2,4-D JMPR 1975
Explanation
The Joint Meeting in 1970 considered the use of 2,4-D as a
selective herbicide on a range of cereal crops and data on the nature
and fate of residues therein (FAO/WHO 1971). Recommendations were not
made for maximum residue limits until an acceptable daily intake was
established in 1971. (FAO/WHO 1972). In 1974 the use of 2,4-D as a
pre- and post-harvest treatment for citrus fruit and as a growth
regulator for potatoes was also evaluated and recommendations were
made (FAO/WHO 1975).
In view of the world-wide use of 2,4-D herbicides it was
considered that the residue data, originating mainly in Europe,
examined in 1970 possibly did not reflect the practices in countries
with more extensive agriculture. Requests were therefore made for
further data on the nature and level of 2,4-D residues in cereal
crops.
The Codex Committee on Pesticide Residues at its 8th Session in
1975 expressed the view that the maximum residue limits proposed were
too low (ALINORM 76/24 para 85). This monograph addendum confirms the
necessity for a higher limit for 2,4-D residues in raw grain.
The additional data which became available are summarized in this
monograph addendum.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOCHEMICAL ASPECTS
Absorption, distribution and excretion
Following a single administration by gastric intubation to albino
rats of sodium and diethylamine salts of 2,4-D at the doses of 555 and
405 mg/kg respectively (the doses corresponding to the LD50 for these
compounds) the highest blood concentrations were reached after 3
hours. The half-retention periods were of 1 hour for the sodium salt
and 72 hours for the diethylamine salt. Three hours after treatment
the organs with the greatest distribution of the diethylamine salt
were the liver and kidneys; the highest levels of this salt in tissues
(heart, liver, kidney, muscles and brain) were observed 24 hours after
administration and there was a substantial decrease after 10 days
after the treatment.
In the same study, albino rats were given by gastric intubation,
daily doses corresponding to 1/20 and 1/5 respectively of the LD50 of
2,4-D (23 and 91 mg/kg), sodium salt of 2,4-D (28 and 111 mg/kg),
diethylamine salt of 2,4-D (20 and 80 mg/kg) and
2-methyl-4-chlorophenoxypropionic acid (49 and 1975 mg/kg) for a
period of 50 days.
The tissue distribution (heart, liver, kidneys, muscles and
brain) at the end of the testing period was found to be dose dependent
(Buslovish et al., 1973)
TOXICOLOGICAL STUDIES
Special studies in teratogenicity
Groups of 3-month old NMRI female mice randomly bred were
injected subcutaneously with levels of 0, 50, 100 mg/kg bw of
commercial mixture of 2,4-D and 2,4,5-T in dimethyl sulfoxide solution
from day 6 through day 14 of gestation. The content of dioxins of the
mixture was less than 1 ppm and the most common dioxin was
2,3,7,8-tetrachlorodibenzo-p-dioxin. On day 18 of gestation, the
animals were sacrificed, living foetuses removed, weighed and examined
for gross malformation; microscopic examination for internal
malformation was also carried out. At high dose foetal mortality was
significantly increased, the frequency of cleft palate was increased,
foetal weight considerably reduced, skeletal malformations were double
with respect to the other group and controls, subcutaneous bleeding
was three times as common, renal malformation such as dilated renal
pelves, smaller and opaque medullae were slightly increased (Bage et
al. 1973).
OBSERVATIONS IN MAN
Seventeen farm workers concerned with the transport of
derivatives of chlorophenoxy acetic acid were examined by
electroencephalography before and after massive exposure. EEG tracings
before exposure showed slight abnormalities in 7 cases. After 4 to 28
days of exposure disturbances of the cerebral bioelectrical activities
were observed in 11 cases. In 5 of these cases overt pathological
changes were observed in EEG tracings as revealed by the slowing down
of the basal frequency and the presence of slow, high amplitude theta
waves (Kontek et al., 1973).
A man lost consciousness 2-3 hours after inhalation of vapours
originating from a spraying pump containing a herbicide formulation
(44% 2,4-D). Early manifestations included urinary incontinence and
vomiting followed by myalgia, muscular hypertonia, slight fever,
headache and constipation as well as intermittent nodal tachycardia as
revealed by EEG. The cardiac arrhythmia and muscular hypertonia
gradually subsided within 5 days of administration of quinidine
hydrochloride (450 mg/day, 7 days). No abnormalities in the thyroid
functions were observed. The patient was released from hospital in
good health after 23 days (Paggiaro et al., 1974).
Comments
An ADI for man of 0 - 0.3 bw was allocated for this compound at
the 1971 Joint Meeting.
Since then further studies have become available on tissue
distribution after gastric intubation to rats of sodium and
diethylamine salts of 2,4-D. These studies supplement earlier studies
in rodents.
A teratology study in mice administered 2 4-D by subcutaneous
injection showed no embryotoxic or teratogenic effect at 50 mg/kg body
weight. Effects were found at 100 mg/kg.
The results confirmed the no-effect level in earlier oral studies
in rodents.
Reports on apparent effects from occupational exposure to phenoxy
herbicides were noted.
The previously estimated ADI was reaffirmed.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 625 ppm in the diet equivalent to 31 mg/kg bw
Estimate of acceptable daily intake for man
0 - 0.3 mg/kg bw
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
No information on new use patterns has become available and, in
view of the fact that 2,4-D herbicides have been in world-wide use for
more than 25 years it is assumed that there have been no now
developments.
Depending on the type of cereal crop, the weed spectrum, cultural
practices and climatic factors, 2,4-D herbicides may be applied as
salts, esters, amines or free acid formulations at rates ranging from
250 g to 2 kg/ha (rarely up to 4 kg/ha). Application is usually made
when weeds and cereal crop plants are small but in the case of maize
(corn) and sorghum, treatment may be necessary when the crop is well
advanced.
With some varieties of wheat early treatment is essential to
avoid phytotoxic damage which may occur once the seed-head has begun
to develop. Usually wheat and oats are treated when the crop is 10-15
cm tall and maize (corn) when 30-35 cm tall.
However, when tall weeds growing up in the crop make harvesting
difficult, if not impossible, 2,40 herbicides nay be applied 14-21
days prior to harvest to destroy, defoliate or regulate the growth of
the weeds so as to prevent interference with harvesting.
During 1966 the US production of 2,4-D exceeded 31 000 000 kg
(USA 1967). World consumption is estimated to exceed 50 000 000 kg.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Cereal grains
Data derived from supervised residue trials carried out in
various regions of the USA have been provided by the US Department of
Agriculture. These data were generated during the years 1960, 1961 and
1965 and represent typical use patterns involving amine salt, butyl,
iso-octyl, isopropyl and polypropylene glycol butyl ether ester
formulations of 2,4-D. The residue analysis was carried out by the US
FDA.
Early post-emergence application
Grain samples collected from plots sprayed 3-4 weeks after
emergence with various formulations of 2,4-D were found to contain no
residues of 2,4-D (limit of determination of 0.01-0.04 mg/kg) except
in the case of oats, and then only when 4 kg/ha was applied. Wheat
grain from crops receiving the same heavy application was free from
residues.
Pre-harvest application
Trials carried out in Kansas during 1960 involved the application
of butyl, isopropyl and iso-octyl esters of 2,4-D at 1 and 10 kg
2,4-D/ha at intervals ranging from 5 to 23 days before harvest.
The residue levels found are set out in Table 1.
The data in Table 1 indicate that there is a noticeable
accumulation of 2,4-D residues in the grain during the two weeks
following application when treatment is made within 3 weeks of
harvest. This is not unexpected in view of the systematic properties
of the herbicide. However the amount of 2,4-D found in grain is not
particularly great following normal rates of application, reaching
levels above 0.5 mg/kg only at excessive rates of the order of
10 kg/ha.
TABLE 1. Residues of 2,4-D in wheat following application of 2,4-D ester
Pre-harvest interval
Ester Rate. kg/ha days Residue, mg/kg
butyl 1 15 0.07
1 10 0.05
1 5 0.06
10 15 2.45
10 10 1.50
10 5 0.60
isopropyl 1 17 0.05
1 11 0.04
1 5 0.02
10 17 0.22
10 11 1.18
10 5 0.44
Iso-octyl 1 23 0.09
1 18 0.40
1 13 0.27
1 8 0.05
10 23 0.73
10 18 1.06
10 13 0.84
10 8 0.51
The tendency to accumulate in grain during the post-application
period was confirmed by trials in Nebraska in 1960, in which the
residues resulting from treatment 20 days before sampling were
compared with those in the grain at application. The data presented in
Table 2 show that the residue level is higher after 20 days and
increases as the rate of application is increased.
From the limited data it would appear that slightly more residues
accumulate from the use of the water-soluble amine formulation than
from the oil soluble ester form. Volatility of the latter could play a
part.
TABLE 2. Residues of 2,4-D in grain on day of application and after
20 days
Pre-harvest interval
Formulation Rate, kg/ha (days) Residues, mg/kg
ester 0.5 0 0.04
1 0 0.11
2 0 0.11
amine 1 0 0.05
ester 0.5 20 0.09
1 20 0.14
2 20 0.34
amine 1 20 0.27
Trials carried out in Kansas compared the residues of 2,4-D
resulting from the use of the water-soluble dimethylamine salt with
those from the volatile isopropyl ester and the less volatile
iso-octyl ester. The results, which are presented in Table 3,
generally support the observation that lower residues result from the
use of the volatile ester than from the amine salt and the
less-volatile ester. The difference is, however, not great.
TABLE 3. 2,4-D Residues on Bison Wheat harvested at Hays, Kansas,
at various intervals after treatment
Residue, mg/kg after pre-harvest interval, days
7 14 21
Dimethylamine salt
0.0 lb/acre 0.05 0.01 0.02
0.5 0.16, 0.08, 0.10 0.19, 0.18 0.06, 0.06
1.0 0.29, 0.06 0.31, 0.15 0.09, 0.12
2.0 0.39 0.50 0.29, 0.22
4.0 1.24 1.46 0.32
Isopropyl ester
0.0 0.07 0.02 0.01
0.5 0.05, 0.16, 0.11 0.03, 0.06, 0.03 0.04, 0.04, 0.05
1.0 0.14, 0.22 0.15, 0.09 0.06, 0.04, 0.06
2.0 0.21, 0.49 0.31, 0.31 0.13, 0.17
4.0 0.78 1.80 0.38
Iso-octyl ester
0.0 0.02, 0.02 0.0, 0.01 0.0, 0.03
0.5 0.12, 0.12 0.10 0.15, 0.11 0.04, 0.06, 0.07
1.0 0.18, 0.26, 0.36 0.35, 0.23, 0.23 0.09, 0.05, 0.16
2.0 0.35, 0.45 0.63 0.15, 0.22
4.0 1.31 1.16 0.53
Cochrane and Russell (1975), using the extraction procedure of
Yip (1962) found that when mixed n-butyl/isobutyl ester was applied at
the rate of 430 g/ha to young wheat plants (three-leaf), the ester was
immediately converted into free 2,4-D acid. Immediately after
application 8.35 mg/kg of 2,4-D was found in the wheat plants and this
level declined to 1.87 mg/kg on the third day after treatment.
Thereafter decline continued at a rapid rate to less than 0.01 mg/kg
after 44 days. No trace of 2,4-D could be found in grain or straw at
harvest 80 days after treatment.
Studies made at the University of California (Harvey, 1970) of
the residues resulting from the application of 2,4-D amine to barley,
oats and wheat at various growth stages have revealed that the
residues in grain at harvest vary according to the growth stage at
time of treatment. These data indicate that even though the residue in
the whole plant exceeded 10 mg/kg 7 days after application, there was
a steady decline in the residue level, so that less than 3 mg/kg
remains in the straw and less than 0.3 mg/kg in the grain at harvest.
The results of these studies are summarized in Table 4.
Klingman et al (1966) found 58 mg/kg 2,4-D acid one half-hour
after applying 2.25 kg butyl ester/ha and this decreased to 5 mg/kg on
the fifth day.
Lokke (1975) developed improved analytical techniques for the
determination of 2,4-D and amino acid conjugates in cereal grains and
with these found that the application of 4 kg (4 times the normal
rate) of 2,4-D per ha to barley at the three-leaf stage resulted in
residues of only 0.04-0.06 mg/kg in the grain at harvest. By
conventional methods of extraction the same grain was estimated to
have less than 0.02 mg/kg of 2,4-D. Treatment made at the same
excessive rate after the spikes formed on barley left residues of
0.35-0.45 mg/kg when measured by the method of Lokke (1975) or Yip
(1971). By direct extraction methods, only 0.04 mg of 2,4-D could be
recovered per kg of barley. Lokke reported that treatment at the same
rate after the green grains were fully formed resulted in residues of
4.0-4.3 mg/kg. This is 8-10 times higher than the residue found in the
same sample by conventional extraction procedures.
In Sweden and other Scandinavian countries where the harvesting
of berries and mushrooms regularly takes place in forests, the use of
2,4-D and 2,4,5-T herbicides has become a regular feature of forest
management to regulate the growth of underbrush.
Erne and Hartman (1973) made an extensive study of the residues
of 2,4,5-T in mushrooms and both 2,4-D and 2,4,5-T in berries
harvested in forests following the aerial and ground application of
brush control herbicides. The results of their findings with respect
to 2,4-D are summarized in Table 5.
TABLE 4. 2,4-D residues in whole plant, grain and straw following treatment at different stages of growth
Residues found at different growth stages, mg/kg
(Intervals from treatment/days)
Application Stage of Late Mature Mature Mature
Crop rate kg/ha treatment Tillering Tillering Boot Harvest Dried (plant) (grain) (straw)
Oats 0.75 Tillering 4.4 2.7 1.1 0.57 - - 0.05 1.8
1.5 " 12.3 5.2 2.8 0.77 - - 0.07 2.6
(7) (14) (28) (56) (110) (110)
Barley 0.75 Late - 0.84 - 0.37 0.18 - 0.03 0.48
1.5 tillering - 9.5 - 1.2 0.28 - 0.02 0.85
(7) (15) (28) (63) (63)
Barley 0.75 Late boot - - - 6.5 2.8 2.6 0.14 2.3
1.5 " - - - 13.8 7.7 6.5 0.3 5.5
(7) (14) (28) (49) (49)
Wheat 0.75 Tillering - 5.5 2.3 - 0.31 - 0.02 0.11
1.5 " - 17.5 8.2 - 0.45 - 0.02 0.11
(7) (14) (28) (65) (65)
Wheat 0.75 Boot stage - - - - 4.8 0.6 0.02 0.54
1.5 " - - - - 13.5 1.5 0.02 1.10
(7) (28) (50) (50)
Barley 0.75 Tillering 3.3 - 1.0 - 0.02 - 0.02 0.02
1.5 " 11.8 - 2.4 - 0.35 - 0.02 0.05
(7) (14) (28) (58) (58)
Barley 0.75 Boot stage - - - 4.5 3.1 - 0.02 0.03
1.5 " - - - 14 7.7 - 0.03 0.02
(7) (14) (43) (43)
TABLE 5. Residues of 2,4-D in berries resulting from the aerial
spraying of forests
Residue, mg/kg, at interval, days,
after spraying. (No. of samples in
parenthesis)
Rate of Application
Commodity kg/ha 2-5 10-14 24-32
Raspberries 1.375 0.4-0.9 0.3-0.6 <0.03-0.3
(3) (3) (3)
Lingonberries 0.980 2.6-7.7 0.8-7.0 1.2-3.6
" (3) (8) (9)
" 1.290 0.8-3.5 0.4-1.0 1.2-2.5
(3) (3) (3)
" 1.075 - - 0.7-2.7
(3)
" 0.980 - 0.3 0.6-0.8
(1) (2)
" nil <0.03 <0.03 <0.03
" 1.075 1.5-4.0 1.2-2.0 0.7-2.0
(3) (3) (3)
" 1.015 2.0 0.9-1.5 -
(3) (3)
Bilberries 1.290 2.0-2.4 0.5-1.3 0.9-1.8
(3) (3) (3)
" 1.075 1.4-2.9 1.3-2.5 -
(4) (3)
" nil <0.03 <0.03-0.2
(1) (2)
FATE OF RESIDUES
In plants
An enormous amount of research has been carried out over more
than 25 years on the mode of action of 2,4-D, the reason for its
selective action and the mechanisms of degradation in plants.
Loos (1969) has published a 50 page review including references
to 166 papers on the degradation of phenoxyalkanoic acids of which
2,4-D is by far the most important. Only a few of the basic principles
can be touched upon in this monograph.
In the experiments referred to in the previous section (p. 179),
Klingman et al (1966) found that virtually all the butyl and 75% of
the 2-ethylhexyl esters of 2,4-D had been hydrolized to the acid
within 30 minutes after application to forage. When 2.25 kg butyl
ester per ha was applied, initial residues of 58 mg/kg decreased to 5
mg/kg in five days. This work confirmed studies with radio-labelled
2,4-D (Crafts, 1960) and others in which residues were determined by
bioassay (Morré and Rogers, 1960) or gas chromatography (Hagin and
Linscott, 1965).
Similar trials by Cochrane and Russell (1975), in which the butyl
ester was applied to wheat, were described in the previous section
(p.179). No trace of butyl ester was found after the application of
430 g/ha, but residues of 8.35 mg/kg of the free acid were found
immediately after application and decreased rapidly.
There appear to be three principal mechanisms for the metabolism
of 2,4-D by plants, viz. degradation of the acetic acid side chain,
hydroxylation of the aromatic ring and conjugation with plant
constituents.
Degradation of the side chain has been observed in many plants
but in only a few species or varieties does it appear to play a major
role in the breakdown of herbicidal activity. Loss of the side chain
from a phenoxyacetic acid without further metabolic changes to the
molecule would yield the corresponding phenol. Luckwill and
Lloyd-Jones (1960) and Chkanikov et al. (1965) have demonstrated the
production of 2,4-dichlorophenol in strawberries, beans, sunflowers,
corn and barley. Simultaneously the side-chain carbon atoms are
released as CO2 in some plants.
Fawcett et al. (1959) showed that wheat and pea tissue
hydroxylated 2,4-D in the 4-position. Similar reactions were observed
in oats, barley and maize (corn), but not in various legumes, by
Wilcox et al. (1963).
The identity of the principal 2,4-D metabolite in bean, which was
believed by Holley (1952) and Crosby (1964) to be a
hydroxyphenoxyacetic acid, was studied by Thomas et al. (1964) who
confirmed the major phenolic acid as
2,5-dichloro-4-hydroxyphenoxyacetic acid and the minor phenolic acid
as 2,3-dichloro-4-hydroxyphenoxyacetic acid. The 4-hydroxylation of
2,4-D in bean was thus made possible by a chlorine shift from the 4
to the 5 or 3 position. These two metabolites accumulate in bean as
the glucosides.
The esterification of glucose with phenoxyacetic acids has been
observed. Klambt (1961) reported the formation of the glucose ester of
2,4-D in wheat, and Thomas et al. (1964) reported that oats converted
2,4-D to its beta-D-glucose ester.
Aspartic acid combines with 2,4-D to form
2,4-dichlorphenoxyacetyl-aspartic acid in wheat (Klambt, 1961) and
probably in other plants.
Feung et al. (1971, 1972, 1973a, b) demonstrated that 2,4-D is
rapidly conjugated by means of an amide bond with a number of amino
acids. Seven amino acid conjugates have been isolated and identified
(glutamic and aspartic acids, alanine, valine leucine, phenylalanine,
tryptophane) and these have been shown to have 2,4-D-like herbicidal
activity (Feung et al., 1974). Such conjugation cannot be considered
as a detoxification mechanism but perhaps as an activation step. Feung
et al., 1974, have postulated that the conjugated form of 2,4-D could
be exclusively the physiologically active form.
Feung et al. (1975) demonstrated that the two ring-hydroxylated
metabolites (4-OH-2, 5-dichloro and 4-OH-2, 3-dichloro) which together
represent 97% of the soluble metabolites do not possess any
growth-stimulating activity and exist as aglycones. In later studies,
corn, the only monocotyledon tested, was shown to produce also
3-hydroxy-2, 4-dichlorophenoxyacetic acid (3-OH-2, 4-D) and
4-hydroxy-2-chlorophenoxyacetic acid which were not found in other
plants tested. The authors were prompted to suggest that corn possess
a significant alternative pathway of metabolism that may account for
its resistance to herbicidal quantities of 2,4-D.
On the other hand Hagin et al. (1970) have shown that three
grasses metabolize 2,4-D to 2,4-dichlorophenoxypropionic acid, which
is biologically inactive and this is assumed to be a major
detoxification mechanism of these grasses.
In animals
Jensen and Miller (1975) report studies in which chickens were
fed rations containing 10 or 100 mg/kg 2,4-D for 30 days. Tissue
samples and eggs from these birds were analysed for residues of 2,4-D
and 2,4-dichlorophenol using a method which had a validated
sensitivity of 0.05 mg/kg for either compound. No dichlorophenol was
detected in any sample. The average 2,4-D residues found are given in
Table 6.
TABLE 6. 2,4-D residues in chickens fed 2,4-D in the diet
2,4-D residues (mg/kg)
2,4-D in diet
(mg/kg) muscle/skin fat liver eggs
10 <0.025 <0.025 <0.05 <0.025
100 <0.2 <0.05 0.5 0.1
There is no reasonable expectation of residues in poultry tissues
and eggs from ingestion of feeds containing up to 10 mg 2,4-D/kg. This
level is far above the amount of 2,4-D (<0.2 mg/kg) that might be
expected from treatment of crops used for chicken feed.
EVIDENCE OF RESIDUES IN FOOD IN COMMERCE OR AT CONSUMPTION
The only new information on the incidence and level of 2,4-D
residues in food in commerce came from Hungary. In 1974 56 samples of
barley, oats, rye and wheat from lots which were known to have been
treated with 2,4-D were analysed by food inspection laboratories. None
of the samples contained residues above the limit of determination
(0.005 mg/kg). Whether these laboratories used methods capable of
measuring conjugated residues is not known.
METHODS OF RESIDUE ANALYSIS
Several studies, reviewed by Loos (1969) and Feung et al.
(1973a,b) have confirmed the conjugation of chlorophenoxy acids,
including 2,4-D, with plant constituents. The conjugates are suggested
to consist mainly of combinations of chlorophenoxy acids and amino
acids. In spite of this these conjugates are not hydrolysed during
most of the published analytical methods for chlorophenoxy acids. Chow
et al. (1971) studied the original procedure of Yip and Nay (1966)
which involves extraction (without hydrolysis) with 50% diethyl
ether/hexane in the presence of sulphuric acid. By heating wheat plant
tissue under alkaline conditions they found that less than 25% of the
residue could be accounted for by analysing only the organic phase as
in the Yip and Nay (1966) method.
Lokke (1975) following the lead of Chow et al. (1971) developed a
procedure involving hydrolysis of the starch under acidic conditions
followed by treatment with diastase and further hydrolysis of amino
acid conjugates through the action of proteolytic enzymes. These steps
resulted in a considerable increase in the yield of 2,4-D residues
from barley treated at various stages of growth with 2,4-D. The
proteolytic enzyme (papain or ficin) was shown to be responsible for
releasing about 50% of the 2,4-D found.
In parallel experiments Lokke found that a straightforward
extraction with 65% acetonitrile (Yip, 1971) gave comparable recovery.
In the light of the efficient liberation of residues through
hydrolysis by proteolytic enzymes, it is remarkable that the simple
extraction with acetonitrile is of similar efficiency. Lokke went on
to show, however, that neither the extraction procedure nor the
enzymic hydrolysis can be considered completely exhaustive. It is not
yet clear what amounts of 2,4-D conjugates remain after either of
these procedures have been applied to grain.
Glas (1975) has used aqueous sodium hydroxide to extract 2,4-D
from grain and straw before purification on an alumina microcolumn for
GLC quantitation using an electron capture detector.
NATIONAL TOLERANCES REPORTED TO THE MEETING
Particular attention was drawn to the following tolerances which
have been established in national legislation (Table 7).
TABLE 7. National tolerances reported to the meeting
Country Commodity Tolerance mg/kg
USA forage of barley, oats, rye and wheat 20
grain of barley, oats, rye and wheat 0.5
flour of barley, oats, rye and wheat 0.5
other milled fractions of barley, oats,
rye and wheat 2
potable water 0.1
APPRAISAL
In response to the requirements of the 1970 Meeting, data from
supervised trials on grain crops were received, together with a number
of papers published on the degradation of 2,4-D in plants and soils
and on the nature and measurement of conjugates in plants. Some
information was also received on 2,4-D residues in food sampled in
commerce.
Most of the supervised trials were conducted in the 1960/65
period and there is now evidence that the extraction methods then in
use only recovered a portion of the free 2,4-D and none of the residue
conjugated with amino acids. More recent experimental evidence
indicates that there may be more significant residues present in grain
at harvest following approved use of 2,4-D herbicides than was
revealed in most of the data generated previously. On the basis of
this evidence a higher maximum residue limit is recommended.
Following the application of 2,4-D herbicides for brush control
in forests in Sweden an extensive published study indicates that
significant amounts of 2,4-D residue will be found in raspberries,
lingonberries and bilberries harvested from the treated forests. The
Meeting felt justified in extending limits based on this study to
other vaccinium berries and blackberries. Maximum residue limits for
2,4-D in these berries are therefore recommended.
Since 2,4,5-T is usually combined with 2,4-D in brush-killing
herbicides used in forests and in view of the evidence that residues
of 2,4,5-T can occur in berries and mushrooms, it would appear to be
necessary to recommend maximum residue limits for 2,4,5-T in these
commodities also.
RECOMMENDATIONS
Previous recommendations for maximum residue limits are amended
(raw grain) and new recommendations are made (berries) as follows.
MAXIMUM RESIDUE LIMITS
Commodity Limit, mg/kg
Milk and milk products 0.05*
Meat and eggs 0.05*
Raw grain 0.2
Vaccinium berries
e.g. lingonberries, bilberries 5
Blackberries, raspberries 5
* At or about the limit of determination
REFERENCES
Bage, G., Cekanova, E. and Larson, K. D. (1973) Teratogenic and
embryotoxic effects of the herbicide Di- and Trichlorophenoxyacetic
acids (2,4-D and 2,4,5-T). Acta pharmacol. et toxicol., 32:408-416.
Buslovich, S. Yu., Voinova, I. V. and Milchina, G. (1973) Distribution
of herbicides (phenoxy acid chloroderivatives) in the blood of albino
rats. Gig. Tr. Prof. Zabol., 17(3):35-37
Chkanikov, D. I., Pavlova, N. M. and Gertsuskii, D. F., Khim, V.
(1965) Sel'skom Khoz., 3:56 (in Russian); through CA, 63, 8250c
Chow, C., Montgomery, M. L. and Yu, T. C. (1971) Bull. Env. Cont. &
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See Also:
Toxicological Abbreviations
D, 2,4- (AGP:1970/M/12/1)
D, 2,4- (WHO Pesticide Residues Series 1)
D, 2,4- (WHO Pesticide Residues Series 4)
D, 2,4- (Pesticide residues in food: 1980 evaluations)