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



    Chemical name

    2,4-dichlorophenoxyacetic acid


    2,4-D acid

    Structural formula


    Other relevant chemical properties

    White powder: m.p., 140.5°C; solubility in water at room temperature
    is 620 mg/1; soluble in aqueous alkali and in alcohols; insoluble in
    petroleum oils. V.p., 0.4 mm Hg at 160°C. Can be used as alkali metal
    salt, amine salts and esters.


    Technical, 98 percent pure


    N.B. Except when otherwise specified, toxicity studies on 2,4-D are
    assumed to have been performed using the free acid.


    Absorption, distribution and excretion

    When administered orally as an amine salt, 2,4-D is rapidly absorbed
    in animals, concentrations in plasma reaching a peak after two hours
    for chickens, or four to seven hours for rats, calves and pigs.

    Similar results are seen after oral administration of alkali metal
    salts of 2,4-D. In the case of an ester of 2,4-D, absorption by the
    oral route is poor, as evidenced by low plasma and tissue levels
    following administration. The intact eater has not been detected in
    plasma or urine following treatment to rats, pigs or calves; only the
    free acid is found, a fact which indicates that hydrolysis occurs
    before absorption. Absorbed 2,4-D is distributed throughout the body;
    levels in liver, kidney, spleen and lung reach a maximum after six
    hours and after this time levels in these organs often exceed the
    level in plasma, particularly in chickens and rats. There appears to
    be little variation of distribution between the sexes. In a study with
    pigs, high levels of 2,4-D were also found in endocrine glands and in
    the excretory organs. The brain level was usually low, relative to the
    plasma level. However, 2,4-D passes the placental barrier, as
    evidenced by experiments in pigs. The distribution pattern after
    administering an ester of 2,4-D is similar to that of the salts,
    although tissue levels are lower. A partial binding of 2,4-D to plasma
    proteins may occur. The biological half-life in plasma for chickens,
    rats, calves and pigs was found to be 8, 3, 8 and 12 hours,
    respectively. Elimination of 2,4-D when administered as an ester is
    less rapid than that of salts. Excretion is principally via the
    kidney, and only low levels have been found in the faeces or bile.
    Hens have been reported to excrete 2,4-D in their eggs, the compound
    occurring largely in the yolk (Erne, 1966a, 1966b).

    Rats were given by stomach-tube doses of 2,4-D labelled with 14-carbon
    in the 1 or 2 positions; the compounds had specific activities of 3.03
    mCi/mM and 1 mCi/mM, respectively. They were given in doses of 1, 5,
    10, 40, 60, 80 or 100 mg per rat. Urine, faeces and expired air were
    collected. No radioactivity was detected in the breath at any time
    during three days following administration. In the rats given 1 to 10
    mg of 2,4-D, 94 to 99 percent was excreted over a 72 hour period,
    mostly during the first 24 hours. In animals fed the higher doses of
    20 to 100 mg, the percentage excreted bore an inverse linear
    relationship to the close administered for both sexes, being 75.5
    percent. After 144 hours in the rats given the maximum dose of 100 mg.
    This changed pattern of excretion indicated a slower excretion of the
    higher doses. In the case of six rats which were given 1 mg of
    labelled 2,4-D per rat and a group of seven rats which were given 80
    mg, these animals were sacrificed at varying intervals from 1 to 41
    hours following administration, and levels of radioactivity in various
    organs and tissues were determined. Radioactivity was found in all
    tissues examined and reached a maximum six to eight hours after
    administration. Excretion was also rapid and after 41 hours in the
    animals given 80 mg, only the liver and kidney contained more than 1
    ppm (on a dry tissue weight basis) of 2,4-D, the figures for these
    organs being 1.5 and 1.8 ppm, respectively. With the rats given 1 mg,
    levels below 0.1 ppm were reached in all organs except the stomach
    after 12 hours (Khanna and Fang, 1966).

    A phenomenon of declining plasma levels following repeated treatment
    with 2,4-D has also been observed in chickens and pigs and has been

    suggested as being indicative of the animal's developing an adaption
    to 2,4-D (Erne, 1966a). See also under 'Fate of residues'.

    In a case of fatal poisoning in many 2,4-D was found in blood, urine
    and tissues of all organs the brain had the lowest concentration 
    - less than one fiftieth of that in the blood (Nielzen et al., 1965).

    Effects on enzymes and other biochemical parameters

    In rats which were given 10 mg/kg body-weight of the sodium salt of
    2,4-D by stomach tube for 120 days, the oxygen uptake decreased from
    2.14 to 1.88 mm3/mg of dry tissue in the heart, from 2.3 to 2.2 in
    the liver and from 5.7 to 2.32 in the kidneys (Stanosz, 1969).

    The effect of ingested phenoxy-acid herbicides on muscular function
    has been suggested to be related to interference with carbohydrate
    metabolism. Transitory diabetiform conditions have been reported in
    individuals spraying these compounds. However, hyperglycaemia or
    glycosuria could not be reproduced with certainty in rabbits; only one
    in five animals responded in this manner following administration of
    doses ranging from 125 to 500 mg/kg body-weight from 6 to 50 days.
    (Lorenzen and Lyngsoe, 1957; Dalgaard-Mikkelsen and Poulsen, 1962).

    Attention has been drawn to the increase in nitrate content which has
    been observed in certain plants after spraying with 2,4-D. This
    increase has been thought to be the cause of toxic effects which have
    been observed in grazing animals. Abortions in cattle have also been
    attributed to this phenomenon. Information on this possible indirect
    toxic action of 2,4-D has been summarized (Way, 1969). Manifestation
    of toxicity appears, however, to be confined to farm animals, and no
    reports have been encountered which would indicate that human food
    exposed to 2,4-D as a growing crop has become toxic in this manner.


    Special studies on carcinogenicity


    Repeated injections of 2,4-D have not influenced the growth rate of
    two transplated sarcomas in mice. Mitotic counts performed at various
    intervals in these tissues after a single injection of 200 mg/kg body-
    weight of 2,4-D did not differ significantly from a control not
    treated with 2,4-D (Bucher, 1946).

    Groups of 18 mice of each sex from two hybrid strains were given 2,4-D
    from seven days of age for 18 months. The compounds were given daily
    by gavage at levels of 0, 46.4 or 100 mg/kg body-weight until weaning,
    after which time 2,4-D was incorporated into the diet at the
    corresponding levels of 0, 149 or 323 ppm, respectively. There was no
    significant increase in tumours between the controls and the groups
    given the two levels of 2,4-D (Innes et al., 1969).

    Special studies on reproduction

    Chicken embryo

    When injected into fertile eggs at 5 or 10 mg/egg, 2,4-D did not
    produce malformations, although it was stated that certain
    phenoxyacetic acids produced feather blanching. The percentage hatch
    was 70 and 50 percent for the eggs receiving the two respective levels
    of 2,4-D (Dunachie and Fletcher, 1967).


    Groups of three-day old chicks were given 0 (25 chicks) or 1000 ppm
    (29 chicks) of 2,4-D in their drinking water. Weight-gain, age of
    sexual maturity and onset of egg production did not differ between the
    test and control groups. However, the number, and possibly the weight,
    of the eggs was reduced in the group given 2,4-D (Björkland and Erne,


    Mice which underwent daily injections of about 90 mg/kg body-weight of
    2,4-D became pregnant and bore apparently normal litters at the end of
    a normal gestation period (Bucher, 1946).


    Groups, each comprising five newly mated female rats, received 0 or
    1000 ppm of 2,4-D in their drinking water during their pregnancy and
    for a further ten months. Pregnancy and parturition were normal.
    Litter size was not significantly different between the test and
    control groups. No malformations were observed in the young nor were
    any clinical or morphological abnormalities revealed. After weaning,
    the young rats were given 0 or 1000 ppm of 2,4-D in the same manner as
    their parents for up to two years. The group receiving 2,4-D had
    reduced food intake and depressed growth rate. Clinical-chemical
    parameters were normal. Mortality was higher in the group given 2,4-D.
    Relative organ weights and gross and histopathological examination
    revealed no changes in the test group (Björkland and Erne, 1966).

    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 reduced in the animals fed these potatoes (An der Lan,


    A female pig was fed 500 ppm of an amine salt of 2,4-D during her
    entire seventh pregnancy and for a further six weeks. Anorexia was
    observed. One mummified foetus and 15 underdeveloped live young were
    delivered. Ten of these died by the first day. Autopsy revealed a
    generalized anaemia. No malformations were observed. The surviving

    five young were fed 500 ppm of 2,4-D amine salt; growth was retarded
    and locomotor disturbances were observed. Clinical-chemistry results
    were the same as described under the chronic feeding study for the pig
    (Björkland and Erne, 1966).

    Special studies on toxicity of impurities

    There is no information that the presence of chlorinated
    dibenzodioxins, such as occur in some batches of technical 2,4,5-T,
    has been looked for in technical 2,4-D. It is reported that the
    condensation of the phenol precursors to form such compounds could not
    occur in the manufacture of 2,4-D (Dow, 1970).

        TABLE I
    Acute Toxicity of 2,4-D

    Animal            Route      mg/kg                  References

    Chicken           oral       380-765 (amine salt)   Bjorn and Northen, 1948

    Chicken (mixed)   oral       541                    Rows and Hymas, 1954

    Mouse             oral       375                    Hill and Carlisle, 1947

    Mouse (m)         oral       368                    Rowe and Hymas, 1954

    Mouse             s.c.       280                    Bucher, 1946

    Rat               oral       666                    Hill and Carlisle, 1947

    Rat (m)           oral       375                    Rowe and Hymas, 1954

    Guinea,pig        oral       1000                   Hill and Carlisle, 1947

    Guinea pig
    (mixed)           oral       469                    Rowe and Hymas, 1954

    Rabbit            oral       800                    Hill and Carlisle, 1947

    Dog               oral       100                    Drill and Hiratzka, 1953

    Dog               oral       541                    Rowe and Hymas, 1954

    Monkey            oral       > 428                  Hill and Carlisle, 1947
    For man the lethal dose of 2,4-D has been estimated to be greater than
    80 mg/kg body-weight (Nielsen et al., 1965).

    Symptoms of myotonia in mice were evident after the parenteral
    administration of 150-200 mg/kg body-weight (Bucher, 1946).

    Initial signs following the administration of a lethal dose of 2,4-D
    to dogs were often not present until six hours following oral
    administration. The animal then became ataxic with progressive
    increase in spasm. Pathological changes were limited to the
    gastrointestinal tract, lungs and liver. Death in most cases appeared
    to be due to hepatic congestion or to pneumonia, which followed the
    development of anorexia, weight loss and myotonia (Drill and Hiratzka,

    No toxic symptoms were observed when monkeys received 214 mg/kg
    body-weight orally, but 428 mg/kg caused nausea, vomiting, lethargy,
    muscle incoordination and head drop. All species reacted similarly;
    death from large doses was thought to be due to ventricular
    fibrillation (Hill and Carlisle, 1947).

    Short-term studies


    Groups, each of five chickens, were given an amine salt of 2,4-D three
    times a week in oral doses of 0, 0.28, 2.8, 28, or 280 mg/kg
    body-weight (acid equivalent) for up to four weeks (a total of 12
    doses). Weight gain was reduced only at the 280 mg/kg level (Bjorn and
    Northen, 1948).

    In the study described under "Reproduction" three day old chicks were
    given 0 or 1000 ppm of 2,4-D. In the group given 2,4-D, gross
    pathology revealed enlarged kidneys, and histopathology showed changes
    in the kidney tissue mostly in the proximal convoluted tubules
    (Björkland and Erne, 1966).


    Injection of 50 to 90 mg/kg body-weight of 2,4-D subcutaneously to
    mice for three weeks to three months failed to produce a clear-cut
    syndrome of chronic toxicity. Levels of 70 mg/kg retarded growth,
    however, probably due to reduced food intake (Bucher, 1946).


    Rats were fed a dietary level of 1000 ppm of 2,4-D for one month
    without harmful effects (Hill and Carlisle, 1947).

    Groups each comprising five or six young female rats were given 0, 3,
    10, 30, 100 or 300 mg/kg body-weight of 2,4-D by stomach tube five
    times a week for periods up to four weeks. The animals which received
    30 mg/kg or less showed no adverse effects, as judged by gross

    appearance, behaviour, mortality, growth, haematological values,
    blood-urea nitrogen, organ weights, gross pathology and
    histopathology. The rats on 100 mg/kg showed varying degrees of
    gastrointestinal irritation, slight cloudy swelling of the liver and
    depressed growth rate. The animals given 300 mg/kg failed rapidly and
    died principally of severe gastrointestinal irritation (Rowe and
    Hymas, 1954).

    In a separate experiment, groups each of five young female rats, were
    fed dietary levels of 0, 100, 300, 1000, 3000 or 10,000 ppm of 2,4-D
    for periods up to 113 days. The animals fed 300 ppm or less showed no
    adverse effects as judged by the parameters described in the previous
    experiment. Those given 1000 ppm had increased mortality, depressed
    growth rate, slightly increased liver weight and slight cloudy
    swelling of the liver. The animals fed 3000 or 10,000 ppm were
    sacrificed after 12 days because of food refusal and rapid
    weight-loss. Autopsy revealed increased liver and kidney weights and
    there were slight pathological changes in the organs (Rowe and Hymas,

    Guinea pig

    Guinea pigs tolerated 10 oral doses of 100 mg/kg bodyweight of 2,4-D
    given over a 12 day period. Inhalation of the sodium salt of 2,4-D as
    a dust failed to produce systemic effects (Hill and Carlisle, 1947).


    Groups of from two to four dogs of mixed sexes were given 0, 2, 5, 10
    or 20 mg/kg body-weight of 2,4-D orally by capsule on five days a week
    for 13 weeks. All the dogs given 10 mg/kg or less survived the 90-day
    test period. Of two male dogs given 20 mg/kg, one died after 18 days,
    the other after 25 days. A female given 20 mg/kg/day in two divided
    doses died after 49 days; another male dog on the same dose regimen
    survived the 90-day period. Loss of weight occurred only in the dogs
    which ultimately died, and this phenomenon began seven to 12 days
    prior to death. Dogs that survived 90 days were free of symptoms: in
    the others, ataxia and increased muscle tonus occurred prior to death.
    The blood picture was normal, except for a terminal fall in lymphocyte
    count prior to death. Weights of thyroid, adrenals, heart, liver and
    kidney were not different from the controls in the surviving animals;
    in two of the dogs that died, there was a slight increase in heart and
    kidney weights. Two dogs, one receiving 2 and the other 20 mg/kg
    showed redness in the duodenum. Histopathology revealed no changes in
    heart, lungs, thyroid, adrenal or testes. Two dogs receiving an
    unspecified level of 2,4-D showed areas of focal necrosis in the
    liver, which was considered not to be related to administration of
    2,4-D (Drill and Hiratzka, 1953).


    An amine salt of 2,4-D and 2,4-D ester were given to young pigs in
    doses of 50, 100 or 300 mg/kg body-weight at varying intervals up to

    103 days. Symptoms of intoxication were similar to those reported from
    studies with laboratory animals, and autopsy revealed similar
    pathological findings. Clinical signs of anorexia and retarded growth
    were evident in one pig given 51 doses of 50 mg/kg during 103 days
    (Björklund and Erne, 1966).

    On the basis of this experiment it has been suggested that the pig may
    be more sensitive to 2,4-D than other animals tested, since the
    no-effect level appears to be less than 50 mg/kg body-weight/day
    (Erne, 1966a).

    Five pigs were fed an amine salt of 2,4-D at 0 or 500 ppm in their
    diet for up to 12 months. Food consumption and growth rate was reduced
    in the controls, and after about one month, three animals developed
    locomotor disturbances of increasing severity. The animals were
    sacrificed after two to 12 months. Organ weights were normal, and
    gross pathological changes were not evident. Clinical-chemical
    observations involved lowered haemoglobin and haematocrit values,
    elevation of glutamic-oxaloacetic transaminase and reduced albumin and
    albumin-globulin ratios in the treated animals (Björklund and Erne,


    When steers were given oral doses of 0, 50, 100, 200 or 250 mg/kg
    body-weight of an amine salt of 2,4-D for five days a week, poisoning
    was evident at 250 mg/kg after 15 treatments and at 100 mg/kg after 86
    treatments. A dose of 50 mg/kg given 112 times had no effect on one
    steer (Palmer, 1963).

    Long-term studies

    No complete long-term studies appear to have been conducted.


    A man has been reported to have taken 500 mg of 2,4-D daily for three
    weeks (approximately 8 mg/kg body-weight) without experiencing any
    harmful effects. No further details are given (Assouly, 1951).

    A man aged 23 committed suicide by oral intake of the dimethylamine
    salt of 2,4-D. Pronounced degenerative changes of the ganglion cells
    of the brain were found upon histological examination (Nielsen et al.,

    Subjective clinical symptoms have been reported among workers using
    various esters of and the sodium salts of 2.4-D. Individuals
    complained of rapid fatigue, headache, liver pains, loss of appetite,
    etc. Certain functional shifts were noted in the cardiovascular
    system, and sensitivity to taste and smell was lowered (Fetisov,

    In workers employed in factories manufacturing 2,4-dichlorophenol and
    other chlorinated phenols, a moderately high incidence of urinary
    porphyria, chloracne and hirsutism has been reported. The authors
    suggest that a highly chlorinated phenolic ether may be the compound
    responsible (Bleiberg at al., 1964).

    Clinical symptoms of peripheral neuropathy have been reported in three
    individuals who had direct skin contact with an eater of 2,4-D. An
    electromyographic examination supported the diagnosis (Goldstein et
    al., 1959).


    Information on the absorption and excretion of 2,4-D in several
    species indicates that the compound is rapidly excreted unchanged, and
    that it is not stored in the tissues in mammals. Reproduction studies
    are limited to a single generation but do not indicate that 2,4-D is a
    teratogen. There is no information that toxic chlorinate
    dibenzodioxins have been looked for in commercial 2,4-D.

    Increased nitrate formation has been reported to occur in plants
    treated with 2,4-D and is thought to have resulted in toxic effects in
    grazing animals. This observation is of concern if 2,4-D is to be used
    on edible crops.

    Attention was drawn to the absence of any complete long-term studies
    in any species. For this reason, no acceptable daily intake for 2,4-D
    could be established.



    A pre- or post-emergent selective herbicide in cereals used for
    prevention of preharvest fruit drop, the production of harvest fruit
    drop, the production of seedless fruit and the regulation of the
    growth of plants.

    Acid in oil formulations control many broad-leaved annual and
    perennial weeds on roadside verges, around farm buildings, etc.


    In animals

    When a cow was fed 5 ppm of 2,4-D in a 23 kg ration for five days,
    none of the herbicide could be detected in the milk or faeces
    throughout the study; the analytical limit of detection was 0.1 ppm.
    The compound was found to disappear from the rumen, due presumably to
    dilution, followed by absorption on the gut wall and by decomposition.
    When 2,4-D was added to artificially collected rumen at a level of 2
    ppm it was not decomposed (Gutenmann and Lisk, 1963; Gutenmann et al.,

    In pigs which developed symptoms of poisoning following repeated
    administration of from 50 to 300 mg/kg body-weight of an amine salt of
    2,4-D or of 2,4-D ester, high plasma levels of 2,4-D were found (200
    to 400 µg/ml) even 24 hours after the dose was given. Elimination
    occurred at an enhanced rate after repeated administration and
    eventually decreased to about 10, µg/ml (Björkland and Erne, 1966).

    A capsule containing 539.6 µCi of 2-14 C-labelled 2,4-D was
    administered orally to a female sheep of weight 26.6 kg. This dose was
    equivalent to 4 mg/kg body-weight, which was stated to be the amount
    that the animal would receive while grazing in a treated pasture.
    Urine and faeces were collected separately, and blood samples were
    withdrawn from the jugular vein at intervals after administration of
    the dose.

    The animal was sacrificed after four days, and tissues were assayed
    for carbon-14. Levels of radioactivity in the blood rose during the
    first half hour following treatment and reached a peak after one and a
    half hours. By 24 hours, the radioactivity level in blood had
    decreased to background. About 15 percent of the original dose of
    2,4-D was found in the urine after one and a quarter hours, 50 percent
    after eight and a half hours and 96 percent after 70 hours. Total
    collected faeces contained about 1.4 percent of the dose. Paper
    chromatography and electrophoresis from urine extracts revealed only
    one spot of the same Rf as 2,4-D, indicating that the compound is
    excreted unchanged in the urine. Tissue levels, as determined
    following slaughter four days after administration, contained less
    than 0.05 ppm radioactive equivalents, with the exception of thyroid
    and urinary bladder, which contained 0.56 and 0.5 ppm, respectively.
    The nature of these residues in tissue was not determined (Clark et
    al., 1964).

    In plants

    It has been demonstrated by a number of workers that 2,4-D is
    translocated in plants (Dhillon and Lucas, 1950; Holley et al., 1950;
    Fang et al., 1951), since free phenoxyacetic acids could be isolated
    from parts well removed from the site of application. Jaworski and
    Butts (1952) demonstrated the formation of a complex of 2,4-D in
    plants, and Holley et al. (1950) indicated that plants could detoxify
    2,4-D to form hydroxylated products. Weintraub and Norman, (1950) and
    McIlrath and Ingle (1953), showed that this destruction was not rapid
    in all plants. 14C-labelled material led to the recognition that
    some of the applied material was complexed (Jaworski and Butts, 1952).
    Existence of oxidative degradation of 2,4-D was shown by Holley et al.
    (1950) and Weintraub et al. (1952b) Holley et al. 1950) and Holley
    (1952) demonstrated the evolution of 14CO2 after treating plants
    with 14C-2,4-D, and the formation of a product more water soluble
    than 2,4-D acid. Evolution of 14CO2 from plants treated with either
    methylene-labelled or carboxyl-labelled 2,4-D has been shown by Holley
    (1952) and Weintraub et al. (1952a, 1954). The side chain of
    phenoxyacetic acids can be removed by such plants as currants
    (Luckwill and Lloyd-Jones, 1960), wild cucumber (Slife et al., 1962)

    and tick beans (Canny and Marcus, 1960). Roots have been shown by
    Cann and Marcus (1960) to be of greater efficiency in decarboxylation
    than shoots. Not all of the carbon liberated from breakdown of the
    side chain of phenoxyacetic acids is evolved as 14CO2, but some is
    incorporated into plant constituents (Weintraub at al., 1952a;
    Luckwill and Lloyd-Jones, 1960). Luckwill and Lloyd-Jones (1960)
    studied the degradation of 2,4-D by currants, apples and strawberries.
    They showed that carboxyl-labelled phenoxyacetic acid more readily
    yielded 14CO2 than did the methylene-labelled acid.

    By spectrophotometric analysis, Schieferstein (1957) showed that the
    rate of penetration of 2,4-D through ivy cuticle varied with the age,
    and hence thickness of the cuticle. Orgell (1957) found cationic and
    anionic surfactants hindered the sorption of 2,4-D at low pH; nonionic
    surfactants had little effect. At high pH, cationic surfactants caused
    sorption, whereas anionic and non-ionic surfactants had little effect.
    2,4-D applied to roots may move to tops only in minute quantities, and
    only after some days; applied to leaves, it may pass downward into the
    stem and roots in quantity within a few hours.

    In soil

    2,4-D has been shown to be biodegradable in soils by DeRose and Newman
    (1948), Brown and Mitchell (1948) and Audus (1950). Audus (1964)
    listed numerous micro-organisms which are capable of degrading 2,4-D.

    Evidence of residues in food in commerce or at consumption

    After application of 2,4-D to bean plants and oats, 25-60% was found
    in tissues, but only 0.33-1.66% in oats (Boyle, 1954). Some
    unpublished data was presented (BASF, 1970) regarding residues of
    2,4-D in cereals (grain and straw) found to occur following
    applications of the herbicide either alone or in admixture with other
    phenoxyacid herbicides (MCPA, mecoprop). A summary of the data
    relating to 2,4-D is given in Table II. Williams (1964) was unable to
    detect 2,4-D in a number of total diet samples at a sensitivity of
    0.01 ppm. Duggan and Weatherwax (1967) in total diet studies found
    herbicide chemicals infrequently, averaging an intake of about 0.01
    mg/kg of which one-third was 2,4-D. Very small amounts of 2,4-D were
    found in oils and fats (0.001 mg in 1964/5, and sugars and sugar
    products (0.004 mg 1964/5, and 0.002 mg in 1965/6).

        TABLE II
    Residues of 2,4-D in cereals

    Crop           Rate of          Intervals (days)           Residues found
                   Application      Applic.-Harvest       Grain             Straw

    Barley         375 g/ha         64                    <0.01             0.08
                                    77                    <0.01             0.02

    TABLE II (cont'd)
    Residues of 2,4-D in cereals

    Crop           Rate of          Intervals (days)           Residues found
                   Application      Applic.-Harvest       Grain             Straw
    Barley         520 g/ha         64                    n.d.1             0.1
                                    77                    n.d.              n.d
                   735 g/ha         64                    0.015             0.34
                                    77                    n.d.              n.d

                   375 g/ha         76                    n.d.              0.02
                                    89                    n.d.              0.04
    Wheat          520 g/ha         76                    n.d.              n.d
                                    89                    n.d.              n.d
                   735 g/ha         76                    n.d.              0.03
                                    89                    n.d.              n.d

                   375 g/ha         76                    0.01              0.02
                                    89                    n.d.              n.d
    Oats           520 g/ha         76                    n.d.              n.d
                                    89                    n.d.              n.d
                   735 g/ha         76                    n.d.              0.02
                                    89                    n.d.              n.d

                   375 g/ha         76                    n.d.              0.04
                                    89                    n.d.              n.d
    Rye            520 g/ha         76                    n.d.              n.d
                                    89                    n.d.              n.d
                   735 g/ha         76                    n.d.              0.04
                                    89                    n.d.              <0.02
    1 n.d. =      not detected.

    Residues of 2,4-D can be determined after suitable extraction,
    separation and isolation by gas chromatography, ultraviolet
    spectrophotometry, fluorimetry, thinlayer and paper chromatography.
    The preferred method is to methylate the isolated 2,4-D and determine
    by GLC. This method has been used for the following sample substrates:

    forage (Hagin and Linscott, 1965; Gutenmann and Lisk, 1963; Yip and
    Neys, 1966)

    oysters (Duffy and Shelfoon, 1967), water (Devine and Zweig, 1969),
    milk (Yip and Neys, 1966; Crosby and Bowers, 1966)

    in fruit peel (Meagher, 1966), citrus fruit (Erickson and Hield, 1962)

    and pineapple and orange peel (Hendrickson and Meagher, 1969).

    Benvenue et al. (1962) determined residues of 2,4-D in dry crops and
    walnuts by microcoulometric gas chromatography. Clerk et al. (1967),
    extracted animal tissues and, after isolation of the 2,4-D, hydrolysed
    it to 2,4-dichlorophenol, purified by steam distillation and then used
    GLC. 2,4-D can be determined colorimetrically by the use of
    chromotropic acid in sulphuric acid at a wavelength of 565 nm
    (Marquardt and Luce, 1951 and 1955; Erickson and Brannaman, 1954). Aly
    and Faust (1964) suggested using 6-amino-1-naphthol-3-sulphonic acid
    and 6-anilino-1-naphthol-3-sulphonic acid, which are more sensitive
    (1´-2´ times) than chromotropic acid. Marquardt and Luce (1961)
    cleaved the phenoxy acid with pyridine hydrochloride, releasing the
    phenol derivative 2,4-dichlorophenol, added 4-amino antipyrine and
    potassium ferricyanide, and determined the complex at 515 nm.
    Ultraviolet spectrophotometry at a wavelength of 284 nm was used by
    Warshowsky and Schantz (1950), Aly and Faust (1963) and Gordon and
    Beroza (1952). Kuznetsov and Gagarina (1962) determined 2,4-D in
    plants by paper chromatographic separation, elution from strips and
    colorimetric determination with butyl rhodamine at a wavelength of 564
    nm. Salo and Makinen (1964) used silica gel thin-layer chromatography
    with Blankopher DCB and examination under ultraviolet light at 360 nm
    for visualization. Abbott et al. (1964) used paper and thin-layer
    chromatography for detection, separation and identification. Guilbault
    and Sadar (1969) used a thin-layer chromatographic separation followed
    by a fluorimetric determination based on the breakdown of 4-methyl
    umbelliferone heptanoate by lipase.

    Country                  Crop             Tolerance(ppm)

    United States of      Apples, pears,            5
    America               lemons, oranges,
    (December 1969)       grapefruits

                          Barley, oat, rye,         20
                          wheat and forage

    Netherlands           Barley, oat, rye,         0.5
                          wheat and grain

                          Vegetables,               0.05
                          (except potatoes)
                          fruits of vegetables
                          and fruit crops

    Fed. Rep. of Germany  Leafy and other           0.05
                          sprouting vegetables,
                          fruiting vegetables,
                          root vegetables


    2,4-D is used in cereals as a selective pre- and post-emergence
    herbicide for the control of broad-leaved weeds. It in also used to
    prevent early fruit drop, as a plant growth regulator and for weed
    control on roadside verges, around buildings, etc. Some evidence from
    supervised trials regarding the possible occurrence of residues of
    2,4-D in cereal grain and straw was provided. Insufficient information
    relating to residues resulting from other uses was available. Total
    diet studies in the U.S.A. have very occasionally revealed minimal
    quantities of 2,4-D in oils and fats or sugar and sugar products. No
    evidence regarding the need to establish practical residue limits was
    apparent. Gas chromatographic methods are available which should be
    adaptable for regulatory purposes where required.

    Since no acceptable daily intake had been established, it was decided
    not to recommend tolerances. Nevertheless, it was decided to record
    that following officially acceptable use in various countries.
    residues of 2,4-D can occur in the following crops:

    Wheat, barley, oats, rye and grain              0.02 ppm

    Wheat, barley, oats, rye and straw              0.5 ppm


    REQUIRED (before an acceptable daily intake for man can
    be established).

    1.   An adequate long-term oral study in a rodent
         species and at least a two-year study in a
         nonrodent mammalian species.

    2.   A three-generation reproduction study in at
         least one mammalian species.

    3.   Information on the nature of the impurities
         occurring in commercial preparations of 2,4-D.


    1.   Further information on the metabolism of 2,4-D
         in plants, laboratory animals and man.

    2.   Elucidation of the problem of increased nitrate
         formation in plants treated with 2,4-D, to
         determine if this phenomenon could create a
         toxic hazard to man.

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


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    See Also:
       Toxicological Abbreviations
       D, 2,4- (WHO Pesticide Residues Series 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)