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    PESTICIDE RESIDUES IN FOOD - 1980


    Sponsored jointly by FAO and WHO






    EVALUATIONS 1980





    Joint meeting of the
    FAO Panel of Experts on Pesticide Residues
    in Food and the Environment
    and the
    WHO Expert Group on Pesticide Residues
    Rome, 6-15 October 1980



    METHACRIFOS

    IDENTITY

    Chemical name

    O-2-methoxycarbonylprop-1-enyl O,O-dimethyl phosphorothioate
    (IUPAC)

    Synonyms            CGA-20168 (trans), C-23763 (trans), Damfin(R)
                        OMS-2005

    Chemical structure

                                S            CH3
                        CH3O    "            '
                             \  "            '
                               \"            '
                                P - O - CH = C - COOCH3
                              /
                        CH3O /


    Molecular formula:  C7H13O5PS

    Molecular weight:   240.21

    Description:        colourless liquid

    Specific gravity:   1.225 g/cm3 at 20C

    Boiling point:      90C at 0.01 mm Hg

    Volatility:         saturated vapour conc. at 20C: 16 mg/m3

    Solubility:         400 ppm in water at 20C; soluble in methanol,
                        methylene chloride, benzene, hexane and other
                        organic solvents

    Stability:          half-lives at 20C in water were:
                        9.5 days at pH 9
                        29 days at pH 7
                        44 days at pH 5
                        66 days at pH 1
                        at  200C decomposition of both isomers

    Purity:             >93%

    DATA CONSIDERED FOR DERIVATION OF ACCEPTABLE DAILY INTAKE

    BIOLOGICAL ASPECTS

    Absorption, distribution, excretion and biotransformation

    The fate of methacrifos was followed in male and female RAI-SPF
    rats by using methacrifos 14C-labelled in the carboxy group:

    CHEMICAL STRUCTURE 2

    Following a single oral dose of about 5 mg/kg 14C-methacrifos, the
    excretion in urine, faeces and expired air was in males 30.2, 10.2
    and 54.7% of the administered dose, respectively, and in females
    43.8, 8.7, 52.7%, respectively.  Most of the radioactive label was
    excreted in the first 24 hours.  Total recovery was 97.4 and 106.6%
    for males and females, respectively.  Excretion half life time was
    8 hours.

    The animals were killed five days after dosing, the tissues
    investigated showed the following residues:

                                          
                Tissue residue 
            (in mg/kg methacrifos eq.)
                                          
                males   females
                (n=4)    (n=4)
                                          
    Liver       0.306    0.287
    fat         0.110    0.040
    kidneys     0.087    0.089
    muscles     0.035    0.020
    blood       0.041    0.040
    brain       0.027    0.023
    spleen      0.052    0.048
    testes      0.033      - 
    ovary         -      0.043
                                          
    (Ifflaender and Mke, 1975)

    In a similar experiment, in which about 25 mg/kg 14C-methacrifos
    was orally administered, the mean excretion pattern for males and
    females was 41.5, 10.5 and 38.0% of the given dose in urine, faeces
    and expired air respectively.  The main urinary metabolite,
    representing 12% of the dose, was isolated and identified as
    N-acetyl-S-(2-methoxycarbonylprop-1-enyl) cysteine.  It was
    demonstrated that this cysteine conjugate when injected i.v. to
    rats is excreted via the kidney mainly unchanged.

    Another urinary metabolite, representing 4% of the dose was
    probably the monodemethylated phosphoric acid derivative of
    methacrifos.  Both metabolites were also found in the faeces. 
    Most, if not all, of the radioactivity expired was 14CO2.  The
    following metabolic pathways of methacrifos in the rat are
    proposed: see Figure 1.

    FIGURE 1

    TOXICOLOGICAL STUDIES

    Special studies on teratogenicity and reproduction

    Rat

    After successfully being mated with male Sprague-Dawley albino rats
    four groups of 2-month old female rats (25 animals/group) of the
    same strain were orally incubated with methacrifos at doses of 0,
    5, 25 or 50 mg/kg bw.  In a preliminary study 6 out of 10 dams
    died, when the compound was administered at the dose of 150 mg/kg
    bw.

    Treatment started at day 6 of pregnancy and was continued through
    day 15.  During the experiment a reduction in body weight gain was
    found in the dams of the 50 mg group, starting half-way through the
    dosing period.  This reduction was accompanied by a temporary
    decrease in food consumption at the 11th and 16th day of dosing
    (food consumption was measured at day 6, 11, 16 and 21 of dosing). 
    Further a dose-related increase in the percentages of embryonal
    deaths (early resorptions) was found, which already started at the
    5 mg/kg level.  No structural abnormalities related to the
    methacrifos treatment were observed in the pups.  The number of
    foetuses with still incomplete ossified sternebrae was slightly
    higher in the 50 and 25 mg/kg dose groups.  (35.8% in control
    versus 35.0, 43.0 and 52.8% for the 5, 25 and 50 mg/kg groups,
    respectively).  In the treated groups no foetal deaths or dead
    foetuses were found (Fritz et al, 1978).

    Groups of rats (8 males and 16 females/group) were fed methacrifos
    in the diet at dosage levels of 0, 1, 10 or 100 mg/kg (mean
    analytical concentrations of <0.1, 0.79, 7.4 and 73 mg/kg), and
    subjected to a standard 3-generation, 2-litter per generation
    study.

    Gross and histopathologic examinations were conducted on the
    parenteral animals of the F0, F1, F2 and F3.  Gross
    pathological evaluations were made on at least 10 male and 10
    female weanlings of the 0 and 100 mg/kg group.  No
    treatment-related changes were noted in the tissues and organs
    examined.  Throughout the study a dose-related increase in
    mortality of the male parent animals was observed in all treated
    groups, whereas the mortality was also higher in the females of the
    treated groups.  The cause of mortalities was ascribed to acute
    bronchopneumonia superimposed on lesions of chronic murine
    pneumonia. There was no clear effect on the body weight gain or
    organ weights of the treated groups.

    The total number of pups delivered was dose-related decreased in
    almost all litters, where the mean number was not clearly affected.

    In addition somewhat reduced survival percentages after 21 days
    were noted in comparison to the controls in the 10 and 100 mg/kg
    F1a and F1b, 1 mg/kg F3b and 100 mg/kg F3a and F3b litters
    (Charles et al, 1980a).

    Special studies on mutagenicity

    Bacteria

    Histidine-autotrophic mutants of Salmonella typhimurium were
    treated with methacrifos in concentrations of 0.25, 0.75, 2.25,
    6.75 or 20.25 mg/ml with or without microsomal activation, in order
    to study the possible induction of point mutations by methacrifos. 
    The test results were negative (Arni and Mller, 1979).

    Mice

    Twenty male albino mice were administered methacrifos orally in
    single doses of O, 7, and 21 mg/kg and then mated to two untreated
    female albino mice over a period of six weeks.  At the end of each
    week the females were replaced by new ones.  The effects on mating
    ratio and the number of implantations and embryonic deaths as well
    as the effects on the loss of pre-implantation zygotes and the rate
    of deaths of post-implantation stages of embryonic development were
    studied.  No evidence of a dominant lethal effect was observed
    (Hool and Mller, 1980).

    Special studies on carcinogenicity

    Groups of 5-7 week old Swiss, white mice (60/sex/group) were
    dietary fed 0, 1, 10 or 100 mg/kg methacrifos (purity 94.6%) for
    21-22 months (sacrifice of male and females at 50% mortality).

    Body weight, food consumption and mortality were not clearly
    affected. Haematological investigations carried out at the end of
    the study revealed increases in total leucocyte count for males of
    the 1 and 10 mg/kg groups.  Urinalysis, performed also on 10
    animals/sex/group, were normal at sacrifice but blood chemistry
    revealed a significant increase in total protein in females and in
    cholesterol in males at 100 mg/kg.  In females an obvious
    dose-related, but not significant, increase was found in absolute
    and relative weight of gonads at 100 and 10 mg/kg.  At 1 mg/kg a
    tendency to an increase was found.  The other organ weights were
    within normal limits.

    At sacrifice the activity of cholinesterase in plasma, appeared
    inhibited at 100 and 10 mg/kg in both males and females; in
    erythrocytes it was inhibited in females at 100 mg/kg.  Brain
    cholinesterase was not dose-related affected.

    At histopathology no effects on tissues were apparent.

    Carcinogenicity has not been found in this experiment (Charles et
    al, 1980b).

    Special studies on inhalation

    Groups of 7/8 week-old rats (9/sex/group) were exposed to 0, 90,
    191 or 467 mg methacrifos/m3 air, 15 times over a period of 21
    days.

    Thereafter 4 animals/sex of the control and highest dose group were
    kept for a recovery period of 21 days.  The compound was injected
    into an air stream discharged into the exposure chamber through a
    spray nozzle under a pressure of 2 atmospheres at a rate of 10
    1/min.; the exposure concentrations were determined.  The animals
    were kept separately in PVC tubes, which were positioned radially
    around the exposure chamber.  The animals at the highest dose group
    showed a significant decrease in food consumption and body weight
    gain, but returned to normal during the recovery period.  In the
    191 mg/m3 group the body weight was also decreased at the end of
    the study. Haematology and blood biochemistry revealed a
    significant increase in SGPT in the 467 mg/m3 group.  No clear
    effects on the weight of the organs were observed.  Blood urea
    concentration was increased in all doses tested, which disappeared
    after the recovery period.  The cholinesterase activity of plasmal
    erythrocytes and brain was significantly depressed in all treated
    groups.  After the recovery period, brain cholinesterase activity
    was still decreased.

    One male and one female rat died during the treatment: congestion
    often with haemorrhages were observed in various tissues.  All
    other gross or microscopic findings were not related to the
    treatment (Ullmann et al, 1977).

    Special studies on dermal toxicity

    Groups of KA 46, Himalayan strain rabbits (3/sex/group: 1.3-2 kg)
    were dermally exposed to 0, 10, 50 or 250 mg/kg methacrifos, once
    a day, 5 times a week for a period of 3 weeks.  Thereafter 1
    animal/sex/group was kept for a recovery period of 3 weeks.  The
    compound was diluted in PEG 400 and saline and applied to the
    shaven skin of the back, with occlusive dressings.  All treated
    groups showed reversible erythema at the application site.  The
    animals of the 50 and 250 mg/kg groups showed clinical symptoms
    (tremors, ataxy, especially during the first week).  At 250 mg, 5
    animals died within 9 days of the study.  In the other groups no
    effects on food consumption, body weight gain, haematological and
    clinical chemistry were observed.

    All the treated groups showed after 3 weeks a dose-related
    inhibition of the cholinesterase activity of plasma and
    erythrocytes of 30-80%, and 10-75% respectively.  Brain
    cholinesterase values revealed an inhibition of approximately
    10-30, 55 and 85% of the control values in the treated groups.  At
    the end of the 3-week recovery period the blood and brain
    cholinesterase activities of the 10 and 50 mg/kg groups had almost
    returned to normal values.

    Due to the small number of animals the effects on the organ weights
    are difficult to evaluate.

    Histopathological examinations revealed not pathological changes
    which could be attributed to the treatment (Sachsse et al, 1978).

    Special studies on skin sensitisation

    Groups of guinea pigs of the Pirbright White strain (10/sex/group)
    were intradermally injected saline, methacrifos and
    dinitrochlorobenzene (DNCB) (positive control) (0.1 ml of the test
    substance, 0.1%) every other day for 3 treatments.

    During the second and third week of induction 6 sensitizing doses
    of 0.1 ml, with Freund's adjuvants, were injected intracutaneously.

    Two weeks after the last exposure, the animals were challenged and
    examined for sensitisation.  Ten days thereafter a second challenge
    was given.  There were indications that methacrifos induced a
    sensitisation reaction, but it was less severe than DNCB (Ullmann
    and Sachsse, 1975).

    Special studies on neurotoxicity

    In hens of the White Leghorn strain, over 12 months of age, which
    were orally dosed by gavage with 0, 25, 50, 101 or 202 mg/kg
    methacrifos (10, 15, 20 and 30 animals/group resp.) on day 0 and
    21, no symptoms of delayed neurotoxicity were described in the
    intermediate observation period of 21 days nor in the 42-day
    observation period thereafter.  At all doses the treatment resulted
    within 1 hour to 4 days in ataxy, curved or ventral position,
    sedation and salivation. Histopathological lesions in the spinal
    cord and the sciatic nerve were not observed.

    In the positive control animals, which had been treated with TOCP,
    delayed neurotoxicity was found, obviously with slight to severe
    lesions in the spinal cord and the peripheral nerves (Sachsse et
    al, 1979).

    Special studies on potentiation

    In a study with RAI f-SPF rats (5 animals/sex/group) in which acute
    oral LD50 values were determined no potentiation was found with the
    insecticides dichlorvos, phosphamidon, diazinon and CGA 15324;
    however a potentiation did occur with the insecticides methidathion
    and malathion.

                                                                        
                                                   LD50 in mg/kg
    techn. compound   techn. compound   techn. compound  +  CGA 201681
                                         theoretically      experimentally
                                                                        

    phosphamidon              12               347               400
    dichlorvos                54               395               611
    CGA 15324                426               581               568
    diazinon                 534               635               520

    methidathion              43               389.5             201
    malthion                1397              1066.5             454
                                                                        

    1 acute oral LD50 of CGA 20168: 745 mg/kg (Sachsse and Bathe,
    1978)

        TABLE 1.  Acute toxicity of methacrifos

    Mammals

                                                                                           
                            route of          LD50 in mg/kg     reference
    species      sex     administration         or mg/m3
                                                                                           

    Chicken                   oral              1011             Sachsse et al, 1979
    Rat         M + F         oral              6782             Bathe, 1974a
    Mouse       M + F         oral              662              Bathe, 1974b
    Mouse       M + F         oral              582              Bathe and Sachsse, 1978
    Dog         M + F         oral              5731             Bathe and Sachsse, 1975
    Rat         M + F        dermal             >31002           Bathe, 1974c
    Rabbit      M + F        dermal             27321            Ullmann and Sachsse, 1977
    Rat         M + F      inhalation           >2500            Ullmann and Sachsse, 1976
                                                                                           

    1 observation period of 14 days
    2 observation period 7 days
    

    Fish

                                                                           
                    exp. temp.   96 hour LC50
    Species         in  C        mg/kg          Reference
                                                                           

    Rainbow trout      14            0.4
    Crucian carp       14           30
    Catfish            21            6          Sachsse and Ullmann, 1974a
    Bluegill           14            2
    Guppy              21            3
                                                                           

    Short-term studies

    Quail

    Groups of adult Japanese quails (3 males and 7 females/group) were
    given, 0, 1000, 6000, or 10,000 mg/kg methacrifos in the feed for a
    5-day period.  They were held for observation during a further 3 days.
    The mortality observed during the entire 8-day period was used to
    calculate the LC50 which appeared to be approximately 10,000 mg/kg.
    Observation of symptoms, egg production, food consumption and body
    weight revealed sedation and ruffled feathers, partly to complete
    refusal of food and a decrease in body weight over the whole dosing
    period and a stop in egg production (Sachsse and Ullmann, 1974b).

    Chicken

    Groups of one-day old Hubbard chickens (32 sex/group) were dietary fed
    0, 10, 100, 250, 500 or 1000 mg/kg methacrifos for 63 days.

    Mortality was found to be 1.6, 0, 1.6, 3.1, 37.6 and 98.2% in the 0,
    10, 100, 250, 500 and 1000 mg/kg groups, respectively.  Most animals
    died in the first period (0-14 days).  The dying animals of the 500
    and 1000 mg/kg groups showed signs of ataxia, lack of appetite,
    somnolence and ruffled plumage.  Body weight and food consumption were
    significantly decreased at 250 and 500 mg/kg during the whole
    experiment, at 100 mg/kg temporarily up to at least 28 days.  No
    effects on haematology and histopathology were found.

    Final cholinesterase activity measurement in the brain on 8 animals/
    sex/group revealed a dose-related inhibition at 100, 250 and 500 mg/kg
    (Strittmatter and Gfeller, 1975).

    Rat

    Groups of Sprague-Dawley derived rats (150-170 g; 5 or 10, sex/group)
    were given 0, 10, 100 or 1000 mg/kg methacrifos in the feed for 30
    days, followed by a recovery period of 28 days for the control and
    1000 mg/kg groups but nearly complete recovery was found in food
    consumption at about 25 days; loss of hair in males was also noted. 
    In the males of the 1000 mg/kg group abnormalities in blood
    composition were observed: a significant decrease in Hb, PCV, number
    of erythrocytes and lymphocytes and prothrombin time and a slight
    increase in neutrophils.  At 100 mg/kg in the males the number of
    lymphocytes and neutrophils appeared affected, also.

    A decrease in cholinesterase activity in plasma and erythrocytes was
    found at the end of the dosing period in both males and females of the
    100 and 1000 mg/kg groups; plasma cholinesterase activity was also
    decreased in males of the 10 mg/kg groups.  At the end of the
    experiment partial recovery was observed.  Cholinesterase activity in
    plasma and erythrocytes in the 1000 mg/kg group was still about 20%
    decreased in both males and females.  Brain cholinesterase has not

    been determined.  Further effects on clinical-chemical parameters and
    urinalysis were not found.  In the male animals of the 1000 mg/kg
    groups the weight of the kidneys was decreased in comparison to the
    control value (Drake, 1975).

    Dog

    Groups of pure bred beagle dogs (6.5-11 kg; 2 or 4 sex/group) were
    dietary fed 0, 10 or 100 mg/kg for 28 days.  Another group of dogs
    received 1000 mg/kg for 11 days but treatment had to be stopped
    because of a deterioration in the bodily condition of the dogs.  After
    7 days the animals then received 500 mg/kg for 4 weeks.  Thereafter 4
    animals were sacrificed and 4 were allowed a 4-week recovery period.
    Due to dose changes evaluation of the effects of 1000 or 500 mg/kg
    methacrifos is difficult.  However body weight and food intake
    drastically decreased and two animals showed higher SGPT values.

    There was a marked depression of plasma and red cell cholinesterase
    values, with a partial recovery.  One animal was sacrificed in poor
    bodily condition.  Macroscopically a whitening of the splenic capsule
    and a small amount of free blood beneath the membranes of the spinal
    cord was observed.

    In the other treated groups food consumption, body weights and organ
    weights were measured and haematology, blood biochemistry, urinalysis,
    ophthalmoscopy and histopathology performed but no toxic effects were
    found except for a reduced water intake at 100 mg/kg and 10 mg/kg in
    the males and a final inhibition of cholinesterase activity both in
    the erythrocytes and plasma at 10 and 100 mg/kg in males and females.
    Brain cholinesterase activity was not affected (Chesterman et al,
    1975).

    Groups of adult pure bred beagle dogs (8.5-15 kg; 8 sex/group) were
    dietary fed 0, 1, 10 or 100 mg/kg methacrifos (94.6%) for 26 weeks.
    Thereafter 2 animals/sex/group were kept for a recovery period of 4
    weeks.

    No effects were found on food consumption and body weight gain but the
    animals in the dose groups vomited more often and showed more
    pronounced diarrhoea, when compared with the controls.  Haematology
    and urinalysis after 4, 13 and 26 weeks, were normal but blood
    biochemistry showed a decrease in blood glucose at 26 weeks in all
    dose groups, which fully recovered in the 1 mg/kg groups in the 4-week
    recovery period but which only partially recovered in the 100 and 10
    mg/kg groups in this period.

    The main effects were found on cholinesterase activity.  Plasma
    cholinesterase was dose-related inhibited in the 100 and 10 mg/kg
    groups at 4, 13 and 26 weeks and in the 1 mg/kg groups after 4 and 13
    weeks only, with about 30%.  Complete recovery was found after 4
    weeks.

    Erythrocyte cholinesterase was also dose-related inhibited in the 100
    and 10 mg/kg groups at 4, 13 and 26 weeks but recovery was incomplete
    after 4 weeks, inhibition was still present in males and females at
    100 mg/kg and in females at 10 mg/kg.  Brain cholinesterase was not
    affected.  Gross and microscopic examinations of organs and tissues
    showed no effects attributed to methacrifos (Bathe et al,1977).

    Pig

    Groups of large white pigs (about 44 kg; 2/sex/group) were dietary fed
    0, 10, 100 or 1000 mg/kg for about 4 weeks.  No effects were found on
    food consumption, body weights, blood chemistry, and haematology,
    except for an influence on cholinesterase activity.  At day 15 and 29
    an inhibition of cholinesterase activity in plasma and erythrocytes
    was found at 1000 mg/kg, at day 29 also in brain at 1000 mg/kg and in
    erythrocytes also at 100 mg/kg.  No histopathological changes were
    found (Gfeller, 1974).

    Long-term studies

    Rat

    Groups of about 40-day old CR strain rats (65/sex/group) were dietary
    fed 0, 1, 10 or 100 mg/kg methacrifos for 2 years.  Haematology,
    coagulation, clinical chemistry and urinalysis studies were carried
    out in 10 rats/sex from the control and 100 mg/kg group.

    No clear effects were found on mortality, food consumption, body and
    organ weights, haematology, clinical chemistry and urinalysis.
    Cholinesterase activity in plasma and erythrocytes, which was measured
    at 3, 6, 12, 18 and 24 months, was influenced.  Cholinesterase
    activity in plasma was inhibited in females of the 100 mg/kg group at
    3, 6, 12 and 24 months, in males of the same group at 3, 6 and 12
    months and in females of the 10 mg/kg group at 3 and 24 months.
    Cholinesterase activity in erythrocytes was inhibited in females of
    the 100 mg/kg groups at 6 months and in males of the same group at 12
    months.  Finally, cholinesterase activity in brain, which was measured
    at 24 months, was not affected.  The results of the microscopic
    examination indicated that methacrifos did not produce
    histopathological changes.  A no-effect level in this study is 1 mg/kg
    in the diet (Basler et al, 1980).


    RESIDUES IN FOOD

    USE PATTERN

    Methacrifos is an organophosphorus insecticide and acaricide, with a
    rapid and long-lasting action on a number of major pests of stored
    products.  It is mainly used as a grain protectant but also against
    insect pests in other stored products.  It is effective against
    insects showing resistance to commonly used stored product
    insecticides, including other organophosphorus compounds.

    The main fields of application are cereal grains (maize, rice,
    sorghum), cocoa, coffee, peanuts, pulses and tobacco.

    The material shows a wide spectrum of activity notably against
    Sitophilus spp., Rhizopertha dominica, Tribolium spp., Oryzaephilus
    surinamensis, Lasioderma serricorna, Dermestes frisehii,
    Anugasta Kuhniella, Plodio interpunetella, Acarus siro,
    Glycophagus domesticus (Wyniger et al, 1977).

    The major formulations are emulsifiable concentrate, solution in
    organic solvents and dusts.

    The dosage rate under usual conditions of storage and infestation is
    10 mg ai/kg, which gives protection to stored products for several
    months.  At lower storage temperatures, or if infestation is moderate,
    satisfactory protection can be obtained with 5 mg/kg.  In some
    situations (e.g. in Australia against a resistant strain of
    Rhizopertha dominica) a rate of 20 mg ai/kg may be needed to
    achieve satisfactory control.

    Methacrifos is also used for space treatment in empty silos at 50-75
    mg ai/m3, for surface treatment of stored products and as a wall
    treatment in storage premises.

    Methacrifos application does not affect germination, baking quality,
    taste or odour.


    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Residue data are available from supervised trials carried out in
    various countries, including Australia, France, Spain, Switzerland,
    Mali and South Africa, on a variety of cereal grains, dry pulses,
    tropical seeds and products of animal origin.  The data were obtained
    from both large and small-scale trials performed under practical
    conditions.

    Wheat, barley, oats

    ln laboratory experiments, simulating grain storage, in Australia, it
    was shown that the residue of methacrifos decreased more rapidly with
    increased temperature and moisture content (Table 2); increased rate
    and/or repeated application did not influence the dissipation rate
    (Table 3); some evidence was obtained that enzymic activity in the
    grain was at least partially responsible for the more rapid initial
    breakdown (Table 3).  The rate of residue decrease after treatment of
    wheat, barley and oats is similar.  On all variety loss during storage
    at 36C is more rapid than at 31C as shown in Table 3. (McDougall,
    1974; Moore, 1973; Moore et al, 1974).

    Several small-scale trials in which wheat, barley or oats were stored
    in mini-silos (5 ton of each grain) or in drums (120 l) showed

    similar results.  As in the laboratory experiment, the application
    rate of methacrifos does not affect the rate of dissipation in any of
    the grains investigated (McDougall, 1975; McDougall, 1976) (Table 4
    and 5).  From these trials half-life periods could be calculated using
    the formula t = (t2 - t1) log 2 / [2 - (logC2/C1)  100], where
    C1, C2 are concentrations of the insecticide at times t1 and t2
    respectively. Only data for 84 days storage were used since the
    temperature dropped after that period.



        TABLE 2. Laboratory trials on the dissipation of methacrifos in stored grains

                                                                                                                         
                          Storage Conditions    Application       Residues of methacrifos, in mg/kg, after storage
                                                   rate                                                                  
    Commodity           Moisture %    Temp. C     mg/kg     0/1     7      14      28      42      56      70       84
                                                                                                                         

    Wheat                9.3              28        24       17.3           16.1    14.7           12.3             12.1
                        10.3              "         "        14.8           14.0    12.0            8.8              7.6
                        11.3              "         "        13.4           12.4     9.5            6.7              4.9
                        12.3              "         "        13.4           10.7     7.7            5.0              3.0

                         9.3              35        24       14.5           13.8    12.5           8.5              6.3
                        10.3              "         "        13.8           11.5     8.1           4.8              3.2
                        11.3              "         "        13.3           10.2     6.1            -                -
                        12.3              "         "        12.9            8.2     4.4            -                -

                         9.6              42       24        13.1            8.5     4.8            -                -
                        10.4              "         "        12.6            6.7     3.1            -                -
                        12.3              "         "        4.9             2.0      -             -                -
                        12.4              "         "        11.1            4.1     1.2            -                -

    Wheat               11.9              31       20        16.4    12.8    9.6     7.6    5.4             4.1
                        11.8              36        "        16.2    11.4    8.9     4.5    3.2              -
    Barley              11.7              31        "        16.9    14.2   12.0     8.0    5.8             3.4
                        11.8              36        "        18.9    11.6    8.7     4.4    2.5              -
    Oats                11.7              31        "        19.2    13.2   11.6     6.9    5.1              -
                        11.9              36        "        18.8    11.6    8.4     3.7    2.5              -
                                                                                                                         

 

    TABLE 3. Laboratory trials on the relative disspation of methacrifos in wheat

                                                                                                                             
                              Storage Condition     Application       Residues of methacrifos as %
                                                       rate             of initial residue (=100)
    commodity           moisture %     temp. C        mg/kg         0     2     14    28     42     Reference
                                                                                                                             

    Wheat                  11.2           35            24          100    82    48    30     22     Moore & McDougall, 1974
                           11.2           "             50          100    73    45    28     21
                           11.1           "             1501        100    74    47    34     25
                           1O.91          "1            24          100    98    60    36     22
                           11.2           "             24          100    93    44    29     21
                           12.5           "             4 + 15      100    79    49    33     -
                                                                                                                             
    1 applied in "dead" grain


    TABLE 4.  Mini-silo storage trials (Australia) on the dissipation of methacrifos in stored grains

                                                                                                                                               
                      Storage Condition        Application             Residues of methacrifos mg/kg after.....days
    Commodity       % moisture   temp. C       rate mg/kg     0    2/3  6-8  13-15    28   56    84   105   126  147  168    Reference
                                                                                                                                               

    Wheat              10.2       22-26.5          10         4.7   5.8  5.0   5.0    4.2   4.1    -   3.0    -   2.9         McDougall, 1975
    Barley             12.8       "                "          9.4   8.6  8.6   8.0    5.7   3.9   2.9   -    2.0   -   1.8
    Maize              12.9       "                "          7.2   7.0  7.0   6.8    7.0   3.9   4.0   -    2.4   -   2.9
    Sunflower          7.2        "                "          7.7   7.5  7.2   6.7    7.4   5.0   4.9   -    3.6   -   2.7
                                                                                                                                               

    TABLE 5.  Drum trials (Australia) on the dissipation of methacrifos in stored grains

                                                                                                                                               
                       Storage Condition       Application    Residues of methacrifos in mg/kg after.....days
    Commodity        % moisture    temp. C    rate mg/kg     0     2     5     7     12    28    56   84    126   175   210   Reference
                                                                                                                                               

    Wheat             8.3-10.2        32         5            5.3    -    -    5.5    5.4   4.0   3.1  2.5   1.6   1.2   1.1   McDougall, 1976
                                                 10           8.8    -    -    9.9    8.2   7.1   5.3  4.3   3.1   2.4   1.8
    Oats              7.4-8.0         10         10           4.1    -   4.4    -     3.6   2.8   2.4  1.7   1.5    -    0.4
    (in sealed
    bags)             7-8-8.4         32         10           4.1    -   4.8    -     4.4   3.4   2.4  1.7   1.3    -    0.4
    Maize             8.6-10.3        32         5            2.6   2.9   -     -     2.4   2.0   1.8  1.4   1.0   0.6   0.5
                                                 10           4.2   6.0   -     -     6.0   4.5   4.0  2.5   1.9   1.5   1.3
    Peanuts           4.4-7.9         32         10           7.3    -    -    7.1    6.5   4.2   2.4  2.8   1.8   1.2   1.1
                                                 20           16.0   -    -    14.2   12.0  9.0   6.6  4.7   3.2   2.2   2.2
    Soybeans          5.5-7.4         32         5            2.3   2.6   -     -     2.5   2.1   1.6  1.4   1.1   0.9   0.9
                                                 10           7.1   7.6   -     -     7.1   6.3   5.7  4.8   3.8   3.6   3.2
                                                                                                                                               
    

    TABLE 7.  Half-life of methacrifos on various grains stored in mini
    silos at 26C
                                                                 
    Commodity         Storage conditions       Half-life (days)
                      moisture      temp.C
                                                                 
    Wheat               10.2          26          105
    Barley              12.9          26           44
    Maize               12.8          26          100
    Sunflower seed       7.2          26           90
                                                                 

    From the trial in which the grains were stored in drums at 32C the
    following half-life periods were calculated; for the moisture content
    (see table 5).

    Commodity   Half-life(days)

    Wheat             70
    Oats              60
    Maize             85
    Peanuts           55
    Soybeans         100


    Large-scale trials

    Wheat and barley

    Large-scale trials in silos were carried out under a range of storage
    conditions in various countries e.g. Australia, Argentina, Morocco,
    Spain, Switzerland and France.  As in the small-scale trials it was
    found that the application rate did not affect the rate of dissipation
    of the residues in any of the grain investigated (McDougall 1976)
    (table 8).

    The experiments under practical conditions confirmed that the
    dissipation of methacrifos is mainly dependant on time and
    temperature.  The residue decrease under storage conditions prevailing
    normally in Europe (temperature 15-25C) is much slower than in
    regions where storage temperatures are generally higher e.g. Australia
    (Formica, 1975).

    In the trials carried out in Australia in which the grain was aerated
    during the storage period, there were indications of a decreased rate
    of dissipation, compared with silos in which the grain was stored
    under the same conditions of temperature and moisture at the start of
    the experiment, but not aerated.  Aeration was started 24 hours after
    treatment and functioned only during the cooler hours of the day for a
    total of 84 hours a week for the first 4 weeks and about 30 hours
    weekly thereafter (Table 9) (Moor and McDougall 1975).  In other
    experiments aeration had little or no effect on residue dissipation
    (Formica, 1978g).



        TABLE 8.  Dissipation of methacrifos in small grain
    Large-scale trials in silo. (Moore and McDougall, 1974a, 1974b and 1975).

                                                                                                                                                
    commodity    country      size        storage conditions     dosage     sampling   residues of methacrifos after
                             of lot     % moisture   temp. C     rate       depth      ..... weeks in mg/kg
                             (tons)                               mg/kg     ..... m    0,15    1     6    11/12   16  21  22/23   26    34   41
                                                                                                                                                

    Wheat       Australia     100          11.3         30        20         0.6            21.8  11.8    7.5   5.6       4.1    4.2
                (Queensl.)                 10.3                    20         1.5            14.2   9.6    5.3   3.9       2.9    2.6
                1974                       10.8                    20         6.0            15.5   8.6    5.2   3.0       1.8    1.6

                Australia     800          11.5        26-28       20         0.6             9.3   6.4    4.8   4.0       4.1    3.7
                (N.S.W.)                   11.3                    20         1.5             8.6   6.3    4.9   3.8       3.0    2.5
                1974                       10.9                    20         6.0             10.7  8.1    5.7   4.9       4.6    3.3

    (aerated)   Australia     550          12.4       (note 1)     15         0.1       9.7         5.0    3.6             2.3          1.4   1.6
                (Queensl.)                 11.4                    15         2         9.0         5.6    4.2             2.6          2.1   2.6
                                           11.0                    15         4         9.6         5.7    4.8             3.6          2.8   2.2
                                           11.0                    15         6        11.9         6.0    5.3             3.3

    not                                    10.9       (note 2)     15         0.1      11.4         6.0    3.7             2.3          1.6   1.5
    aerated                                10.2                               2        9.8          6.1    3.6             1.6          0.75  0.8
                                           10.4                               4        10.0         3.8    1.7             1.6          0.6   0.6
                                           9.9                                6        10.4         4.8    2.6             1.8
                                                                                                                                                

    1 Mean temperature in silo first 18 weeks 25-31C; from 23-41 week 14-23C.
    2 Mean temperature in silo first 18 weeks 27.5-34C; from 23-41 week 17-20C.

    TABLE 9.  Dissipation of methacrifos in small grains
    Large scale trials in silos. (Formica, 1978a, 1978b).

                                                                                                                                               
    commodity    country    size        storage conditions     dosage     sampling   residues of methacrifos after
                           of lot     % moisture   temp. C     rate       depth      ..... weeks in mg/kg
                           (tons)                               mg/kg     ..... m    0    45    70    87    171/   322/  430   463   504    560
                                                                                                            180    339
                                                                                                                                               

    Barley     Switzerland   51                      2-25       22.3         2      13.8        7.6         2.6    3.8         2.5   1.5   0.86
                                                                                                           (3.0-  (7.8-       (2.9-  (2.9-
                                                                                                           1.75)   1.6)        1.7)  0.3)

    Barley        Spain      100          11.6       13-26       10          2      4.1     3.7       3.2    1.3   2.8   1.7

    Wheat         Spain      100          11.0       13-26       10          2      9.4     5.6       3.0    2.8   2.1   1.0
                                                                                                                                               
    

    The effect of aeration was also evaluated in a residue trial carried
    out under Swiss conditions.  A bin of barley treated with methacrifos
    at 10 mg/kg was aerated twice during the storage period (after one and
    three weeks) and another bin in the same warehouse was not aerated.
    The residue on the aerated barley was 12.4 mg/kg at the beginning of
    the experiment, 6.6 mg/kg after one week; 4.6 mg/kg after 32 weeks and
    2.0 mg/kg after 74 weeks.  The residues in the non-aerated bin were
    11.3, 8.6, 4.2 and 2.5 mg/kg at the same sampling times, showing that
    aeration had little or no effect on the residue dissipation.  The
    residue in oats stored at the same farm (without aeration ) were 10.2,
    9.0, 6.0 and 3.7 mg/kg at these sampling times.  Comparable results
    were obtained in a similar trial on wheat in Switzerland in which one
    bin was aerated after 54, 103 and 142 days post-treatment, by
    circulating the wheat through the conveyer system and back to the
    silo, and another bin not aerated.  The initial residues were 6.0 and
    6.1.  Residues after the three aerations were 4.2, 3.7 and 3.4 mg/kg
    on the aerated wheat and 4.8, 4.2 and 3.9 mg/kg on the nonaerated.

    Again the rotation and resulting aeration of the wheat had little, if
    any, influence on the dissipation rate (Formica, 1978d, 1978e).  The
    residue dissipation at different levels in a silo was studied in
    Switzerland under typical European continental storage conditions with
    temperatures of about 5C in winter and 22C in summer.  Methacrifos
    was mixed with the grain in a closed conveyer system, at a rate of 11
    mg/kg; there was no ventilation during the storage period.  The
    initial concentration was 50 - 70% of the nominal value calculated
    from the application rate and the volume treated.  The residue at 2 m
    depth increased during the following 5 weeks to almost the nominal
    value and slowly decreased thereafter.  It is assumed that the active
    ingredient was not homogeneously dispersed immediately after
    application but became more uniformly distributed through migration.
    From a comparison of the residues in the samples taken from the
    surface and at 2 m depth, it seems evident that the dissipation was
    somewhat slower in the interior than on the surface of the stored
    grain (Formica, 1976f). (Table 10).

    In a study of the influence of the formulation on dissipation an
    aqueous formulation showed more rapid dissipation than a formulation
    with kerosene.  After treatment with a nominal 10 mg/kg the residues
    of the aqueous formulation were 0.2/0.16 and 0.15/0.25 mg/kg after 2
    and 15 weeks respectively, whereas the residues of the kerosene
    formulation were 9.1/9.3 and 4.0/3.5 mg/kg.



        TABLE 10.  Dissipation of methacrifos in wheat (Switzerland)

                                                                                                            
    Days after
    treatment      1        7      21      35        77        162      252   324     470     526     653
                                                                                                            
    samples from

    Surface       5.3      3.3     3.2   8.6/6.1   5.9/5.9   4.0/4.0    3.5   2.4     1.3     0.7      -
    2 metres    4.6/3.9    5.2     6.0  10.1/7.4   6.7/5.6   6.2/6.5    5.2   4.0      2.6    2.8   1.4/2.25
                                                                                                            
    

    Maize

    Several small-scale trials were carried out with maize kernels and/or
    cobs stored under various conditions of temperature and moisture
    content.  Although the distribution of the active ingredient was
    rather inhomogeneous, it was evident, as with the other grains, that
    the dissipation is dependant on time and temperature.

    Under tropical conditions (temperature 35C and higher) the residue
    decreased much more rapidly than at moderate temperatures (Giannone
    and Formica, 1979b).

    The dissipation of methacrifos in maize was studied in a large scale
    trial in Switzerland; 80 tons of maize kernels (moisture content
    14.5%) were treated at 10 mg/kg on a conveyer system during the
    filling of concrete silo cells, which were closed without ventilation.
    Results are shown in Table 11.


    TABLE 11.  Dissipation of methacrifos in maize

                                                                        

    Temp. in silos C1     19                 9         14        27

    Days after treatment    6                76        300       376

    Residue, mg/kg         7.8              3.62     3.9/3.4   0.4/0.7
                        (5.7-9.6)         3.1-4.2
                                                                        

    1 Temperature at a depth of 2 metres.
    2 Mean value of 4 samples; two samples analysed 5 months later than
    the other two samples; samples stored at -20C.


    Rice

    Small-scale trials on the dissipation of methacrifos under various
    storage conditions were carried out in Australia.  Brown and polished
    rice were treated at the rate of 10 mg/kg and stored in bags, at
    temperatures of 13-26C.  The moisture content of the brown rice was
    approximately 14.2% and of the polished rice 14.4%.  The initial
    residue of 9.1 mg/kg in brown rice decreased to 5.0 mg/kg after 12
    weeks and to 3.9 mg/kg after 24 weeks.  In the polished rice the
    corresponding residue levels were 7.9, 6.3 and 4.4 mg/kg respectively.

    In other trials paddy rice, brown rice and polished rice were stored
    in cardboard drums, and paddy rice also in mini-silos of about six
    tons capacity.  The decrease of the residue in paddy rice stored at
    about 32C was faster than in brown or polished rice.  Under the
    conditions occurring in the trials the dissipation rate of methacrifos
    was independent of the application rate (Hart and Moore 1975;
    McDougall 1976b) (Table 12).



        TABLE 12.  Dissipation of methacrifos in rice (McDougall, 1976b; Hart and Moore, 1976

                                                                                                                                  
                          Storage conditions          dosage                     Residues of methacrifos in mg/kg
                                                       rate                              after ..... days
                  mini-silo     moisture   temp. C    mg/kg
                  or cardboard     %
    Type of rice     drums                                            0        12          23       54/51    124/121    166   205
                                                                                                                                  

    paddy rice       silo         13.7       17-26      10           8.2       5.8                  4.7        3.7      2.6
    paddy rice       drums      8.8-12.8      32        10          10.8                   6.2      4.4        2.2            1.2
                     drums      8.8-12.8      32         5           4.5                   2.6      1.9        0.9            0.5
    brown rice       drums      8.8-12.8      32        10           9.1                   7.0      5.5        3.8            2.7
                     drums      8.8-12.8      32         5           3.7                   3.2      2.4        1.2            1.0
    polished rice    drums      8.8-12.8      32        10          13.0                   9.6      7.2        4.6            2.7
                     drums      8.8-12.8      32         5           4.7                   3.9      3.2        1.6            1.0
                                                                                                                                  

    TABLE 13. Dissipation of methacrifos in sorghum

                                                                                                                          
                          Storage conditions          dosage                     Residues of methacrifos in mg/kg
                                                       rate                              after ..... days
                  silo or       moisture   temp. C    mg/kg
    Country       bags             %                                  0       15     21       45     56       90      147
                                                                                                                          

    Australia      silo           13         27         15           13.6            9.3             7.7              6.3
                                  13         27         15           9.1             4.1             7.1              4.3
                                  13         27         7.5          8.0             4.7             4.9              2.7

    Mali           bags                     25-30       10(dust)              3.6             3.0             1.9
                                            25-30       10(solution)          6.1             4.2             2.1
                                                                                                                          

    TABLE 14.  Dissipation of methacrifos in peanuts, stored in drums (McDougall, 1976a)

                                                                                                                 
                    Storage conditions         dosage            Residues of methacrifos in mg/kg
                                                rate                      after ..... days
                  moisture %   temp. C        mg/kg
    Country           %                                    7      12     28     56     84     126    175    210
                                                                                                                 

    Peanut

    whole          7.8-4.4        32             20       14.2   12.0    9.0    6.6    4.7    3.2    2.2    2.2
    kernel                                                0.6    1.5     1.7    0.3    0.3    0.4    1.0    0.4
    shell                                                 50.8   49.5    30.6   30.5   29.2   10.3   8.8    7.7

    Peanut

    whole          7.8-4.4        32             10        7.1   6.5     4.2    2.4    2.8    1.8    1.2    1.1
    kernel                                                 0.6   0.3     <0.3   0.3    <0.3   <0.3   <0.3   <0.3
    shell                                                 41.5   21.5    23.7   12.9   7.3    7.3    4.1    5.7
                                                                                                                 
    

    Sorghum

    Data are available from large-scale trials in Australia where sorghum
    treated at 7.5 and 15 mg/kg was stored in silo bins and from Mali
    where sorghum treated according to the so-called "sandwich method"
    with a dust or a spray was stored in bags.  The rate of dissipation
    was similar to that in the other grains (Hart and Moore 1976, Giannone
    and Formica, 1980) (Table 13).

    Pulses (dried legume vegetables)

    In a small-scale trial in Switzerland, a mixture of beans and peas
    (Vicia faba, Phaseolus nanus and Pisum sativum) was
    treated with a dust (10 or 20 mg/kg ai/kg) or a liquid formulation (10
    mg ai/kg) and stored in drums at 25  1C; moisture content before
    treatment was 9.8%.  Three hours after the application the residues in
    the lots treated with the dusts at 20 and 10 mg ai/kg and the solution
    at 10 mg ai/kg were 5.5, 3.9 and 2.7 mg/kg respectively.  After 27
    days the residue levels in these lots were 6.5, 2.6 and 2.6 mg/kg and
    after 142 days 3.5, 1.7 and 1.7 mg/kg respectively.

    In a small-scale trial in Nigeria, cowpeas were treated with 10 mg/kg
    methacrifos and stored in open jute bags under tropical conditions. 
    No residues (<0.12 mg/kg) were found 65 and 92 days after treatment.

    Peanuts

    A mini-silo (drum) trial was carried out in Australia.  Methacrifos
    was applied at 10 and 20 mg/kg to whole peanuts, which were stored in
    120 l cardboard drums at 32C.  On all sampling dates kernels and the
    shells were analysed separately.  The results show that nearly all the
    residue is contained in the shell (McDougall, 1976).

    In Mali, peanut kernels were treated with 10 mg/kg methacrifos and
    stored in closed plastic bags under tropical conditions (25-30C).
    Residues after 15, 60 and 90 days were 7.6, 5.6, 5.2 mg/kg
    respectively (McDougall 1976).

    Cocoa-beans

    Cocoa-beans stored in closed jute bags in a warehouse were treated
    with methacrifos at 0.4 g ai/m2 on the outside of the bags.  Samples
    were taken at four sampling dates from the outside layer of cocoa-
    beans, which had been exposed to the treatment, and from the interior
    of the bags.  The residues in samples from near the outside of the
    bags were higher than in the internal samples; 34 days after treatment
    the residues in the outer samples were 1.0 and 1.2 mg/kg and in the
    inner samples <0.025.  After 98 days the levels were 0.83 and 0.32
    mg/kg respectively.

    The methacrifos residues were found mainly in the peel.  34 days after
    treatment the residues in the whole beans were 1.0 and 1.2, in the
    peel 5.6 and in the kernel 0.5 mg/kg (Formica, 1978c).

    Coffee beans

    Raw coffee beans imported from Nigeria were treated in Switzerland
    with methacrifos in 10 and 20 mg/kg.  The treated beans were stored in
    closed drums at 20  2C.  After 4 months storage the residues from
    the 20 mg/kg treatment were 2 mg/kg but 0.5 mg/kg in the lot treated
    with 10 mg/kg (Renfer, 1976).


    FATE OF RESIDUES

    In animals

    General

    As grain treated with methacrifos and grain products derived from
    treated grain may be used as animal feed, it was necessary to study
    the fate of methacrifos in livestock animals and to demonstrate that
    no significant residue would remain in livestock and poultry, milk or
    eggs.  Special trials therefore, were carried out to study possible
    carry-over from residues in feed to tissues or products of animal
    origin.

    Chickens

    In a preliminary experiment, four young male broilers were given a
    single oral dose of 20 mg/kg methacrifos by capsule.  The birds were
    slaughtered 6, 12, 24 and 48 hours after dosing.  Samples of fat,
    muscle, liver, kidney, heart, gizzard and skin were analysed.  The
    residues in all muscle and heart samples were 0.01 mg/kg or less.
    Residues in the other samples decreased very rapidly (Moore and
    McDougall, 1974c) (Table 15).

    TABLE 15.  Residues of methacrifos in chicken tissues after single
    oral treatment with 20 mg/kg

                                                  
    Tissue     Residues in mg/kg
               time (hours post-treatment)
                 6        12       24        48
                                                  

    Fat         0.22     0.06    <0.01     <0.01
    Liver       0.02     0.01     0.01     <0.01
    kidney      0.08    <0.03    <0.03     <0.03
    Gizzard     0.42    <0.01    <0.01     <0.01
    Skin        0.06     0.02    <0.01     <0.01
    Muscle     <0.01    <0.01    <0.01     <0.01
    Heart       0.01    <0.01    <0.01     <O.01
                                                  


    In a further experiment 5 groups of 77 one-day old chicks each were
    given feed fortified with methacrifos at levels of 0, 10, 100, 250 or 

    500 mg/kg for 63 days.  At the end of the feeding period 20 chickens
    from each group (10 males and 10 females) were slaughtered and the
    combined muscles, skin, kidney and liver used for analysis.  In all
    tissues examined residues were less than 0.01 mg/kg (Formica, 1974).

    Eggs

    Three groups of 15 laying hens were fed a diet containing 0, 10 or 20
    mg/kg methacrifos.  Egg samples were collected one day before
    treatment, on the 16th day of treatment and 0, 2, 3, 7 days after the
    end of the treatment.  In none of the samples were residues found
    (<0.01 mg/kg) (Schnabel and Formica, 1979).

    Milk

    Two lactating cows were given 30 mg methacrifos by capsule daily for
    10 days.  This dose corresponds to about 3 kg of cereals treated at a
    rate of 10 mg/kg daily in the total ration.  Pooled morning and
    evening milk samples were taken before, during the feeding period and
    three days after its completion.  No residues (<0.001 mg/kg) could be
    detected in the milk of the treated cows before, during or after the
    10 day period (Formica, 1977).

    In plants

    Stored grain

    The degradation of carbonyl 14C methacrifos (specific radioactivity
    31.1 Ci/mg) in grain treated with 10 mg/kg was studied under
    laboratory conditions for one year; 84-94% of the applied
    radioactivity was recovered at all sampling times, indicating very
    limited volatility of methacrifos or its degradation products.  After
    one year about 25% of the then recovered radioactivity was present as
    parent compound.  The fact that little volatilisation of the
    radioactivity occurred during the storage indicates that methacrifos
    and its degradation products were strongly absorbed to the wheat
    grain.  Less than 15% of the recovered radioactivity could be washed
    off the surface of the grain with methylene chloride.  The bulk of the
    radioactivity could be extracted only after grinding of grain.  The
    non-extractable portion of radioactivity was low at the early sampling
    dates but rose to 9-14% after 140 and 385 days.  The low but
    continuous evolution of 14C during the experiment may demonstrate
    that the insecticide is eventually metabolised by the wheat grain. 
    The organosoluble radioactivity on or in the grains consisted mainly
    of the parent compound.  The oxon was not detected.  Mono- and
    di-demethylated methacrifos were detected by ethylation followed by
    GLC analysis.  Their identity was confirmed by methylation with
    deuterated diazomethane (CD2N2) followed by GCMS.

    The results give strong evidence for the degradation pathways shown in
    figure 2 (Blattmann 1978).

    Figure 2.  Degradation of methacrifos in grain

    FIGURE 2

    The decrease of the protective effect of methacrifos against insects
    is closely related to the decrease of the amount of the unchanged
    methacrifos still present.  This suggests that the degradation
    products are less toxic to insects than the parent compound (Renfer
    1977).

    TABLE 16.  Distribution and characterization of radioactivity in
    stored wheat after the application of 10 mg/kg 14C-methacrifos

                                                                
                             % of radioactivity recovered after
                             storage for (days)
    Compounds                 0      23     140    294    385
                                                                

    Extractable

    methacrifos parent        99.7   98.5   51.6   33.3   25.2
    demethylated
    methacrifos-derivatives     -      -    34.1   45.4   6O.2
    unknowns                    -      -     5.1    6.8    2.9

    Non-extractable            0.3    1.5    8.7   13.8   10.9

    CO2                      -      0.02   0.5    0.7    0.8
                                                                


    The formation of the demethylated degradation products has been
    studied in various products stored under practical conditions.  The
    results are summarized in table 17.



        TABLE 17.  Formation of the demethylated metabolites during storage (treatment in all
    cases 10 mg/kg)

                                                                                                      
                     Storage after            Residues mg/kg              Reference
                       treatment      methacrifos       demethylated
                         days                           metabolites
                                                                                                      

    Wheat grain          215            2.7/2.9            1.6/1.8        Formica, 1978d
                         365            1.7/1.8            1.7            Formica, 1978c
                         430            1.0                2.4            Formica, 1978b

    Barley grain          76            4.2                2.0            Giannone and Formica, 1980a
                         300            3.0                4.2                "           "       "
                         370            1.5                3.8                "           "       "
                         430            1.3                2.5            Formica, 1978b

    Maize grain           76            6.4                1.6            Giannone and Formica, 1980a
                         300            4.1                2.0                "           "       "
                         370            0.7                5.0                "           "   , 1979

    Maize cob1           231            3.5/3.7            11.4/11.6      Giannone and Formica, 1979

    Sorghum grain        15             6.1                1.3            Giannone and Formica, 1980b
                         45             4.2                0.7                "           "       "
                         90             2.1                1.4                "           "       "

    Peanut kernels       15             7.6                0.2            Giannone and Formica, 1980c
                         45             5.6                0.5                "           "       "
                         90             5.2                0.6                "           "       "

    Cocoa beans          15             0.44/0.41          O.27/0.29      Giannone and Formica, 1979a
                                                                                                      

    1 Cobs stored in open wired cribs were treated by spraying the surface of cribs with 10 mg
    ai/kg related to the total quantity of maize cobs.  As the samples were taken from the periphery
    of the crib a rate of their treatment higher than 10 mg/kg must be expected.
    


    In processing

    Residues of methacrifos have been followed through milling and baking
    procedures in several experiments.  As the insecticide is primarily
    located in the outer layers of the grain, most of the residues are
    found in the bran and the low grade flour fractions after milling.

    The residue in flour milled 1 month after the treatment of the grain
    was about 1/10 of that in whole grain.  After prolonged storage the
    residues in flour tend to increase, but they do not exceed 1 mg/kg
    even after storage for 21 months.  In the baking process methacrifos
    and its metabolites are degraded to a large extent resulting in low or
    undetectable residues (maximum about 0.1 mg/kg or lower).  (Table 18).



        TABLE 18.  Residues of methacrifos in milled wheat fractions and bread

                                                                                                                  
                                                      Residues (mg/kg) in
    Treatment  Storage
    mg/kg       time      whole wheat  white flour  low grade flour    bran     white bread     Reference
                flour
                                                                                                                  

        10      1 month     4.0/3.8      0.4/0.4        1.7/1.6      7.6/6.4      <0.03         Formica 1978b
        10      7 months    3.1/2.9      0.6/0.6        8.1/8.4      10.0/9.2     0 01/<O.01       "    1978d
        10      21 months   1.4/1.6      1.0/0.8        10.3/9.1     7.4/7.5      0.02/0.08        "    1978f
        15      1 month     7 8/7.8      0.6/0.6        2.5/2.7      10.4/11.2    <0.03            "    1978b
        20      1 month     8.0/7.4      0.9/0.85       3.1/3.2      15.6/18.0    0.03/0.04        "    1978h
        10      265 days    0.751        ca. 0.30                    2.6          <0.04         Tournayre 1978
         5      265 days    0.261        ca. 0.10                    0.8          <0.04             "      "
        10      265 days    2.01         ca. 0.50                    6.1          <0.04             "      "
                                                                                                                  

    1 after 252 days
    


    In experiments with the radio-labelled insecticide it was shown that
    the same degradation products are formed during baking as are found in
    stored grains (Blattmann 1978).

    Further data on the effect of processing rice, oats and barley,
    including malted barley are presented in table 19.  In these
    experiments the initial concentrations are in most cases higher than
    recommended.  As with wheat, the milling of paddy rice treated with
    methacrifos resulted in a considerable loss of insecticide.  More than
    90% of the initial residue was removed with the hulls (McDougall
    1976), resulting in a decrease of the residue in going from paddy to
    brown rice by a factor of 5 to 8.  Most of the insecticide present in
    the brown rice was again removed with the bran fractions.

    The amount of methacrifos residue is further decreased on cooking.
    Short cooking of about 15 minutes decreased the residue by a factor of
    about 2.6 whereas the more usual cooking of 25 minutes resulted in a
    reduction by a factor of about 8.

    Processing treated barley grain to malt, which was then used to brew
    beer, gave very low level in the beer.

    The processing of treated cocoa beans to cocoa mass decreased the
    initial methacrifos on the beans at least by a factor of 10.  Since
    further diluting processes take place the overall decrease of
    methacrifos from the raw product to the consumed chocolate is even
    higher.


    METHODS OF RESIDUE ANALYSIS

    Residue of the parent compound in:

    Cereal grains and grain derivatives.  Methanol or acetone extracts can
    be used to determine the active ingredient by GLC without cleanup.
    Recoveries range from 80-115%; the limit of determination is about
    0.05 mg/kg.  (Desmarcherlier et al 1977; Moore and McDougall, 1973
    and Formica, 1973g).

    Chicken tissues.  Residues in chicken tissues are determined by GLC
    with a phosphorus-specific detector after extraction with acetonitrile
    and clean-up by partition (Formica 1974b).

    Milk.  Milk is coagulated with acetone.  After a partition step,
    methacrifos is determined by GLC with a phosphorus-specific detector.

    'Total residue':

    A method has been developed to determine unchanged methacrifos and the
    dealkylated metabolites in a two-step procedure in cereal grains, eggs
    and cocoa mass.  Extraction with aqueous methanol is followed by
    partition of the parent compound into hexane.  The dealkylated
    metabolites are then extracted from the aqueous phase with methyl

    acetate and methylated with diasomethane.  The residues are determined
    by GLC with a phosphorus-specific detector.  Limits of determination
    are 0.025 mg/kg for the parent compound and 0.04-0.1 mg/kg for the
    dealkylated product.

    Both the method for residues of the parent compound in cereal grains
    and the method for the total residue are suitable or can be adapted
    for regulatory purposes.




        TABLE 19.  Effect of processing on methacrifos residues

                                                                                                         
    Raw product     Treatment        Storage       Residue before     Processing or       Residue after
                     level                           processing       processed product    processing
                     mg/kg                              mg/kg                                mg/kg
                                                                                                         
    Paddy rice        18             6 months            3.1          brown rice raw         0.65
                                                                      cooked 15 min.         0.23
                                                                      white rice raw         0.12
                                                                      cooked 15 min.         <0.02

    Paddy rice        10             3 months            3.0          brown rice             0.36
                                                                      hulls                  18.4
                                                                      white rice             <0.2
                                                                      bran                   2.7

    Hulled rice       18             3 months            7.1          cooked 5 min.          4.4
                                                                      cooked 15 min.         2.7
                      18             6 months            4.8          cooked 25 min.         0.75

    Polished rice     18             3 months            7.5          cooked 15 min.         2.6

    Oats              18             3 months            4.7          cooked 15 min.         0.9

    Barley            18             3 months            4.8          malted barley          0.1

    Malt1             10                 -               9.8/10.1     brewer's grains        1.7/2.0
                                                                      wort before boiling    0.27/0.31
                                                                      yeast                  <0.1
                                                                      beer                   <0.01

    Cocoa beans       10             7 days              5.0/5.2      cacao mass             0.46/0.44
                      surface of
                      bags with      97 days             0.32         cacao mass             0.02
                      0.4 g a.i./m2
                                                                                                         

    1 Malt has been directly treated to follow the dissipation during further processing.  Under normal 
    practical conditions only barley grain is to be treated.
    


    EVALUATION

    COMMENTS AND APPRAISAL

    Methacrifos is an organophosphorous insecticide which is almost
    exclusively used as a grain protectant and as a control agent against
    insect pests in other stored products.  It may be used as an acaricide
    in the same stored commodities.  It gives good and long-lasting
    protection of grain and other stored products against a broad spectrum
    of pests including those which show resistance to commonly used stored
    products insecticides such as other organophosphorous compounds,
    lindane, etc.  The major formulations are emulsifiable concentrate,
    solutions in othanic solvents and dusts.  The normal application rate
    is about 10 mg ai/kg grain.  Lower rates may be used at lower
    temperatures; exceptionally a higher rate up to 20 mg/kg may be
    needed.

    Methacrifos is rapidly absorbed, metabolised and excreted in mammals.
    Two metabolites detected in urine and faeces were identified as
    N-acetyl-S(2-methoxycarbonylprop-1-enylcysteine) and P-O-desmethyl
    methacrifos.  Neither methacrifos nor its metabolites were found to
    accumulate in the tissues.

    Methacrifos has a moderate acute toxicity following oral
    administration to various animal species.  Signs of poisoning are
    typical of cholinesterase inhibitors.  The acute toxicity was found to
    be potentiated by several other organophosphorous esters.

    Methacrifos did not induce a delayed neurotoxic response in hens.  In
    short- and long-term studies methacrifos caused signs and symptoms of
    cholinesterase inhibition, which were associated with effects on body
    weight gain and food consumption.  Brain cholinesterase activity was
    inhibited at 100 mg/kg.  In rats at high dose levels, effects on
    several haematological parameters were observed.  Cholinesterase
    activity in plasma was inhibited at doses above 10 mg/kg and recovery
    of cholinesterase activity was relatively slow.

    In long and short term studies, cholinesterase depression was observed
    at 10 mg/kg and above.  A no-effect level of 1 mg/kg was observed.

    Because of parental mortality in a 3-generation reproduction study and
    foetal death in teratology bioassays, the meeting could not evaluate
    fully the potential effects in these areas.  Further studies are
    required for a full evaluation of this compound.

    Mutagenicity studies with bacteria, a mouse carcinogenicity study and
    a rat teratology study were all negative.

    Acceptable data were available to allow the meeting to establish
    no-effect levels in two mammalian species and a temporary ADI was
    allocated.

    The fate of methacrifos in stored cereals, beans, peanuts and cocoa
    has been elucidated in extensive laboratory trials as well an in many
    supervised small and large-scale trials under practical conditions in
    various countries and under a variety of storage conditions.  The
    following conclusions can be drawn.

    The rate of degradation depends on time and storage conditions.  The
    residues decrease faster with increasing temperature and moisture
    content of the food commodity.  Other factors, such as grain variety,
    rate of application, application technique and type of formulation,
    have little or no influence on the dissipation rate.  Aeration of the
    stored cereals has only a minor effect on the rate of loss.

    The metabolic pathways of methacrifos on grain and other stored
    products were elucidated.  The compound is demethylated to mono- and
    di-desmethylated methacrifos; there is some evidence that these
    metabolites are not cholinesterase inhibitors.  These are further
    metabolised to CO2 at a slow rate.

    The residues remain primarily on the outer layers of the grain. 
    During prolonged storage only limited penetration into the endosperm
    takes place.  Processing of the raw commodities, such as milling of
    cereals, dehusking and polishing rice, removing shells and seed-coats
    from peanuts and shells from cocoa, reduce the residue considerably.

    During baking and brewing methacrifos and its main metabolites are
    further degraded, resulting in residues at or about the limit of
    determination in bread and beer.  Degradation also occurs during
    cooking to an extent that depends upon the time of cooking.

    When grains treated at normal rates are fed to livestock animals or
    poultry, no residues are found in meat, milk or eggs.

    Methods of residue analysis are available for methacrifos residues
    (parent compound) in stored products by GLC with a
    phosphorous-specific thermionic detector after extraction with
    methanol or acetone.  The limit of determination is about 0.05 mg/kg.
    Methods are also available for methacrifos in meat of poultry, eggs
    and milk after extraction with acetonitrile or acetone followed by
    various partition steps and GLC with a phosphorous detector; the limit
    of determination is 0.01 mg/kg.  The methods are suitable or can be
    adapted for regulatory purposes.

    Residues of the unchanged parent compound and the dealkylated
    metabolites can be determined, in a two step procedure, in cereal
    grains, eggs and cocoa-mass. The limits of determination are about
    0.025 mg/kg for the parent compound and 0.04 - 0.1 for the dealkylated
    metabolites.  The method can be adapted for regulatory purposes.

    When establishing maximum residue limits for methacrifos on grain or
    other stored food commodities, the following factors have to be
    considered.

    1. The residue level depends largely on the application rate, which
    has to be chosen according to the nature of the insect or mite
    infestation and the desired period of protection.  Variation in
    residue levels are to be expected among different countries even when
    the same dosages are applied and the same storage period is used,
    since the rate of dissipation may differ according to the local
    climate and storage conditions.
    2. The distribution of the insecticides may be heterogeneous,
    depending on local application techniques.
    3. Stored products may move in international trade at different times
    after treatment according to commercial need.

    Based on these considerations the maximum residue limits have to be
    set at levels that will cover all situations encountered after the
    normal applications, even if in some cases the actual residues will be
    much lower.

    The meeting examined residue data from supervised trials reflecting
    established and/or anticipated good storage practice on a number of
    stored food or feed commodities.  From these data the meeting was able
    to estimate the maximum residue levels that were likely to occur when
    methacrifos is used in practice.

    Level causing no toxicological effect

    Rat: 1 mg/kg in the diet equivalent to 0.05 mg/kg bw/day.
    Dog: 1 mg/kg in the diet equivalent to 0.025 mg/kg bw/day.

    Estimate of temporary acceptable daily intake for man

    0-0.0003 mg/kg bw.

    RECOMMENDATION OF RESIDUES LIMITS

    The meeting concluded that the maximum residue levels listed below are
    suitable for establishing maximum residue limits.

    These levels refer to the parent compound only.

                                                  
    Commodity                  Estimated maximum
                                 residue levels
                                      mg/kg
                                                  
    cereal grains                     10
    wheat flour (whole meal)          10
    wheat flour (white)                2
    wheat bran (unprocessed)          10
    beans and peas (dry)               5
    cocoa beans                       10
    peanuts (including shell)         10
    peanuts                            1
    poultry meat                       0.011
    eggs                               0.011
    milk                               0.011
                                                  

    1 The levels refer to the maximum residue levels which might occur
    when the animals concerned are fed with commodities treated during
    storage with recommended amounts of methacrifos.


    FURTHER WORK OR INFORMATION

    Required (by 1983)

    1. Teratogenicity studies in rat and rabbits.
    2. An appropriate reproduction study.

    REFERENCES

    Arni, P. and Mller, B. Samonella/mammalian-microsome mutagenicity
    test with CGA 20168. (1979) Unpublished report, May 23, submitted by
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    Basler, W. et al. Two-year chronic oral toxicity study with
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    by Ciba-Geigy from the original Industrial Bio-test Laboratories
    records, May 15, submitted by Ciba-Geigy to WHO.

    Bathe, R. Acute oral LD50 of technical CGA 20168 in the rat. (1974a)
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    Bathe, R. Acute dermal LD50 of technical CGA 20168 in the rat.
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    Bathe, R. and Sachsse, K. Acute oral LD50 in the mouse of technical
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    Bathe R. et al. 26 weeks feeding study in dogs with technical CGA
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    Charles, J.M. et al. A chronic oral carcinogenic toxicity study with
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    May 15, submitted by Ciba-Geigy to WHO.

    Chesterman, H. et al. CGA 20168, 28-day dietary feeding study in
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    Sachsse, K. and Bathe, R. Potentiation study. CGA 20168 versus 6
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    See Also:
       Toxicological Abbreviations
       Methacrifos (Pesticide residues in food: 1982 evaluations)
       Methacrifos (Pesticide residues in food: 1986 evaluations Part II Toxicology)
       Methacrifos (Pesticide residues in food: 1988 evaluations Part II Toxicology)
       Methacrifos (Pesticide residues in food: 1990 evaluations Toxicology)