WHO Pesticide Residues Series, No. 1
1971 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD
THE MONOGRAPHS
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
Geneva
1972
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
2,4-D
Explanation
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.
IDENTITY
Purity
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.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
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).
TOXICOLOGICAL STUDIES
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
dosage.
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.,
1971).
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.,
1971).
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,
1971).
(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.,
1971).
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).
Comments
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.
TOXICOLOGICAL EVALUATION
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.
RESIDUES IN FOOD AND THEIR EVALUATION
See the previous monograph (FAO/WHO, 1971).
RECOMMENDATIONS FOR TOLERANCES, TEMPORARY TOLERANCES OR
PRACTICAL RESIDUE LIMITS
Tolerances
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
Desirable
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.
REFERENCES
An Der Lan, H. (1966) The present situation of toxicology in the field
of crop protection. Res. Rev., 15: 31-43
Bashirov, A.A. (1969) The state of health of workers manufacturing the
herbicides, the amine salt and the butyl ester of 2,4-D acid.
Vrachebnoe Delo No. 10: 92-95. Hlth Aspects Pest. Abstr. J. 71-0509
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