WHO Pesticide Residues Series, No. 1



    The evaluations contained in these monographs were prepared by the
    Joint Meeting of the FAO Working Party of Experts on Pesticide
    Residues and the WHO Expert Committee on Pesticide Residues that met
    in Geneva from 22 to 29 November 1971.1

    World Health Organization



    1 Pesticide Residues in Food: Report of the 1971 Joint Meeting of
    the FAO Working Party of Experts on Pesticide Residues and the WHO
    Expert Committee on Pesticide Residues, Wld Hlth Org. techn. Rep.
    Ser., No. 502; FAO Agricultural Studies, 1972, No. 88.

    These monographs are also issued by the Food and Agriculture
    Organization of the United Nations, Rome, as document AGP-1971/M/9/1.

    FAO and WHO 1972



    Since the last consideration of 2,4-D (FAO/WHO, 1971) further
    information has become available particularly on reproduction and
    long-term oral studies. This new information is summarized in the
    following monograph addendum. Except where otherwise specified
    biochemical and toxicological studies on 2,4-D are assumed to have
    been performed using the free acid.



    The herbicide 2,4-D was reconsidered in light of new data that had
    recently become available. At the 1970 Joint Meeting a request for
    information on the nature of the impurities occurring in commercial
    preparations of 2,4-D was put forth (FAO/WHO, 1971). A survey of
    polychloro-dibenzo-p-dioxin content in selected pesticides (Woolson,
    E. A. et al., undated) has shown that 27 out of 28 commercial
    preparations of 2,4-D, 2,4-D B. and dichlorprop had no measurable
    amounts of dioxins (<0.5 ppm). One sample of 2,4-D contained traces
    (<1O ppm) of hexachlorodibenzo-p-dioxin which was presumed to arise
    from the condensation of various tetrachlorophenol impurities with
    each other.


    Biochemical aspects

    Absorption, distribution and excretion. Oral administration of a
    single dose of 5 mg/kg body-weight of 2,4-D in a male human subject
    resulted in a plasma level of 35 µg/ml two hours after administration
    which decreased slowly to 25 µg/ml after 24 hours and 3.5 µg/ml after
    48 hours. Levels in whole blood decreased from 21 µg/ml after two
    hours to 2.1 µg/ml after 48 hours. A total of 73% of the dose was
    excreted in the urine within 48 hours following treatment. Complete
    details of this study are not available (Gehring and Gorden, 1971).
    Based upon this study it has been estimated that 1 mg/kg body-weight
    of 2,4-D can be eliminated by man within 24 hours.

    Biotransformation. After administration of 14C-labelled 2,4-D
    (labelled in the 1 or 2 positions) most of the 14carbon in the urine
    and tissues was present as unchanged 2,4-D, but minute amounts (0.25%
    of the dose) of an unidentified metabolite were found, particularly in
    the liver (Khanna and Fang, 1966). [This observation is in contrast to
    the situation in many plants; thus in beans only one-third of the
    radioactivity from labelled 2,4-D is in the form of unchanged 2,4-D
    (Holley et al., 1950)].

    Effect on enzymes and other biochemical parameters. In rat liver
    mitochondria. 2,4-D has been demonstrated to uncouple oxidative
    phosphorylation. At concentrations of 1 × 10-3M there was little
    effect on respiration yet the P:0 ratio fell to 20% of the control
    level. Uncoupling effects were observed at levels as low as
    5 × 10-5M (Brody, 1952).

    2,4-D produces a dose related decrease in acetate metabolism in vivo
    in rats. Groups of male and female rats were administered sodium
    acetate labelled with 14carbon in the 1 or 2 positions. Expiration
    of radioactivity was measured. Pretreatment with 2,4-D reduced the
    expiration of the carbon dioxide, the effect being related to the dose
    of 2,4-D administered and also to the time lag between treatment with
    the herbicide and administration of the sodium acetate. A dose of 10
    mg/kg body-weight of 2,4-D had some effect on carbon dioxide
    elimination from sodium acetate. A dose of 400 mg/kg of 2,4-D
    persisted through a period of 48 hours. but carbon dioxide elimination
    approached control values when sodium acetate was administered 168
    hours later. This time factor is presumably due to the rapid excretion
    of 2,4-D (Philleo and Fang, 1967).

    A subcutaneous injection of 80 mg/kg body-weight of 2,4-D to male rats
    did not affect thyroid, pituitary, adrenal or testicular weight.
    However, when 100 mg/kg was injected both thyroid and body-weight
    decreased. Uptake of 131iodine by the thyroid in vivo is markedly
    increased by ingested 2,4-D). There was no change in serum and
    pituitary thyrotropin levels or other parameters of thyroid function
    and the authors concluded that 2,4-D has a direct effect on the
    peripheral iodide pool. This direct effect was confirmed by isotope
    equilibrium analysis of the serum iodide level. After hypophysectomy
    or iodine depletion this effect was not observed (Florsheim and
    Velcoff, 1962).

    In a later study involving dialysis, thyroxine stabilization and
    in vitro incubation. it was demonstrated that 2,4-D lowers the serum
    protein bound iodine by lowering serum binding of thyroxine. The
    iodine is displaced from the serum into the liver and to a lesser
    extent the kidney, creating a "hyperthyroid" state on these organs
    (Florsheim et al., 1963),

    Following the oral administration of 625 mg of 2.4-D to rats the serum
    aldolase and blood cholinesterase decreased and the serum
    glutamic-oxaloacetic transaminase increased. The serum glutamic-pyruic
    transaminase first decreased and then increased while the blood liver
    catalase revealed a reverse pattern. Electrophoresis showed a decrease
    of the alpha1 and gamma globulins and an increase of the alpha2
    and ß globulins (Szocs et al., 1970).

    Based upon genetic studies with soya bean seedlings and with E. coli
    it has been demonstrated that auxin herbicides such as 2,4-D may react
    with a receptor in the cytoplasm of plant cells. The complex formed is
    then transported through the nuclear membrane where it appears to
    react with RNA polymerase or otherwise alters its specificity in a way

    that allows the enzyme to transcribe different genomes. The author
    draws attention to the structural similarity of the native plant
    auxin, 3-indoleacetic acid, and the animal hormone seratonin. Without
    direct experimental evidence it is suggested that since 2,4-D alters
    the transcriptional capacity of genomes in plants it might also affect
    genome transcription at the molecular level in animals and if so could
    have serious effects on animals during differentiation and development
    (Cherry, 1970).


    Special studies

    (a)  Toxicological significance of plant metabolites

    Although there is no information on the toxicity of plant metabolites
    of 2,4-D the extent and occurrence of such metabolites has been
    extensively reviewed. Evidence indicates that small amounts of
    unidentified or incompletely identified metabolites, which may be
    conjugated, occur soon after application. It is considered that these
    metabolites would not be present under conditions of good agricultural
    practice (Leng, 1968).

    (b)  Toxicity of impurities

    Based on information on the manufacturing process for 2,4-D it is
    unlikely that dioxin impurities could occur. A chemically feasible one
    would be 2,7-dichlorodibenzo-p-dioxin. Tests at the Dow Chemical
    Company have been unable to detect this compound in current batch
    samples using a method sensitive to 0.2-0.5 ppm. The oral LD50 of
    this dioxin is >2000 mg/kg body-weight in mice and >1000 mg/kg in
    rats. It did not cause chloracne, caused no irritation to the rabbit
    eye and was not teratogenic or embryotoxic in rats. A dose level of
    100 mg/kg body-weight per day for 10 days caused no apparent maternal
    toxicity or effect on the developing embryo (Rowe et al., 1971).

    (c)  Carcinogenicity

    Rat. Groups of 25 male and 25 female Osborne-Mendel rats were fed on
    diets containing 0, 5, 25, 125, 625 or 1250 ppm 2,4-D for up to two
    years. An unstated number of rats were lost through autolysis. The
    occurrence of tumours in the animals which were not so lost but which
    were examined at post mortem during the experiment or at its
    termination is presented in tabular form. The number of survivors at
    the end of the experiment and the incidence of rats with (a) tumours
    and (b) malignant tumours was as follows:

     Dose     Sex      Survivors      Total rats       Total rats with
    (ppm)             at 2 years     with tumours     malignant tumours
        0      M          15               3                  1
               F                          12                  5

        5      M          14               5                  2
               F                           9                  6

       25      M          18               5                  4
               F                          13                  3

      125      M          20               6                  2
               F                          14                  5

      625      M          23               6                  5
               F                          17                  3

    1 250      M          22               7                  6
               F                          15                  8

    These data are imprecise in that numbers of rats of each sex that
    survived to two years are not separately given and that the times of
    death with tumours of tumour-bearing rats that died during the
    experiment are not provided. The authors point out that there is a
    statistically significant (P <0.05) linear relationship between the
    proportion of female rats with tumours and the level of the log dose
    but not the arithmetic dose, indicating that there is a tendency for
    the proportion of female rats with tumours to increase with the log

    They also point out that there is a statistically significant
    (P <0.05) linear relationship between the proportion of male rats
    with malignant tumours and the level of arithmetic and log dose. There
    was not a statistically demonstrable (P >0.05) linear relationship
    with arithmetic dose or log dose for the proportion of female rats
    with malignant tumours or for the proportion of male rats with total
    tumours. (Later in the paper, however, on the grounds that the tumours
    referred to affected a wide variety of sites, the authors state their
    belief that the raw data do not support the view that their experiment
    indicates that 2,4-D is carcinogenic for the rat.) (See also
    "Long-term study. Rat" (Hansen et al., 1971.)

    (d)  Reproduction

    Bird embryo. Spraying non-incubated eggs, or eggs incubated for 3.5
    days, with a preparation of an mine salt of 2,4-D caused embryo death
    in 399 of 520 pheasant, 148 of 345 red partridge and 155 of 201 grey
    partridge eggs. Surviving embryos were affected by paralysis, neck

    rigidity and gonadal development disorders. The authors report that
    the nests were sprayed at 1-2 1/ha. The exact dilution of the product
    is unclear nor is there information on the age of the embryos nor are
    there values for controls (Lutz and Lutz-Ostertag, 1970).

    When a 1:1 mixture of the isooctyl esters of 2,4-D and 2,4,5-T were
    sprayed on chicken and pheasant eggs at rates up to 28 lb/acre (acid
    equivalent) there was no difference in hatchability of sprayed and
    unsprayed eggs. The detailed report was not available (Somers et al.,

    Mouse. When mice of four strains were injected subcutaneously with
    levels of 24 to 106 mg/kg body-weight of 2,4-D or its esters in
    dimethyl sulfoxide solution on days 6 to 14 or 15 of gestation, there
    was a statistically significant increase in the proportion of litters
    containing abnormal foetuses and an increased incidence of abnormal
    foetuses within litters, but only in one of the four strains of mice.
    The tests on butyl and isopropyl esters of 2,4-D were statistically
    significant at the 0.01 level for one or more tests in C57BL/6 mice,
    and tests on the isooctyl ester were significant at the 0.05 level in
    the same strain. The methyl ester of 2,4-D induced only an increase in
    the proportion of abnormal foetuses within litters in this strain and
    the statistical significance was relatively weak. Similarly, 2,4-D
    produced only an increase in the proportion of abnormal litters in AKR
    mice in some tests but not others, depending on the period that the
    tests were conducted. Groups of positive and negative controls were
    run periodically throughout the duration of the study but they were
    not matched with respect to either route or date of administration. No
    significant increase of anomalies was noted with 2,4-D isooctyl ester
    in C3H, A/Ha, or AKR mice; with 2.4-D butyl ester in C57 and AKR mice;
    with 2,4-D isopropyl ester in C57 and AKR mice; with 2.4-D methyl
    ester in AKR mice and in a hybrid foetus resulting from mating a
    C57BL/6 female with an AKR male; with 2,4-D ethyl ester in C57 and AKR
    mice; and with 2,4-D in C57, C3H, and hybrid C57 × AKR mice
    (Bionetics, 1969).

    Rat. Groups of pregnant female rats were administered orally, on
    days 6 to 15 of gestation, four samples of 2,4-D and one sample each
    of its isooctyl, butyl and butoxyethanol esters and of its
    dimethylamine salt. Levels of 0, 25, 50, 100 or 150 mg/kg body weight 
    were used depending upon the compound. (The impurity
    2,3,7,8-tetrachlorodibenzo-p-dioxin found in 2,4,5-T was looked for
    but not detected.) Maternal survival, weight gain or fertility of
    offspring was not affected by the compounds. Levels of 100 or 150
    mg/kg daily induced foetopathy and an increase in skeletal
    abnormalities. In one sample only of 2,4-D there was an increase in
    abnormalities at 50 mg/kg. Abnormalities not detected in the controls
    were fused ribs, small sized distorted scapula, laterally convex or
    distorted humerus shaft and bent radius or ulna. Defects of the
    thoracic limbs resulted in micromelia. The incidences did not appear
    to be dose or compound related. The no-effect level with respect to
    formation of these abnormal offspring appears to be 25 mg/kg
    body-weight/day (Khera and McKinley, 1971).

    Unspecified numbers of female rats were fed 2,4-D at dietary levels of
    0, 1000 or 2000 ppm for 95 days and were then mated to untreated
    males. The females were then continued on their respective diets
    through the period of gestation and lactation. The young from the
    animals fed 2000 ppm were very small at birth and 94% died before
    weaning. Mortality among the young was also higher from the group fed
    1000 ppm than from the controls (Gaines and Kimbrough, undated).

    A three-generation rat reproduction study has recently been conducted,
    involving two litters of each generation (a total of six litters). The
    2,4-D used was analysed for impurities and the levels of
    2,7-dichlorodibenzo-p-dioxin and
    2,3,7,8-tetrachlorodibenzo-p-dioxin were below the limit of
    detection (i.e. 1 ppm). Dietary levels of 0, 100, 500 or 1500 ppm of
    2,4-D were fed to 20 female and 10 male rats in each of the test and
    control groups except in those generations where insufficient young
    were available. Animals from both litters of each generation were
    mated. No difference in fertility, litter sizes, viability during the
    first 21 days, or weaning weight was evident between the controls and
    the animals fed 100 or 500 ppm of 2,4-D. At 1500 ppm there was no
    effect upon fertility or upon average litter size but the percentage
    of young born that survived to 21 days of age was sharply reduced by
    this level of 2,4-D and the weaning weight was also depressed. In a
    study made in the F2b litter neither liver aliesterase nor liver
    acylamidase activity differed between the test and control groups.
    This fact was true for whole liver homogenates as well as for
    mitochondrial and microsomal fractions (Hansen et al., 1971).

    It has been stated that the long-term feeding to rats of potatoes
    which had been treated with 2,4-D affected reproduction. In the F2
    generation and even more in the F3 generation the ability to
    reproduce was markedly reduced in the animals fed these potatoes (An
    der Lan, 1966). The original report of this work (Schiller, 1964) has
    recently been re-evaluated statistically. In the first experiment
    there was no difference in fertility (defined as the number of rats
    weaned per female mated) in the test and control groups. In a combined
    second and third experiment the fertility of the parent and F1, F2
    and F3 generations was not significantly different for the controls
    and test groups although a trend towards reduced fertility was
    apparent in the test group of the F3 generation. Chemical analysis
    for 2,4-D in the potatoes was not given (Hansen et al., 1971).

    Pregnant female rats of the Sprague-Dawley strain were administered
    orally suspensions of 2,4-D or solutions of its esters in corn oil
    (the levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the compounds
    were below the limit of detection of 0.2 ppm). The rats received 0,
    12.5, 25.0, 50.0, 75.0 or 87.5 mg/kg body-weight of 2,4-D or the molar
    equivalent of its propyleneglycolbutyl ether ester (hereinafter termed
    the butoxy ester) or iso-octyl ester. The top dose level approached
    the maximum tolerated. The compounds were administered on gestation
    days 6 to 15 inclusive to test for teratogenicity or on days 5 to 18
    to evaluate effect on implantation. Other groups received the
    iso-octyl ester on days 8 to 11 or days 12 to 15 to evaluate the

    effect on early or late organogenesis. Treatment with 2,4-D or its
    iso-octyl ester did not increase the incidence of foetal resorption.
    With the butoxy ester, the lowest dose level, 12.5 mg/kg, caused a
    significant increase in the number of litters having one or more
    resorptions but the overall incidence of resorption was not greater
    than the controls, and this effect on litters with resorptions was not
    found in higher doses. Dose-related decrease in foetal body-weight was
    apparent in all three compounds at levels above the molar equivalent
    of 25 mg/kg of 2,4-D. Certain embryonic responses such as subcutaneous
    oedema, lumbar and wavy ribs, delayed ossification of bones including
    the skull, increased with increasing doses of the agents studied but
    these abnormalities also occurred in the controls. Incidences of
    missing sternebrae were increased only in three groups, those treated
    with 87.5 mg/kg of the butoxy ester and at 12.5 and 87.5 mg/kg of
    2,4-D. The no-effect level with respect to foetal body-weight was 25
    mg/kg or its molar equivalent for all three compounds (Schwetz et al.,

    Rat and guinea-pig. Doses of 1/30 and 1/50 of the LD50 of the
    butyl ester of 2,4-D (see below) administered repeatedly during the
    pregnancy of rats and guinea-pigs revealed strong embryotoxic effects
    (no details are available) (Konstantinova, 1967).

    Hamster. Groups of eight to 12 golden hamsters were given 2,4-D from
    three different commercial sources. None of the samples contained
    detectable amounts of the tetrachlorodibenzodioxins; existence or
    non-existence of other chlorinated dioxins could not be demonstrated
    with certainty due to limitation in the methods of analysis. The
    hamsters were given by oral intubation levels of 0, 20, 40, 60 or 100
    mg/kg body-weight of the various samples of 2,4-D on days 6 to 10 of
    gestation. Slight but significant increase in foetal viability was
    evident at 60 and 100 mg/kg in one sample and at 40 mg/kg only in
    another sample. Incidence of abnormalities per number of live litter
    was not significantly greater in test and control groups. When
    encountered, fused ribs were the most frequently observed terata but
    the effect could not be clearly dose related (Collins and Williams,

    (e)  Cytotoxicity

    The effect of 2,4-D on L 929 cells in monolayer cultures has been
    studied. It was found that 2,4-D in the range of 50 to 500 µg/ml had a
    dose-dependent inhibitory effect on cell growth. With 350 and 500
    µg/ml complete inhibition of growth occurred after about 24 hours of
    incubation. On removal of 2,4-D a rapid resumption of cell
    multiplication took place. This occurred even after exposure to 500 µg
    2,4-D/ml for 12 days. In the presence of 250 to 500 µg/ml, vacuoles,
    which stained with lipid soluble dyes, appeared in the cytoplasm. On
    prolonged incubation with the herbicide, these vacuoles disappeared
    (Kolberg et al., 1971).

    Acute toxicity

    The acute oral toxicity of the butyl ester of 2,4-D is given in the
    following table.


                    LD50 mg/kg
         Animal     body-weight        Reference

         Mouse          380       Konstantinova, 1967
         Rat            920       Konstantinova, 1967
         Cat            820       Konstantinova, 1967

    Short-term studies

    Fish. Bluegills were exposed to 0.1-10 ppm of the
    propyleneglycolbutyl ether ester of 2,4-D and the fish and pond
    environment studied for five months to measure chronic effects on the
    fish. Small amounts of the ester were found in pond water for six
    weeks after application. None of the ester was detected in fish after
    four days. About 20% of the fish treated with 10 ppm died within eight
    days; mortality was almost negligible among bluegills exposed to 5 ppm
    or less. Pathological lesions were seen in the fish and the fish
    treated with the high levels had early and severe effects. The
    pathology involved liver, vascular system and brain, with depletion of
    liver glycogen, globular deposits in the blood vessels, and stasis and
    engorgement of the circulatory system of the brain. The pathological
    lesions regressed to such an extent that after 84 days only an
    occasional specimen from the 10 ppm group still exhibited residual
    lesions. The higher the 2,4-D treatment level the greater the fish
    growth, possibly because mortality of other fish gave a greater
    availability of food. The fish in the ponds treated at 10 and 5 ppm
    spawned about two weeks later than the fish in the other ponds but the
    number of offspring was the same in the control and in all other ponds
    (Cope et al., 1970). It is reported that the butyl, butoxyethanol and
    propyleneglycolbutyl ether esters of 2,4-D are much more toxic to fish
    than other 2,4-D formulations (Walker, 1964).

    Mouse, rat, guinea-pig, rabbit and cat. Mice, rats, guinea-pigs,
    rabbits and cats were used for the investigation of the toxicity of
    the butyl ester of 2,4-D. The repeated introduction of the compound
    into the stomach in small doses (1/5, 1/10, 1/30 of LD50) showed a
    cumulative effect. The fourfold application of the ester on the skin
    surface of rabbits in dose of 2000 mg/kg caused the death of the
    animals. Also the breathing of the air containing the compound in a
    concentration of 0.13 mg/l caused the death of animals. Miotic
    syndrome accompanied with the damage of the nervous system was
    characteristic for the administering of the butyl ester of 2,4-D into
    the stomach, on the skin surface, as well as for inhalation. In the

    case of cats, the compound significantly weakened or caused complete
    loss of vision. Details were not available (Konstantinova. 1967),

    Dog. In a two-year feeding study, groups, each comprising three male
    and three female dogs, were fed 0, 10, 50, 100 or 500 ppm of 2,4-D in
    their diet, feeding of 2,4-D being started at six to eight months of
    age. The dogs were sacrificed after the completion of the test for
    autopsy. Organ weights and organ to body-weight ratios were determined
    for brain, heart, liver, kidney. thyroid. adrenals and testes. One
    male dog fed 10 ppm died after 10 months on the test diet and one
    female dog fed 100 ppm was thin and emaciated at the end of the
    two-year period. All other dogs remained in fair to good condition.
    Histopathological examination of the animal that died revealed a
    slight atrophy of the testis. In the female on 100 ppm, which was in
    poor condition, no significant lesions were seen. The lesions in the
    other dogs were incidental and consisted of the following: the
    controls and the 100 ppm groups tissues showed no significant lesions;
    in the 10 ppm group two dogs had a slight nephrosis and one dog had a
    cystic pituitary; in the 50 ppm group there was one dog with a slight
    atrophy of the testis and one with a slight interstitial nephrosis.
    The 500 ppm group had one dog with a small haemangioma of the adrenal.
    None of the gross or microscopic lesions in the dogs were believed to
    be due to the ingestion of 2,4-D (Hansen et al., 1971).

    Long-term studies

    Rat. Groups, each comprising 25 male and 25 female Osborne-Mendel
    rats, were fed dietary levels of 0, 5, 25, 125, 625 or 1250 ppm of
    2,4-D for up to two years, There was no significant difference in
    mortality between test and control groups. At the end of the test
    period 17, 12, 18, 17, 19 and 16 rats from the respective control and
    dose levels were still alive and were sacrificed for autopsy. There
    was no difference in body-weights nor in organ to body-weight ratios
    for liver, kidney, heart, spleen and testes between the control and
    test animals, with the exception of slightly enlarged spleens in one
    male rat fed 125 and one male fed 625 ppm. Blood picture was normal
    for all dose levels except in the final count performed at 22 months
    when a possible tendency towards macrocystosis in the groups fed 5,
    625 and 1250 ppm of 2,4-D was evident as well as slight polychromasia
    and hypochromasia. Except for macrocystosis which was not present,
    these changes were present only to a very minor degree, in the
    controls. Incidence of tumours is described under "Special studies (c)
    Carcinogenicity". Other lesions were slight hepatitis in one rat each
    in the groups fed 5 ppm and 25 ppm and three rats each in the groups
    fed 625 and 1250 ppm. but not in any rats in the control group. In
    addition, bile duct proliferation and nephritis occurred slightly more
    often in the groups fed 2,4-D than in the controls (Hansen et al.,

    Observations in man

    A man who accidentally ingested 2,4-D (estimated to be 30 ml of a
    concentrated aqueous solution) exhibited fibrillary twitching and
    paralysis of the intercostal muscles. There was evidence of
    generalized skeletal muscle damage as indicated by marked elevation of
    serum glutamic-oxaloacetic transaminase, serum glutamic-pyruvic
    transaminase, lactic dehydrogenase, aldolase and creatine phospho-
    kinase levels, as well as haemoglobinuria, myoglobinuria (thought to
    be previously unreported in this condition) was observed. Recovery was
    complete after several months (Berwick, 1970).

    Observations were made on 220 men exposed to 30 to 40 mg per day of
    2,4-D in a manufacturing plant. Work experience ranged from 0.5 to 22
    years. Medical evaluation revealed no difference when compared to a
    control group of 4600 men. In the exposed group, 10 men were
    karyotyped. There was no effect on the structural integrity or
    rearrangement of the genetic material of the lymphocyte chromosomes
    (Johnson, 1971).

    In another study there were complaints of general weakness, rapid
    fatigability, frequent headache and vertigo among a number of workers
    at a plant manufacturing the amine salt and butyl ester of 2,4-D.
    Objectively incidences of arterial hypotension were encountered and
    there were possible indications of liver dysfunction, the latter
    appearing to occur more frequently in workers with long exposure to
    the herbicides. Full details of this study were not available
    (Brashirov, 1969).


    After the administration of 2,4-D to animals and man the compound is
    rapidly excreted in the urine virtually unchanged. An estimate was
    presented that 1 mg/kg body-weight can be eliminated by man within a
    24-hour period. Although 2,4-D is extensively metabolized by plants
    there is ample evidence that the presence of these plant metabolites
    is transitory in nature. For this reason and because the major uses of
    2,4-D are not on food crops, separate toxicological evaluation of
    plant metabolites in mammals does not deserve high priority.
    Information has previously been reported (FAO/WHO, 1971) that
    increased nitrate formation may result in plants exposed to 2,4-D.
    Further information is required on the extent of this increase and the
    conditions under which it occurs.

    A two-year feeding experiment is available in two species, the rat and
    dog, as well as a number of multigeneration reproduction studies.
    Despite certain statistical calculations on tumour incidence in rats
    fed on 2,4-D for up to two years, consideration of all the data from
    the two-year feeding study does not support the view that 2,4-D is
    carcinogenic in these species. The fact, previously reported,
    (FAO/WHO, 1971) that mice receiving the substance orally for their
    lifespan exhibited no increase in incidence of neoplasms of any site
    or type was regarded as reinforcing the view that 2,4-D is not a

    potential carcinogen. Nevertheless, further life-time feeding studies
    in rats and in a non-rodent species would be desirable. At high dose
    levels of 2,4-D, an embrytoxic effect is observed. Furthermore certain
    esters have induced congenital malformations at sub-lethal doses
    administered to the mother. Lower doses were not teratogenic. A
    further study reporting induction of malformation from the butyl ester
    could not be evaluated as no details were available.

    The absence of measurable (<0.5 ppm) amounts of dioxins including
    2,3,7,8-tetrachlorodibenzo-p-dioxin, in 27 out of 28 commercial
    preparations of 2,4-D (see "Identity") and the fact that it is
    feasible to ensure that dioxin contaminants can be kept below this
    level of detection remove cause for concern about risk of
    contamination of this kind.

    Based upon this information the Meeting agreed that an acceptable
    daily intake for man could be established from the results of the
    two-year study in the rat.


    Level causing no toxicological effect

    Rat: 625 ppm in the diet equivalent to 31 mg/kg body-weight per day.

    Estimate of acceptable daily intake for man

    0-0.3 mg/kg body-weight.


    See the previous monograph (FAO/WHO, 1971).



    Following the establishment by this Meeting of an ADI for 2,4-D, the
    evidence presented to the 1970 Joint Meeting (FAO/WHO, 1971b) has been
    reassessed and the following tolerances are commended:

    Barley, oats, rye, wheat - 0.02 ppm

    Further work or information


    1.   Further life-time studies in the rat and in a non-rodent species.

    2.   Information on the extent of increased nitrate formation in
         plants treated with 2,4-D.

    3.   Information on the metabolism and excretion of 2.4-D in animal
         species other than the rat particularly in non-rodent species and
         in man.

    4.   Information on the occurrence of 2,4-D residues in crops
         following uses other than on cereals.


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    See Also:
       Toxicological Abbreviations
       D, 2,4- (AGP:1970/M/12/1)
       D, 2,4- (WHO Pesticide Residues Series 4)
       D, 2,4- (WHO Pesticide Residues Series 5)
       D, 2,4- (Pesticide residues in food: 1980 evaluations)