DIQUAT        JMPR 1976


         Since diquat was last evaluated by the Joint Meeting in 1972
    (FAO/WHO, 1973), additional studies have been undertaken on
    residues occurring in meat, milk and eggs. The available data on
    studies with ruminants and hens is reviewed below.

         These studies show that diquat, and its photochemical
    degradation products which are formed on plant surfaces, are poorly
    absorbed from the gut of animals and do not accumulate in tissues,
    milk and eggs.


    General comments

         Diquat undergoes rapid photochemical degradation on plant
    surfaces. When barley and oats were desiccated with
    14C-ring-labelled and 14C-bridge-labelled diquat and kept in
    daylight for one or two weeks, unchanged diquat accounted for only
    about 30% of the radioactivity present on the plants. Compound II
    (Figure 1) was a minor degradation product, normally constituting
    approximately 10% of the residue and traces (2% each) of compounds
    III and VI were formed. The majority of the residue on the plants,
    usually 50-70%, was present as a complex mixture of photochemical
    degradation products which appear to be strongly associated with
    natural plant materials (Leahey et al., 1973).

         Animal transfer studies have therefore been carried out with
    diquat alone and with diquat plus a mixture of photochemical
    degradation products. This was necessary as in some instances
    diquat is the sole or major residue in animal feed (e.g. in meal
    from oil seed rape), whereas in others, e.g. in small grain cereals
    and alfalfa, the photoproducts may constitute up to 70% of the
    residue in the feed. In reviewing the feeding studies conducted on
    ruminants and hens, the studies carried out on diquat alone are
    considered separately from those carried out with diquat plus its
    photoproducts. The structures of diquat and its derivatives
    referred to in this evaluation are shown in Figure 1.

    In animals

    Studies with ruminants using diquat alone

         Diquat is poorly absorbed from the gastro-intestinal tract of
    ruminants and the small amount absorbed is rapidly excreted in the
    urine. Residues of diquat and its metabolites in milk and tissues
    are extremely low.

    FIGURE 1

         Thus, when a single dose of 14C-bridge-labelled diquat was
    administered orally to a goat, 96.3% of the radioactivity was
    excreted within 7 days, 94.2% in the faeces and 2.2% in the urine.
    Diquat was the major radioactive compound present in the faeces,
    with only 1-4% of compounds II and III. Diquat accounted for 20% of
    the radioactivity present in urine collected on the first day after
    dosing, compound II for 6% and compound III for 44%.

         Only very small amounts of radioactivity (0.02%) were
    transferred to the milk. The administered dose was equivalent to
    145 mg/kg of diquat in the daily diet whereas the maximum
    radioactive residue in the milk was only 0.014 mg/kg diquat ion
    equivalent. Diquat accounted for 22% of this total, compound II 13%
    and compound III 7%. Incorporation of radioactivity into lactose,
    fat and protein accounted for a further 25% (Griggs and Davis,

         In other experiments, when cows were fed a single dose of up
    to 20 mg/kg of either 14C-bridge-or 14C-ring-labelled diquat
    dibromide, only 0.001-0.015% of the radioactive dose was excreted
    in the milk (Stevens and Walley, 1966).

         When a cow was dosed for seven consecutive days with
    14C-ring-labelled diquat, at a rate equivalent to 30 mg/kg in its
    diet, the radioactivity was again eliminated rapidly, mainly in the
    faeces. 91% of the dose was recovered in the faeces, principally as
    unchanged diquat, and 0.4% in the urine.

         After three days the total radioactive residue in milk reached
    a maximum of 0.004 mg/kg diquat ion equivalents. 13% of this
    residue was unchanged diquat, 7% compound II, 15% compound III and
    38% due to incorporation of radioactivity into lactose, fat and
    protein. Within four hours of the final radioactive dose the cow
    was slaughtered. The radioactive residues found in the tissues were
    all very low - less than 0.01 mg/kg diquat ion equivalents except
    in liver (0.05 mg/kg) and kidney (0.08 mg/kg) (Leahey et al.,

         In a longer term study, non-radiolabelled diquat was
    incorporated into the diet of cows to give a residue of 0.5 mg/kg
    in the total diet. The diet was fed for 31 days. No residues of
    diquat were found in milk, sampled daily (limit of detection 0.005
    mg/kg), or in various tissues (limit of detection 0.01-0.035 mg/kg)
    (Sipos, 1973).

    Studies with ruminants using diquat plus its photoproducts

         Since a mixture of diquat and its photoproducts will be the
    residue consumed by animals fed crops such as desiccated barley and
    alfalfa, several studies have been carried out to investigate the
    safety of this residue mixture.

         In metabolic studies, a single dose of barley straw desiccated
    with 14C bridge- and ring-labelled diquat was fed to goats at
    levels of 2 and 7% (approx.) of the daily intake. Virtually all of
    the administered radioactivity, which contained 59-62% unidentified
    photoproducts, was eliminated within 10 days, mainly in the faeces,
    with about 5% in the urine. A small radioactive residue (0.0028
    mg/kg diquat ion equivalent) was detected in the milk. This
    radioactivity was shown to be mainly due to incorporation of 14C
    into the natural milk constituents. Residues of diquat and compound
    II were less than 0.0003 mg/kg (Hemingway et al., 1973).

         In an extension of this study a cow was given a single oral
    dose of barley straw containing radioactive diquat and its
    photoproducts. Total residues were equivalent to about 10% of a
    daily intake for a cow maintained wholly on diquat-desiccated

         Virtually all of the radioactivity was eliminated from the cow
    within 10 days, mainly in the faeces. Approximately 0.4% of the
    dose was excreted in the urine. Only small radioactive residues
    (maximum 0.0014 mg/kg diquat ion equivalent) were detected in the
    milk. The radioactivity in milk was shown to be mainly (77-90%)
    incorporated into the natural milk constituents, i.e. the lactose,
    fats and proteins. A small percentage of the radioactivity in the
    milk was identified as diquat (0.3-2.0%) and compounds II, III, V
    and VI (each 0.3-1.0%) (Hemingway et al., 1974).

         A study, in which a goat was dosed for five successive days
    with diquat-desiccated barley, showed that if a ruminant was
    maintained on a diet consisting solely of diquat desiccated fodder,
    the residue in the milk would be unlikely to exceed 0.04 mg/kg
    diquat ion equivalent. This residue was again due mainly to
    incorporation of 14C into natural milk constituents. Residues in
    the meat and fat are unlikely to exceed 0.01 mg/kg diquat ion
    equivalent (Leahey, 1974).

         In feeding trials with non-radiolabelled materials,
    diquat-desiccated alfalfa or clover, or silage made from
    diquat-desiccated grass, was fed to cows and sheep for
    approximately 1-4 months without ill effects. No diquat was
    detected in meat, fat or milk (the limit of detection of the
    analytical method was normally 0.01 mg/kg) (Black et al., 1966;
    Calderbank et al., 1966; and Cardinali et al., 1967).

         When diquat-desiccated sunflower seed was fed to cows for
    approximately nine months and to sheep for 4 1/2 months, again no
    ill effects were noted. No residues of diquat were detected in meat
    or milk. Furthermore, no residues of diquat were detected in the
    liver and kidneys of a calf born to one of the cows at the end of
    the study (limit of detection of the analytical method: 0.03 mg/kg
    in meat, 0.01 mg/kg in milk) (Lembinski et al., 1971).

         More recently cows were fed for 30 days on diets containing
    20, 50 and 100 mg/kg diquat ion (on a dry weight basis) together
    with diquat photoproducts which were present as field weathered
    residues in grass nuts prepared from grass sprayed with 4 kg diquat
    ion/ha. No residues of diquat were detected in milk samples (limit
    of detection 0.01 mg/kg) taken throughout the trial. Similarly
    residues of diquat in samples of liver, kidney, fat and muscle taken
    from animals at the end of the trial were all less than 0.02 mg/kg
    diquat (Edwards et al., 1976).

    Studies in hens using diquat

         When hens were fed on a diet containing residues of diquat,
    there was little transfer of residue to the eggs or tissues.

         In a series of radiochemical experiments, bridge-labelled
    14C-diquat was given to three hens.

    i)   A single oral dose equivalent to 4-5 mg. diquat ion/kg in the
         diet was recovered quantitatively within three days. 98.5% of
         the dose appeared in the faeces, 90% of it in the first 24

    ii)  Following five such daily doses, 94.5% of the radioactivity
         was again recovered in the faeces within five days of final
         dosing; diquat accounted for 75-80% of this radioactivity.
         Approximately 0.06% of the administered radioactivity was
         present in eggs: 35-40% as diquat and 55-60% as compound III.
         Total radioactive residues in the eggs did not exceed
         approximately 0.02 mg/kg diquat ion equivalents. Tissue levels
         in this hen seven days after the final dose did not exceed
         0.004 mg/kg diquat ion equivalent.

    iii) The eggs of a hen given 14 daily doses of 14C-diquat at a rate
         equivalent to 0.4-0.5 mg diquat/kg in the daily diet,
         contained a maximum residue of less than 0.03 mg/kg diquat ion
         equivalent. Tissue levels four hours after the final dose did
         not exceed 0.0005 mg/kg diquat ion equivalent (Leahey &
         Hemingway, 1974)

         In a longer term experiment, hens were fed a diet containing
    up to 10 mg/kg of diquat ion for 6 weeks. Eggs collected throughout
    the trial contained no residues of diquat (<0.05 mg/kg) in white
    or yolk. Tissues from hens slaughtered after 16, 28 and 45 days
    feeding also contained no detectable residues of diquat (<0.05
    mg/kg in meat and liver; <0.2 mg/kg in kidney). Food consumption,
    egg production and hatchability were not affected by diquat at
    these levels. (Edwards & Smith, 1975).

    Studies in hens with diquat and its photoproducts

         Mature barley plants were sprayed with 14C-ring-labelled
    diquat and left in sunlight for 4 days before harvesting. Residues

    of diquat and its photoproducts on the grain were measured and the
    sample was then fed to three hens. The first was given a single
    oral dose, 96% of which was recovered in the faeces within 5 days.
    The other two hens were dosed for 11 consecutive days at rates
    equivalent to 1.0-1.5 mg/kg diquat and photoproducts in the total
    diet. There was a very small transfer of radioactivity into the
    eggs, the maxima in the albumen and yolk being 0.0006 and 0.0039 mg
    diquat ion equivalent/kg. Radioactive residues in the tissues of one
    of the hens sacrificed 4 hours after its final dose did not exceed
    0.005 mg/kg diquat ion equivalents, except in the kidney where 0.014
    mg/kg was detected.

         These results show that, as with other animals, residues of
    diquat and its photoproducts are rapidly excreted by hens and there
    is only an extremely small transfer of residue into eggs and
    tissues (Hughes & Leahey, 1975).

    Safety to animals consuming treated fodder

         In the above-mentioned studies, ingestion of diquat and its
    photoproducts, at levels higher than would be found in practice,
    did not produce ill effects in ruminants or hens.


         The following national tolerances have been reported to the

    TABLE 1. National tolerances reported to the Meeting

    Country             Commodity                     Tolerance,

    West Germany        Potatoes                      0.1
                        Oil seed rape                 0.7
                        All other crops               0.05

    Holland             Apples              )
                        Pears               )
                        Green vegetables    )         0.05
                        Potatoes            )

    Hungary             All crops                     0.5

    USA                 Sugarcane                     0.05


         Since diquat was evaluated in 1972 additional information has
    been obtained on the fate of the compound in goats, cows, sheep and

         Using radio-labelled diquat and its photoproducts it has been
    shown in the above ruminants that about 90-96% of these compounds

    are excreted in the faeces; small amounts were found in the urine.
    Longer term experiments with cows using unlabelled diquat again
    showed that over 90% was excreted in the faeces and only a very
    small amount (ca 0.01%) in the milk. In another long-term
    experiment where cows were fed for 30 days on diets containing both
    diquat and its photoproducts, residues in milk were undetectable
    throughout the trial (limit of detection 0.01 mg/kg).

         When hens were fed on a diet containing residues of
    radio-labelled diquat there was little transfer to the eggs or
    tissue, 94-98% was excreted in the faeces and only 0.06% was found
    in the eggs. Food consumption, egg production and hatchability were
    not affected during these experiments.

         These further studies support the recommendations made in 1972
    for limits in milk, meat and meat products at or about the limit of
    determination. A further residue limit in eggs is recommended.


         In addition to the previous recommendations the following
    maximum residue limit is recommended.

              Commodity         Limit, mg/kg

                Eggs                0.01*


    * at or about the limit of determination.


    Black, W.M.J., Calderbank, A., Douglas, G. and McKenna, R.H.
    1966                Residues in Herbage and Silage and Feeding
                        Experiments following the Use Of Diquat as a
                        Desiccant. J. Sci. Fd. Agric., 17:506.

    Calderbank, A., McKenna, R.H. and Welley, J.K. Bipyridylium
    1966                herbicides: Feeding clover, hay and barley
                        desicatted with diquat, to cattle. ICI
                        Agricultural Division Report No. AR126,569

    Cardinali, A., Fratteggiani Branchi, R., Businella, M. and
    1967                Martin, A. Making hay of lucerne dessicated
                        with diquat. I Progresso Agricola, XIII (1):

    Edwards, M.J., Hayward, G.J., Ward, R.J. and Iswaren, T.J.
    1976                Diquat: Residue and toxicology trials with
                        cows fed treated grass. ICI Plant Protection
                        Division Report No. AR2653A (Unpublished).

    Edwards, M.J. and Smith, D.C. Diquat: Residue transfer and
                        hatchability study in laying hens. ICI Plant
                        Protection Ltd. Report No. AR2604B

    FAO/WHO 1972 Evaluations of some pesticide residues in food,
    1973                AGP:1972/M/9/1; WHO Pesticide Residue Series,
                        No. 2.

    Griggs, R.E., and Davis, J.A. Diquat excretion and metabolis in
                        a goat. ICI Plant Protection Ltd. Report No.

    Hemingway, R.J., Leahey, J.P., Davis, J.A. and Burgess, J.G.
    1974                Diquat: Metabolism of diquat and its
                        photoproducts in a cow. ICI Plant Protection
                        Ltd. Report No. AR2530B (Unpublished).

    Hemingway, R.J., Leahey, J.P., Davis, J.A. and Griggs, R.E.
    1973                Diquat: Metabolism of diquat and its
                        photoproducts in goats. ICI Plant Protection
                        Ltd. Report No. AR2448B (Unpublished).

    Hughes, H.E. and Leahey, J.P. Diquat: Residues resulting in the
                        eggs and tissues of hens dosed with
                        14C-Diquat-dessicated barley grains. ICI Plant
                        Protection Division Report No. AR2581B

    Leahey, J.P. Diquat: Residues in the tissues of rats and a
    1974                goat dosed with diquat and its photoproducts.
                        ICI Plant Protection Ltd. Report No. AR2503A

    Leahey, J.P., Gatehouse, D.M. and Carpenter, P.K. Diquat:
    1976                Metabolism and residues in a cow. ICI Plant
                        Protection Division Report No. TMJ1349A

    Leahey, J.P., Griggs, R.E. and Allard, G.B. Diquat: Residues
    1973                of diquat and its photoproducts on barley and
                        oats after dessication with 14C-diquat. ICI
                        Plant Protection Ltd. Report No. AR2478B

    Leahey, J.P. and Hemingwah, R.J. The metabolism of diquat
    1974                in hens and residues in eggs and tissues.
                        Proc. 3rd Int. Congress Pesticide Chem.,

    Lembinski, F., Ponikiewska, T., Trezbny W. and Krzywinska,
    1971                F. Ground seed of sunflower dessicated with
                        `Reglone' as fodder for ruminants. Pamietnik
                        Pulawski Prace IUNG 49.

    See Also:
       Toxicological Abbreviations
       Diquat (HSG 52, 1991)
       Diquat (PIM 580F, French)
       Diquat (AGP:1970/M/12/1)
       Diquat (WHO Pesticide Residues Series 2)
       Diquat (Pesticide residues in food: 1977 evaluations)
       Diquat (Pesticide residues in food: 1978 evaluations)
       Diquat (Pesticide residues in food: 1993 evaluations Part II Toxicology)