2,4-D JMPR 1974
Explanation
2,4-D was evaluated at the joint Meetings in 1970 (FAO/WHO, 1971)
and 1971 (FAO/WHO, 1972). At the 1971 Meeting an ADI of 0-0.3 mg/kg
was allocated and a tolerance of 0.02 ppm was established for barley
oats, rye and wheat. Further work or information was desired on the
metabolism and excretion of 2,4-D in animal species other than the rat
and the occurrence of 2,4-D residues in crops following uses other
than on cereals. Since the last evaluation (FAO/WHO, 1972b), further
information on the use and residues of 2,4-D has become available and
is summarized in the following monograph addendum.
IDENTITY
Purity
No new information on the nature of the impurities occurring in
commercial preparations of 2,4-D was available to the Meeting.
However, the undated paper by Woolson et al. discussed in the 1971
Monograph has been published (Woolson et al., 1972).
EVALUATION FOR ACCEPTABLE DAILY INTAKE
The compound was reconsidered by this Meeting on the basin of the
published experimental data. Based upon this information there is no
indication to change the previously allocated acceptable daily intake
for man (0-0.3 mg/kg b.w.).
A survey of "dioxin" content in 2,4-D has shown that the
manufacturing process for 2,4-D in itself obviates the likelihood of
the formation of "tetra, hexa and octadioxin" but it does not rule out
the occurrence of other impurities.
RESIDUES IN FOOD AND THEIR EVALUATION
USE PATTERN
The citrus industry has three registered uses for 2,4-D. One, as
a pre-harvest orchard spray for oranges, grapefruit, and other citrus
fruits to promote size and to prevent late season fruit drop. Two, as
a post-harvest flooding or drip for lemons to retain the buttons
(calyx) in a green condition and hence to increase the vitality of the
fruit, thus retarding fungal growth during storage. Three, as a low
pressure spray to the grove floor to control vine and broadleaf weeds.
The use of 2,4-D as a growth regulator to promote size and to
control fruit and leaf drop was reported by Hield et al. (1964) and
Sarvoski and Stannard (1974) and is recommended for California citrus
crops (California Agricultural Extension Service, 1974).
The washing, dipping or flooding of lemons with 2,4-D where fruit
is to be held in storage is a standard procedure and is effective in
reducing Alternaria rot (De Wolfe et al., 1959). This use has
reduced Alternaria from being one of the most serious fungus
diseases of stored lemons to a minor cause of storage decay, and
maintains the buttons in a sound green condition which helps the fruit
retain its fresh appearance.
2,4-D is registered for use on potatoes as a growth regulator in
the U.S.A. It in claimed to reduce the yield of large, less desirable,
tubers and increase that of the preferred medium size (Nelson and
Nyland, 1963), and to intensify the skin colour on red varieties of
potatoes (Nyland, 1956).
Reports on the use of 2,4,D for the control of Eurasian water
milfoil (Wojtalik et al., 1971) and water hyacinth (Schultz and
Whitney, 1974) in aquatic environments have been published.
Examples of some use patterns of 2,4-D are given in Table 1.
RESIDUES RESULTING FROM SUPERVISED TRIALS
Data are available on 2,4-D and 2,4-dichlorophenol residues in
milk and cream from cows fed levels of 10 to 1000 mg/kg in their
ration (Bjerke et al., 1972). Residues above the limit of
determination (0.05 mg/kg) were found only at the highest dosing level
(Table 2). Low residues of 2,4-D (0.6 mg/kg) were found in milk from
cows grazing on pasture sprayed with 2,4-D (Klingman et al., 1966).
Residue levels of 2,4-D in fish varied from <0.01 to 0.16 mg/kg in 60
samples of fish taken from 3 different locations at various intervals
following spraying of an aquatic environment (Shultz and Whitney,
1974). Further details of all three experiments are given in the
section "Fate of residues in animals."
Washington navel orange trees were sprayed with 20 mg/kg (acid
equivalent) 2,4-D (isopropyl ester) as practised for growth regulation
and preharvest fruit drop. Orange samples were taken before, 1 day
after and 7 days after spraying. Residues of 2,4-D averaged <0.1
mg/kg before, 0.1 mg/kg 1 day after, and <0.1 mg/kg 7 days after
treatment (Erickson and Hield, 1962).
Grapefruit and pineapple orange plots were sprayed with 2,4-D
(butoxyethyl ester) for weed control. Orange and grapefruit samples
were picked 5 mouths after treatment. Residues of 2,4-D were below the
limit of detection (<0.01 mg/kg) in all samples of pulp and peel from
washed and unwashed fruit analyzed (Phillips, 1969).
TABLE 1.
Some examples of use patterns of 2,4-D.
Dosage levels Pre-harvest
Crop Use Material Used (acid equivalent) interval
Citrus pre-harvest fruit 2,4-D (isopropyl 4-24 mg/kg (spray) 7 days
drop and growth ester, ethyl ester,
regulator amine salt)
Lemons increase storage 2,4-D (isopropyl 500 mg/kg -
life, retard ester)
fungal growth
Citrus control vine and 2,4-D (butoxyethyl 2.2 kg/ha 5 months
broadleaf weeds ester)
Potatoes growth regulator 2,4-D (propylene 70-140 g/ha 1 month
glycol butyl
ether ester)
Aquatic control Eurasian 2,4-D (dimethylamine 22 and 44 kg/ha -
environment water milfoil salt)
Aquatic control water 2,4-D 4.48 kg/ha -
environment hyacinth (dodecyltetradecyl
amine salts)
TABLE 2.
Residues of 2,4-D and 2,4-dichlorophenol in milk and cream from cows fed a ration containing
1000 mg/kg of 2,4-D (Bjerke et al, 1972
Days 2,4-D (mg/kg) 2,4-dichlorophenol (mg/kg)
on diet Milk, cow no. Cream, Milk, cow no. Cream
22 7 12 composite 22 7 12 composite
3 0.05 0.06 <0.05 - <0.05 0.06 0.05 -
10 <0-05 0.08 <0-05 - <0.05 0.06 <0.05 -
17 0.05 0.11 0.05 0.12 <0.05 0.05 <0.05 <0-05
18 0.05 0.12 <0-05 <0.05 <0.05 0.06 <0-05 <0.05
19 0-05 0.09 <0.05 0.05 <0-05 0.06 <0-05 <0-05
20 0.06 0.12 <0-05 0.06 0.08 0.06 <0.05 <0-05
21 <0-05 0.07 <0.05 <0.05 <0.05 0.05 <0.05 <0-05
Residue data for lemons treated with 2,4-D formulations to
increase storage life and retard fungal growth were available from the
U.S.A. (Erickson et al., 1963) and Australia (Johns, 1974). The U.S.A.
data, summarized in Table 3, show that 2,4-D residue levels ranged
from 0.25 to 0.56 mg/kg 1 day after treatment with different
formulations at 500 mg/kg. These residues were persistent up to 42
days. The storage conditions for the fruit were not given. In the
Australian trial lemon fruit were treated with 2,4-D (sodium salt) at
several rates and modes of application. The data shown in Table 4
indicate that relatively low levels of 2,4-D occurred at the time of
treatment at rates up to 500 Mg/kg. The residue levels had declined to
<0.01 mg/kg at the end of 8 weeks storage. Only in the case of double
treatment (two 500 mg/kg applications) were residues, 0.6 mg/kg,
detected after 10 weeks storage.
Potatoes treated with 2,4-D as a growth regulator (Bristol and
Nelson, 1974) contained 2,4-D and 2,4-dichlorophenol residues of
approximately 0.1 and 0.005 mg/kg respectively. The data are
summarized in Table 5. Phenolic metabolites other than
2,4-dichlorophenol were not detected. 2,4-D was stable in potatoes
under conditions of frozen storage but residues in whole tubers stored
at 38°C decreased with a half-life of approximately 12 weeks. See also
"Fate of residues in plants," and "in storage."
TABLE 3. 2,4-D residues in lemon fruit following treatment with various
2,4-D formulations.
Residue, mg/kg, in whole fruit
at interval (days) after treatment
Formulation1 1 7 14 42
2,4-D (emulsifiable acid) 0.42 0.33 0.35 0.22
2,4-D (isopropyl ester) 0.56 0.27 0.31 0.22
2,4-D (sodium salt) 0.30 0.39 0.50 0.33
2,4-D (diethanolamine salt) 0.29 - 0.29 -
2,4-D (triethanolamine salt) 0.25 - 0.39 -
1 All treatments were applied as a wax emulsion at 500 mg/kg acid
equivalent.
TABLE 4. 2,4-D residues in lemon fruit following treatment with 2,4-D (sodium salt)
Residues in whole fruit (mg/kg),
at interval (weeks) after treatment
Treatment No. of 6 weeks (11°C) 8 weeks (11°C) 20 weeks (11°C)
(2,4-D sodium salt) Samples 0 +2 weeks (20°C) +2 weeks (20°C) + 2 weeks (20°C)
100 mg/kg, wax foam 4 0.5 <0.01 <0.01 <0.01
100 mg/kg, wax dip 4 0.5 <0.01 <0.01 <0.01
200 mg/kg, war foam 4 0.6 <0.01 <0.01 <0.01
300 mg/kg, war foam 4 0.8 <0.01 <0.01 <0.01
500 mg/kg, wax foam 4 1.1 <0.01 <0.01 <0.01
500 mg/kg, wax dip 4 1.3 <0.01 <0.01 <0.01
500 mg/kg,
pre-processing dip +
500 mg/kg wax foam 1 - - 0.6 -
TABLE 5. 2,4-D residues in potatoes (Bristol and Nelson 1974)
Residue, mg/kg
Treatment
rate Variety No. of 2,4-D 2,4-dichlorophenol
Year (g/ha)1 of potato samples Range Average Range Average
1972 0 Red Pontiac 10 <0.02 <0.02 <0.002 <0.002
1972 140 Red Pontiac 10 0.06-0.10 0.08 <0.002-0.003 <0.002
1972 280 Red Pontiac 10 0.07-0.14 0.10 <0.002-0.004 <0.002
1973 0 Red Pontiac 4 <0.02 <0.02 <0.002 <0.002
1973 140 Red Pontiac 4 0.09-0.14 0.11 0.003-0.005 0.004
1973 0 Red Norland 4 <0.02 <0.02 <0.002 <0.002
1973 140 Red Norland 4 0.07-0.11 0.09 0.006-0.011 0.008
1973 0 Norland 4 <0.02 <0.02 <0.002 <0.002
1973 140 Norland 4 0.07-0.11 0.09 0.004-0.009 0.006
1 Spray applications were made in two equal treatments two weeks apart.
FATE OF RESIDUES
General comments
Information was available from experiments with 2,4-D-14C that
showed that 4-hydroxy metabolites were found in plants. These were
present as glycosides as well as the free aglycones. Low levels of
2,4-D residues are excreted in the milk of dairy cows fed high levels
of 2,4-D in their ration. Information is lacking on the levels and
fate of residues in tissues, soils and crops grown on contaminated
soils. Some of the experiments described below are also mentioned in
the section "Residues resulting from supervised trials."
In animals
Milk from cows grazing on pasture sprayed at the rate of
2.2 kg/ha with either the isopropyl, 2-ethylhexyl, or butyl esters of
2,4-D contained residues of 2,4-D ranging from 0.01 to 0.06 mg/kg
during the first 2 days after spraying and declined to 0.01 mg/kg or
lower by day 3 (Klingman et al., 1966). Analysis of forage samples
from these trials showed 2,4-D residue levels after spraying of 59 and
48 mg/kg for the butyl and 2-ethylhexyl ester treatments,
respectively. The residues had declined to 5 and 15 mg/kg on day 7.
Cows were fed rations containing 2,4-D at 10, 30, 100, 300 and
1000 mg/kg levels for 2 or 3 weeks at each level (Bjerke et al.,
1972). Residues were determined in samples of milk and cream from
these cows during the feeding period and for 7 days following
withdrawal at the highest feeding level. No residues of 2,4-D or
2,4-dichlorophenol greater than 0.05 mg/kg (limit of determination)
were found in milk or cream at the 300 mg/kg or lower feeding levels.
Residues of 2,4-D and 2,4-dichlorophenol determined in milk and cream
from cows fed at the 1000 mg/kg level are shown in Table 2. The
highest residues found in any sample were 0.12 and 0.06 mg/kg of the
acid and phenol respectively. No residues greater than 0.05 mg/kg were
found in any of the samples taken during the withdrawal period. An
acid hydrolysis extraction procedure was used to extract any phenoxy
acid or phenol that might have been bound physically or chemically to
natural constituents of the milk.
2,4-D residues were determined in 5 different species of fish
(total of 60 samples) taken from 3 different locations at various
intervals following spraying of an aquatic environment with 2,4-D
(dodecyl-tetradecyl amine salts) at a rate of 4.48 kg/ha (Scholtz and
Whitney, 1974). Residue levels varied from <0.01 (limit of detection)
to 0.16 mg/kg. Of the 60 samples analyzed, 3 contained residues of
2,4-D greater than 0.1 mg/kg and 8 had residue levels between 0.01 and
0.1 mg/kg.
In Plants
Residues arising in treated citrus are discussed above.
("Residues resulting from supervised trials.")
Low residues of 2,4-D and 2,4-dichlorophenol (approximately 0.1
and 0.005 mg/kg respectively) were found in potatoes following
treatment with 2,4-D for growth regulation (Bristol and Nelson, 1974.)
See Table 5. The potato samples were analyzed by two different
procedures: a total residue analysis which involved hydrolysis with
sulphuric acid before extraction, and a free residue procedure without
the initial hydrolysis. Differences between total and free residue
levels of 2,4-D were small but significant, indicating the presence of
small amounts of conjugated and/or bound residues. Phenolic
metabolites of 2,4-D other than 2,4-dichlorophenol were not detected
in any of the potato samples. The small differences in residue levels
between the different varieties of potato sampled in the 1973 test
were not significant.
Experiments with carboxyl - MC labelled 2,4-D acid indicated that
part of the 2,4-D reacted with some plant constituents of lemons to
produce an ester-like complex (Erickson et al., 1963).
In bean plants treated with 2,4-D-1-14C the major metabolite was
2,5-dichloro-4-hydroxyphenoxyacetic acid, while
2,3-dichloro-4-hydroxyphenoxyacetic acid was a minor metabolite
(Hamilton et al., 1971). These metabolites accumulated as glycosides
but were also present as the free aglycones. The glycosides appeared
to be relatively stable in bean plant tissue since they were still
the predominant residue 22 days after treatment. Similar metabolites
were found in wheat, barley, oats and soybeans but not in buckwheat
or maize. In further experiments with soybean cotyledon callus tissue
cultures Feung et al, (1971) confirmed that the major water-soluble
metabolites were similar to those in bean plants. In addition a major
ether-soluble metabolite was identified as the 2,4-D glutamic acid
conjugate. Chkanikov et al., 1971) used 2,4-D-2-14C to study the
water-soluble metabolites of maize and bean plants. They confirmed
that the major metabolites in bean plants were glucosides of
hydroxylated 2,4-D and that the metabolism in bean plants differs from
that in maize.
In storage
Chopped potato samples were fortified with 0.05, 0.1 and 0.2
mg/kg levels of 2,4-D before being put into frozen storage (Bristol
and Nelson, 1974). Analysis of samples removed from storage at times
varying from 12 to 73 weeks gave an average recovery of 87.6 ± 2.3%
for 26 of these samples compared with 87.9 ± 3.0% before storage,
demonstrating that 2,4-D was stable under these conditions. In another
study residue levels of 2,4-D decreased with a half-life of
approximately 12 weeks, while those of 2,4-dichlorophenol remained low
throughout the period, in whole potatoes stored at 38°C. The data are
shown in Table 6.
TABLE 6. Effect of storage at 38°C on 2,4-D residues in potatoes
(Bristol and Nelson, 1974)
Residue, mg/kg.
Storage
period, Control Sample Treated Samples1
weeks 2,4-D 2,4-dichlorophenol 2,4-D 2,4-dichlorophenol
0 <0.02 <0.002 0.10, 0.14 0.005, 0.005
16 <0.02 <0.002 0.04, 0.05 0.004, 0.005
20 <0.02 <0.002 0.04, 0.03 0.006, 0.005
25 <0.02 <0.002 0.03, 0.02 0.004, 0.005
30 <0.02 <0.002 <0.02, <0.02 0.003, 0.004
35 <0.02 <0.002 <0.02, <0.02 0.005, 0.004
1 Individual residue data are given for each of two treated samples.
METHODS OF RESIDUE ANALYSIS
The chromatographic methods of analysis of 2,4-D residues have
been reviewed by Cochrane and Purkayastha (1973). This review covers
extraction, clean-up, derivation and GLC conditions for residue
determinations in water, soil, plant material, animal tissue and fish.
Methods for the analysis of 2,4-D residues in animal and plant
tissue, soil and water have been made available since the 1970
evaluation and these are summarized in Table 7. Only 2 methods (Bjerke
et al., 1974; Bristol and Nelson 1974) included the 2,4-dichlorophenol
metabolite. The extraction procedures range from extraction with
acetone for plant tissue to alkali and acid hydrolysis for mussel
tissues. It is known that 2,4-D conjugates with plant constituents
(Hamilton et al., 1971) and most of these procedures probably do not
hydrolyse the conjugates. Development and validation of extraction
procedures to determine total 2,4-D residues including 2,4-D acid,
2,4-D-dichlorophenol and conjugates of each are needed.
TABLE 7. Methods for the determination of 2,4-D residues
Sensitivity Recovery
Substrate Extraction Clean-up Esterification Determination1 (mg/kg) (%) Reference
Fish Hexane/ Acid-hexane/ 2-chloroethanol/ GLC-ED 0.001 70 Renberg,
acetone ether partition; sulphuric acid; 1974
Sephadex diazomethane
QAE ion exchange
Fish Methanol/ Acid/ diazomethane GLC-E Cond. 0.01 90 ± 2.5 Schultz
phosphoric alkalichloroform and
acid partition Whitney,
1974
Fish, Alkali and acid Acid/buffer-ether/ boron tri-fluoride/ GLC-EC 0.1 - Wojtalik
mussels hydrolysis of petroleum ether methanol et al.,
ethanol extract partition; 1971
of fish alkali Florisil
and acid column
hydrolysis of
mussel tissue.
Meat, Ethanol/ Acid/ diazomethane GLC-EC; 0.01 74-98 Yip,
fish, sulphuric alkalichloroform GLC-MC 1971
poultry, acid/chloroform partition;
dairy Florisil
products column after
esterification
Milk, Acid Alumino diazomethane GLC-EC; Bjerke
cream hydrolysis, column, acid/ (2,4-D only) GLC-MC 0.05 90-100 at al.,
ether alkali-benzene (2,4-D); 1972
partition for 84-100
2,4-dichlorophenol; (2,4-
acid-ether dichlorophenol)
partition for
2,4-D
TABLE 7. (Cont'd.)
Sensitivity Recovery
Substrate Extraction Clean-up Esterification Determination1 (mg/kg) (%) Reference
Plant Acetone Acid/ methanol/ GLC-MC 0.01 72-96 Munro,
tissues buffer-chloroform sulphuric 1972
partition; sweep acid
co-distillation
after esterification
Oranges, Acetone Acid/ dimethyl GLC-EC 0.01 73-95 Phillips,
grapefruit buffer-chloroform sulphate 1969
partition
Cereals, 35% Acid/alkali diazomethane GLC-EC; 0.01 84-100 Yip
fruits, aqueous chloroform (2,4-D) GLC-MC 1971
vegetables acetonitrile partition;
or Florisil column
acetonitrile after
esterification
Potatoes Alkali Acid/ diazomethane GLC-E Cond. 0.02 (2,4-D); 87.9 ± 3.0 Bristol
extraction; alkali-benzene (2,4-D) (2,4-D); and
acid partition; 0.002 (2,4- 84.5 ± 5.7 Nelson,
hydrolysis alumina column; dichlorophenol) (2,4- 1974
acid/alkali-benzene dichlorophenol
partition for
2,4-dichlorophenol;
acid-ether
partition for 2,4-D
Barley Acid and Partition diazomethane GLC-EC 0.02 75-82 Lokke,
enzymic into ether/ 1974
hydrolysis hexane;
alumina
column
TABLE 7. (Cont'd.)
Sensitivity Recovery
Substrate Extraction Clean-up Esterification Determination1 (mg/kg) (%) Reference
Soil Alkali Sephadex 2-chloroethanol/ GLC-EC 0.001 70-74 Renberg,
extraction QAE ion sulphuric acid; 1974
exchange diazomethane
column
Soil Diethyl Acid/alkali-ether boron trichloride/ GLC 0.01 84-103 Woodham
ether/ partition 2-chloroethanol et al.,
sulphuric 1971
acid
Soil (a) Ethanol/ Acid/alkali-ether diazomethane; GLC-EC 0.03-0.05 84-100 Purkayastha,
sulphuric partition diazobutane (methyl 1974
acid/di-ethyl ester);
ether
(b) Alkali/ 76-92
chloroform (butyl
ester)
Sediment Acetone/ Acid/ Boron trifluoride/ GLC-EC 0.1 - Wojtalik
petroleum buffer-chloroform methanol at al.,
ether/ 1971
sulphuric acid/
ethyl ether
Water - Sephadex QAE 2-chloroethanol/ GLC-EC 0.0001 97 Renberg,
ion exchange sulphuric acid; 1974
column diazomethane
Water Diethyl Alkali/ diazomethane; GLC-EC 0.05 82-94 Purkayastha,
ether/ buffer-diethyl diazobutane 1974
sulphuric ether
acid
TABLE 7. (Cont'd.)
Sensitivity Recovery
Substrate Extraction Clean-up Esterification Determination1 (mg/kg) (%) Reference
Water Chloroform/ - diazomethane GLC-E Cond. 0.001 97.5 ± 2.5 Schultz
sulphuric and
acid Whitney,
1974
Water Alkali Acid/sodium Boron trifluoride/ GLC-EC 0.001 - Wojtalik
hydrolysis; sulphate- methanol et al.,
chloroform/ chloroform 1971
phosphoric partition
acid
1 GLC-EC = GLC - electron capture detection
GLC-MC = GLC - microcoulometric detection
GLC-E Cond = GLC - electrolytic conductivity
TABLE 8. Comparison of three extraction procedures for determining
2,4-D in barley (Lokke, 1974)
2,4-D, mg/kg, in field-treated barley
Extraction Recovery of 2,4-D
Procedure Sample 1 Sample 2 Sample 3 Added to barley, %
Lokke,
1974 0.06 0.45 4.3 75-82
Yip,
1971 0.04 0.35 4.0 68-102
Ether/
hexane <0.01 0.04 0.51 72-95
Most of the clean up procedures require an acid/alkali-organic
solvent partition step. The methods that include the
2,4-dichlorophenol employ an alumina column step to separate the
phenol, which is determined separately from 2,4-D. Esterification of
the acid is usually with diazomethane but other reagents such as boron
trifluoride/methanol, 2-chloroethanol/sulphuric acid,
methanol/sulphuric acid and diazobutane have also been used. A
Florisil column (Yip, 1971) and sweep co-distillation (Munro, 1972)
have been used for further clean-up of the esterified extract.
GLC with the electron capture, microcoulometric or electrolytic
conductivity detectors were used as the determinative step.
Sensitivities claimed ranged from 0.1 to 0.0001 mg/kg. Yip (1971)
reported lower background responses and generally higher recoveries
with the microcoulometric detector than with the electron capture
detector. The increased specificity would make either the
microcoulometric or electrolytic conductivity the detector of choice.
Recoveries of >70% were reported for all methods.
Lokke, 1974 compared three methods for the determination of 2,4-D
in barley grain. Barley was field-treated with 2,4-D to obtain samples
with weathered residues. The extraction procedures used were acid and
enzymic hydrolysis (Lokke, 1974, Table 7), 35% aqueous acetonitrile
(Yip, 1971, Table 7) and extraction with ether/hexane. The results
from the study are summarized in Table 8 and show that the extraction
procedures of Lokke, 1974 and Yip, 1971 give similar results but the
ether/hexane extraction procedure gave residues lower by a factor of
10. The three procedures gave essentially the same recovery values
from fortified samples. These investigations demonstrate the
importance of the extraction procedure. Lokke, 1974 reported that
further analysis of the filter cakes from both the Lokke and Yip
extraction procedures indicated still unhydrolyzed 2,4-D conjugates.
Although the clean-up, esterification and determinative steps for
2,4-D residues appear to be satisfactory, extraction Procedures
require development and validation, as mentioned above.
NATIONAL TOLERANCES REPORTED TO THE MEETING
Some examples of national tolerances were reported to the Meeting
and are listed in Table 9.
TABLE 9. Examples of national tolerances reported to the meeting
Tolerance
Country Commodity mg/kg
Australia Apples, apricots, beets, carrots,
citrus, corn, cucumbers, grapes,
melons, onions, peaches, pears,
peppers, plums, potatoes, tomatoes 5
Belgium Apples, apricots, boots, carrots,
citrus, corn, cucumbers, grapes,
melons, onions, peaches, pears,
peppers, plums, potatoes, tomatoes 0.05
Canada Asparagus 5
Barley, corn, flax, oats, rye, Negligible
strawberries, wheat Residue
Fed. Rep. Apples, apricots, beets, carrots,
of Germany citrus, corn, cucumbers, grapes,
melons, onions, peaches, pears,
peppers, plums, potatoes, tomatoes 0.1
Netherlands Apples, apricots, beets, carrots,
citrus, corn, cucumbers, grapes,
melons, onions, peaches, pears,
plums, potatoes, tomatoes 0.05
Switzerland Apples, apricots, citrus, grapes,
melons, peaches, pears, plums 0.05
U.S.A. Forage of barley, oats, rye,
and wheat 20
Apples, asparagus, citrus, pears,
quinces 5
Barley, oats, rye, wheat 0.5
TABLE 9. (Cont'd.)
Tolerance
Country Commodity mg/kg
Potatoes 0.2
Cucurbits, forage grasses,
forage legumes, fruiting
vegetables, leafy vegetables,
nuts, root crop vegetables, seed
and pod vegetables, small fruits,
stone fruits, and the individual
raw agricultural commodities,
avocados, cotton-seed, hops, and
strawberries 0.1
APPRAISAL
Information was presented to the Meeting on several uses of 2,4-D
on citrus: for weed control, as a pre-harvest growth regulator and for
post-harvest treatment of lemons and mandarins to retain buttons and
hence prolong storage life and assist in control of fungus. It is also
used on potatoes as a growth regulator, and in aquatic environments
for weed control.
2,4-D translocates into plants from the soil and from topical
application. Metabolites of 2,4-D accumulate as glycosides and are
also present as the free aglycones. In bean plants,
2,5-dichloro-4-hydroxyphenoxyacetic acid and
2,3-dichloro-4-hydroxyphenoxyacetic acid were identified as major
and minor metabolites respectively. Similar metabolites were found in
wheat, barley, oats and soybeans but not in buckwheat or maize. Small
amounts of conjugated and/or bound residues of 2,4-D were found in
potatoes and lemons. Low levels of 2,4-dichlorophenol were detected
in potatoes and in milk from cows.
Residue data indicated that low residues occurred from the
pre-harvest use of 2,4-D on citrus and potatoes. The post-harvest use
on lemons resulted in residues of <2 mg/kg.
Low residue levels of 2,4-D occurred in the milk of cows fed
rations containing high levels of 2,4-D (1000 mg/kg) in their diet.
Residues decreased to below detectable levels on withdrawal of 2,4-D
from the diet.
Experiments with potatoes demonstrated that 2,4-D was stable for
periods exceeding 1 year under conditions of frozen storage. 2,4-D
residues in whole potatoes stored at 38°C decreased with a half-life
of approximately 12 weeks.
Gas-chromatographic methods utilizing electron capture,
micro-coulometric and/or electrolytic conductivity detection should
be adaptable for regulatory purposes. A hydrolysis procedure prior
to extraction is required to liberate conjugated and/or bound
residues. Additional clean-up steps before and after esterification
appear to be of advantage for some samples.
National tolerances are in effect in a number of countries.
RECOMMENDATIONS
In addition to the tolerances of 0.02 mg/kg for barley, oats, rye
and wheat recommended at the 1971 Joint Meeting (FAO/WHO, 1972), the
following tolerances are recommended.
TOLERANCES
Tolerance
Commodity mg/kg
Citrus 2
Potatoes 0.21
Milk 0.052
1 The tolerance is based on a pre-harvest interval of 30 days
2 At or about the limit of determination
FURTHER WORK OR INFORMATION
Desirable
1. Information on the storage and fate of 2,4-D in food animals.
2. Information on the fate of 2,4-D in soils and residue data on
crops grown on contaminated soil.
3. Development of extraction procedures to determine total 2,4-D
residues including 2,4-D acids, 2,4-dichlorophenol and their
conjugates.
REFERENCES
Bjerke, E.L., Herman, J.L., Miller, P.W. and Wetters, J.H. (1972).
Residue study of phenoxy herbicides in milk and cream. J. agr. Food.
Chem., 20:963-967.
Bristol, D. and Nelson, D.C. (1974). Residue levels of
2,4-dichloro-phenoxyacetic acid and 2,4-dichlorophenol in red potato
tubers. North Dakota State University, Fargo, U.S.A. (unpublished)
California Agricultural Experiment Station Extension Service (1974).
1974-1975 Treatment guide for California citrus crops. p. 50-51.
Chkanikov, D.I., Makeev, A.M., Pavlova, N.N. and Dubovoi, V.P. (1971).
Water-soluble metabolites of 2,4-D in green plants of maize and beans.
Fiziol. Rast., 18:107-115.
Cochrane, W.P. and Purkayastha, R. (1973). Analysis of herbicide
residues by gas chromatography. Toxicol. Environ. Chem. Rev.,
1:137-268.
DeWolfe, T.A., Erickson, L.C. and Brannaman, B.L. (1959). Retardation
of Alternaria rot in stored lemons with 2,4-D. Proc. Am. Soc. Hort.
Sci., 74:367-371.
Erickson, L.C., Brannaman, B.L. and Coggins, C.W. (1963). Residues in
stored lemons treated with various formulations of 2,4-D. J. agr. Food
Chem., 11:437-440.
Erickson, L.C. and Hield, H.Z. (1962). Determination of
2,4-dichloro-phenoxyacetic acid in citrus fruit. J. agr. Food Chem.,
10:204-207.
FAO/WHO (1971). 1970 Evaluations of some pesticide residues in food.
AGP/1970/M/12/1; WHO/Food Add./71.42.
FAO/WHO (1972). 1971 Evaluations of some pesticide residues in food.
AGP/1971/M/9/1; WHO Pesticide Residues Series, No. 1.
Feung, C., Hamilton, R.H. and Witham, F.H. (1971). Metabolism of
2,4-dichlorophenoxyocetic acid by soybean cotyledon callus tissue
cultures. J. agr. Food. Chem., 19:475-479.
Hamilton, R.H., Hurter, J., Hall, J.K. and Ercegovich, C.D. (1971).
Metabolism of phenoxyocetic acids. Metabolism of 2,4-dichlorophenoxy
acid and 2,4,5-trichlorophenoxy-acetic acid by bean plants. J. agr.
Food. Chem., 19:480-483.
Hield, H.Z., Burns, R.M. and Coggens, C.W. (1964). Pre-harvest use of
2,4-D on citrus. University of California Experimental Station
Circular 528, p. 3-10.
Johns, T.H. (1974). 2,4-D residues in lemons. New South Wales
Department of Agriculture, Rydalmere, Australia. (Unpublished)
Klingman, D.L., Gordon, C.H., Yip, G. and Burchfield, H.P. (1966).
Residues in the forage and in milk from cows grazing forage treated
with esters of 2,4-D. Weeds, 14:164-167.
Lokke, H. (1974). Analysis of free and bound chlorophenoxy acids in
cereals. Presented at the 3rd International Congress of Pesticide
Chemistry, Helsinki, Finland.
Munro, H.E. (1972). Determination of 2,4-dichlorophenoxyacetic acid
and 2,4,5-trichlorophenoxyacetic acid in tomato plants and other
commercial crops by microcoulometric gas chromatography. Pestic. Sci.,
3:371-377.
Nelson, D.C. and Nyland, R.E. (1963). Influence of 2,4-D on uniformity
and specific gravity of potatoes. Am. Potato J., 40:391-395.
Nylund, R.E. (1956). The use of 2,4-D to intensify the skin color of
Pontiac potatoes. Am. Potato J., 33:145-154.
Phillips, R.L. (1969). 2,4-D - oranges and grapefruit. University of
Florida, Gainesville, U.S.A. (Unpublished)
Purkayastha, R. (1974). Simultaneous determination of
2,4-dichloro-phenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid,
and 2-methoxy-3, 6-dichlorobenzoic acid in soil and water by gas
chromatography with electron capture detector. J. agr. Food Chem.
22:453-458.
Renberg, L. (1974). Ion exchange technique for the determination of
chlorinated phenol and phenoxy acids in organic tissue, soil and
water. Analyt. Chem., 46:459-461.
Sarooski, R.A. and Stannard, M.C. (1974). Controlling preharvest drop
of citrus. New South Wales Agricultural Gazette, September 1974. P.
3-5.
Schultz, D.P. and Whitney, E.W. (1974). Monitoring 2,4-D residues at
Loxahatchee National Wildlife Refuge. Pestic. Monit. J., 7:146-152.
Wojtalik, T.A., Hall, T.F. and Hill, L.O. (1971). Monitoring
ecological conditions associated with wide-scale applications of DMA
2,4-D to aquatic environments. Pestic. Monit. J., 4:184-203.
Woodham, D.W., Mitchell, W.G., Loftis, C.D. and Collier, C.W. (1971).
An improved gas chromatographic method for the analysis of 2,4-D free
acid in soil. J. agr. Food Chem., 19:186-188.
Woolson, E.A., Thomas, R.F. and Ensor, P.D.J. (1972). Survey of
polychlorodibenzo-p-dioxin content in selected pesticides. J. agr.
Food Chem., 20:351-354.
Yip, G. (1971). Improved method for determination of chlorophenoxy
acid residues in total diet samples. J. Ass. off. analyt. Chem.,
54:966-969.