IPCS INCHEM Home


    CARBARYL      JMPR 1976

    Explanation

         Carbaryl has been evaluated by the Joint Meeting on a number
    of occasions. An acceptable daily intake has been established and
    maximum residue limits for carbaryl residues in many commodities
    have been recommended (FAO/WHO 1965b, 1967b, 1968b, 1969b, 1970b,
    1971b, 1974b, 1976b).

         The Meeting was informed of two important applications for
    carbaryl -

         (a) for the control of cereal leaf beetle, armyworm and
    grasshoppers affecting small grain crops, and

         (b) for post-harvest application for the protection of stored
    grain, particularly for the control of the lesser grain borer,
    Rhyzopertha dominica, when used in conjunction with approved
    organophosphorus grain protectant insecticides.

    Extensive new data on these uses and on the level and fate of
    residues resulting from such applications have been made available
    to the Joint Meeting. These data have been evaluated and the
    following monograph addendum is offered. It should be noted that
    recommendations for a maximum residue limit for carbaryl in raw
    grains were made in 1965 and 1966 by the Joint Meeting. These were
    apparently overlooked when carbaryl was re-evaluated in 1968. In
    the meantime carbaryl has been widely used on grain crops against
    a wide variety of insect pests.

    RESIDUES IN FOOD AND THEIR EVALUATION

    USE PATTERN

    Pre-harvest

         Cereal leaf beetle, armyworm, grasshoppers and locusts are
    typical of many insect pests which often appear in plague numbers
    and attack small grain crops such as wheat, oats, barley and rye
    and inflict extensive damage. Carbaryl-based insecticides have
    proved effective against all of the above pests in the larval
    (nymph) and adult form. The rate of application ranges from 0.5 to
    2 kg/ha depending upon the degree of infestation, density of
    foliage and whether or not the pests are in advanced stages of
    their life cycle.

         The usual commercial formulation used for these purposes
    include wettable powders and suspensions. Two or more applications
    may be required but usually it is not necessary to apply carbaryl
    sprays to small grain crops within 21 days of harvest.

         Extensive documentation on these uses and on the performance
    of carbaryl against the major pest species has been provided by
    Union Carbide (1976a).

    Post-harvest

         Since the early 1960s malathion has been the main means of
    protecting stored grain against the wide spectrum of insect pests
    attacking a variety of stored grain in Australia, Argentina, South
    Africa and many other countries. Recently, several strains of
    insect pests have developed resistance to malathion, in particular
    the lesser grain borer Rhyzopertha dominica, which is most
    destructive, and the rust red flour beetle Tribolium castaneum,
    which is most prevalent.

         Recently, several candidate insecticides have been evaluated
    as grain protectants in laboratory and field trials set up by the
    Australian Wheat Board (Bengston et al, 1975, 1976a, 1976b).
    However, no single chemical gave satisfactory control of all the
    common pest strains screened. Among the grain protectant
    insecticides found to be most valuable were pirimiphos-methyl,
    fenitrothion and chlorpyrifos-methyl. Although these compounds
    controlled most common strains including those resistant to
    malathion, all failed to control Rhyzopertha dominica. The
    synthetic pyrethroid bioresmethrin, however, was shown to be
    specifically effective against Rhyzopertha dominica at economic
    rates. Several mixtures of bioresmethrin with organophosphorus
    insecticides were successfully evaluated, Currently, bioresmethrin
    is recommended for use at a concentration of 1-2 mg/kg in admixture
    with malathion, pirimiphos-methyl and fenitrothion. However, the
    widespread use of bioresmethrin raises several problems including
    cost, the possibility of resistance developing and limitations in
    world production and supply. Consequently, there is a need for an
    alternative to bioresmethrin. One alternative is carbaryl.

         Extensive trials carried out in the U.S.A., South Africa,
    England, the Philippines, Argentina, Brazil and Uruguay in 1963-64
    showed carbaryl to be effective against a wide spectrum of stored
    product pests but a number were sufficiently tolerant to require
    unacceptably high concentrations for adequate control. (Union
    Carbide, 1976a). It was shown by Roan (1964) and Strong and Sbur
    (1961) that formulation was highly critical in obtaining the
    desired effect against stored product pests.

         Extensive work carried out in Australia in 1963, 1965 and 1967
    (Greening, 1976) showed that carbaryl effectively controlled
    Rhyzopertha dominica at concentrations as low as 1 mg/kg in
    laboratory trials and at 10 mg/kg in field trials.

         Carbaryl has a number of distinct advantages for use in
    combination with organophosphorus grain protectant insecticides. It
    is cheap; it is readily available; it has been widely used and


    evaluated as a general insecticide for more than 10 years; it is 
    in a different class of compounds from organophosphorus or pyrethroid
    grain protectants, which reduces the possibility of resistance
    developing.

         Extensive studies carried out in Australia have clearly
    demonstrated the advantage of carbaryl for the control of
    Rhyzopertha dominica (Davies, 1976a, 1976b; Desmarchelier,
    1976a, 1976b, 1976c; Bengston, et al, 1976b).

         Desmarchelier showed that carbaryl applied to wheat at rates
    ranging from 3-6 mg/kg and held at 25C gave 100% control of adult
    Rhyzopertha dominica and prevented reproduction of this species
    for more than 6 months. Although ineffective against other species
    at this concentration, the addition of normal rates of other
    organophosphorus insecticides produced complete control of all
    species for more than 6 months. Davies (1976) reports equally
    impressive results for periods of at least 31 weeks after
    treatment.

         Commercially acceptable control of all major stored product
    pests and complete protection of stored grains can be obtained by
    the use of combinations of approved organophosphorus insecticides
    to which carbaryl is added at rates equivalent to 5 mg/kg of
    treated grain.

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Pre-harvest

         When carbaryl tolerances were first established on crops,
    knowledge of the composition of the residue in or on plants was
    limited and data for the parent compound and its hydrolytic
    product, 1-naphthol, were considered adequate to define the total
    toxic residue for carbaryl.

         Continued study of the fate of carbaryl over the succeeding
    years has shown that the small amount of carbaryl residue which
    enters the plant undergoes biotransformation into a variety of
    products. Residue data are therefore presented for free carbaryl,
    conjugated carbaryl and conjugated methylol carbaryl. These three
    compounds represent the major portion of the total residue.

         The residue data on small grains presented in this monograph
    are of two types. Those obtained prior to 1972 are for free
    carbaryl, conjugated carbaryl, conjugated methylol carbaryl and
    conjugated naphthol. The latter data reflect continued study of the
    nature of the residue and the development of new analytical
    techniques or the determination of additional constituents of it.
    The pre-1972 studies are of value in comparing the results for the
    free parent compound with those for the same compound in the later
    studies since free carbaryl is determined separately in both cases.

    The pre-1972 studies are additionally valuable for forage since the
    recent studies have shown carbaryl to constitute all but a small
    fraction of the total residue.

         Table 1, taken from studies by Conterio (1969), shows
    generally low residues of free carbaryl in barley and wheat grain
    (1.7 mg/kg or less), even after four and five applications of an
    exaggerated 2 kg/ha treatment with samples taken immediately after
    treatment. The grain residues show a drop to barely detectable
    levels (0.06 mg/kg or less) and 35 days after treatment.

        TABLE 1. Carbaryl residues in barley and wheat grain, mill fractions and forage
               (W.A. Conterio, Illinois, 1968-1969)
                                                                                    
                           Interval
    Treatment              after last
              Rate         application,   Free carbaryl residues, mg/kg, in          
    No        kg a.i./ha   days           grain   flour   shorts   red dog    hulls
                                                                                    
    Barley

    1         1.1          35             0.06    0.05    0.05     0.04       0.06
    4         2.2          0              1.0     0.11    0.35     0.24       0.45

    Wheat

    1         2.2          30             0.03    0.15    0.11     -          0.11
    5         2.2          0              1.7     0.10    0.19     -          0.50

                                                          Straw                     
    5         1.1          0              0.98            0.41
    4         1.1          9              0.10            0.19
    3         1.1          16             0.10            0.11
    2         1.1          23             0.53            0.15
    1         1.1          30             0.03            0.10
    5         2.2          0              1.7             35
    4         2.2          9              0.06            2.0
    3         2.2          16             0.12            0.10
    2         2.2          23             0.03            0.08
    1         2.2          30             0.03            0.09
                                                                                    
    
         Table 2, taken from studies by Phillips (1972) presents data for
    barley heads and grain. The total residues (carbaryl and metabolites
    on the grain at harvest range up to 2.7 mg/kg, this value being from
    two applications of 1.1 kg/ha, with samples taken 48 days after the
    last application.

         Table 3 presents residue data from wheat and barley forage which
    are of value in determining the amount of total residue which may be
    present on the plant portions consumed by livestock. The data in Table
    3 show that free carbaryl is by far the predominant constituent of the
    forage residue. Conjugated carbaryl is usually the next most prominent
    component but is only a small fraction of the free carbaryl residue at
    any given sampling interval except when total residues are very low.
    The maximum free carbaryl residue in wheat forage is 44 mg/kg
    immediately after an application of 3.4 kg/ha, an exaggerated rate and
    in barley it is 77 mg/kg immediately after the second of two 1.7 kg/ha
    applications. The conjugated carbaryl residues show a maximum of 1.5
    mg/kg. There is rapid attenuation of the total deposit.

         Table 4 presents data for residues in wheat and barley grain and
    mill fractions. They reflect both recommended and exaggerated
    application rates. Total carbaryl residues in grain are lower than in
    barley (0.36 - 2.7 mg/kg) in wheat (0.08 - 0.24 mg/kg).

    Post-harvest

         From extensive laboratory trials in Australia Davies (1976a)
    measured the decline of active carbaryl residues on wheat by bio-assay
    using Rhyzopertha dominica. From his data illustrated in Figure 1,
    Davies calculated the approximate biological half-life of carbaryl in
    wheat treated with 5 mg/kg to be 40 weeks at 35C, 60 weeks at 30C,
    80 weeks at 25C and much longer than 80 weeks at 20C.

         Table 5 indicates the fate of carbaryl applied alone or in
    combination with pirimiphos-methyl to wheat held in the laboratory in
    sealed bins at approximately 25C and determined by GLC analysis of
    samples drawn at intervals over a 39-week storage period
    (Desmarchelier, 1976b).

         Degradation was more rapid in field trials. Desmarchelier (1976b)
    reported on the recovery of carbaryl from bulk wheat of 12.5% moisture
    held in silos over a 26-week period at different temperature ranges.
    In one silo the average level fell from 4.8 to 2.4 mg/kg at 30-22C
    and in another from 9.0 to 5.8 mg/kg at 27-13C.

         Desmarchelier (1976c) reports substantially similar stability for
    carbaryl applied to oats (12% moisture), malting barley (13%
    moisture), paddy rice (13% moisture), brown rice (12.5% moisture) and
    white rice (12-7% moisture) when stored at 25C. In other words, a
    reduction to approximately half the original concentration after some
    6 months of storage.


    
    TABLE 2. Carbaryl residues in barley heads, grain and forage (I.L. Phillips and
             R.O. Leininger, California, 1971-1972)

                                                                                                

                                                          Carbaryl residues, mg/kg
                        Days                                                                    
         Treatment      after                                              Conjugated
         Rate,          last          Free       Conjugated   Conjugated   Methylol      Total
    No.  kg. a.i./ha    application   Carbaryl   Carbaryl     Naphthol     Carbaryl      Residue
                                                                                                

                                      Heads and Grain
    1    1.1            7             1.5        0.31         0.06         0.05          1.9
                        14            0.66       0.17         0.06         0.07          1.0
                        21            1.0        0.18         0.10         0.11          1.4
                        48*           0.28       0.56         0.14         0.12          1.1

    2    1.1            7             3.6        0.31         0.07         0.08          4.1
                        14            5.6        0.34         0.20         0.35          6.5
                        21            3.3        0.59         0.37         0.42          4.7
                        48*           0.82       1.5          0.20         0.20          2.7

    1    1.7            58*           0.18       0.33         0.84         0.09          1.4
                                                                                                

    *Grain at harvest.

    TABLE 3. Carbaryl residues in wheat and barley forage

                                                                                                                           
                                                         Carbaryl residues, mg/kg                                          
    Crop,               Treatment         Days                                                      Conjugated
    location                 Rate,        after last     Free        Conjugated     Conjugated      Methylol        Total
    (Reference)         No.  kg a.i./ha   application    Carbaryl    Carbaryl       Naphthol        Carbaryl        Residue
                                                                                                                           

    Wheat,              1    1.7          0              29.9        1.2            0.06            0.04            31.2
    California                            7              25.6        1.5            0.13            0.35            27.6
    (Leininger, 1972)                     14             12.1        1.2            0.07            0.17            13.5
                                          58             5.5         1.0            0.18            0.37            7.1

    Wheat,              2    1.7          0              0.44        0.02           0.04            0.05            0.6
    Illinois                              7              0.21        0.05           0.05            0.02            0.3
    (Conterio, 1972)                      14             0.09        0.03           0.04            0.05            0.2
                                          24             0.06        0.01           0.04            0.03            0.1

                        2    1.7          0              0.96        0.14           0.05            0.02            1.2
                                          3              0.18        0.04           0.04            0.03            0.3
                                          7              1.4         0.25           0.06            0.04            1.8
                                          14             0.16        0.05           0.09            0.02            0.3
                                          24             0.06        0.01           0.04            0.03            0.1

                        2    1.7          0              20.2        0.45           0.05            0.06            20.8
                                          3              11.8        0.29           0.07            0.07            12.2
                                          7              11.5        0.17           0.09            0.03            11.8
                                          14             1.5         0.27           0.08            0.09            1.9
                                          24             0.59        0.22           0.14            0.06            1.0

    Wheat               1    1.7          0              32.9        0.54           0.12            0.17            33.7
    California                            3              12.9        0.39           0.12            0.29            13.7
    (Leininger, 1973)                     7              15.2        0.47           0.13            0.43            16.2
                                          14             10.1        0.37           0.24            0.46            11.2
                                          21             8.8         0.32           0.17            0.46            9.8

                        1    3.4          0              43.6        1.5            0.10            0.20            45.4
                                          3              34.1        1.1            0.16            0.39            35.8
                                          7              28.0        0.82           0.18            0.48            29.5

    TABLE 3. (Cont'd.)

                                                                                                                           
                                                         Carbaryl residues, mg/kg                                          
    Crop,               Treatment         Days                                                      Conjugated
    location                 Rate,        after last     Free        Conjugated     Conjugated      Methylol        Total
    (Reference)         No.  kg a.i./ha   application    Carbaryl    Carbaryl       Naphthol        Carbaryl        Residue
                                                                                                                           

                                          14             18.8        0.52           0.13            0.53            20.0
                                          21             18.4        0.63           0.16            0.67            19.9

    Wheat,              1    3.4          1              12.8        0.50           0.14            0.06            13.5
    Minnesota                             3              5.9         0.73           0.06            0.08            6.8
    (Ruppel, 1974)                        14             0.76        0.31           0.08            0.14            1.3
                                          28             0.12        0.11           0.05            0.12            0.4

    South Dakota        1    3.4          1              45.3        1.2            0.05            0.05            46.4
    (Kantack, 1974)                       7              8.5         0.70           0.07            0.17            9.4
                                          14             0.51        0.24           0.18            0.12            1.1
                                          21             0.19        0.09           0.07            0.08            0.4
                                          35             0.15        0.15           0.08            0.13            0.5

    Barley
    Illinois
    (Conterio, 1972)    2    1.7          0              76.5        0.23           0.03            0.03            76.8
                                          7              31.6        0.10           0.06            0.03            31.8
                                          14             0.24        0.10           0.08            0.02            0.4

    California          1    1.7          0              47.0        0.57           0.08            0.15            47.8
    (Phillips and                         7              33.0        0.75           0.37            1.2             35.3
    Leininger, 1971,                      14             15.1        0.24           0.27            0.88            16.5
    1972)
                                                                                                                           

    TABLE 4. Carbaryl residues in wheat and barley grain and mill fractions at harvest
                                                                                                                           

                     Application                                     Carbaryl residues, mg/kg
                     rate, kg a.i./ha                                                                                      
    Crop,            (days                                                                          Conjugated
    location         after last           Mill         Free          Conjugated     Conjugated      Methylol        Total
    (reference)      application)         Fraction     Carbaryl      Carbaryl       Naphthol        Carbaryl        Residue
                                                                                                                           

    Wheat            1.7                  grain        0.08          0.03           0.03            0.03            0.17
    California       (58)                 bran         0.05          0.06           0.09            0.05            0.25
    (Leininger,                           flour        0.03          0.07           0.03            0.01            0.14
    1972)
    Minnesota        3.4                  grain        0.01          0.02           0.04            0.01            0.08
    (Ruppel,         (36)                 bran         0.02          0.17           0.02            0.03            0.24
    1974)                                 flour        0.04          0.04           0.04            0.01            0.17

    South Dakota     3.4                  grain        0.12          0.05           0.04            0.03            0.24
    (Kantack,        (35)                 bran         0.08          0.10           0.11            0.06            0.35
    1974)                                 flour        0.06          0.05           0.04            0.02            0.17

    Illinois         2 x 1.7              bran         0.02          0.06           0.04            0.03            0.15
    (Conterio,                            flour        0.02          0.02           0.01            0.02            0.07
    1972)

    Barley,          1.1                  grain        0.28          0.56           0.14            0.12            1.1
    California       (48)                 hulls        0.18          2.2            0.51            0.36            3.3
    (Phillips,                            flour        0.26          0.28           0.11            0.15            0.8
    1971)
                     2 x 1.1              grain        0.82          1.5            0.20            0.20            2.7
                     (48)                 hulls        0.31          12.0           1.4             0.43            14.1
                                          flour        0.17          0.75           0.22            0.24            1.4

    California       1.7                  grain        0.27          0.32           0.08            0.07            0.74
    (Leininger,      (58)                 hulls        0.12          1.9            0.17            0.19            2.4
    1972)                                 flour        0.06          0.06           0.04            0.02            0.18

    Illinois         2 x 1.7              grain        0.18          0.06           0.08            0.04            0.36
    (Conterio,       (24)                 hulls        0.07          0.26           0.14            0.04            0.51
    1972)                                 flour        0.04          0.07           0.05            0.03            0.19
                                                                                                                           

    

    FIGURE 1

    
    TABLE 5. Residues in wheat after laboratory application of carbaryl and/or
              pirimiphos-methyl

                                                                                     
                                    Residues recovered by GLC analysis,
                     Calculated                        mg/kg
                     rate                                                            
    Treatment        mg/kg          Day 1    Week 9    Week 18    Week 26    Week 39
                                                                                     

    Carbaryl         5              3.1      2.8       -          -          1.9

    Carbaryl         10             6.5      9.8       5.0        4.3        4.2

    Pirimiphos-
    methyl           6              5.1      -         -          -          3.1

    Pirimiphos-
    methyl           6              4.2      -         -          -          2.3
    +                +
    Carbaryl         5              3.4      3.1       -          -          2.5

    Pirimiphos-
    methyl           6              1.8      -         -          -          1.1
    +
    Carbaryl         10             5.7      5.4       5.0        4.5        4.6

                                                                                     

    
    FATE OF RESIDUES

    In animals

         Ingested carbaryl is rapidly metabolised in cows and other
    animals, 70-80% being excreted in urine within 24 hours. In a
    continuous feeding study in cows, equilibration of total radioactive
    residues in milk, urine and faeces occurred by the second day. Within
    18 hours after the last of 14 days continuous feeding, the highest
    total of residues were found in the kidneys. These data are summarised
    in Table 6. The lowest residues were found in fat, indicating that
    metabolites are not stored in body tissues. The major components of
    the residue in tissue were carbaryl, naphthol, naphthyl sulphate,
    5,6-dihydrodihydroxycarbaryl and 5,6-dihydrodihydroxynaphthol. Methods
    are available to determine these compounds in beef kidney and liver.
    Of the radioactivity appearing in the milk, carbaryl per se comprised
    less than 10%. The two principal residues were
    5,6-dihydrodihydroxycarbaryl and conjugated
    5-methoxy-6-hydroxycarbaryl. An analytical method is available to
    measure the major metabolites in milk. The concentration of the total

    radioactive residue in the milk was only about 1/300, and in the
    tissues 1/100 or less of the carbaryl concentration in the feed. These
    ratios and the composition of the metabolites in the milk did not vary
    significantly over the three feeding levels studied (Dorough, 1974;
    Union Carbide Corporation, 1974).

    TABLE 6. Residues in meat and milk from carbaryl in feed.

                                                             

                   Total 14C expressed as carbaryl (mg/kg) at
                   indicated feeding levels (ppm)
                                                             

    Tissue,
    etc.           10 ppm          30 ppm          100 ppm
                                                             

    Kidney         0.095           0.531           1.003

    Liver          0.033           0.100           0.411

    Milk           0.024           0.071           0.278

    fat            0.000           0.015           0.025
                                                             

         Ingested carbaryl is also rapidly metabolised in poultry by
    pathways similar to those in mammals. In continuous feeding studies
    with radio-labelled carbaryl (Andrawes et al, 1972), residues reached
    maximum levels within one day in the excrement, 2 days in egg white
    and 6-8 days in egg yolk. The residues in the whole egg (yolk plus
    white) were directly proportional to the amount of carbaryl fed. An
    intake of 7 mg/kg of carbaryl in the feed resulted in a residue of
    0.04 mg/kg carbaryl equivalents in the whole egg. Radio-labelled
    residues in the excrement 15 hours after the initial treatment reached
    80-100% of the dose. Within one day after the discontinuation of
    dosing, the highest tissue residues were found in the excretory organs
    while very low residues were found in the fat indicating that carbaryl
    residues are not stored in body tissues. This work shows that carbaryl
    is metabolised in laying hens by pathways similar to those in mammals.

    In plants

         Of the carbaryl deposited on plant surfaces, only the relatively
    small proportion which penetrates the plant tissues is metabolised.
    Once in the plant, the insecticide is largely transformed by
    hydrolysis or oxidation to several hydroxylated metabolites. These
    compounds in turn are rapidly conjugated to form watersoluble
    glycosides. The metabolic transformations which take place are similar
    whether the compound is applied by surface application, root

    absorption or artificially by stem injections. In general, all plant
    and animal metabolites of carbaryl are considered to be less toxic
    than the parent compound, some substantially so.

         The metabolites found in greatest abundance in plants and those
    judged of most toxicological significance are conjugated 1-naphthol,
    conjugated methylol carbaryl, and carbaryl per se. The latter is found
    in both the free state and/or conjugated with plant constituents. The
    residue methods available are capable of releasing the metabolites
    from their conjugates and determining their concentration either
    individually or collectively. The remaining metabolites are of either
    no toxicological or no quantitative significance.

    TABLE 7. Effect of milling and baking on carbaryl residues in wheat

                                                                        

                                              Location          Location
                                                 N                 B
                                                                        
    

    Carbaryl applied, mg/kg                   5                 10
    Carbaryl recovered, day 1, mg/kg          3.4               6.5

    Wheat withdrawn after                     19 weeks          13 weeks

    Residues in wheat, mg/kg                  3.1               6.0

    Residues in mill fractions, mg/kg
      wholemeal flour                         1.2               2.6
      wholemeal bread                         0.7               1.5
      bran                                    7.0               14
      shorts                                  1.5               3
      white flour                             0.07              0.15
      white bread                             <0.05             0.08

    Reduction in residues, %

      wheat/wholemeal bread                   77                75
      wholemeal flour/wholemeal bread         42                42
      wheat/white flour                       97                97
      white flour/white bread                 50                50
      wheat/white bread                       98                99
                                                                        

    In processing and cooking

         A number of studies are available to show the distribution and
    fate of carbaryl residues on various grains, milling fractions of
    grains and prepared cereals subjected to cooking.

         Table 1 indicates the distribution of free carbaryl residues and
    Table 4 the distribution of carbaryl and its metabolites, in grain and
    milling fractions of barley and wheat following the pre-harvest
    application of carbaryl. Again these results show that free carbaryl
    and conjugated carbaryl together represent the major proportion of the
    residues. These data indicate that residues resulting from pre-harvest
    application are substantially confined to the outer portion of the
    grain and therefore do not find their way into flour. There is a
    significant partitioning of the residues in the milling offals.

         Desmarchelier (1976b) showed that wheat treated with carbaryl 3-5
    months previously but still containing residues of 3-6 mg/kg carbaryl
    when converted into wholemeal flour, yielded a flour containing 1-3
    mg/kg of carbaryl. When the same grain was milled for the preparation
    of white flour (approximately 70% extraction), the residue level in
    flour was reduced to about 0.1 mg/kg. The baking of wholemeal or white
    bread resulted in a further loss of about half the carbaryl content,
    bringing the final residue in wholemeal bread into the range of 1
    mg/kg, and in white bread to below 0.1 mg/kg. Thus the reduction in
    residues between raw grain and white bread was 99%, and between grain
    and wholemeal bread about 75% (Table 7). Using other wheat containing
    carbaryl, residues in the range 2.5-3 mg/kg, Desmarchelier (1976b)
    showed that the final residue in white bread was less than 0.05 mg/kg
    and in wholemeal bread 0.5 mg/kg.

         In a series of experiments representing the most primitive type
    of processing to which husked rice, polished rice, oats and barley
    would be subjected, Desmarchelier (1976c) showed that simple boiling
    in minimal amounts of water for 15 minutes reduced carbaryl residues
    in husked rice, polished rice and oats by 84%. A primitive malting
    procedure reduced residues in barley by 77% (Table 8).

    METHODS OF RESIDUE ANALYSIS

         Methods of residue analysis have been dealt with at length in
    previous monographs. A number of modifications were developed to
    obtain the data on grain, forage and milling offals as well as beef
    tissues and milk. References to these methods were provided by Union
    Carbide Ltd. The method of Holden (1973) is widely used for the
    determination of carbaryl residues on a number of commodities.

         Desmarchelier (1976e) using the principles discovered by Pschorr
    and Sumuleanu (1899) and Lumiere et al (1906) and further developed by
    Chattaway (1931) has developed a method for the esterification of
    phenols, at residue levels, in dilute aqueous base. The method is
    based on a procedure for the acetylation of amines by reaction with
    anhydrides in aqueous solution which is successful because amines
    react with certain anhydrides more quickly than the anhydrides are
    hydrolyzed. Chattaway's work extended this reaction to phenols, by
    reacting them at 0C in dilute sodium hydroxide with acetic anhydride.
    Acetylation was quantitative and instantaneous. By using Chattaway's
    procedure and either acetic or propionic anhydride as reagents,


    
    TABLE 8. Effect of storage at 25C, processing and cooking on carbaryl residues in treated grains

                                                                                                                             

                                               Residue, mg/kg,
                                 Application   after storage for     Processed                     Residue, mg/kg
                     Moisture    rate          3        6            after         Processed       after cooking for
    Grain            %           mg/kg         months   months       (months)      into            -         15 min    25 min
                                                                                                                             

    Barley           13          10.6          6.5      3.5          3             Primitive       1.5
                                                                                   malt

                                                                     6             Commercial      0.2
                                                                                   malt

    Oats             12          10.0          7.5      3.5          3             Rolled          -         1.2
                                                                                   oats

    Rice in husk     13          10.0          7.5      3.5          6             Husked          0.4       0.2

                                                                     6             Milled          0.07                <0.05

    Husked rice      12.5        10.0          7.5      3.4          3             Cooked                    1.2

                                                                     6             Cooked                              0.7

    Polished rice    12.7        10.0          7.5      3.5          3             Cooked                    1.2

    Wheat            12          10.0          7.2      6.3          5             wholemeal       2.5                 1.5
                                                        (4.2 after
                                                        storage for
                                                        9 months)
                                                                                                                             

    

    Desmarchelier (1976d) esterified the phenols from parathion,
    fenitrothion, chlorpyrifos, fenchlorphos, cyanophos and carbaryl.

         To test the procedure for determining carbaryl in grain,
    Desmarchelier extracted 10 g of wheat with 25 ml of acetone for 24
    hours. An aliquot of 1 ml was hydrolysed with 1 ml of 1 M sodium
    hydroxide in 90% ethanol (one hour at ambient temperature) and mixture
    diluted and washed with ether. The aqueous solution was adjusted to pH
    10 and stirred at 0C with 2 x 20 ml of 1% chloracetic anhydride in
    ether. The organic extracts were diluted, dried and analysed by gas
    chromatography on 5% SE-30 Chromosorb W at 175C with electron capture
    detection. Recoveries were better than 90% at residue levels in the
    range 0.1-5 mg/kg. This procedure was used for developing much of the
    data on the level of carbaryl residues on grain and milling fractions
    following post-harvest use of carbaryl as a grain protectant.

         Desmarchelier (1976d) evaluated two TLC procedures with
    fluorescent layers suitable for estimating carbaryl residues on grain.
    One used aluminium oxide developed with 15% ethyl acetate/85% hexane,
    and the other polyamide developed with 50% methanol/50% water.
    Carbaryl was detected by hydrolysing with 1 M sodium hydroxide in 90%
    ethanol. 1-naphthol shows as a blue colour at 254 nm with a detection
    limit of 0.1 g.

         The method outlined in "Official Methods of Analysis", of the
    Association of Official Analytical Chemists, 11th Edition (1970),
    Section 29.071. for the use of chromogenic reagent is both more
    precise and more sensitive when using the polyamide system. 0.05-0.1
    microgram can be readily detected. Desmarchelier (1976d) indicated
    that similar results were obtained on aged residues of carbaryl on
    wheat. Acetone proved the most suitable solvent, giving good
    resolution free of interference from water. Although the GLC procedure
    described above is more precise and more sensitive, the TLC procedure
    is simpler and requires less expensive equipment.

         A paper on the significance of pesticide residues which discussed
    the importance and variability of analytical procedures applied for
    the determination of residues on raw grains, was presented at the
    International Working Conference on Stored Product Entomology (Snelson
    and Desmarchelier, 1975).

    NATIONAL TOLERANCES

         References to the following national tolerances for carbaryl
    residues in raw grain were reported to the Meeting.

    TABLE 9. National tolerances for carbaryl on grains reported to the
             Meeting

                                                   Tolerance
    Country        Grain                              mg/kg

    Argentina      barley grains, oats, rye, wheat    0
                   rice                               2

    Australia      rice                               3

    Belgium        raw rice                           0.8

    Canada         barley, oats, rye, wheat           2

    Germany        rice                               0.8

    India          rice                               1.25

    Israel         rice                               2.5

    Japan          rice (unpolished)                  0.1

    Netherlands    rice (coarse)                      0.8

    South Africa   all food products                  10

    Switzerland    rice                               2.5

    U.S.A.         grains of barley, oats, rye, wheat 0
                   rice                               1

    U.S.S.R.       maize                              not permitted

    APPRAISAL

         Following the evaluation of carbaryl by the Joint Meeting on a
    number of occasions (FAO/WHO, 1965b, 1967b, 1968b, 1969b, 1970b,
    1971b, 1974b, 1976b) the Meeting was informed of two important
    applications for carbaryl:

         (a)  the control of pests of small grain crops previously
    controlled with organochlorine or organophosphorus compounds, and 

         (b)  the protection of stored grain, particularly for the control
    of lesser grain borer, Rhyzopertha dominica, when used in
    conjunction with approved organophosphorus insecticides.

         Extensive new data on these uses and the level and fate of
    residues resulting from such applications, have been made available to
    the Joint Meeting.

         For pre-harvest use the rate of application ranges from 0.5 to 2
    kg/ha depending upon the degree of infestation, density of foliage and
    whether or not the pests are in advanced stages of their life cycle.
    For post-harvest use the rate of application depends upon the humidity
    and temperature of the grain, whether high temperatures will be
    maintained during storage, whether the grain will be aerated, and the
    expected period in storage. Treatment is usually at the rate of 5
    mg/kg but hotter grain kept in unaerated storage for long periods will
    require a higher rate of application or repeated treatment.

         Extensive studies in the U.S.A. indicate that when carbaryl is
    used for the pre-harvest control of major pests of small grain crops,
    residues of carbaryl and its more important metabolites in the grain
    will usually range between 1 and 3 mg/kg, though some data indicate
    the likelihood of residues reaching the vicinity of 4 mg/kg, when the
    pre-harvest interval is 21 days. In the case of treatments made 14 to
    7 days prior to harvest, the residues may be significantly higher but
    it is generally considered that such treatments would seldom be
    necessary.

         Such spray treatments give rise to residues on the forage of
    grain crops ranging up to 50 mg/kg on the day following application.
    However, the loss of residues from the forage is rapid so that 21 days
    later they seldom exceed 1 mg/kg.

         Extensive studies on stored wheat and confirmatory data from
    trials on barley, oats and rice indicate that carbaryl residues on
    grain are relatively stable having a half-life between 26 and 80
    weeks, depending upon the temperature.

         Studies with radio-labelled carbaryl indicate that only a
    relatively small proportion of the amount applied penetrates the plant
    tissue where it may be metabolised. The nature and extent of the
    metabolism is well documented.

         A number of studies are available to show the distribution and
    fate of carbaryl residues on various grains and milling fractions of
    grains and prepared cereals subjected to cooking. Carbaryl residues
    are not completely destroyed when prepared cereals are cooked but the
    loss ranges from 75 to 99%, depending upon the cereal, the processing
    and the cooking. The least loss occurs in the preparation of wholemeal
    bread where a residue of the order of 1-1.5 mg/kg could remain in the
    finished bread.

         No residue data are presented for rye but, because of the close
    similarity in physical composition and use of the two crops, the
    residue data for wheat and its milled fractions can be translated to
    rye and its milled fractions.

         A number of national governments have already established maximum
    residue limits for carbaryl on raw grains. The Joint Meeting has
    previously recommended a limit of 3 mg/kg for rice (FAO/WHO 1968b) and
    10 mg/kg for sorghum (FAO/WHO 1974b).

         Extensive data are available to indicate the fate of such
    residues on grain or forage when fed to livestock or poultry. These
    indicate that the feeding of forage from treated small grain crops or
    of mill offals from such grain or grain treated post-harvest, could
    give rise to small but significant residues in animal tissues and
    milk. The magnitude of such residues is not likely to be higher than
    that arising from the feeding of other forage for which a limit of 100
    mg/kg has been recommended. For this reason the limits for carbaryl
    residues in meat, milk and eggs expressed as the parent compound are
    confirmed.

         In 1973 the Meeting advised that the AOAC colorimetric method
    (Holden 1973) remained the method of choice for regulatory purposes.
    This method only determines the carbaryl parent and the free 1-
    naphthol.

         The Meeting studied the recommendations made in 1973 and all data
    available and came to the conclusion that the residues determined in
    the supervised trials represented the carbaryl parent and that the
    maximum residue limits were intended to represent only the sum of
    carbaryl and 1-naphthol not withstanding the fact that the heading of
    the list of recommendations for maximum residue limits indicates that
    the limits are expressed in terms of carbaryl and metabolites.

    RECOMMENDATIONS

         The following maximum residue limits are recommended to cover
    residues resulting from either pre-harvest or post-harvest use of
    carbaryl. They refer to carbaryl only. The limit for rice is raised to
    provide for postharvest application.

    Commodity                                  Limit (mg/kg)

    Bran                                         20

    Barley, oats, rice (in husk and hulled)
    rye, wheat                                   5

    wholemeal flour                              2

    Wheat flour (white)                          0.2

    (The level and fate of carbaryl residues in processed cereal products
    is given in the monograph but, in keeping with accepted practice,
    separate limits have not been proposed for such processed foods.)

    FURTHER WORK OR INFORMATION

    DESIRABLE

    1.   Further studies to elucidate the effects of carbaryl on renal
         function.

    2.   Further studies to resolve the differences in observations of
         different investigators on reproductive physiology, especially
         with regard to neuroendocrine and behavioural changes.

    3.   Details of analytical methods for use in the determination of
         carbaryl and metabolite residues in raw grain, milled cereal
         fractions, bread, meat and milk.

    REFERENCES

    Andrawes, N.R., Chancey, E.L., Crabtree, R.J., Herrett, R. A.
    1972                and Weiden, M.H.J. Fate of Maphthyl-1-14C
                        Carbaryl in laying chickens. J. agr. Food Chem.,
                        20:608.

    Argauer, R.J. J.agr. Food Chem., 17: 889
    1969

    Association of Official Analytical Chemists, "Official Methods of
    1970                Analysis", 11th Ed., p.

    Bengston, M., Cooper, L.M., and Grant-Taylor, F.J. A comparison
    1975                of bioresmethrin, chlorpyrifosmethyl and
                        pirimiphos-methyl as grain protectants against
                        malathion resistant insects in wheat. Queensland
                        J. agr. Animal Sci., 32,(1): 51-78.

    Bengston, M., Connell, M., Crook, I.D., Desmarchelier, J., Hart,
    1976a               R.J., Phillips, M., Snelson, J.T. and Sticka, R.
                        Field trials to compare CGA-20168 (methacriphos),
                        chlorpyrifos-methyl, fenitrothion,
                        pirimiphos-methyl and malathion for control of
                        malathion resistant insects infesting wheat in
                        Australia. Submitted for publication in J. Stored
                        Prod. Res. 1976.

    Bengston, M., Connell, M., Desmarchelier, J., Phillips, Snelson,
    1976b               J.T., and Sticka, R. Report of study of new grain
                        protectant insecticides. Report to Australian
                        Wheat Board. June 1976.

    Chattaway, F.D. J. Chem. Sox. 2495
    1931

    Conterio, W.A. Carbaryl residues in barley and wheat grain,
    1969                mill fractions and forage. Report to Union Carbide
                        Corporation from Crop Chemical Testing Service,
                        Humbolt, Illinois.

    Davies, R.A.H. Carbaryl plus pirimiphos-methyl for stored grain
    1976a               protection. 1 Laboratory bioassay and residue
                        analysis: Social Report for J.T. Snelson -
                        Pesticides Co-ordinator. ICI Australia Ltd., Rural
                        Division, August 1976.

    Davies, R.A.H. Carbaryl plus pirimiphos-methyl for stored grain
    1976b               protection. 2 Silo pilot trials 1975-76. Special
                        Report for J.T. Snelson - Pesticides Co-Ordinator.
                        ICI Australia Ltd., Rural Division, August 1976.

    Desmarchelier, J.M. Field trials with fenitrothion plus fenoxythrin
    1976a               and pirimiphos-methyl plus carbaryl. Part 1.
                        Biological efficiency. Preliminary report of
                        ongoing study. CSIRO Division of Entomology,
                        Canberra, Australia, August 1976.

    Desmarchelier, J.M. Field trials with fenitrothion plus fenoxythrin
    1976b               and pirimiphos-methyl plus carbaryl. Part 2.
                        Residue studies - Preliminary report of ongoing
                        study. CSIRO Division of Entomology, Canberra,
                        Australia, August 1976.

    Desmarchelier, J.M. Degradation of carbaryl, CGA 20168,
    1976c               fenitrothion, pirimiphos-methyl and carbaryl on
                        rice, oats and barley. Preliminary report of
                        ongoing study. CSIRO Division of Entomology,
                        Canberra, Australia. August 1976.

    Desmarchelier, J.M. Analytical procedures for carbaryl. Personal
    1976d               Communication. CSIRC Division of Entomology,
                        Canberra, Australia. August 1976.

    Desmarchelier, J.M. Esterification of phenols, at residue levels,
    1976e               in dilute base. (In preparation) CSIRO Division of
                        Entomology, Canberra, Australia.

    Dorough, H.W. Animal feeding studies with carbaryl. Details to be
    1974                provided by Union Carbide.

    FAO/WHO 1973 evaluation of some pesticide residues in food.
    1974b               FAO/AGP/1973/9/1; WHO Pesticide Residues Series,
                        No. 3.

    Greening, H.G. Wheat-protectant dust trials 1965-67. N.S.W.
    1976                Department of Agriculture. Biological and Chemical
                        Research Institute, Rydalmere, N.S.W. Report
                        prepared for publication September 1976.

    Holden, E.R. Gas chromatographic determination of residues
    1973                of methylcarbamate insecticides in crops as their
                        2,4-dinitrophenyl ether derivatives. J.A.O.A.C.,
                        56-713.

    Leininger, R.O. Carbaryl residues in wheat forage, Report to Union
    1973                Carbide Corporation from R.O. Leininger,
                        Greenfield. California,

    Lumire, A., Lumire, L., and Barbier, H. Bull. Soc.Chim.
    1906                Fr., 35: 625.

    Phillips, I.L. Carbaryl residues in barley heads, grain and
    1972                forage. Report to Union Carbide Corporation from
                        Soilserv. Inc., Salinas, California.

    Pschorr, R., and Sumuleanu, P. Ber. der Deutsch. Chem. Ges.,
    1899                22: 3407.

    Roan, C.L. Comparison of performance of various carbaryl formulations
    1964                against rice weevil and confused flour beetle.
                        Report from Entomology Department, Kansas State
                        University to Union Carbide Corporation.

    Snelson, J.T. and Desmarchelier, J.M. The significance of pesticide
    1975                residues. Proc. 1st int. Wking Conf.
                        Stored-product Entomology. Savannah, Georgia,
                        U.S.A., 1974, p. 465-477.

    Strong, R.G., and Sbur, D.E. Evaluation of insecticides as
    1961                protectants against pests of stored grains and
                        seeds. J. Econ. Entom., 54: 235-238.

    Tilden, R.L., and van Middelem, C.H. Determination of carbaryl
    1970                as an amide derivative by electron capture GLC. J.
                        Agric. Food Chem., 18(1): 154-6.

    Union Carbide. Summary of studies on the nature of residues of
    1974                carbaryl in the meat of dairy cattle. Union
                        Carbide Corporation Report, May 24, 1974.

    Union Carbide. Submission to FAO by Union Carbide Corporation,
    1976a               September 1976.

    Union Carbide Corporation. Results of tests investigating
    1976b               Sevin as a stored grain insecticide (1958-1962).
                        Extract of petition 2859.

    


    See Also:
       Toxicological Abbreviations
       Carbaryl (EHC 153, 1994)
       Carbaryl (HSG 78, 1993)
       Carbaryl (ICSC)
       Carbaryl (PIM 147)
       Carbaryl (FAO Meeting Report PL/1965/10/1)
       Carbaryl (FAO/PL:CP/15)
       Carbaryl (FAO/PL:1967/M/11/1)
       Carbaryl (FAO/PL:1968/M/9/1)
       Carbaryl (FAO/PL:1969/M/17/1)
       Carbaryl (AGP:1970/M/12/1)
       Carbaryl (WHO Pesticide Residues Series 3)
       Carbaryl (WHO Pesticide Residues Series 5)
       Carbaryl (Pesticide residues in food: 1977 evaluations)
       Carbaryl (Pesticide residues in food: 1979 evaluations)
       Carbaryl (Pesticide residues in food: 1984 evaluations)
       Carbaryl (Pesticide residues in food: 1996 evaluations Part II Toxicological)
       Carbaryl (JMPR Evaluations 2001 Part II Toxicological)
       Carbaryl (IARC Summary & Evaluation, Volume 12, 1976)