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    FAO/PL:1967/M/11/1
    WHO/Food Add./68.30

    1967 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD

    THE MONOGRAPHS

    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party of Experts and the WHO Expert
    Committee on Pesticide Residues, which met in Rome, 4 - 11 December,
    1967. (FAO/WHO, 1968)

    FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
    WORLD HEALTH ORGANIZATION
    Rome, 1968

    DICHLORVOS

    This pesticide was evaluated by the 1966 Joint Meeting of the FAO
    Working Party and the WHO Expert Committee on Pesticide Residues
    (FAO/WHO, 1967). Since the previous publication, the results of some
    additional experimental work have been reported. This new work is
    summarized and discussed in the following monograph addendum.

    IDENTITY

    Chemical names

    2,2-dichlorovinyl dimethyl phosphate

    0,0-dimethyl-2,2-dichlorovinyl phosphate

    Synonym

    DDVP

    Names of Proprietary Products

    Dichlorvos or formulations containing dichlorvos appear under trade
    names of "Vapona", "Nuvan", "Nogos", "Cossman's Fly-Cake",
    "Phoracide", "Herkol", "Alco Fly Fighter Insect Spray", "Lethalaire
    Bantam 8", "Lethalaire F-83", "Real-Kill Fly and Mosquito Killer",
    "Kill-Fly Resin Strip", "Misect", "Atgard V", "De-Pester Insect
    Strip", "Vaponex", "Vaponicide", "Vaporette Bar", "Dedevap", "No-Pest
    Strip".

    Empirical formula

    C4H7O4PCl2

    Structural formula

    CHEMICAL STRUCTURE 

    Relevant physical and chemical properties

    The technical material usually contains 95 to 99 percent dichlorvos, 
    1 to 4 percent related compounds, and about 1 percent of unrelated
    impurities. It is a clear, mobile liquid with a mild, rather pleasant
    aromatic odor.

              Boiling point:           84C at 1 mm Hg

              Specific gravity:        1.415 at 25C

              Vapor pressure:          0.01 mm Hg at 20C
                                       0.032 mm Hg at 32C
                                       0.30 mm Hg at 60C

              Solubility:            About 3 percent in kerosene and
                                     mineral oils and 1 percent in water
                                     and glycerine. Miscible with
                                     aromatic and chlorinated
                                     hydrocarbon solvents.

              Volatility:            145 mg/m3 at 20C
                                     350 mg/m3 at 30C
                                     800 mg/m3 at 40C

              Stability:             Stable in organic solvents but
                                     hydrolyzes in presence of water.
                                     Alkalis accelerate and acids reduce
                                     aqueous hydrolysis.

    Composition of the Technical Product

    Dichlorvos is available in oil solutions, emulsifiable concentrates,
    aerosol formulations, and impregnated in polyvinyl chloride resin and
    sold in the form of pellets, strips, blocks, and other forms. The
    impregnated-resin stock usually contains about 20 percent of
    dichlorvos by weight.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    Acute Toxicity

    In acute oral toxicity studies in male rats, the toxicity of
    dichlorvos was markedly potentiated when administered in combination
    with malathion. It was slightly potentiated when administered in
    combination with trichlorofon, phosdrin and phosphamidon. No
    potentiation was observed when it was administered in combination with
    twenty-three other pesticides (Narcisse, 1967).

    Short-term studies

    Dog. For two years, groups of three males and three females were fed
    diets to which 0, 0.1, 1, 10, 100 and 500 ppm of dichlorvos had been
    added. The individual portions were alloted weekly. Analyses of
    composite samples representing the average diets over one week showed
    respectively, 0.01, 0.09, 0.32, 3.2, 32 and 256 ppm of dichlorvos.
    Erythrocyte and plasma cholinesterase activities were reduced at the
    two highest levels; erythrocytic activity only was affected at the
    nominal level of 10 ppm but recovered to essentially normal level at
    the end of the feeding period. This recovery was also recorded at the
    nominal 100 and 500 ppm levels. Brain cholinesterase, measured at the
    end of the two year period, was not affected at any level.

    Histological examination of major organs revealed dose-related
    hepatocellular oedema, slight in degree and in one animal only at the
    nominal 10 ppm level, and found to a more marked degree and in all
    animals at the high level. Liver weights were slightly increased in
    males at the nominal 100 ppm level and in both sexes at the highest
    level. However, no difference from controls was seen in serum alkaline
    phosphatase or transaminase activities, total serum proteins or A:G
    ratios. No effect of dichlorvos was seen at any level on general
    appearance, survival, rate of weight gain, food consumption,
    peripheral blood picture or urine. (Jolley, Stemmer and Pfitzer,
    1967).

    Man. Dichlorvos was given orally to 4 separate 5-man groups at 1,
    1.5, 2.0 and 2.5 mg doses. The 2.0 mg dose produced a depression of
    plasma cholinesterase to 71 percent of control two days after a 28-day
    feeding period. The plasma cholinesterase of the group given 2.5 mg
    daily was depressed to 70 percent of control after feeding for 20
    days. There was no significant effect on RBC cholinesterase at this
    time. (Rider, et al., 1967).

    Long-term studies

    Rat. Initial groups of 40 males and 40 females were fed diets to
    which 0, 0.1, 1, 10, 100 and 500 ppm of dichlorvos had been added, for
    two years. Five males and five females from each group were to be
    selected for necropsy at 26, 52 and 78 weeks. Individual diets were
    allotted weekly; analysis of composite samples representing average
    diets over one week enabled estimates of average dietary
    concentrations to be made; respectively, 0, 0.047, 0.467, 4.67, 46.7
    and 234 ppm. Plasma and erythrocyte cholinesterase activities were
    depressed at the high level and generally slightly depressed at the
    nominal 100 ppm level. Brain cholinesterase, measured at 26, 52, 78
    and 104 weeks, was depressed at the high level. Histological
    examination of major organs disclosed fine vacuolization of the
    hepatic cells of the high level animals, with some fatty change and
    bile stasis. Fine vacuolization only was found in 80 percent of
    females and 62 percent of males at the nominal 100 ppm level. However,
    no effect was seen on serum total proteins or A:G ratios, and, in a
    supplementary experiment, no effect on hexabarbital sleeping time was
    found by prolonged feeding of dichlorvos up to 1000 ppm or by single
    sub-lethal oral doses. No hepatocellular change was seen at the three
    lower test levels. No effect of dichlorvos at any level was seen in
    behaviour or mortality rate, rate of weight gain, food consumption,
    terminal body and organ weights, peripheral blood picture, urine and
    tumour incidence (Witherup, Stemmer and Pfitzer, 1967).

    Comments

    Recent information has disclosed that dichlorvos is rapidly converted
    in plants, to dichloro-acetaldehyde and further to dichloroethanol. As
    these metabolites are also known to occur in mammals after dichlorvos
    administration, it was concluded that the assessment of the safe
    levels of dichlorvos included that of the metabolites.

    In two-year oral feeding studies on dogs and rats the decrease of the
    cholinesterase activity of erythrocytes and plasma is proportional to
    the applied dose of dichlorvos. Recovery to essentially normal level
    at the end of the experiment is especially visible in dogs. Depression
    of the brain cholinesterase activity could be ascertained in rats
    only, but only at the highest nominal dietary level 500 ppm.

    Cytoplasmatic vacuolisation in hepatic cello, while dose-related, may
    be considered as a variation within physiological limits. In dogs the
    increase in the weight of the liver at nominal levels of 100 ppm and
    500 ppm was not associated with changes of liver function tests. No
    stimulation or inhibition in the activity of microsomal enzymes were
    proved in rats by means of indirect test using the hexabarbital
    sleeping time.

    For the establishment of the ADI the dose-related effect on the
    cholinesterase activity resulting from the two year experiment on rats
    and dogs can be taken into consideration. The oral level of 0.25
    mg/kg/day was without toxicological effect in the rat. In dogs the
    corresponding value was 0.08 mg/kg/day.

    In man the dose of 0.033 mg/kg/day caused toxicologically
    insignificant depression of plasma cholinesterase activity. The
    erythrocyte cholinesterase was not affected.

    TOXICOLOGICAL EVALUATION

    Level causing no toxicological effect

         Man :   0.033 mg/kg/day

    Estimate of acceptable daily intake for man

         0 - 0.004 mg/kg body-weight.

    EVALUATION FOR TOLERANCES

    USE PATTERN

    Pre-harvest treatments

    Because of its very short persistence and lack of systemic action, the
    use of dichlorvos on growing crops is limited and somewhat
    specialized. Its most common pre-harvest use is for the control of
    aphids, red spider mite (Tetranychus telarius), white fly
    (Trialeurodes vaporariorum), leaf miners, and other pests of crops
    growing in greenhouses; and for the control of mushroom flies in
    mushroom houses. The crops and uses for which dichlorvos has been
    registered or approved in various countries are as follows :

              Cotton, date palms       Iraq
              Deciduous trees          Austria, Bulgaria, Germany, Great
                                       Britain, Hungary, Italy,
                                       Netherlands, Switzerland
              Greenhouses              Austria, Bulgaria, Germany, Great
                                       Britain, Hungary, Switzerland
              Horticulture             Austria, Great Britain

              Mushroom houses          Great Britain, Hungary,
                                       Netherlands, United States
              Ornamentals              Germany, Great Britain, Switzerland
              Vegetables               Austria, Great Britain,
                                       Netherlands, Switzerland
              General use              Austria, Ceylon, Chile, India,
                                       Japan, Mexico, Pakistan, Venezuela
              Dairy and meat           United States
              animals

    Dichlorvos has been approved in the United Stated for direct
    application to livestock, including lactating animals. It has also
    been approved to control flies, fleas, and mites in animal barns,
    piggeries, and chicken houses. In the United Kingdom it can be used in
    pig and poultry houses for ectoparasite control.

    Post-harvest treatments

    To date, the use of dichlorvos on food as post-harvest treatments has
    been largely experimental. However, the results have been so promising
    that it may find extensive use for protecting raw and processed
    agricultural products. Uses of dichlorvos investigated are as a direct
    spray or dust treatment to grain; as aerosol or impregnated-resin
    strips applied in the overhead space of storage bins for the control
    of insects infesting grains; and as sprays, vapors, fogs, aerosols,
    and impregnated-resin strips for controlling insects in facilities
    where foods are stored, handled, processed, transported, and marketed.

    Other uses

    Dichlorvos has been used for a number of years in the U.S.A. and in
    other countries as a spray or aerosol in tobacco warehouses for the
    control of cigarette beetles (Lasioderma serricorne) and the tobacco
    moth (Ephestia elutella) at the rates of 2 g/1,000 cu ft (71 mg/m3)
    biweekly and 1 g/1,000 cu ft (35 mg/m3) weekly, respectively. It has
    also been used in tobacco processing rooms after working hours at 0.5
    to 1 g/1,000 cu ft (18 to 35 mg/m3) daily.

    The principle use of dichlorvos, however, has been in the domestic and
    public health field. In the U.S.A., formulations containing 0.5
    percent of dichlorvos have been approved for the control of household
    pests such as ante, bedbugs, cockroaches, flies, mosquitoes,
    silverfish, spiders, ticks, and wasps in private and public buildings

    and outdoors. Resin strips impregnated with dichlorvos have been
    approved for use in the home kitchen in the United Kingdom and in
    homes and certain commercial establishments in the United States.

    Dichlorvos has been found effective for disinsection of aircraft
    during flight. Vapor concentrations of 0.15 - 0.30 g/litre of air
    produced 100-percent mortality of flies and mosquitoes after 30-minute
    exposures (Jensen, Flury, and Schoof, 1965). No effect was noticed on
    the cholinesterase level of three individuals exposed 24 times to
    30-minute aircraft treatments, during which time the dichlorvos vapor
    concentration was 0.20 to 0.24 g/litre of air (Schoof et al., 1961).

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    Crops grown under cover

    Mushrooms

    In the United States dichlorvos has been approved for mushroom houses
    at the rate of 2 g/1,000 cu ft (71 mg/m3) and can be applied every 4
    days provided no mushrooms are picked within 1 day after treatment. In
    trials conducted by Snetsinger and Miner (1964) no dichlorvos residue
    was found in mushrooms picked 24 hours after treatment at 4 g and 6 g
    of dichlorvos per 1,000 cu ft (141 and 212 mg/m3) nor were cumulated
    residues noted with consecutive applications. Ciba Laboratories Ltd.
    (unpublished) reported residues of 0.85 ppm 24 hours after, 0.03 ppm
    48 hours after, and 0.12 ppm 72 hours after treatment of the mushroom
    house with dichlorvos at the rate of 4.8 g/1,000 cu ft (170 mg/m3).
    Mushrooms exposed to application of 3 g/1,000 cu ft (106 mg/m3) had a
    maximum of 0.3 ppm 2 hours after, 0.02 ppm 24 hours after, and 0.3 ppm
    of dichlorvos 48 hours after treatment.

    Lettuce

    Tests conducted by Ciba Laboratories Ltd. (unpublished) with lettuce
    grown in greenhouses produced the following residues after one
    application :

                                                                                   
    Rate and method                  Dicohlorovos residues (ppm) at
    of application                   intervals after harvest (hours)
                                                                               

                                  1         2         24        48        72
                                                                               

    4 g/1,000 cu ft
    (141 mg/m3) by spray gun      78        53        4.9       -         -

    2 g/1,000 cu ft
    (71 mg/m3) by microsol        -         -         2.1       0.4       0.2
    generator

                                                                               
    Rate and method                  Dicohlorovos residues (PPE) at
    of application                   intervals after harvest (hours)
                                                                               

                                  1         2         24        48        72
                                                                               

    1 g/1,000 cu ft
    (35 mg/m3) by microsol        -         -         1.3       0.4       0.3
    generator
                                                                               
    
    Shell Chemical Company (unpublished) reported lettuce growing in
    greenhouses treated with dichlorvos at 1.4 g/1,000 cu ft (49 mg/m3)
    had residues of 4.4 ppm 4 hours after treatment and no detectable
    residue after 24 and 48 hours.

    Tomatoes

    Ciba Laboratories Ltd. (unpublished) reported tomatoes growing in a
    greenhouse treated with dichlorvos at 1 g/1,000 cu ft (35 mg/m3)
    (microsol generator) had residues of nil to 0.4 ppm. Shell Chemical
    Company (unpublished) conducted test treatments with dichlorvos at 1.4
    g/1,000 cu ft (49 mg/m3) on tomatoes growing in greenhouses. Residues
    found at intervals after spraying were 0.13 ppm after 15 minutes, 0.10
    ppm after 13 hours and nil after 23 hours.

    Cucumbers

    Shell Chemical Company Ltd. (unpublished) found no residues on
    cucumbers sprayed with dichlorvos at 1.4 g/1,000 cu ft (49 mg/m3) 16,
    24 and 48 hours after treatment. Ciba Laboratories Ltd. (unpublished)
    found residues of 7.2 ppm 24 hours after, 0.2 ppm 48 hours after, and
    0.02 ppm 72 hours after spraying with dichlorvos at the rate of 0.54
    g/1,000 cu ft (19 mg/m3).

    Crops grown in the open

    Ciba Laboratories Ltd. (unpublished) carried out trials on the
    application of dichlorvos to various vegetable crops in the field at
    the rate of 1 g/100 sq ft (108 mg/m2) equivalent to about 1 g/1,000
    cu ft (35 mg/m3) in greenhouses. The results were as follows :

    Vegetable                 Dichlorvos residue (PP2)
                              at intervals after treatment
                                                            
                        1 hour         72 hours       6 days

                                                            

    Dwarf beans         0.2            0.02           Nil
                        0.3            Nil            Nil

    Cauliflower         0.2            0.01           Nil
                        -              0.01           Nil

    Spinach             0.03           0.02           Nil
                        0.03           0.03           Nil

    Lettuce             15.4           0.03           Nil
                        21.7           0.02           Nil
                                                            

    Residues resulting from use on animals

    Studies conducted by Casida, McBride and Niedermeier (1962) concluded
    that dichlorvos sprayed, rubbed, or painted on milk cows appeared
    unlikely to produce significant residues in milk. The organosoluble
    insecticide equivalent in milk 12 and 24 hours after cows were fed 
    1 mg/kg and 2 mg/kg of dichlorvos was 0.46 ppb and 0.39 ppb, and 21.1
    ppb and 7.3 ppb, respectively. Hens subjected to a dichlorvos spray of
    1.5 g/1,000 cu ft (53 mg/m3) (twice recommended does) 5 times at
    3-day intervals produced eggs with dichlorvos residues of 0.11 ppm or
    less, and the dichlorvos residue in the edible tissue of the birds
    sacrificed the day after the third treatment was loss than 0.1 ppm
    (Ciba Laboratories Ltd., unpublished).

    Residues resulting from use on cereals and cereal products

    Trials conducted in the United Kingdom in 1964 by the Pest Infestation
    Laboratory (unpublished) showed that feed barley treated with 4 ppm of
    dichlorvos while being turned had 1.8 ppm of dichlorvos immediately
    after treatment, 0.93 ppm after 1 week, 0.25 ppm after 6 weeks and
    0.26 ppm after 10 weeks, and none could be detected after 15 weeks. In
    another trial, Green and Tyler (1966) treated barley (13-15 percent
    moisture) with 4 ppm dichlorvos. The dichlorvos residues on the grain
    immediately after treatment and 1 and 2 weeks later were 0.53 to 0.63
    ppm, 0.13 to 0.26 ppm, and 0.05 to 0.09 ppm, respectively. With drier
    grain and improved treatment methods, they obtained higher and more
    persistent residues with the same rate of application: 1.90 ppm during
    treatment and 1.06 ppm 1 week after, 0.45 ppm 3 weeks after, 0.25 ppm
    6 weeks after, and 0.26 ppm 10 weeks after treatment.

    Strong and Sbur (1964) studied the persistency of dichlorvos as a
    spray on wheat (16-percent moisture) at 10 ppm and found its toxicity
    to the rice weevil (Sitophilus oryzea) was lost after 2 weeks at
    high storage temperature; whereas when stored at 60F (15.6C), the
    treated wheat still killed rice weevils for as long as 3 months'
    storage.

    Research conducted by the Stored-Product Insects R and D Laboratory,
    U.S. Department of Agriculture, (unpublished) showed dichlorvos vapor
    concentrations of 4 to 6 g/1 for 6 hours [2 g/1,000 cu ft (71
    mg/m3)] applied weekly will protect food in storage against insect
    infestation. Dichlorvos residues in packaged noodles, raisins, rice,
    beans, and sugar after 21 consecutive weekly applications were less
    than 2 ppm.

    Test conducted by Schulten and Kuyken (1966) on the effectiveness of
    dichlorvos resin strips for the control of the cocoa moth (Ephestia
    elutella) (Hbner) showed that 46 dichlorvos-impregnated strips (20
    percent) in 2,200m3 of warehouse space produced air concentrations of
    0.05 g/1 in 27 days and 0.05 g/1 in 54 days. The highest dichlorvos
    residues in the stored cocoa beans were 0.02 - 0.03 ppm.

    Residues in meat

    Samples of mincemeat, bacon, steak, and fat were exposed in a hut at
    daily intervals following a 30-minute treatment with vapors of pure
    dichlorvos labeled with 32P. During the treatment, the dichlorvos
    concentration was maintained at approximately 0.5 microgram/liter of
    air and the prevailing temperature within the hut fell rapidly after
    each application, and no insecticide was detectable in the air after 2
    hours. Meat samples introduced into the hut immediately following
    treatments still accumulated dichlorvos although they were of a very
    low level. Those in fat were generally lower than those in the
    corresponding steak, mincemeat, or bacon. The maximum dichlorvos
    residues found after 12-hour exposures in the various types of meats
    in the same order listed above were 0.08, 0.22, 0.19 and 0.19 ppm
    (Millar and Aitken, 1965).

    In 1964, the Shell Chemical Co. carried out an unpublished trial at a
    meat factory in Britain. Dichlorvos was applied by a watering can at a
    rate of 1.5 g/1,000 cu ft. The highest concentration of dichlorvos in
    the atmosphere was found to be 0.7 microgram/liter one hour after
    application. Nine hours after application, the atmospheric
    concentration had dropped to 0.25 microgram/liter and to 0.08
    microgram/liter by 24 hours. Residues of dichlorvos in samples of
    cooked meat and offal exposed to the atmosphere over a 25-hour period
    after application were less than 0.1 ppm. In processed meat, residues
    reached 0.4 ppm within 1/2 hour of application and fell to less than
    0.05 ppm after 25 hours.

    Residues resulting from other uses

    In trials conducted by Shell Chemical Company, U.S.A., (unpublished)
    16 dichlorvos resin strips were used in a kitchen with 20,000 cu ft
    (566 m3) and 4 resin strips in another kitchen with 2,352 cu ft (66.6
    m3). Usual restaurant exhaust fans over the stoves ran
    intermittently. Five days later, meals exposed to the insecticide
    vapors for 24 hours contained dichlorvos residues of about 0.15 ppm.
    Meals exposed in a similar manner 10 days after the strips were hung
    had 0.05 ppm of dichlorvos. Other trials showed cheese from a cheese
    factory using one 2-  10-in (5-  25.4-cm) strip per 1,000 cu ft
    (28.3 m3) contained less than 0.01 ppm of the decomposition product
    dichloroacetaldehyde. Fish exposed to the same concentration had no
    more insecticide residue than unexposed fish.

    FATE OF RESIDUES

    In plants

    It has been shown that dichlorvos residues in food disappear rather
    rapidly. For example, the trials conducted by Ciba Laboratories Ltd.
    (unpublished) showed that dichlorvos residue in mushrooms decreased
    from 0.85 ppm 24 hours after treatment to 0.03 ppm 24 hours later.
    Lettuce with 78 ppm of dichlorvos 1 hour after treatment had 0.02 ppm
    72 hours later. Tests conducted by the Pest Infestation Laboratory in
    the United Kingdom showed that the 1.8 ppm of dichlorvos on barley
    immediately after treatment was down to 0.93 ppm in 1 week and to 0.25
    ppm in 6 weeks. Ciba Ltd. (unpublished) found wheat grain with 60 ppm
    of dichlorvos had 85 percent less dichlorvos after 1 month and 97.5
    percent less after 4 months of storage. These tests also showed that
    the higher the moisture content of the grain and of the storage
    temperature, the faster the dichlorvos residue disappeared from the
    grain.

    In plant material the hydrolysis product dichloroacetaldehyde can be
    present in rather significant quantities. In tests conducted by Shell
    Chemical Company in the U.S. (unpublished), five vegetables were
    sprayed with a solution of dichlorvos in acetone at rates calculated
    to give 5 ppm residues on the commodities. Analyses were conducted of
    the dichlorvos (DDVP) and of the dichloroacetaldehyde (DCA). The
    results obtained were :

                                                ppm after aging
                                                                                

    Crops                  1 hour             3 days                7 days

                        DDVP      DCA      DDVP      DCA         DDVP       DCA
                                                                                

    Cucumbers           6.1       0.1      3.9       0.2         2.6        0.1

    (cont'd)                                ppm after aging
                                                                                

    Crops                  1 hour             3 days                7 days

                        DDVP      DCA      DDVP      DCA         DDVP       DCA
                                                                                

    Lettuce             3.6       0.06     0.9       0.06        Nil        Nil

    Mushrooms           1.2       0.06     Nil       Nil         Nil        Nil

    Spinach             6.5       0.3      2.0       0.2         1.0        0.1

    Tomatoes            5.1       0.1      2.4       0.2         1.3        0.1
                                                                                
    
    Studies conducted by Shell Development Company, U.S.A., (unpublished)
    showed the acute oral toxicity to rats of dichlorvos when combined
    with certain other insecticides could be more then additive
    (potentiation). Of the 27 insecticides combined with dichlorvos, no
    potentiation was found with 20, marginal potentiation with 3, and
    positive potentiation with 4. The most marked potentiation was
    obtained when dichlorvos was combined with malathion. The combined
    LD50 acute oral toxicity to rats of the two pesticides was 135 mg/kg,
    whereas the expected additive value was 1,298 mg/kg, or a 9.61-fold
    increase.

    In storage and processing

    Processing and cooking also removed large percentages of dichlorvos
    which may be present on food. For example, wheat with 23.8 ppm of
    dichlorvos after treatment produced flour with 4.6 ppm of dichlorvos.
    Three months later, the wheat had 2.8 ppm of dichlorvos and the white
    flour milled from it had 1.7 ppm. The dichlorvos residue in this flour
    after 14 days' storage fell below the limits of detection. Shell
    Chemical Company, U.S.A. (unpublished) found that biscuits made from
    flour containing 0.35 ppm and 1.8 ppm of dichlorvos had 80 and 60
    percent less dichlorvos, respectively. Flour with 9.5 ppm of
    dichlorvos heated for 30 minutes at 100C, 150C, and 200C had 0.2
    ppm, 0.03 ppm, and 0.02 ppm of dichlorvos, respectively. Rice with 5.3
    ppm of dichlorvos had only 0.06 ppm after cooking. Miller and Aitken
    (1965) found frying and cooking completely destroyed dichlorvos in the
    meat, leaving only products of hydrolysis.

    METHODS OF RESIDUE ANALYSIS

    Shell Development Company analytical method MMS-30/64 entitled
    "Determination of Vapona Insecticide in Crops and Animal Products,
    Enzyme Inhibition-Spectrophotometric Method". Sensitivity is as low as
    0.1 ppm of dichlorvos. This method is not specific for dichlorvos.

    Shell Chemical Company analytical method PMS-G-900/60 entitled
    "Determination of Dichloroacetaldehyde Residues in Crops and Animal
    Tissues, GLC Electron Capture Method". Sensitivity is as low as 0.01
    ppm.

    Woodstock analytical method WAMS 32-1 entitled "Determination of
    Vapona in Technical Grade Products, Formulations and Extracts from
    Certain Crops and Similar Samples. - Gas-Liquid Chromatographic
    Method."

    Other gas-liquid chromatography methods for dichlorvos and its
    breakdown products are being investigated.

    NATIONAL TOLERANCES

                                                                      

         Country        Tolerance, ppm           Crop
                                                                      

         Australia      2                        fruit, vegetables and
                                                 grain recommended by the
                                                 Food Additive Committee
                                                 of National Health and
                                                 Medical Research

         Canada         None

         Germany        *

         Holland        0.1                      vegetables (including
                                                 mushrooms, roots, bulbs
                                                 and tubers) and fruits

         Switzerland    0.1                      vegetables

         United States  **

    *    The residue on edible crops may not exceed the lower limit of
         detectability of the analytical methods.

    **   Petitions have been submitted to U.S. Food and Drug
         Administration for approval of tolerances of 0.5 ppm of
         dichlorvos in packaged processed foods resulting from space
         treatments in warehouses and 0.25 ppm of dichlorvos in canned
         tomatoes resulting from direct application to tomatoes for
         Drosophila control.

    RECOMMENDATIONS FOR TOLERANCES

    Temporary tolerances

    Dichlorvos in/on food disappears very rapidly and to very low levels.
    Processing and cooking further reduce dichlorvos residues in food.

    In the hydrolysis of dichlorvos, dichloroacetaldehyde is formed and
    this metabolite may be present in food in detectable amounts. The
    temporary tolerances for dichlorvos residues, therefore, include
    dichloroacetaldehyde when it is reported as being present.

    Because an analytical method specific for dichlorvos that can be used
    for regulatory purposes is not available at this time, the tolerances
    being recommended for dichlorvos residues are temporary and are to be
    reviewed by 31 December 1970.

    The recommended temporary tolerances are :

              Cereals                          2.0

              Cereal products and
              fresh vegetables                 0.3

              Canned and frozen vegetables,
              fresh fruit (other than citrus)  0.1

    Considering the loss of dichlorvos that takes place by aging, 
    processing, and cooking and based on the ninth decile of consumption
    derived from consumer intake studies, the amount of dichlorvos
    reaching the consumer in the above foods will be less than 0.1 mg/day
    of the 0.24 mg/day permitted by the ADI. The remainder will be
    available for respiratory intake and for residues that may be present
    in other foods.

    FURTHER WORK

    Further work required before 30 June 1970

    A specific analytical method with a sensitivity of about 0.01 ppm
    suitable for regulatory purposes.

    Data on other uses of dichlorvos, the residues resulting from such
    uses, and the affects of aging, processing, and cooking.

    Actual dichlorvos residues present in food moving in commerce.

    Total diet studies.

    REFERENCES PERTINENT TO EVALUATION FOR ACCEPTABLE DAILY INTAKES

    FAO/WHO. (1967) FAO Mtg. Rept. PL:CP/15; WHO Food Add./67.32

    Jolley, W.B., Stemmer, K.L. and Pfitzer, E.A. (1967) unpublished
    report submitted by Shell International.

    Narcisse, J.K. (1967) unpublished report submitted by Shell
    International.

    Rider, S.A., Moeller, H.C. and Puletti, E.J. (1967). Fed. Proc.,
    26, 427

    Witherup, S., Stemmer, K.L. and Pfitzer, E.A. (1967) unpublished
    report submitted by Shell International

    REFERENCES PERTINENT TO EVALUATION FOR TOLERANCES

    Casida, J.E., McBride, L. and Niedermeier, R.P. (1962) Metabolism of
    2,2-dichlorovinyl dimethyl phosphate in relation to residues in milk
    and mammalian tissues. J. Agric. Fd. Chem., 10 (5): 370 - 377.

    Green, A.A., and Tyler, P.S. (1966) A field comparison of malathion,
    dichlorvos, and fenitrothion for the control of Oryzaephilus
    surinamensis (L) (Coleoptera, Silvanidae) infesting stored barley.
    J. Stored Prod. Res., 1 (3): 273 - 285.

    Jensen, Jens A., Flury, Vincent P. and Schoof, Herbert F. (1965)
    Dichlorvos vapour disinsection of aircraft. Bull. Wld. Hlth. Org., 32:
    175 - 180.

    Millar, K.R. and Aitken, W.M. (1965) Residues in meat following
    exposure to P-Labeled dichlorvos vapor in an enclosed space. N.Z. J1
    Agric. Res., 8(2): 350 - 362.

    Schoof, H.F., Jensen, J.A., Porter, J.E. and Maddock, D.R. (1961) 
    Disinsection of aircraft with a mechanical dispenser of DDVP vapour.
    Bull. Wld. Hlth. Org., 24: 623 - 628.

    Schulten, G.G.M. and Kuyken, W. (1966) Dichlorvos resin strips for
    control of cocoa moth, Ephestia elutella. Int. Pest Control, 8(3):
    18, 19, 21, 23.

    Snetsinger, R. and Miner, D. (1964) Tests with dichlorvos vapours for
    the control of mushroom flies. J. Econ. Ent., 57(1): 182 - 183.

    Strong, R.G. and Sbur, D.E. (1964) Influence of grain moisture and
    storage temperature on the effectiveness of five insecticides as grain
    protectants. J. Econ. Ent., 57(1): 44 - 47.
    


    See Also:
       Toxicological Abbreviations
       Dichlorvos (EHC 79, 1988)
       Dichlorvos (HSG 18, 1988)
       Dichlorvos (ICSC)
       Dichlorvos (FAO Meeting Report PL/1965/10/1)
       Dichlorvos (FAO/PL:CP/15)
       Dichlorvos (FAO/PL:1969/M/17/1)
       Dichlorvos (AGP:1970/M/12/1)
       Dichlorvos (WHO Pesticide Residues Series 4)
       Dichlorvos (Pesticide residues in food: 1977 evaluations)
       Dichlorvos (Pesticide residues in food: 1993 evaluations Part II Toxicology)
       Dichlorvos (IARC Summary & Evaluation, Volume 53, 1991)