WHO/FOOD ADD/71.42



    Issued jointly by FAO and WHO

    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
    Group on Pesticide Residues, which met in Rome, 9-16 November, 1970.



    Rome, 1971



    This pesticide was evaluated by the 1965, 1966 and 1967 Joint Meetings
    of the FAO Working Party and WHO Expert Committee on Pesticide
    Residues (FAO/WHO 1965, 1967, 1968). Since the previous publications,
    the results of some additional experimental work have been reported.
    This new work in summarized and discussed in the following monograph


    Composition of the technical product

    Technical dichlorvos contains not loss than 93 percent w/w of
    o,o-dimethyl-2, 2-dichlorovinyl phosphate and not more than 7 percent
    w/w of related compounds.



    The rate of detoxification of dichlorvos appears to vary among
    different mammalian species. Based upon studies where dichlorvos was
    infused into the jugular vein of animals and the time to mortality
    measured, the detoxification rate for dogs, pigs, sheep and monkeys is
    3.0, 5.5, 0.9 and 0.4 mg/kg/hr., respectively (Young, 1969).

    Studies in vivo and in vitro in the rat, rabbit, goat and cow
    using 32P-labelled or unlabelled dichlorvos (Casida et al., 1962;
    Hodgson and Casida, 1962) have previously been described, and the
    results of these experiments have fairly clearly established the fate
    of the phosphorous containing portion of the molecule (FAO/WHO, 1967).

    Rats were administered intraperitoneally with 0.5 mg of dichlorvos or
    1.7 mg of its metabolite o-demethyldichlorvos. Both compounds were
    32P-labelled. Dimethylphosphate was by far the most predominant
    urinary metabolite (64.1 percent); methylphosphoric acid and
    phosphoric acid accounted for a further 9.2 percent of the
    radioactivity and the remaining 1.7 percent was o-demethyldichlorvos.
    In the urine from the rats administered o-demethyldichlorvos directly,
    21.2 percent was excreted unchanged, but the major metabolites were
    methylphosphoric acid and phosphoric acid (43.6 percent) and an
    unknown compound (metabolite E), which was chromatographically similar
    to an unknown metabolite obtained from rats fed the related
    insecticide trichlorphon. This compound was not found after
    administration of dichlorvos itself. The authors speculated that the
    compound was a conjugate of a non-toxic metabolite with glucuronic
    acid, or perhaps sulphuric acid, but this fact was not established.
    Based upon the results of this experiment, the cleavage of the vinyl

    group appears to greatly exceed o-demethylation (Bull and Ridgeway,

    Three male rats were exposed for one hour to the vapour of dichlorvos
    labelled with 14C in the vinyl group. A separate group of three male
    rats of the same age were given an oral dose of the same 14C-labelled
    dichlorvos. The excretion of the radioactivity of both groups in the
    urine, faeces and respired air was measured for four days, and the
    identity of the radioactivity in the liver of the inhalation group was
    also determined. Metabolism was rapid with both groups, and the rates
    and routes of excretion were very similar. The radioactivity in the
    livers of the group studied was found to be largely glycine and serine
    incorporated into the protein (Blair et al., 1970).

    Further information on the metabolism of dichlorvos is given in the
    section entitled "Fate of residues - In animals".

    The hydrolytic degradation of 32P-labelled dichlorvos was
    investigated using postmitochondrial supernatant fluid from rat liver
    and reduced glutathione as a methyl group acceptor. It was found that
    the rate of hydrolysis of dichlorvos was much greater than was found
    in some phosphorothiono insecticides. The monomethyl derivative was
    the major hydrolytic product (Palut et al., 1969).

    Based upon the experiments described above and those reviewed
    previously, the metabolic scheme for dichlorovos in represented is
    Fig. 1.

    Using purified human serum anticholinesterase, the I50 value for
    dichlorvos is 10-6M. An enzyme considered to have similar esteratic
    site, namely chymotrypsin, had a value of 10-3M (Arthur and Casida,

    More recently, I50 values for dichlorvos using human plasma and
    erythrocyte cholinesterase have been shown to be the same, 4.1 ×
    10-6M (Boyer, 1969).


    Special studies on reproduction

    Chicken embryo

    When 10 mg of dichlorvos or less were injected into the yolk sac of
    fertile eggs prior to incubation, there were no teratogenic effects
    (Roger et al., 1964).

    When 1 mg dichlorvos was injected in eggs on day four of incubation,
    borderline teratogenic signs (shortened body and legs) occurred (Roger
    et al., 1969).



    Reproduction studies in rats fed 0, 0.1, 1,0, 10.0, 100 or 500 ppm in
    the diet through three successive generations did not show any
    significant effect on numbers and sizes of litters, survival of young
    or growth of young being suckled while dichlorvos was still being fed
    to the dams. Dichlorvos appeared to be without teratogenic effect
    (Witherup et al., 1965; see FAO/WHO, 1967).

    Dichlorvos was administered at unspecified levels intraperitoneally to
    female rats on day eleven after insemination. Doses of 20 mg/kg
    body-weight killed the animals; 15 mg/kg produced toxic signs and
    weight loss. There was no adverse effect on litter size or on the
    placenta at 15 mg/kg, but three foetuses from one of four litters
    available had omphaloceles, although none were observed in the six
    litters from control animals (Kimbrough, 1970).


    A total of 168 adult female rabbits were artificially inseminated with
    20-30 million viable and mobile rabbit sperm, and on days 6 to 18 of
    gestation were administered daily oral doses of 0, 6 or 18 mg/kg
    body-weight of dichlorvos by capsule, or 31 mg/kg on days 6 to 11 of
    gestation. Foetuses were recovered by Caesarean section. There was
    increased incidence of in utero and neonatal toxicity in the top
    dose group only, which was of doubtful significance. There were no
    teratogenic effects observed, based upon skeletal examination of the
    foetuses. Maternal mortality was increased in the 31 mg/kg group
    (Carson, 1969).

    In a separate experiment, 104 female rabbits were artificially
    inseminated with rabbit sperm and administered 0, 3 or 12 mg/kg
    body-weight of dichlorvos by capsule on gestation days 6 to 16
    inclusive. Other rabbits were given higher doses, but they could not
    tolerate levels of 24 mg/kg or higher, and no live litters were
    produced from such groups. At 12 mg/kg, there was a significant
    reduction in the number of implant sites and foetuses compared to the
    control or lower dose group. At 3 mg/kg, the number of implant sites
    and foetuses were not lower than the controls. However, one deformed
    stillborn foetus was encountered from this group. Liver sections from
    parents and foetuses displayed no pathological abnormalities that
    could be related to dichlorvos treatment (Vogin, 1969).


    Female pigs were fed dietary levels of 0, 200, 250, 288, 400, 500 or
    750 ppm of dichlorvos for up to 37 months. The animals were first
    mated after they had received the test diet for six months, and the
    study was followed through two generations. Initially, a total of 22
    females and one male were used, but after the first generation, four
    more males were used in order to prevent in-breeding. The males
    received 0, 288 or 400 ppm of dichlorvos in their diets. Dichlorvos
    did not affect either the numbers of litters or their size and the

    survival in the groups fed dichlorvos. A total of 490 piglets were
    examined and none showed anatomical abnormalities (Singh and Rainier,

    Special studies on mutagenicity

    Secondary roots of Vicia fabia were treated with varying
    concentrations of dichlorvos for one hour. Concentrations down to 1 mM
    were mostly lethal, and root tips surviving this and lower
    concentrations had a low mitotic index and showed c-mitotic effects,
    and chromatid breaks and gaps were observed. In another experiment, a
    streptomycin dependent, Sd-4, mutant of E. coli was treated in the
    lug phase at cell densities of about 108 cells/ml during one hour.
    The LD50 concentration for the bacteria of dichlorvos in the medium
    was estimated to be between 10 and 60 mM (2200 ppm and 1.3 percent).
    At concentrations of 1-4 mM, which caused no significant killing, an
    increased mutation rate was observed when compared with controls and
    measured as revertants to streptomycin independency (Löfroth, 1969 a,
    1969 b).

    Segments of Vapona-strips of various sizes were placed in an inflated
    6000 ml plastic bag containing an uncovered petri-dish with
    germinating onion seeds. There was no retardation of root growth or
    mitotic frequency, but the number of chromosome aberrations, when
    scored at anaphase, increased constantly with increasing size of the
    Vapona-strip segment. The lowest concentration used was about ten
    times as great as one strip in a 1000 ft3 room (Sax and Sax, 1968).

    Attention has been drawn to the alkylating property of a number of
    alkyl phosphates (Preussman, 1967). For this reason, possible
    mutagenic effects have been looked for. Calf thymus deoxyribonucleic
    acid (DNA) was incubated with varying concentrations of dichlorvos
    solution. In a typical experiment with 2 percent dichlorvos incubated
    for 66 hours, there was a yield of 1 percent of N-7-methylguanine from
    the available guanine. Similar experiments with deoxyguanosine gave a
    3-5 times higher yield of N-7-methylguanine than from DNA (Löfroth,

    Eight mice were injected intraperitoneally with 10-20 mg/kg
    body-weight of dichlorvos. After 23 hours, 100 cells of their bone
    marrow were examined. The incidences of aberrations were not greater
    than observed in four control mice (Hunter, 1970).

    A human subject was exposed to 1 mg/m3 of dichlorvos for six hours.
    A sample of blood cultured for leucocytes for 72 hours showed no
    increase in chromosome aberrations in 100 cells compared to the
    pre-exposure values (Hunter, 1970).

    No chromosomal aberrations were seen after examination of blood
    samples from a family of four female and one male human subjects which
    had been exposed to dichlorvos strips. A control group had two male
    and three female subjects (Hine, 1970).

    Special studies on carcinogenicity


    Rats (24) were injected subcutaneously, once weekly, with trichlorphon
    (Dipterex), of which dichlorvos is a known metabolite. Despite a high
    (unspecified) dosage and a latent period of almost 800 days, only two
    local sarcomas developed at the site of injection. No data on controls
    are given. (Preussmann, 1968). In a subsequent publication, Preussmann
    et al. (1969) refer to the above experiment as a "negative result,
    presumably due to the very rapid metabolism of Dipterex."

    Acute toxicity

    After direct infusion of dichlorvos into a peripheral vein at various
    rates, pigs can survive an LD50 dose each hour for at least nine
    hours (page, 1970).

    The acute toxicity of dichlorvos has been compared with the
    metabolites. The LD50 values in mg/kg body-weight for intraperitoneal
    administration to mice are: dichlorvos, 28; o-demethyldichlorvos
    sodium salt, 1500; dichloroacetaldehyde, 440; 2,2-dichloroethanol,
    890; dichloroacetic acid, 250; sodium dichloroacetate, >3000;
    mono- and dimethylphosphoric acid mixture, 1500; sodium
    monodimethylphosphoric acid mixture, >3000 (Casida, et al., 1962).

    Short-term studies

    Comparative studies on inhalation toxicity

    Guinea pigs have been exposed for five hours per day for five
    consecutive days to a concentration of 130 mg dichlorvos/m3 of air
    without visible effects on health. Rats and mice were not visibly
    affected by similar exposures to 50 mg/m3. At concentrations above
    50 mg/m3, the mice became visibly distressed, and prolonged exposure
    to 80 mg/m3 was frequently lethal. Rats were less severely affected
    than mice. In all cases, stress reactions were either apparent during
    the first hours of exposure or they did not occur at all. No
    cholinesterase determinations were made (Stevenson and Blair, 1969).

    Three samples of dichlorvos were investigated (82.5 percent pure,
    Russian produced, 40% pure, Japanese, and 100% pure from Swiss
    origin); the oral LD50 for Russian and Japanese samples was similar
    (87 mg/kg body-weight for mice and 65 mg/kg for rats). The Swiss
    sample was less toxic: oral LD50, mice: 108 mg/kg. Rabbits were found
    to be the most sensitive species (oral LD50, Russian sample: 22.5
    mg/kg). Inhalation toxicity was investigated for exposure periods of
    four hours, The highest concentration which could be produced (30
    mg/m3) was lethal for mice and rats. The LD50 (four hours) for mice
    was 13.2 mg/m3 and for rats 14.8 mg/m3. At 5 mg/m3, blood
    cholinesterase activity in rat was 69 percent of pre-exposure values.
    A level of 0.5 mg/m3 caused no observable effects in blood
    cholinesterase. By interpolation, those concentrations of dichlorvos

    in air were calculated which would after four hours exposure cause a
    50 percent drop in blood cholinesterase activity in rat (I50 = 2.4
    mg/m3) or a 25 percent drop (I25 = 1 mg/m3). Rats and rabbits
    were exposed for 4 hours/day for a period of four months to an average
    dichlorvos vapour concentration of 1 mg/m3 of air. No visible signs
    of intoxication occurred. Cholinesterase activity in the serums
    erythrocytes, medullary tissue and liver of rats varied throughout the
    experiment within the limits of the norm or was slightly depressed.
    After four months, the depression of cholinesterase activity in the
    medulla averaged 8 percent in the liver, serum and erythrocytes the
    depression was 30 percent 22 percent and 24 percent, respectively.
    Blood sugar content, blood sugar curves after loading with galactose,
    synthesis of hippuric acid after loading with sodium benzoate and
    duration of Hexenal induced sleep were not affected. Rabbits exposed
    under the same conditions showed 11-30 percent reduction of serum
    cholinesterase activity and 28-30 percent reduction of erythrocyte
    cholinesterase activity. It was concluded that 1 mg/m3 was the
    threshold for rats and rabbits which caused an insignificant and
    variable depression of cholinesterase. It was also the threshold for
    cats. Rats exposed to an average concentration of 5.2 mg/m3 for 4
    hours/day over a period of two months remained visibly healthy. After
    15 days, the cholinesterase depression in the medulla was on an
    average 22 percent in the serum 58 percent in the erythrocytes 22
    percent. The duration of drug induced sleep was increased from 33
    minutes to 57 minutes. The blood sugar level was unchanged, but the
    rise of the curve after galactose loading was far higher than in the
    controls. After 60 days, the blood sugar curve was affected, the
    duration of Hexenal induced sleep was the same as in the controls, and
    cholinesterase activity in the medulla fell by an average of 31
    percent, in the liver by 35.5 percent, in serum by 52 percent and in
    erythrocytes by 58 percent. At 8.2 mg/m3 for 45 days, rats lost
    appetite and weight, and in some cases trembling of the head and
    entire body was noted. Signs of intoxication occurred in some of the
    rats and some died (Sasinovich, 1968).


    A total of 10 human subjects, in groups of two, ingested pellets of a
    slow-release formulation of dichlorvos in daily dosages, doubling
    weekly, up to 8 mg/kg body-weight/day for periods up to three weeks;
    one group of two received 16 mg/kg/day for 5.5 days. Doses above 1
    mg/kg were administered in two equally divided doses per day. The
    majority of the clinical side effects occurred after the doses had
    reached the 8 mg/kg/day level. Most of the subjective clinical
    complaints referred to the gastrointestinal tract, but none of the
    studies had to be terminated because of side-effects. The study with
    16 mg/kg/day was terminated because of the magnitude of the red blood
    cell cholinesterase activity depression. Doses of 1-8 mg/kg/day for up
    to 21 days produced an average plasma cholinesterase activity
    depression of 70 percent irrespective of dose or duration. Doses of 16
    mg/kg/day for 5.5 days produced approximately 90 percent depression of
    the plasma cholinesterase activity. Red cell cholinesterase activity
    after multiple dosing of 1 mg/kg/day was 11-27 percent depressed.

    Doses which reached 8 mg/kg/day caused 45-86 percent depression. At 16
    mg/kg/day, depressions of 90 percent were observed. Single doses of
    dichlorvos needed to be more than 4 mg/kg in order to cause measurable
    red cell cholinesterase depression. At single doses of 8 mg/kg and
    higher, maximal plasma cholinesterase inhibition was present and did
    not increase at higher dosages. Significant and consistent erythrocyte
    cholinesterase inhibition occurred after single doses of 16 mg/kg (36
    percent inhibition) and 32 mg/kg (46 percent inhibition). About 50
    percent of the dichlorvos was still present in the excreted pellets,
    Therefore, the doses absorbed were assumed to be about one half of the
    above levels (Hine et al., 1966).

    In another study, 12 male subjects ingested 5 mg of dichlorvos daily
    in three equal portions with their food until the plasma
    cholinesterase fell to 75 percent of the pre-exposure value. The time
    required averaged 12 to 20 days. No effect occurred on erythrocyte
    cholinesterase. One of the subjects continued the exposure for a total
    of 77 days. A questionable erythrocyte cholinesterase depression of
    10-15 percent occurred during part of the exposure period, but in the
    beginning and at the end of the exposure period, this activity was
    normal or slightly above (Hunter, 1970).

    Six human subjects were exposed to concentrations of dichlorvos in the
    air, the maximum level being 52 mg/m3 for 62 minutes and the maximum
    period 240 minutes to 13 mg/m3. No clinical abnormalities were
    observed, subjective complaints were only related to the dryness of
    the atmosphere, but the plasma cholinesterase activity was decreased;
    the extent of the depression was proportional to the product of the
    concentration and time of exposure. During some of these exposures, a
    questionable depression of erythrocyte cholinesterase occurred, but
    the extent of depression was not directly related to the product of
    the concentration and time of exposure (Hunter, 1969).

    In six homes in Tucson, Arizona, 18 individuals submitted to exposure
    to dichlorvos strips and six others served as controls.

    In order to maximize exposure, the study was made during the winter
    months, and strips were hung in all rooms in the houses at the rate of
    1 strip/1000 ft3. Maximum concentrations of 0.1-0.2 mg/m3 occurred
    within the first week, levelling off to 0.05-0.10 mg/m3 during the
    remainder of the regular exposure period of 28 days. Samples of meals
    and beverages were collected at various intervals. During the exposure
    period, more than 85 percent of the individual meals contained less
    than 0.3 ppm dichlorvos and more than half the meals 0.1 ppm or less.

    Physical examination, complete blood counts, blood chemical profiles
    and plasma and erythrocyte cholinesterase measurements were performed
    at various intervals. Levels of dichlorvos in the food eaten ranged
    from 0.1 to 0.3 ppm. There were no clinical abnormalities evident, nor
    were there any significant differences in plasma and red-blood cell
    cholinesterase, blood count and blood chemical profiles between the
    exposure and pre-exposure periods (Shell, 1970a).

    A study was made in Italy of the effect of continuous exposure to
    insecticide levels of dichlorvos by patients in hospital wards.
    Control values for plasma and erythrocyte cholinesterase were
    established for 250 healthy male and 100 healthy female adults not
    exposed to dichlorvos. The variation in the activity of the
    cholinesterases of the individuals when measured at different times,
    depending on the time-interval, varied on average between 1.4 and 4.4
    percent for the erythrocyte cholinesterase and on average between 5.0
    and 14.2 percent for plasma cholinesterase. These were average
    variations measured in ten to 20 individuals. In single individuals,
    the maximum variation was 7.7 percent for erythrocyte cholinesterase
    and 23.2 percent for plasma cholinesterase.

    A total of 44 adult male patients with diseases other than liver
    diseases were exposed to atmospheric concentrations of dichlorvos
    ranging from 0.02 to 0.1 mg/m3 for periods of 3 to 29 days. Another
    similar group of 22 male patients was exposed to dichlorvos
    concentrations of 0.1 to 0.28 mg/m3 for periods from 3 to 16 days.
    Only in the case of five patients exposed 24 hours per day at levels
    above 0.1 mg/m3 was there a depression of plasma cholinesterase (35
    to 72 percent) below the pre-exposure level. There was no depression
    of erythrocyte cholinesterase nor were any symptoms typical of
    cholinergic stimulation observed, in any patients. With six other
    patients suffering from liver disease exposed in the same room, all
    showed a reduction in plasma cholinesterase (25 to 66 percent of
    pre-exposure values). Reduction was evident even in patients exposed
    at levels below 0.1 mg/m3. These patients, because of their liver
    disease, had already before exposure a considerably reduced plasma
    cholinesterase activity. However, there was no depression of
    erythrocyte cholinesterase nor any symptoms of poisoning, in spite of
    the fact that in these patients with liver insufficiency had a 40
    percent depression in plasma cholinesterase lasting for one to three
    weeks after the removal from exposure. In babies, sick children and
    women in labour or postpartum exposed to dichlorvos, a similar
    situation to that of sick adults was seen; depression of plasma (but
    not erythrocyte) cholinesterase was observed only in some cases when
    the dichlorvos level was above 0.1 mg/m3. Again, no symptoms were
    seen. Assuming an inhaled volume of 10 m3/24 hours in adults and 1.4
    m3/24 hours in children, the authors calculated that a reduction in
    plasma cholinesterase for a calculated daily inhalation of 1.7 mg of
    dichlorvos could occur in adults with normal liver function and 0.2 mg
    for children. They further calculated that the amount of dichlorvos
    inhaled which might produce a plasma cholinesterase depression is
    about the same for adults and children, viz. 0.028 to 0.030 mg/kg
    body-weight/day. In patients with liver malfunction, daily inhalation
    intake of 0.34 mg (equivalent to 0.005 to 0.006 mg/kg body-weight/day
    was sufficient to produce plasma cholinesterase depression (Cavagna et
    al., 1969; Cavagna and Vigliani, 1970).

    In two nurseries 22 healthy newborn babies were kept from birth for a
    period of five days for 18 hours/day in an atmosphere in which average
    dichlorvos concentrations of 0.15 - 0.16 mg/m3 were maintained. Blood
    cholinesterase levels were determined at birth and after five days.

    There were no effects on the health of the babies nor on the activity
    of their plasma or erythrocyte cholinesterase (Cavagna et al., 1970).

    In a preliminary study with asthmatic patients, there appeared to be
    no subjective worsening of asthma during exposure to dichlorvos at
    levels of 0.1 to 0.2 mg/m3 for two consecutive days. In some cases,
    an increase in airways resistance and sensitivity to acetylcholine
    occurred during and after exposure, but these manifestations may be
    related to other factors (e.g. poor ventilation) than to dichlorvos.
    Further work in this field is reported to be in progress (Vigliani,


    On the basis of recent and earlier studies the metabolic pattern of
    dichlorvos when fed to mammals is now fairly clearly elucidated.
    Evidence is presented that cleavage of the dichlorovinyl group
    proceeds much more rapidly than o-demethylation. Information on the
    exposure of man to varying levels of dichlorvos vapour is available,
    but such studies do not include assessment as to whether the
    metabolism is the same after inhalation as after oral intake. Data on
    the toxicology of the metabolites dichloracetaldehyde and
    dichloroethanol are considered pertinent in evaluating the toxicity of
    dichlorvos. A long-term study in rats reported in the monograph from
    the 1967 Joint Meeting is considered adequate. Feeding studies in rats
    and rabbits did not show any indication of a teratogenic effect.
    Additional information on feeding dichlorvos to man has become
    available, and the no-effect level previously determined in man is
    used as a basis for establishing an acceptable daily intake.


    Level causing no toxicological effect

    Man : 0.033 mg/kg body-weight/day


    0-0.004 mg/kg body-weight



    Pre-harvest treatments

    In addition to its use on beef and dairy cattle and goats, sheep and
    pigs, and in and around buildings which house these animals,
    dichlorvos is finding increasing use on fruit and vegetable crops.
    Fruit and citrus crops account for more than one third of the
    agricultural use. Rice accounts for just over one quarter and field
    crops, including vegetables, approximately one quarter of the
    agricultural uses. There are minor uses on grapes, glasshouse crops,

    mushrooms, tobacco, tea, coffee, cocoa and miscellaneous crops.
    Dichlorvos is known to be registered in at least forty eight

    Recently it has been introduced as an anthelmintic for pigs, poultry
    and horses, being administered in the form of plastic granules for
    this purpose.

    Post-harvest treatments

    Dichlorvos is being increasingly used for the control of insect
    infestation in stored grain. For this purpose it is used as an aerosol
    or as impregnated resin strips, which are applied in the overhead
    spaces of storage bins. In some countries, dichlorvos preparations
    have also been registered for incorporation into stored grain either
    as a dust, as a direct spray or as an aqueous emulsion.

    Dichlorvos aerosols, automatic dispensers, sprays and resin
    impregnated strips are used in many countries for the control of
    insect infestations in stores, in transport and in warehouses holding
    processed food. Food processing establishments are also treated with
    dichlorvos in one of the above forms.

    Other uses

    As defined in the monograph of the 1967 Joint Meeting (FAO/WHO 1968),
    dichlorvos is used extensively in the public health field (homes,
    hospitals, etc.). It is also used in aircraft during flight. Trials
    are being carried out on its use by aerial application against insect
    pests of forests, pastures and field crops.


    Crops grown in the open

    Table I gives typical results of the analysis for dichlorvos residues
    following controlled application to various fruit and vegetable crops
    (Ciba 1970).

    Crops grown under cover

    In glasshouses, the rate of decay of dichlorvos residues is fast, with
    a half-life of approximately one day. Table II gives results of
    residue trials carried out on crops growing under cover (Ciba 1970).

    Livestock and poultry

    Trials in the United States demonstrate that the spraying of
    dichlorvos on livestock (including cattle, sheep, goats and pigs) and
    poultry is unlikely to produce significant residues in meat, milk or
    eggs. When dichlorvos was applied as a single pour-on application of 1
    percent at the rate of 16.5 ounces per cow, no residues were

        TABLE I

    Crops grown in the open


                                                                            Residue         Analytical        Limit of
    Country             Commodity       Rate of           Interval          ppm             Method            Detection
                                        Application       to Harvest                                          ppm

    Switzerland         Apples          0.05% ai          1 day             0.05            ChE1              0.05
                                                          2 days            <0.05

                        Peaches         0.05% ai          0 day             0.8             ChE               0.02
                                                          1 day             0.55            "                 0.02
                                                          2 days            0.35            "                 0.02

                        Strawberries    0.05% ai          2 days            0.35            ChE               0.02
                                                          3 days            0.06            "                 0.02
                                                          8 days            <0.02           "                 0.02

                        Carrots         0.025% al.        28 days           <0.05           ChE               0.05
                                                          31 days           <0.05           "                 0.05

                        Cauliflower     0.05% ai          0 days            0.37            ChE               0.04
                                                          5 days            <0.04           "

                        Brussels        0.05% ai          0 days            1.35            ChE               0.04
                          sprouts                         5 days            <0.04

                        Cabbage         0.05% ai          0 days            1.5             ChE               0.05
                                                          1 day             0.14
                                                          2 days            0.05
                                                          3 days            <0.05

                        Spinach         0.05%             0 days                            ChE               0.05
                                                          1 day             1.6
                                                          2 days            0.06
                                                          3 days            <0.05

    TABLE I (Cont'd.)

    Crops grown in the open


                                                                            Residue         Analytical        Limit of
    Country             Commodity       Rate of           Interval          ppm             Method            Detection
                                        Application       to Harvest                                          ppm

    Switzerland         Lettuce         0.05              0 days                            ChE               0.05
                                                          3 days            <0.05           "                 0.05

                        French beans    0.05              0 days            0.3             ChE               0.05

                        Cucumber        0.05              9 days            <0.05           ChE               0.05

    1  ChE = cholinesterase inhibition method


    Crops grown under cover


                                                                            Residue         Analytical        Limit of
    Country             Commodity       Rate of           Interval          ppm             Method            Detection
                                        Application       to Harvest                                          ppm

    Switzerland         Tomato          20 mg/m3          0 days            0.2             ChE1              0.04
                                                          1 day             0.06            "                 0.04
                                                          2 days            0.04            "                 0.04

    England             Lettuce         130 mg/m3         0 days            78              ChE               0.04
                                                          1 day             4.9

                                        70 mg/m3          1 day             2.1
                                                          2 days            0.4
                                                          3 days            0.2

    Germany             Lettuce         30 mg/m3          0 days            3.4             B.T.2             0.04
                                                          1 day             1.8
                                                          3 days            0.3

                                        20 mg/m3          0 days            2.4             B.T.              0.04
                                                          1 day             0.9
                                                          2 days            0.4
                                                          3 days            0.16

    Switzerland         Cucumber        20 mg/m3          0 days            7.3             ChE               0.04
                                                          2 days            0.15

    U.S.A.              Mushroom        130 mg/m3         1 day             0.1             ChE               0.04

    TABLE II (Cont'd.)

    Crops grown under cover


                                                                            Residue         Analytical        Limit of
    Country             Commodity       Rate of           Interval          ppm             Method            Detection
                                        Application       to Harvest                                          ppm

    England             Mushroom        160 mg/m3         0 days            25              D.N.P.3           0.04
                                                          1 day             0.9
                                                          3 days            0.27

                                        160 mg/m3         1 day             0.9             D.N.P.            0.04
                                                          2 days            0.05

                                        100 mg/m3         0 days            0.3             D.N.P.            0.04
                                                          1 day             0.1

    1  ChE - cholinesterase inhibition method
    2  B.T. - bioassay
    3  D.N.P. - 2,4-dinitrophonylhydrazine colorimetric method

    detectable at the level of sensitivity of the method (0.1 ppm) in any
    of the milk samples collected from 4-5 hours to 5 days, after
    treatment (Singh, 1965). In another study (Noetzel, 1964), groups of
    Holstein and Guernsey cattle received dermal applications, twice daily
    for 28 consecutive days, of 2 ounces of 0.5 percent dichlorvos and 1
    percent dichlorvos, respectively. No residues were detected in the
    milk (<0.02 ppm). In a similar study (Wisconsin, 1968) in which
    dichlorvos was dermally applied to lactating dairy cows at the rate of
    1 ounce/cow or 3 ounces/cow of a 1 percent dichlorvos for thirty days,
    milk samples from 1 through 7 days and thereafter at 3 day intervals
    were analysed for residues of dichlorvos and dichloroacetaldehyde
    (DCA). No residues were detectable in any of the samples (<0.05 ppm
    dichlorvos, <0.01 ppm DCA).

    In other extensive trials (Wisconsin, 1968/1969) Brahma cattle, goats
    and sheep were sprayed 3 times to saturation (1 gallon) at 14 day
    intervals with 0.025 percent dichlorvos emulsion. No residues of
    dichlorvos were detectable at the limits of sensitivity in tissues or
    organs (including renal, omental and subcutaneous fat, muscle, liver
    and kidney) of cattle (<0.25 ppm), goats (<0.25 ppm) or sheep
    (<0.05 ppm).

    Ivey and Claborn (1969a) sprayed lactating dairy cows for 31
    consecutive days with 2 ounces of a 1 percent dichlorvos insecticide
    spray solution. Milk samples were taken at 2 hours, 1, 2, 4, 8, 16, 24
    and 31 days. One day after final treatment, the cows were slaughtered
    and samples of renal, omental and subcutaneous fat, muscle liver,
    kidney and blood were taken. Using a highly sensitive flame
    photometric method (Ivey and Claborn, 1969b) with improved clean-up
    technique, no residues of dichlorvos were detected in milk (<0.003
    ppm) or body tissue (<0.002 ppm).

    Pigs were fed daily at the high dosage of 9 450 ppm dichlorvos for 90
    days (Singh, 1964). Dichlorvos residues were not detectable (<0.05
    ppm) in tissues and organs including spleen, kidney, small intestine,
    lung, heart, muscle and liver 0 and 1 day after last treatment.

    Analysis of meat, fat, liver and eggs derived from poultry sprayed
    with 2 ounces of diluted 2 lb/gal dichlorvos insecticide E.C. (0.295
    ppm grams DDVP/bird) showed residues of equal to or less than 0.03 ppm
    when samples of tissue were taken 6 hours, 3, 5 and 7 days after
    application. Eggs were collected 1, 2, 3, 4, 5, 6 and 7 days after
    treatment (Shell, 1970b). Poultry exposed to dichlorvon in the form of
    2 percent granules (2 lb/100 square feet or 4 lb/100 square feet), or
    to resin strands containing 20 percent dichlorvos (1 foot of strand/1
    foot of cage) caused no residues in either tissue or eggs (<0.02 ppm)
    (Lancaster, 1962; Loomis and Hodel, 1965; Lancaster, 1963; Shaw, 1964;
    Nelson, 1968).

        TABLE III

    Dichlorvos residues following treatment of animals


    Reference           Animal and Route      Quantity        Frequency       Tissue               Residue
                                                                              Analysed1            ppm
                                              cm3             days

    Singh,              Cows, pour on         480             1               Milk2                <0.1

    Noetzel,            Cows, dermal          60              28×1            Milk                 <0.02

    Wisconsin,          Cows, dermal          90              30×1            Milk                 <0.05

    Wisconsin,          Cows, dermal          4540            3×14            Fat, muscle          <0.25
    1968, 1969          Goats, dermal         4540            3×14            Fat, muscle          <0.25
                        Sheep, dermal         4540            3×14            Fat, muscle          <0.05

    Ivey & Claborn,     Cows, dermal          60              31×1            Milk                 <0.003
    1969a               Cows, dermal          60              31×1            Fat, muscle,         <0.002

    Singh,              Pigs, oral            9450            90×1            All tissues          <0.05


    Shell,              Chickens, dermal      0.3             1               All tissues3         <0.03
    1970b               Chickens, dermal      0.3             1               Eggs4                <0.03

    Lancaster,          Chickens, vapour      -               30×1            All tissues          <0.2

    TABLE III (Cont'd.)

    Dichlorvos residues following treatment of animals


    Reference           Animal and Route      Quantity        Frequency       Tissue               Residue
                                                                              Analysed1            ppm

                                              cm3             days

    Loomis,             Chickens, vapour      -               30×1            Eggs                 <0.02

    Nelson,             Chickens, contact     -               28×1            All tissues          <0.03
    1968                Chickens, contact     -               28×1            Eggs                 <0.05


    Pitts,              Chickens, oral        8.5             over 10         Meat                 <0.01
    1961                Chickens, oral        8.5             over 10         Eggs                 <0.04

    1  Waiting period Nil unless otherwise indicated
    2  Waiting period 4 hours and 5 days
    3  Waiting period 6 hours
    4  Waiting period 1 day and 7 days

    Uses in the protection of stored products

    Grain, meals and flour

    Many of the published and unpublished reports available on the rates
    of loss of dichlorvos from grain, meals and flour are not reliable,
    because the investigators have used unsatisfactory methods to recover
    any residues of dichlorvos from the treated grain and cereal products
    (see comments under Methods of Residue Analysis).

    Residues of dichlorvos in flour resulting from the use of resin strips
    in a flour mill have been investigated (Somme, 1967). Strips were hung
    at the rate of 1/1000 feet3, and samples of flour made from grain
    stored in the mill were taken 4 days and 2´ weeks after production had
    rebegun. Analysis showed that residues of 0.04 ppm and 0.06 ppm
    dichlorvos were present in the flour and that bran samples averaged
    0.09 ppm dichlorvos. In another trial (Shell, 1966a) a "Vapona" strip
    was hung inside a covered flour bin of 600 ft3 total capacity. A
    sample of flour drawn from a conveyer belt taking flour from the
    bottom of the bin one week and two weeks after fitting the strip in a
    nearly full bin was found to have a dichlorvos residue of 0.03 ppm.
    Samples taken after the third week and after the bin had been refilled
    with flour, at the end of the fifth week, contained residues no
    greater than the limits of detection, Wheatings exposed at a rate of
    one "Vapona" strip per bin of 1150 feet3 for ten hours to six weeks
    after the strips had been hung also did not contain residues in the
    surface layer above the limit of detection (ca. 0.02 ppm), (Shell,

    Dichlorvos has been successfully used to control Oryzaephilus
    surinamensis and Sitophilus granarius (Green and Wilkin, 1968).
    The insecticide was sprayed into the air stream from a motorized
    knapsack sprayer through to a perforated lance which was inserted into
    the grain. Dichlorvos residues were higher on wheat than on barley and
    greatest in places where dust and frass had accumulated. When
    dichlorvos was injected at 20 ppm, the highest residue found after one
    day was 30 ppm in a dusty pocket of wheat, and this fell to 5.3 ppm
    after six days.

    The range of residues reported for barley were 5.8-24.0 ppm after one
    day, falling to 0.9-1.4 ppm after six days. However, the method of
    analysis may not have extracted all the dichlorvos from the grain (See
    Methods of Residue Analysis).

    In a laboratory study Kirkpatrick et al., (1968) demonstrated that
    dichlorvos residues of 3.8-8.0 ppm decreased 89 percent and 76
    percent, respectively, in 28 days.

    An unpublished study was conducted by USDA Plant Pest Control (Padget,
    1968). Wheat grain was treated with 4, 6 and 8 ppm of dichlorvos
    formulated from a 25% dichlorvos emulsifiable concentrate. Residues on
    the wheat were reported to be less than 2 ppm by the third day after

    application, and by 14 days all dichlorvos residues were <0.5 ppm.
    Details of the analytical method used were not given.


    Shell Chemical Company (1969) conducted an extensive study on rough
    rice and rice products treated for rice weevil control. Rough rice,
    stored as 45 lb lots were each sprayed with 20 ml of a solution
    containing 1.5 percent, 1 percent and 0.5 percent dichlorvos prepared
    from a 23.5% E.C. After treatment, the rough rice was mill processed
    and the products (brown rice, rice bran, milled rice and rice hulls)
    were collected. Residue samples were taken 6 hours, 1, 5, 10, 20 and
    30 days after application. Dichlorvos residues in the rough rice one
    day after treatment were 7.3, 4.6 and 1.6 ppm for the 1.5 percent, 1
    percent and 0.5 percent applications, respectively. After 30 days,
    residues for all three treatment rates had dissipated to less than 1.0
    ppm. Residues in brown rice and milled rice, after 30 days, were
    <0.05 ppm for all treatment rates. Rice bran treated at the highest
    rate contained 0.4 ppm and rice hulls 3 ppm dichlorvos after 30 days.


    Soybeans stored in open bins were exposed to resin strips for
    intervals ranging from 13 to 126 days (Shell, 1970c). Samples were
    taken through depths of 0-2" and 2-4" from the surface and the
    residues observed are summarized in Table IV.

        TABLE IV

    Average residues on soybeans after exposure to dichlorvos


                       0-2 inch depth                   2-4 inch depth
    Period of        Strips per 1000 ft3              Strips per 1000 ft3
    Exposure,           1            1.5                 1            1.5
    Days             Residues,       ppm              Residues,       ppm

    13               .20             -                .06             -

    28               .06             -                .03             -

    42               .11             .07              .08             .03

    57               -               .08              -               .03

    70               .07             .08              .04             .03

    84               .04             .04              .04             .03

    TABLE IV (cont'd)

    Average residues on soybeans after exposure to dichlorvos


                       0-2 inch depth                   2-4 inch depth
    Period of        Strips per 1000 ft3              Strips per 1000 ft3
    Exposure,           1            1.5                 1            1.5
    Days             Residues,       ppm              Residues,       ppm

    97               .04             .075             .04             .06

    111              .05             .04              .04             .04

    125              .04             .04              .04             .04

                     Temperature     - 65-96°F
                     Rel. Humidity - 48-76 percent
    A test conducted by USDA, Stored Products Insect Research and
    Development Laboratory (Padget, 1969), demonstrated that dichlorvos
    residues on soybeans decrease rapidly. Initial residues of 5 ppm
    decreased rapidly to 0.5 ppm or less after one week of storage at
    80°F. Only trace amounts (0.1 ppm or less) of dichlorvos were found on
    the soybeans after the second week of storage.

    Coffee beans

    Residues in bagged coffee beans were examined (Shell, 1965a) following
    storage in a warehouse using resin strips at either one per 1000 cubic
    feet or 1 per 2000 cubic feet. Some natural ventilation was allowed
    for 9 hours daily.

    Samples taken after 15 weeks storage from the surface and interior of
    the bags did not contain detectable residues (limit 0.01 ppm), but one
    sample exposed at the rate of one strip per 2000 cubic feet did
    contain residues of 0.02 ppm, just above the detection limit.

    Cocoa beans

    In a trial with stacks of bagged cocoa beans carried out in the same
    warehouse and under similar conditions (Shell, 1965a) as the above
    coffee, residues in a bulked sample of cocoa from the top of the stack
    reached 0.04 ppm, although none were detected in comparable samples
    from the side of the stack. In a further trial (Shell, 1965a) with
    another stored supply of cocoa beans, detectable residues (0.01 ppm)
    were not found after 14 weeks exposure. Another trial (Shell, 1965b)
    was undertaken in which sacks of cocoa beans were exposed for three
    months. Surface samples taken from the top sacks were found to have a

    maximum content of 0.04 ppm, whilst sub-surface samples and samples
    from the middle of the sack did not contain detectable residues. In a
    further trial in which exposure was 8 weeks, the maximum residue found
    in surface samples from the top sacks was only 0.02 ppm. This was
    mainly in the husks (0.03 ppm); the kernels contained only 0.01 ppm.

    In a series of trials in Switzerland (Ciba), dichlorvos was applied to
    cocoa beans in silos at rates ranging from 10 ppm through 100 ppm to
    500 ppm. After three weeks storage at 15°C, the residues had fallen to
    <0.1, 13 and 50 ppm, respectively, on the raw beans. When beans were
    then roasted, the residues fell to <0.1, 0.2 and 0.5 ppm,
    respectively. In the samples treated at 500 ppm, most of the residue
    was in the mash cake with a minimum in the cocoa butter. Further
    trials (Ciba) showed that the residues in cocoa beans treated at the
    rate of 12 ppm with dichlorvos emulsion fell from 0.8 to 0.09 ppm
    during 28 days in storage at 20°C.


    Sacks of bagged groundnuts (Shell, 1966b) were exposed for 82 days in
    a warehouse at the recommended rate of one strip/1000 cubic feet. One
    residue sample taken from the surface (2 cm) layer of the top sack was
    found to contain 0.10 ppm dichlorvos, but two other similar samples
    were found to contain only 0.01 ppm dichlorvos. One sample from the
    middle of the top sacks contained 0.03 ppm, but in two further samples
    no residues were found.

    Residues arising from the exposure of foods in processing plants

    Plants producing foods not processed further after exposure

    In a cheese factory, in Minnesota, strips were placed throughout the
    milk receiving and processing areas (Shell, 1964). A monitoring
    experiment showed that the finished Cheddar cheese did not contain
    detectable dichlorvos and DCA residues (i.e. below 0.03 ppm and 0.01
    ppm, respectively). Similar trials in butter and ice cream factories
    (Shell, 1965c) showed negligible residues of dichlorvos and DCA in
    both products.

    In tests carried out in cooperation with the German Public Health
    Service in a cheese factory, Lindenberg, Edam and Danish Tilsit cheese
    (each containing 45% fat) were exposed for four hours. Cheese samples
    were cut into 20 mm thick slices following normal practice, and
    exposed for a period of 30 to 60 minutes. Residues, which were
    determined in the outermost 1 mm layers, were not detectable (Anon.,

    Strips were hung in a cheese aging room at the rate of one strip/1000
    cubic feet. Samples of cheese taken after six and ten weeks of
    exposure showed residues of <0.04 to 0.10 ppm (Shell, 1965a). In the
    case of milk (Shell, 1965d), whole milk was exposed in open milk
    churns for periods of 24 and 48 hours in rooms where fresh strips were
    installed at the rate of one strip/1000 cubic feet. None of the

    representative samples taken contained measurable amounts of
    dichlorvos (detection limit 0.02 ppm).

    In a study in Kentucky (Shell, 1965d), strips were installed in a farm
    dairy at the rate of one strip/1000 cubic feet. The air was humid and
    the temperature about 75°F. The milk samples were taken after being
    passed through an open coil cooler during the period 0-14 days after
    the strips were hung. Residues of dichlorvos ranged from the limits of
    detection to 0.04 ppm.

    Plants handling foods which are processed after exposure

    Fresh strips were suspended in areas of a plant where grading and
    filleting of fish was carried out, and after two days exposure,
    residues in the prepared product were not detected (detection limit
    0.05 ppm) (Shell, 1965e).

    Exposure tests were also carried out in a slaughterhouse (Shell,
    1965c). The various products, beef, liver, T-bone steak, hamburger,
    beef tongue and heart, pork liver, pork sausage, pork chops, pork
    tongue and heart were exposed to dichlorvos resin strips during the
    time normally required for processing. None of them showed any
    dichlorvos or DCA residues; detection limit was 0.01 ppm. In this
    test, a sample of bacon showed a residue of 1.4 ppm dichlorvos; DCA
    was not found (detection limit 0.01 ppm). It was subsequently found,
    however, that this particular sample had been returned to the cooling
    room and was exposed for several days longer than normal. Further,
    data cited later (Shell, 1966c) show that residues of dichlorvos are
    removed upon cooking; specifically, bacon is cited as an example.

    An experiment on similar lines was also conducted in a sausage factory
    where strips were installed throughout the processing areas (Anon,
    1966). No residues were detected in either meat or finished sausages.


    In animals

    Page (1970) has reviewed the extensive literature on the metabolism of
    dichlorvos and in the same paper has reported on extensive trials
    designed to show the metabolic fate and tissue residues of dichlorvos
    following oral administration. The results of this work and earlier
    studies are summarized in the metabolic chart given under "Biochemical
    aspects" (Fig. 1).

    A series of experiments have been conducted recently in pigs to
    provide further information on the metabolic fate of the dichlorvos
    portion of the dichlorvos molecule. In a preliminary study, 1-14C
    labelled dichlorvos was infused into the isolated duodenal loop of
    anaesthetized male pigs for four hours at the rate of 1 mg/kg
    body-weight/hour. Urine, bile and peripheral and portal blood were
    collected hourly and analysed for dichlorvos and its previously
    reported mammalian metabolites. Dichlorvos, dichloroacetaldehyde and

    dichloroacetic acid could not be detected in the blood. "The
    concentration of 30 ppm dichlorvos in the intestinal lumen resulted in
    less than 0.05 ppm dichlorvos in the blood. Neither could
    dichloroacetaldehyde or dichloroacetic acid be detected in the blood.
    The level of 2,2 dichloroethanol in the blood rose from 0.2 ppm after
    one hour to 0.9 ppm after four hours" whereas o-demethyldichlorvos
    occurred only near the limit of detection (0.03 ppm or less). In all
    cases, levels of 14-carbon radioactivity in urine, bile and tissue
    were higher than the level of 2,2-dichloroethanol, thus in urine the
    respective figures were 17 ppm compared to 3 ppm; in bile 12 and 0.5;
    in kidney 21 and 1.2; in liver 17 and 0.9 and in muscle 2.2 and 0.6
    ppm. The figures indicated that 2,2-dichloroethanol or its conjugates
    are not the end products of the metabolism. In other experiments, pigs
    were given sustained release pellets of 14C- or 36Cl-labelled
    dichlorvos at an oral dose of 40 mg/kg body-weight, and excreta and
    tissue were analysed after various intervals. A similar situation to
    that found in the infusion experiment occurred. It was concluded that
    there was a rapid dechlorination of dichloroacetaldehyde and that the
    radioactive carbon enters the metabolic pool possibly via glyoxal
    (which compound has been found in in vitro but not in in vivo
    studies). No retention in tissue of any chlorine containing organic
    compound has been found, and the end product of the chlorine fragment
    appears to be chloride ion (Page, 1970).

    All the data support the conclusion that when administered orally over
    a period of weeks, dichlorvos does not result in detectable toxic
    residues in tissues of the parent compound or product-related
    metabolites. The results of some of the published trials are
    summarized in Table III.

    In plants

    New data have become available on the chemical degradation of
    dichlorvos residues on plants. Careful experiments with various plant
    species (cotton, maize, peas, beans) have demonstrated that dichlorvos
    is rapidly lost from leaf surfaces by volatilization and by hydrolysis
    and, disregarding the fraction of insecticide lost by volatilization
    during the first few minutes after application, the half-life of the
    compound under laboratory conditions is of the order of a few hours. A
    small percentage (0.5-5 percent) of the dichlorvos deposited, appears
    to penetrate into the waxy layers of leaf and fruit cuticle where it
    persists longer. Dichlorvos taken up by plants from aqueous solutions
    by the root system and translocated into aerial parts is less rapidly
    lost than insecticide applied to leaf and fruit surfaces, but even
    under these conditions the half-life of the compound is no more than
    12 hours.

    Various measurements have confirmed the rapid disappearance of
    dichlorvos from vegetable and fruit crops under practical conditions
    (see Table 1). Residues in vegetables were below 0.1 ppm two days
    after application and were no longer detectable on the third day.
    Dichlorvos was somewhat more persistent in fruits, but the residues
    are below 0.1 ppm three days after application.

    In vegetable crops or mushrooms grown under cover or in greenhouses,
    losses of dichlorvos from leaf and fruit surfaces by volatilization
    are less rapid than outdoors. However, on all crops analysed so far,
    including such broad leaf vegetables as lettuce, dichlorvos residues
    have been below 0.5 ppm two days after treatment and below 0.3 ppm
    after three days.

    Casida et al. (1962) used 32P-labelling to study the fate of
    dichlorvos residues on maize, cotton and peas; a 0.1 percent aqueous
    solution of dichlorvos was applied uniformly to the upper leaf
    surfaces of each plant. It was found that about half of the dose
    volatilized within five minutes. An additional 45 percent was absorbed
    within 20 minutes, so that only 5 percent remained on the surface 20
    minutes after application.

    The surface residue was nonhydrolysed dichlorvos while 70-80 percent
    of the absorbed material was organosoluble and was presumably
    nonhydrolysed dichlorvos. However, hydrolysis proceeded rapidly.
    Ignoring the dichlorvos lost by volatilization during the first five
    minutes after treatment, the half-life of the dichlorvos was 1.2 hours
    with loss primarily occurring by hydrolysis. In addition to the
    volatilization of the dichlorvos, which resulted in the total
    dichlorvos equivalent to dropping from 100 per leaf at zero time to 35
    per leaf at 30 minutes, the hydrolysis products were also lost from
    the treated leaves. Only 14 units remained after 24 hours and 7 units
    after 72 hours, despite the fact that no dichlorvos or other
    organosoluble derivatives were detected after eight hours.

    The same authors carried out experiments with radio-labelled
    dichlorvos and showed that, when solutions of the insecticide were
    absorbed by the roots of plants, 77 percent of the absorbed dichlorvos
    appeared as hydrolysis products in peas and 33 percent in maize and
    cotton. Once the plants were removed from the insecticide source, the
    hydrolysis of the absorbed dichlorvos followed first order reaction
    kinetics, with half-life values for both maize and cotton of 9 hours
    and for peas for three hours. Following systemic uptake through the
    roots of plants, dichlorvos is hydrolysed rapidly, but the products of
    hydrolysis are not lost from the plant during a 40 hour
    post-absorption period. Bull and Ridgeway (1969) using 32P labelled
    dichlorvos showed that 54 percent of the amount applied was lost
    within one hour by volatilization from the treated leaves. The major
    metabolite of dichlorvos was dimethyl phosphate; only minor amounts of
    o-desmethyldichlorvos were detected.

    Casida et al. (1962) carried out studies with mice on the acute
    toxicity of dichlorvos and potential hydrolysis products and showed
    relatively high toxicity associated only with the parent compound.

    In storage and processing

    Dichlorvos is readily lost by evaporation from stored products,
    including raw grain and cereal products. Except at very low

    temperatures, it appears likely that dichlorvos is also hydrolysed to
    biologically inactive metabolites.

    A study (Shell, 1970d) using a number of materials with abnormally
    high dichlorvos residues showed that residues can be almost completely
    removed by cooking. Rice containing 4.5 ppm dichlorvos has been shown
    to lose 90% of the residues on boiling from 20 to 30 minutes. When
    rice containing 19 ppm was similarly treated, 98% of the residue was
    destroyed. Samples of flour containing dichlorvos residues in the
    range 4.5 to 14 ppm have been found to lose about 90% of the residue
    on baking for 10 to 12 minutes at 230°C in the preparation of
    biscuits. Boiling the flour with water for 2 minutes, as in the
    preparation of gravy, has been shown to decrease residue levels by
    97%. Residues in cocoa have been shown to be lost during the
    manufacture of cocoa butter. No dichlorvos was found in the fat, the
    nibs, liquor or mash cake prepared from beans containing 2.9 ppm

    Residues in food moving in commerce

    Two shiploads of wheat were treated with dichlorvos emulsion
    immediately prior to shipment from Australia. The dichlorvos was
    applied at a nominal concentration of 6 ppm (found to be 4.6 -5.5
    ppm). Upon arrival in the Netherlands, the grain was thoroughly
    sampled and all samples were found to contain residues below 2 ppm
    (range 0.68-1.59 ppm - mean 0.96 ppm). A major portion of each
    consignment was trans-shipped to the United Kingdom,where it was
    sampled for analysis on arrival. All samples revealed dichlorvos
    residues, but at levels lower than those detected in the Netherlands,
    with a range of 0.4-1.3 ppm and a mean of 0.68 ppm. From the results
    of analysis prior to loading and at the end of a 7-week voyage, it was
    calculated that the half-life of the dichlorvos residues was between
    20 and 23 days.

    Before the general release of dichlorvos resin strips, many
    experiments were carried out to simulate the conditions that would be
    encountered in practical usage. Subsequent data which related to food
    exposed in shops, restaurants and homes under various practical
    conditions where the dichlorvos fumigant strips were used according to
    directions, broadly show that results from the simulated experiments
    overestimated the residue levels.

    Surveys have been carried out in the United Kingdom (17 shops) and in
    France (20 shops) to establish the residue level of dichlorvos in
    unwrapped foods bought by the public from shops using the strips at
    the recommended rate under normal practical conditions. The residues
    found are shown in Tables V and VI.

    The somewhat higher results obtained in some of the commodities in the
    French survey may have been due to the common practice there of
    closing the shops completely during the heat of the afternoon.

        TABLE V

    Residues of dichlorvos (ppm) in food purchased from shops in France

                               Sampling time : days after hanging strips
                           7                        42                      70
    Commodity      Range         Mean       Range         Mean      Range         Mean

    Bread          <0.05-0.10    <0.05      <0.05         <0.05     <0.05-0.06    <0.05

    Cakes          <0.05-0.24    0.08       <0.05-0.30    0.10      <0.05-0.17    0.07

    Apples         <0.05-0.14    0.06       <0.05-0.32    0.07      <0.05-0.30    0.06

    Lettuce        <0.05         <0.05      <0.05         <0.05     <0.05         <0.05

    Tomatoes       <0.05-0.08    <0.05      <0.05         <0.05     <0.05         0.05

    Ham            <0.05-0.08    0.06       <0.05-0.28    0.06      <0.05-0.09    0.05

    (cow)          <0.05-0.08    0.06       <0.05-0.16    0.06      <0.05-0.15    0.06

    (goat)         <0.05-0.35    0.13       <0.05-0.25    0.08      <0.05-0.30    0.08
    A number of surveys have been conducted in the U.S.A. on the residue
    levels in foods which had been exposed to resin strips in restaurants.

    In the first of two studies conducted in restaurants near Cincinnati,
    Ohio, typical restaurant meals were subjected to an exaggerated
    exposure of 24 hours to 5-10 day old strips. In a second study, meals
    were exposed for 22 hours to strips which were initially 51 days old.
    Under the conditions of the first survey, residues were only 0.05-0.15
    ppm of apparent dichlorvos: under the second survey, no residues (less
    than 0.04) were found. In another investigation carried out in four
    different restaurants in New York City under normal operating
    conditions, ready to eat meals were sampled as composite samples.
    Whole meals were sampled at various stages in the life of the strips,
    ranging from 24 hours to 4 weeks. The meals consisted of various
    mixtures of meat or fish and vegetables and varied widely, in
    composition. The following residues were found:

    Restaurant            No. of meals sampled       Residue range,ppm
          A                            5                 0.04 -0.10
          B                            5                 0.02 -0.11
          C                            9                 0.03 -0.16
          D                            5                 0.03 -0.08

    To obtain information on food residues arising from the typical
    practice of hanging strips in kitchens, surveys were carried out in
    homes in the U.K. and France. Food samples were made up of whole food
    and beverage intakes for one day. Each home was sampled the day before
    the strips were hung and one week and six weeks later. In the U.K.
    study, no residues exceeded 0.09 ppm, and the mean of all samples
    taken at one week was 0.034 ppm. The samples at six weeks showed no
    residues in excess of 0.05 ppm, with a mean value of 0.034 ppm.
    Similar studies in 14 French homes showed no residues in excess of
    0.07 ppm, and the mean of all samples taken at one week was 0.024 ppm.
    The six week samples showed no residues in excess of 0.03 ppm.


    Cholinesterase inhibition

    A common technique which has been used for routine residue
    determinations in commodities of known treatment history is based on
    cholinesterase inhibition. Human and animal plasma cholinesterases are
    considerably more sensitive to dichlorvos than erythrocyte
    cholinesterases, and are therefore particularly suitable for residue
    measurements. Out of date stocks of human blood plasma or horse serum
    are satisfactory sources of enzyme.

    Extraction and clean-up prior to the cholinesterase assay are normally
    fairly simple, involving maceration of the material with a solvent of
    medium polarity (chloroform, methylene chloride), filtration and
    careful evaporation of the organic phase in the presence of water.
    More elaborate procedures may be required for plant materials with a
    high fat content, each as cocoa beans or groundnuts, and for certain
    animal products such as milk, cheese and butter. Steam distillation of
    dichlorvos prior to the enzyme assay has been suggested, not only for
    removing interference,but also for increasing the specificity of the
    residue method. For the enzyme assay proper, any of the common
    techniques for measuring cholinesterase activity may be used. The
    sensitivity of these methods is 0.05 to 0.1 ppm. Cholinesterase
    residue analysis for dichlorvos has recently been automated by using
    Technicon Auto-Analyser facilities.

        TABLE VI

    Residues of dichlorvos (ppm) in food purchased from shope in the UK1

                                                    Sampling time : days after hanging strips
                  No. of    No. of            2                         28                      70
    Commodity     samples   shops

                                     Range         Mean2       Range         Mean        Range          Mean

    Cooked meat   35        7        <0.05-0.13    <0.05       <0.05-0.10    <0.05       <0.05-0.09     <0.05

    Cheese        35        7        <0.05-0.07    <0.05       <0.05-0.12    0.05        <0.05-0.12     <0.05

    Apples        49        10       <0.05-0.26    0.08         <0.05-0.54    0.14        <0.05-0.19     0.06

    Tomatoes      33        11       All <0.05     <0.05       All <0.05     <0.05       <0.05-0.05     <0.05

    Lettuce       27        9        All <0.05     <0.05       All <0.05     <0.05       All <0.05      <0.05

    Broad         27        9        All <0.05     <0.05       All <0.05     <0.05       All <0.05      <0.05

    Cakes         19        7        <0.05-0.07    <0.05       <0.05-0.05    <0.05       <0.05-0.05     <0.05

    1  No residues of DCA (0.03 ppm) were found in any of the samples

    2  Mean values are geometric means and are calculated by assuming that samples containing less than the
       detectable level (<0.05 ppm) in fact contain <0.025 ppm

    Such automated methods permit rapid routine measurements of large
    series of samples.

    Since other organophosphorus insecticides or carbamates can interfere,
    the cholinesterase inhibition method is not suitable for detecting and
    measuring dichlorvos in samples of unknown or ill-defined treatment
    history. Both thin-layer and paper chromatographic procedures are
    available for separating dichlorvos from other
    cholinesterase-inhibiting pesticides. In these methods, the
    cholinesterase inhibitors are normally revealed by enzymatic spot
    tests involving colour reactions of the substrate or its breakdown
    products after hydrolysis. It must be remembered that dichlorvos is a
    very volatile compound which, upon solvent evaporation, heating,
    aeration, etc. is easily lost from vessels or chromatographic support
    materials. These procedures are therefore recommended for qualitative
    purposes, but great care must be taken when they are used in
    quantitative analysis.


    The vinegar fly (Drosophila melanogaster) and daphnia (Daphnia
    magna) are suitable test organisms for the bioassay of dichlorvos in
    plant materials. A specific test, which involves absorption barrier
    chromatography and which distinguishes between dichlorvos and other
    insecticides, has been described by Sun and Johnson (1963). The
    sensitivity of the bioassay methods is about 0.1 ppm.


    Although colorimetric techniques have been developed mainly for
    measuring traces in air samples or aqueous solutions, some of them can
    be used for the determination of residues in food materials, provided
    that the sensitivity required is not better than 0.3-1 ppm. Thus, the
    color reaction of dichlorvos with alkaline resorcinol has given
    satisfactory results with extracts of animal food commodities. This
    method demonstrates not only the parent insecticide, but also
    dichloroacetaldehyde, one of its potential hydrolysis products. Acting
    on suggestions made by Hodgson and Casida (1962), Hughes (1963)
    measured residues of dichlorvos and of dichloroacetaldehyde in air,
    using colorimetry, following reaction with alkali and
    2,4-dinitrophenylhydrazine. This method can also be used for
    determining residues in food commodities. A further colorimetric
    procedure, based on formation of an orange-red complex between
    dichlorvos and acetone in the presence of alcoholic potassium
    hydroxide, has been described by Mitsui.

    Gas-liquid chromatography (GLC)

    The most specific residue methods currently available rely on the
    separation and detection of dichlorvos by gas chromatography. The
    sensitivity of these procedures is about equal to that obtained with

    the cholinesterase techniques, i.e. 0.03-0.1 ppm. Methods have been
    described by El-Refai and Guiffrida who used the sodium thermionic
    detector selective to phosphorus, and by Boone (1965) who used a
    microcoulometric detection system. Both methods use fairly high column
    temperatures, and the possibility of thermal or catalytic
    decomposition of dichlorvos on certain column materials must not be
    overlooked. Gas chromatographic residue measurements in industrial
    laboratories are usually carried out at lower column temperatures
    (150°C), and such stationary phases an phenyl diethanolamine succinate
    and Reoplex 400 have given satisfactory retention times and
    separations from interfering insecticides.

    Ivey and Claborn (1969) have published a GLC method for the
    determination of dichlorvos in milk, eggs and various body tissues of
    cattle and chickens. Using a gas chromatograph equipped with a flame
    photometric detector, they were able to detect 0.003 ppm of dichlorvos
    in milk and 0.002 ppm in body tissues and eggs. Methylene
    dichloridehexane was used to extract milk and hexane was used for fat
    and chicken skin. To recover dichlorvos from muscle, blood and eggs
    the authors used a preliminary extraction with acetonitrile.

    Abbott at al.(1970) report the successful application of the use of
    the caesium bromide tipped detector of Hartmann (1966) for the
    determination of dichlorvos on a variety of foods in a total diet

    Drager (1968) has published a gas chromatographic method for
    determining dichlorvos residues in plants and milk. In this method,
    plant material is extracted by macerating it with methanol and water.
    The dichlorvos in the extract is partitioned into a mixture of ether
    and petroleum ether. The residue is then transferred into ethanol, and
    dichlorvos is determined by gas chromatography using the phosphorous

    Minett and Belcher (1969) have developed a method for the
    determination of dichlorvos residues in wheat using GLC techniques.
    For the extraction of the ground wheat the authors used ethanol.

    Many of the published methods and many residue reports indicate that a
    variety of non-polar and polar solvents, such as methylene dichloride
    were used to extract the dichlorvos residue from the food commodity.
    Minett and Belcher (1969) and Elms at al. (1970) have shown that
    dichlorvos cannot be recovered quantitatively from plant materials,
    especially grain, by the use of solvents even as polar as methylene
    dichloride. Water or water-miscible solvents, such as methanol or
    ethanol, are absolutely essential for the recovery of dichlorvos
    residues from plant materials.

    Collaborative studies are currently being carried out in the United
    Kingdom on a method of detecting dichlorvos in grain. The procedure
    uses GLC with thermionic or flame photometric detection following
    extraction with methanol or acetone.


    Dichlorvos is used extensively for the control of insect pests of
    importance in public health, in homes, warehouses, food stores and
    transport, stored grain as well as insects attacking domestic animals.
    It is also finding increasing use on horticultural and field crops and
    is registered in over forty eight countries. Dichlorvos impregnated
    resin strips are extensively used to control insect pests, especially
    flies, in homes, stores and food processing establishments.

    Extensive data on residues in food commodities were available from
    many countries in the form of published reports end submissions from
    three manufacturers. All data indicate that the level of residues
    occurring in raw agricultural commodities is low and that the residue
    levels decline rapidly. Due to the comparatively high vapour pressure
    of dichlorvos, the applied deposit is quickly lost by volatilization,
    but that portion which in absorbed into plant tissues undergoes
    hydrolysis to inactive metabolites.

    Dichlorvos applied to or fed to domestic animals undergoes rapid
    detoxification and degradation in all species examined and is unlikely
    to produce significant residues in meat, milk or eggs.

    The use of dichlorvos impregnated strips for controlling insects in
    warehouses, stores and shops gives rise to detectable residues in
    stored or prepared foods. Residues resulting from exposures at rates
    much higher than the recommended ones have been shown to decrease very
    rapidly on exposure to the atmosphere. They also are readily destroyed
    during the preparation of many products for consumption (e.g. by
    washing or by cooking).

    The proposal that a tolerance in meat and meat products was required
    in view of the use of dichlorvos-resin fumigant strips in meat storage
    and processing places in some countries (CCPR, 1971) was considered by
    the Meeting.

    Considerable data were available on the uptake of dichlorvos by many
    different foods under varying conditions of storage and exaggerated
    exposure to dichlorvos-resin strips, It was recognized that, under
    some conditions, residues as high as 0.1 ppm could result but even in
    fatty meat products the uptake was only at the surface. Residues
    declined during atmospheric exposure and were completely destroyed by
    cooking. Meat and meat products were included among the commodities
    for which a 0.1 ppm tolerance was recommended. These products were
    specially considered because of the request made at the 1970 meeting
    of the Codex Committee on Pesticide Residues (CCPR, 1971).


    The following tolerances are for residues likely to be found in raw
    commodities at harvest, in stored products shortly after treatment and
    in miscellaneous prepared foods exposed during preparation and
    storage. Recommendations have been made on broad categories of fruit
    and vegetables, because extensive data have indicated that when
    dichlorvos is applied to these crops the level of residues shortly
    afterwards does not vary significantly on different varieties.

    Due to the transient nature of the insecticide, residue levels will
    continue to decline during shipment and storage, with a probable half
    life of less than one day on fresh fruit, vegetables and miscellaneous
    foods. Residues in food at time of consumption have normally been
    below the limits of detection by current analytical methods.

    Foodstuff                                            Tolerance
                                             Recommended      Period on which

    Cocoa beans                              5 ppm
    Raw grain (wheat, rice,
      rye, oats, barley,
      maize, sorghum, etc,)                  2 ppm
    Coffee beans, soybeans,
      lentils, peanuts (groundnuts)          2 ppm
    Mushrooms                                0.5 ppm          2 days
    Milled products from raw
      grain                                  0.5 ppm
    Fresh vegetables
      (excluding lettuce)                    0.5 ppm          2 days
    Tomatoes                                 0.5 ppm          1 day and post
    Lettuce                                  1 ppm            2 days
    Fresh fruit (apples, pears,
      peaches, strawberries, etc.)           0.1 ppm          2 days
    Meat of cattle, sheep,
      goats, pigs and poultry                0.05 ppm
    Eggs (on shell free
      basis)                                 0.05 ppm
    Milk (whole)                             0.02 ppm
    Miscellaneous food items
      not otherwise
      specified                              001 ppm

    As recommended in previous monographs, the content of
    dichloroacetaldehyde (DCA) should be reported where known.
    Furthermore, the amounts found should be added to those for dichlorvos
    when assessing adherence to the tolerances recommended.



    1.    Continued observation of the effects of repeated exposure of man
          to dichlorvos in order to determine if there is any qualitative
          or quantitative differences between the metabolic route following
          oral or inhalation intake.
    2.    Data from additional countries on residues in commodities moving
          in international trade.
    3.    Analytical methods capable of recovering and determining residues
          of dichlorvos in foods should be established for regulatory


    Abbott, D.C., Crisp, S., Tarrant, K.R. and Tatton, J.O'G. (1970)
    Pesticide residues in the total diet in England and Wales 1966-69.
    Pesticide Science, 1 (i):10-13

    Anon. (1966) Communication from F.I.D. Nordrhein-Westfalen to Deutsche
    Shell Chemie, Frankfurt, dated 20.1.66 (unpublished)

    Anon. (1966) Communication from Hamburg Public Health Service to
    Deutsche Shell Chemie, Frankfurt, dated 19.7.66 (unpublished)

    Arthur, B.W. and Casida, J.E. (1957) Metabolism and selectivity of
    o,o-dimethyl 2,2,2-trichloro-1-hydroxyethyl phosphonate and its acetyl
    and vinyl derivates. J. Agr. Fd. Chem., 5 : 186-192

    Blair, D., Hutson, D.H. and Pickering, B.A. (1970) The comparative
    metabolism of (vinyl-14C) Vapona in rats after inhalation exposure
    and oral ingestion of the compound. Unpublished draft summary from the
    Tunstall Laboratory, Shell Research Ltd., Sittingbourne

    Boone, G.H. (1965) Determination of Dibrom and DDVP residues in some
    fruit and vegetable crops by microcoulometric gas chromatography. J.
    A.O.A.C., 48 : 748-752

    Boyer, A.C. (1969) I50 values for the inhibition of human and monkey
    blood cholinesterases by dichlorvos. Unpublished technical information
    report prepared by Shell Development Co.

    Bull, D.L. and Ridgway, R.L. (1969) Metabolism of trichlorfon 1969 in
    animals and plants. J. Agr. Fd. Chem., 17 : 837-841

    Carson, S. (1969) Teratology studies in rabbits. Unpublished report
    from Food and Drug Laboratories Inc., Maspeth, N.Y., prepared for
    Shell Chemical Co.

    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. Agr. Fd. Chem., 10 : 370-376

    Cavagna, G., Locati, G. and Vigliani, E.C. (1969) Clinical effects of
    exposure to DDVP (Vapona) insecticide in hospital wards. Arch.
    Environmn. Hlth., 19 : 112-123

    Cavagna, G., Locati, G. and Vigliani, E.C. (1970) Exposure of newborn
    babies to 'Vapona' insecticide. Europ. J. Toxicol. 3 : 49-57

    Cavagna, G. and Vigliani, E.C. (1970) Problèmes d'hygiène et de
    sécurité dans l'emploi du Vapona insecticide dans les locaux
    domestiques. Med. d. Lavoro, 61 : 409-423

    CCPR. (1971) Report of the Fifth Session of the Codex Committee on
    Pesticide Residues para. 165. Alinorm 71/24

    Ciba, A.G. (1970) Basle - Submission to FAO/WHO Joint Meeting -

    Drager, G. (1968) Gas chromatographic method for determining
    dichlorvos residues in plants and milk. Pflanzenschutz - Nachrichten.,
    21 : (3) 373-380

    Elms, K.D., Kerr, J.D. and Champ, B.R. (1970) Breakdown of malathion
    and dichlorvos mixture applied to wheat. In press

    FAO/WHO. (1965) Evaluation of the toxicity of pesticide residues in
    food. FAO Meeting Report No. PL/1965/10/1; WHO/Food Add./27.65

    FAO/WHO. (1967) Evaluation of some pesticide residues in food, FAO
    PL:CP/15, WHO/Pood Add./67.32

    FAO/WHO. (1968) 1967 Evaluation of some pesticide residues in food.
    FAO/PL:1967/M/11/1; WHO/Food Add./68.30

    Green, A.A. and Wilkin, D.R. (1968) The control of insects in bagged
    grain by the injection of dichlorvos. J. Stored Prod. Res., 5 :

    Hartmann, C.H. (1966) Phosphorus detector for pesticide analysis. Bull
    Environm. Contam. and Toxicol., 1 : 159-168

    Hine, C.H., Beltran, S., Cavalli, R.D., Keating, J.M., Keating, W.C.
    Jr. and Sample, H.G. Jr. (1966) Pre-clinical pharmacologic studies on
    dichlorvos in formulation (V-12). Unpublished report from the Hine
    Laboratories, Inc., submitted to Shell Chemical Co.

    Hine, C.H. (1970) Arizona Vapona (DDVP) human study program.
    Chromosomal analysis. Unpublished report from the Hine Laboratories,
    Inc., prepared for Shell Chemical Research Development Co.

    Hodgson, E. and Casida, J.E. (1962) Mammalian enzymes involved in the
    degradation of 2,2-dichlorovinyl dimethyl phosphate. J. Agr. Fd.
    Chem., 10 : 208-214

    Hughes, G.T. (1963) Colorimetric determination of low concentrations
    of 2,2-dichlorovinyl dimethyl phosphate in the atmosphere. Analyst,
    88 :  318-319

    Hunter, C.G. (1969) Report on initial studies of deliberate exposure
    to high concentrations of dichlorvos by human subjects. Unpublished
    report from the Tunstall Laboratory, Shell Research Ltd.,

    Hunter, C.G. (1970) Dichlorvos:  inhalational exposures with human
    subjects, Part 1. Group research report TLGR. 0061.70

    Ivey, M.C. and Claborn, H.V. (1969a) Kerrville, Texas, Laboratory,
    Entomology Research Division, ARS, USDA. Results of research on
    residues of dichlorvos in milk and body tissue of dairy cows treated
    for fly control

    Ivey, M.C. and Claborn, H.V. (1969b) GLC determination of dichlorvos
    in milk, eggs and various body tissues of cattle and chickens. Journal
    of the AOAC, 52 (6) : 1248-1251

    Kimbrough, R.D. (1970) Work sited in "Summary of Vapona R
    insecticide review", report of a meeting chaired by L. Golberg at
    Cincinnati, 9 February 1970

    Kirkpatrick, R.L., Harein, P.K. and Cooper, C.V. (1968) Laboratory
    tests with dichlorvos applied as a wheat protectant against rice
    weevils. J. of Econ. Entomol. 61 : 356-358

    Lancaster, J.L. (1962) (in cooperation with Shell Development Co.
    Residue project from University of Arkansas (unpublished)

    Lancaster, J.L. (1963) (in cooperation with Shell Development Co.
    Residue project from University of Arkansas (unpublished)

    Lofroth, G. (1969a) Alkylating property of 2,2-dichlorovinyl dimethyl
    phosphate (dichlorvos, DDVP): a disregarded hazard. Paper presented at
    a meeting of the Children's Cancer Research Foundation, Boston, 3
    September 1969

    Lofroth, G. (1969b) Alkylating property of 2,2-dichlorovinyl dimethyl
    phosphate (dichlorvos, DDVP): a disregarded hazard. Unpublished report 
    reproduced in part in Environmental Mutagen Society Newsletter, No, 2:
    p. 21-24

    Lofroth, G. (1970) Alkylation of DNA by dichlorvos.
    Naturwissenschaften, 57 : 393-394

    Loomis, E. and Hodel, E. (1965) (in cooperation with Shell Development
    Co. Residue project from Rio Linda, California (unpublished)

    Minett, W. and Belcher, R. (1969) Determination of malathion and
    dichlorvos residues in wheat grains by gas-liquid chromatography. J.
    Stored Prod. Res., 5 : 417-421

    Modesto home trials with Vapona insecticide strips

    Nelson, C.B. (1968) (in cooperation with Shell Chemical Co. Residue
    project from Fillmore, California (unpublished)

    Noetzel, D. (1964) (in cooperation with Shell Development Co. Residue
    project from North Dakota State University (unpublished)

    Padget, T.J. (1968) Evaluation of dichlorvos as a grain treatment for
    protection against the white-fringed beetle. USDA Plant Pest Control
    Laboratory (unpublished)

    Padget, T.J. (1969) Communication on the evaluation of dichlorvos as a
    grain treatment for protection against the white-fringed beetle

    Page, A.C. (1970) Metabolic fate and tissue residues following oral
    administration of dichlorvos. Collection of unpublished reports
    prepared and submitted by Shell Chemical Co.

    Palut, D., Grzymala, W. and Syrowatka, T. (1969) Investigation of the
    metabolism of some organophosphorus insecticides on animal model
    systems. II Hydrolytic degradation in vitro (original in Polish),
    Roczn. Zak. Hig. (Warsz.), 20 : 551-555

    Pitts, C.W. (1961) (in cooperation with Shell Development Co. Residue
    project from Kansas State University (unpublished)

    Preussmann, R. (1967) Analytical determination of alkylating agents.
    Zweite Konferenz über aktuelle Probleme der Tabaksforschung, Freiburg,
    p. 92 (cited by Lofroth, 1969, q.v.)

    Preussmann, R. (1968) Direct alkylating agents as carcinogens. Fd.
    Cosm. Toxicol, 6 : 576-577

    Preussmann, R., Schneider, H. and Epple, F. (1969) Untersuchungen zum
    Nachweis Alkylierender Agentien. Arzneimittelforschung, 19 :

    Roger, J.C., Chambers, H. and Casida, J.E. (1964) Nicotinic acid
    analogs: effects on response of chick embryos and hens to
    organophosphate toxicants. Science, 144 : 539-540

    Roger, J.C., Upshall, D.G. and Casida, J.E. (1969) Structure activity
    and metabolism studies on organophosphate teratogens and their
    alleviating agents in developing hen eggs with special emphasis on
    Bidrin. Biochem. pharmacol., 18 : 373-392

    Sasinovich, L.M. (1968) The maximum permissible concentration of DDVP
    in the air of the working zone. Gig. i Sanit, 33 (12) 35-39

    Sax, K. and Sax, H.J. (1968) Possible mutagenic hazards of some food
    additives, beverages and insecticides. Jap. J. Genetics, 43 : 89-94

    Shaw, F. (1964) (in cooperation with Shell Development Co. Residue
    project from University of Massachusetts (unpublished)

    Shell Development Co. (1964) Modesto Project No. RES 64-111

    Shell Research Ltd. (1965a) Woodstock Technical Memo. 165/65

    Shell Research Ltd. (1965b) Woodstock Technical Memo. 159/65

    Shell Development Co. (1965c) Modesto Project No. RES 65-42

    Shell Chemical Company, New York. (1965d) Brief in Support of Vapona
    Insecticide Resin Strips. Section VII : 11-12. Submitted to Panel of
    U.S.P.H.S. and U.S.D.A., 29.10.65

    Shell Development Company. (1965e) Modesto Project No. RES 65-36

    Shell Research Ltd. (1966a) Woodstock Technical Service Note 146/66

    Shell Research Ltd. (1966b) Woodstock Technical Service Note 178/66

    Shell Research Ltd. (1966c) Woodstock Technical Memo 1/66

    Shell Chemical Co. (1967) Petition proposing a tolerance for the food
    additive (pesticide chemical) dichlorvos in or on stored food
    commodities. Section D-III

    Shell Research Ltd. (1968) Woodstock WKGR. 0041.68 (unpublished)

    Shell Chemical Co. (1969) Princeton laboratory residue analysis report
    project no. PRL 69-62, (unpublished)

    Shell Development Co. (1970a) The third Arizona home study. The
    quantification of DDVP residues in foods consumed by human volunteers
    exposed to "No-Pest" strip insecticide. (unpublished report)

    Shell Chemical Co. (1970b) Princeton laboratory residue analysis
    report project no. PRL 70-12, (unpublished)

    Shell Chemical Co. (1970c) Princeton laboratory residue analysis
    report project no. PRL 69-26 (II) (unpublished)

    Shell Research Ltd. (1970d) Interim report - Residues of Vapona in
    meals prepared in domestic kitchens. Woodstock Laboratory

    Singh, V.K. (1964) (in cooperation with Shell Development Co. Residue
    project from Bio/Toxicological Research Associates (unpublished)

    Singh, V.K. (1965) (in cooperation with Shell Development Co. Residue
    project from Bio/Toxicological Research Associates (unpublished)

    Singh, V.K. and Rainier, R.H. (1966) Three year chronic oral toxicity
    of formulated dichlorvos in swine with special reference to possible
    effects upon fertility and the viability of the offspring of the
    animals fed continuously on diets containing the drug. Unpublished
    report from Bio/Toxicological Research Associates, Spencerville, Ohio,
    prepared for Shell Chemical Co.

    Somme, L. (1967) A field trial with dichlorvos vapor for the control
    of Ephestia Kühniella Zell (Lepidoptera, Phycitidae) in flour mills.
    Reprinted from Journal of Stored Products Research, 4 (3)

    Stevenson, D.E. and Blair, D. (1969) A preliminary report on the
    inhalation toxicity of high concentrations of dichlorvos. Shell
    Research Tunstall Report No. TLGR. 0024.69

    Sun, Y.P. and Johnson, E.R. (1963) A new bioassay technique with
    special reference to the specific bioassay of dichlorvos insecticide.
    J. Econ. Entomol., 56 : 635-641

    Vigliani, E.C. (1970) Results of recent studies on Vapona. Paper
    presented at the 7th Shell Industrial Doctors' Meeting, Strasbourg,
    27-29 May 1970, submitted by Shell International Research Ltd.

    Vogin, E.E. (1969) Teratological studies with dichlorvos in rabbits.
    Unpublished report from Food and Drug Laboratories, Inc., Maspeth,
    N.Y., prepared for Shell Chemical Co.

    Wisconsin Alumni Research Foundation No. 8030193 (1968) (in
    cooperation with Shell Chemical Co. Residue project report

    Wisconsin Alumni Research Foundation (1968/9) (in cooperation with
    Shell Chemical Co. Residue project reports on sheep, cattle and goats

    Witherup, S., Caldwell, J.S. Jr. and Hull, L. (1965) The effects
    exerted upon the fertility of rats, and upon the viability of their
    offspring, by the introduction of Vapona R insecticide into their
    diets. Unpublished report from the Kettering Laboratory Cincinnati

    Young, R., Jr. (1969) Dichlorvos infusion studies. Unpublished
    technical information report prepared by Shell Development Co.

    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:1967/M/11/1)
       Dichlorvos (FAO/PL:1969/M/17/1)
       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)