluations are of the
    parent compound only.

         Analyses of wheat grains treated with labelled compounds
    confirmed the low level of both metabolites. No oxygen analogue was
    detected. The level of desethyl analogue was below 0.05 mg/kg over a
    period of 32 weeks, while the parent compound was present at 4 mg/kg.
    The oxygen analogue was not detectable in whole rice seedlings. The
    levels of parent compound in mg/kg and desethyl analogue (expressed as
    parent equivalent) were as follows:

        Compound                 Residue (mg/kg at intervals (days) after treatment

                             1        3       6       8       10       13

    pirimiphos-methyl        0.5      0.51    12      0.6     0.51     0.32
    metabolite (II) and
    unknown compound         0.17     0.11    0.14    0.12    0.15     0.14
    

         The oxygen analogue reached its maximum concentration on plant
    leaves approximately 1 to 3 days after treatment. The ratio of maximum
    levels of oxygen analogue and the parent compound were about 0.3 and 3
    on cotton and citrus leaves, respectively, while the two compounds
    were present in nearly equal concentration on bean leaves. The
    disappearance of pirimiphos-methyl residues was rapid on the leaf
    surfaces of all plants due to evaporation. The total 14C represented
    10-12 percent of the applied material after three days and the
    phosphorous containing metabolites were below 10 percent (Bowker
    1973).


         The Meeting concluded that the metabolites can be excluded from
    the definition of the residue. The MRLs need not be changed because
    the metabolites represent such a minor proportion of the total
    residue. The MRLs refer to the present compound alone.

    APPRAISAL

         Pirimiphos-methyl was evaluated in 1974, 1976, 1977 and 1979 and
    a number of items of information previously requested appear to be
    still outstanding.

         It would appear that there are a number of uses that give rise to
    residues in food moving in international trade, which have not yet
    been considered by the Meeting and about which relevant information
    will be available in 1984.

         An extensive amount of information about the use and fate of
    pirimiphos-methyl when applied after harvest to cereal grains has
    appeared in open scientific literature and this was reviewed by the
    Meeting. The review only serves to confirm the evaluations made
    previously. All authors have drawn attention to the stability of
    pirimiphos-methyl deposits on treated grain and the retention of the
    bulk of the deposit in the seed coat. This is reflected in the low
    transfer of residue into white flour and milled rice and the
    relatively higher residues in wheat bran.

         This review has confirmed that the degradation and metabolism of
    pirimiphos-methyl on grain leads only to the production of 
    2-diethylamino-4-hydroxy-6-methyl pyrimidine. No 
    cholinesterase-inhibiting metabolites occur. However, between 4
    percent and 15 percent of the residue of the parent compound forms a
    complex with the aleurone layer of the grain and resists extraction by
    a variety of solvents. It may be dislodged by digesting the substrate
    with proteolytic enzymes.

         The Meeting, having reviewed all available data, concluded that
    the metabolites can be excluded from the definition of the residue.
    The MRLs, which remain the same, refer to the parent compound alone.


         A further study of the use of pirimiphos-methyl for the control
    of cheese mites in cheese stores confirmed that the MRL previously
    recommended adequately covers the resulting residues.

         Several reviews have been made of analytical methods suitable for
    dealing with various substrates.

         The Meeting considered that the information evaluated in 1983 did
    not indicate any need to amend or modify recommendations previously
    made for MRLs in a range of commodities.

         The Meeting reviewed the requests made by earlier Meetings for
    additional information in the light of knowledge about the current use
    of this insecticide and considered that they had been satisfied.

    FURTHER WORK OR INFORMATION

    Desirable

         Further information about residues in peanuts, oil seeds, lentils
    and citrus.

    REFERENCES - RESIDUES

    Anonymous. Chemical control of stored grain insects 1972. Cyprus
    1972      Agric. Res. Inst. Ann. Rep., p. 69.

    Banks, H.J. & Desmarchelier, J.M. New chemical approaches to pest
    1978      control in stored grain. Chem. Aust. 45(6): 276-281.

    Barry, T.L., Petzinger, G. & Gretch, F.M. GC-MS identification and
    1981      analytical behaviour of pirimiphos-methyl in imported foods.
              Bull. Environ. Contam. Toxicol., 27: 524-528.

    Beasley, C.J. & Lawrence, D.K.: J. Chromatog., 168: 461.
    1979

    Bengston, M., Cooper, L.M. & Grant-Taylor, F.J. A comparison of
    1975      bioresmethrin, chloropyrifos-methyl and pirimiphos-methyl as
              grain protectants against malathion-resistant insects in
              wheat. J. Agric. Anim. Sci., 32: 51-78.

    Bengston, M., Cooper, L.M., Davies, R., Desmarchelier, J., Hart R. &
    1978      Phillips, M. Grain protectants for the control of 
              malathion-resistant insects in stored sorghum. (To be
              submitted for publication).

    Bengston, M., Connell, M.  Davies, R., Desmarchelier, J., Elder, B.,
    1980a     Hart, R., Phillips, M., Ridley, E., Ripp, E., Snelson, J. &
              Sticka, R. Chloropyrifos-methyl plus bioremethrin,
              methacrifos, pirimiphos-methyl plus bioresmethrin and
              synergised bioresmethrin as grain protectants for wheat.
              Pestic. Sci., 11: 61-76.


    Bengston, M., Connell, M., Davies, R., Desmarchelier, J., Phillips,
    1980b     M., Snelson, J. & Sticks, R. Fenitrothion plus phenothrin
              and pirimiphos-methyl plus carbaryl, as grain protectant
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    Bowker, D.M. Pirimiphos-methyl: fate of stored wheat and rice grain in
    1973      the laboratory. Report No. AR2457 AR,submitted to FAO by ICI
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    Bratt, H. & Jones, L.A. Pirimiphos-methyl: Metabolism in rats and
    1973      dogs. Report submitted to FAO by ICI Industrial Hygiene
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    Bullock, D.J.W. Pirimiphos-methyl: Residues in stored grain. Report
    1973      No. AR2472 AR submitted to FAO by ICI Plant Protection Ltd.
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    Bullock, D.J.W. Pirimiphos-methyl: Residues in stored grain, bread,
    1974      flour and milled products. Report submitted to FAO by ICI
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    Bullock, D.J.W. In Analytical Methods for Pesticides and Plant
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    Bullock, D.J.W. & May, M.S. Pirimiphos-methyl: Residue transfer from
    1976      durum wheat to semolina and pasta. Report No. TMJI345A
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    Bullock, D.J.W., Harrison, P.J. & Day, S.R. Degradation of residues in
    1976      flour during baking. Report No. AR2666A submitted to FAO by
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    Cerna, V. & Benes, V. Residues of pirimiphos-methyl in wheat, mill
    1977      products and white bread. Report by Czechoslovakian
              Institute of Hygiene in Epidemiology, Prague.

    Chawla, R.P. & Bindra, O.S. (1971). Residues of some promising grain
    1971      protectants on stored wheat. Proc. Symp. Progress and
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    Curl, E.A. & Leary, J.P. The radioactive residues found in the liver
    1980      and kidney of a goat after administration of a multiple dose
              of pirimiphos-methyl. Report RJO144B submitted to FAO by ICI
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    Desmarchelier, J.M. Selective treatments including combinations of
    1977      pyrethroid and organophosphorus insecticides for control of
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    1978      Sci. 9: 33-38. 

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    1979      in stored grain. Proceedings of the Second International
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              phenothrin, methacrifos and pirimiphos-methyl on rice and
              barley after storage, and losses of these insecticides
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    1980b     Phillips, M., Snelson, J., Sticka, R. & Tucker, K. A
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    1974      wheat and sorghum grain. J. Econ. Entomol., 67(4): 477-478.

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    La Hue, D.W. Pesticide residues of potential protectants of grain.
    1974      Proc. 1st Int. Working Conf. on Stored Product Entomology,
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    La Hue, D.W. Pirimiphos-methyl: Effect on populations of Tribolium
    1977      confusum and T. castaneum in wheat. J. Econ. Entomol.,
              70(1): 135-137.

    La Hue, D.W. & Dicke, E.B. Evaluation of selected insecticides applied
    1976      to high moisture sorghum grain to prevent stored grain
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    Le Berre, R., Escaffre, H., Pendriez, B., Grebaut, S. & Pengalet, P.
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              onchocerciasus in West Africa II. Test by classic
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    Mensah, G.W.K., Watters, F.L. & Webster, G.R.B. Insecticide residues
    1979      in milled fractions of dry or tough wheat treated with
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              Econ. Entomol., 72: 728-731.

    Mills, I.H. Pirimiphos-methyl: Blood concentrations and tissue
    1976      retention in the rat. Report No. CTL/P/247 submitted to FAO
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    Morallo-Rejesus, B. & Carino F.O. The residual toxicity of five
    1976      insecticides on three varieties of corn and sorghum.
              Philipp. Agric., 60(3&4): 96-104.

    Redlinger, L.M. & Simonaitis, R.A. Field tests with pirimiphos-methyl
    1977      as a protectant for farmers stock peanuts. Peanut Sci. 
              4: 27.

    Rishikesh, N., Mathis, H.L., King, J.S. & Nambiar, R.V. A field trial
    1977      of pirimiphos-methyl for the control of Anopheles gambiae
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    Rowlands, D.G. The metabolism of contact insecticides in stored grains
    1975      1970-1974. Residue Rev., 58: 113.

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    Shaw, R.F., Fanara, D.M., Pradhan, G.D., Supratman, Supalin, Bang,
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    Soderstrom, E.L. & Armstrong, J.W. pp-511: (Pirimiphos-methyl-ISO)
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    1983      pirimiphos-methyl. Data submitted to FAO by the Swedish
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    Tempone, M.J. Studies on the effects of insecticides on barley
    1979      malting. Research Project Series No. 50, Victorian
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    Thomas, K.P. & Rowlands, D.G. The uptake and degradation of
    1975      pirimiphos-methyl by Cheshire cheese. J. Stored Prod. Res.,
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    Weaving, A.J.S. Grain protectants for use under tribal storage
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    WHO. Interim specifications for pirimiphos-methyl, technical, water
    1982      dispersible powder and emulsion concentrate VBC/15/82.04.
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    Zakitis, L.H. & McCray, E.M. Gas chromatographic analysis of residues
    1982      of pirimiphos-methyl in water, fish and snails. Bull.
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    See Also:
       Toxicological Abbreviations
       Pirimiphos-methyl (WHO Pesticide Residues Series 4)
       Pirimiphos-methyl (Pesticide residues in food: 1976 evaluations)
       Pirimiphos-methyl (Pesticide residues in food: 1977 evaluations)
       Pirimiphos-methyl (Pesticide residues in food: 1979 evaluations)
       Pirimiphos-methyl (Pesticide residues in food: 1992 evaluations Part II Toxicology)