CHLOROBENZILATE JMPR 1972
Chlorobenzilate was briefly studied by the Joint Meeting in 1965
(FAO/WHO, 1965) and a comprehensive evaluation was carried out in 1968
(FAO/WHO, 1969). At this time information on several matters was
requested and material now available concerning some of them is
Some additional information is included in the comprehensive review by
Bartsch et al. (1971).
RESIDUES IN FOOD AND THEIR EVALUATION
Fulfilment of requirements
In the following paragraphs, the numbers refer to the corresponding
requirement as indicated by the 1968 Joint Meeting (FAO/WHO, 1969).
1. Composition of the technical product
Analysis of technical chlorobenzilate is carried out by
gas-liquid chromatography (6 ft × ¨ in column packed with 3%
Carbowax 20M on Gas Chrom Q) with dibenzylsuccinate as an
internal standard. For quantitative determination of the
chlorobenzilate, a column temperature of 240°C is used, but for
qualitative separation and identification of the impurities,
temperatures of 150°C or 220°C are used. Table 1 shows the nature
and extent of the impurities observed in 13 batches of technical
material over a two-year period. On the basis of retention times,
relative to the parent compound, the unknown compounds are the
same in all typical samples (Ciba-Geigy, 1972a). Methods for
determining the active ingredient in technical material and
formulated products have been described by Bartsch et al.
2. Nature of terminal residues
Knowles and Ahmad (1971) have investigated the comparative
metabolism of chlorobenzilate, chloropropylate and GS-19851
acaricides by rat hepatic enzymes. The limiting reaction was
found to be the cleavage of the ester linkage by
carboxylesterases which showed greater activity for
chlorobenzilate than for the other two compounds. Degradation of
all three materials was inhibited by di-isopropyl
phosphorofluoridate and the main metabolite was 4-chlorobenzoic
acid. Bourke et al. (1970) studied the distribution of residues
TABLE 1 Nature and extent of impurities in technical chlorobenzilate
Component % Found (range)
Chlorobenzilate 93.8 - 97.3
Ethyl 4-chlorobenzoate 0.23 - 0.47
4,4'-dichlorobenzophenone 0.04 - 0.23
Chloropropylate ND3 - 0.05
Ethyl ether of chlorobenzilate 0.14 - 0.59
4,4'-dichlorobenzil )1 <0.01 - 0.11
"Unknown" RRT 0.492 <0.01 - 0.03
" RRT 0.88 0.01 - 0.15
" RRT 1.19 0.06 - 0.10
" RRT 1.46 0.04 - 0.09
" RRT 1.72 0.10 - 0.38
" RRT 1.83 ND - 0.09
Total impurities measured 0.90 - 1.61
Total "unknowns" measured 0.36 - 0.59
1 Not separated by system used.
2 RRT = retention time relative to chlorobenzilate (= 1.00).
3 ND = not detected
of these acaricides in rats. Adult male rats were fed 14C-labelled
compounds and the following distribution was found: 42.78% in faeces,
25.63% in urine, 15.47% in the gastrointestinal tract, 3.31% in liver
and less than 1% in brain, heart, spleen or kidney. It appeared that
chlorobenzilate was degraded to polar water-soluble metabolites more
rapidly than was chloropropylate.
Chlorobenzilate, chloropropylate and GS-19851 (isopropyl
4,4'-dibromobenzilate) labelled with 14C in both aliphatic
carbon atoms of the benzilic acid moiety were applied to leaves
of soybean plants grown in glasshouse pots. Each leaflet was
treated with 25 000 cpm of acaricide in 10 ml of 95% ethanol with
a microsyringe. Specimens were analysed after 0, 4, 8, 12 and 16
days. Only limited transportation of the acaricides to other
tissues of the plant was observed. Recovered radioactivity on Day
0 was 84.7% (chlorobenzilate), 94.8% (GS-19851) and 96.5%
(chloropropylate). On day 16 these values were 10.5%, 17.7% and
10.3%, respectively. Autoradiography of thin-layer chromatograms
revealed that the major component (greater than 95%) was the
parent compound in all cases (Hassan and Knowles 1969).
3. Residue data from countries other than U.S.A.
Table 2 lists data on residues resulting from applications to
fruit according to good agricultural practice in countries other
than U.S.A. (Ciba-Geigy, 1972b). Table 3 gives residues observed
following treatment of tea (Bortsch et al., 1971).
4. Data on disappearance of residues in soils
No further data available.
5. Data on residues in wine
No data available.
6. Occurrence of residues in milk
Data have been received concerning the residues of
chlorobenzilate occurring in milk due to feeding cows with known
dosages of the compound (Ciba-Geigy, 1972 c). Two sets of three
cows in the middle of lactation were fed with either 50 mg or 200
mg of chlorobenzilate per day; milk samples were taken 7, 3 and 1
day before feeding was started and 0, 1, 2, 4, 7, 10, 21, 28, 29,
30, 32, 35 and 42 days after starting the dosed feeds. Two cows
were also used as untreated controls. The feeding levels
corresponded to 5 ppm and 20 ppm of chlorobenzilate in citrus
pulp cattle feed, assuming a maximum intake of 10 kg feed per cow
per day. Residues of chlorobenzilate in the milk from cows on the
50 mg per day dosage were in the range <0.025 to 0.03 ppm
throughout the treatment period. Cows on the 200 mg per day
dosage yielded milk containing from <0.025 to 0.06 ppm of
chlorobenzilate. Residues of the two potential metabolites,
4,4'-dichlorobenzophenone and 4,4'-dichlorobenzilic acid were
below 0.02 ppm in all milk samples examined.
TABLE 2 Chlorobenzilate residues in fruit
Crop and Application Days after Residue in plant
country conc.(% a.i.) No. application parts (ppm)
Switzerland 0.0375 1 0 2.1
control - >0.01
Switzerland 0.0375 1 65 0.13
control - <0.05
Oranges pulp peel
Spain 0.05 1 150 <0.03 2.1
control - <0.03 <0.03
Cyprus 0.02 1 167 <0.03 1.75
control - <0.03 <0.03
Israel 0.03 1 165 <0.03 <0.03
control - <0.03 <0.03
South Africa 0.025 1 14 <0.01 1.6, 1.7
28 <0.01 1.6, 1.6
42 <0.01 2.0, 1.8
control - <0.01 <0.01
Tomatoes dosage fruits
Israel 0.375 kg 2 21 <0.1
a.i. per ha 71 <0.1
control - <0.1
1 Days after second application.
TABLE 3 Chlorobenzilate residues in tea (Bartsch et al., 1971)
Applications Days after Chlorobenzilate
Country conc. No. application (ppm)
Indonesia 50 g 1 1 17.0, 13.0 1.4
a.i./ha 4 12.0, 10.0 1.7
7 1.5, 1.4 <0.20
9 --- 0.63
100 g 1 1 9.1, 18.0 5.60
a.i./ha 4 21.0, 16.0 5.50
7 7.6, 6.1 4.10
9 --- 5.30
India manufactured dried leaves
312 g 1 7 45.6
a.i./ha brewed tea
wet leaves brew
7. Methods of residue analysis
Chlorobenzilate residues have been determined by gas
chromatography following extraction from various foods using
petroleum ether (FAO/WHO, 1969), methanol (Delley et al., 1964)
or mixtures of iso-propanol and benzene (Benfield and Richardson,
1965). Alumina or Florisil columns have been used (U.S. Food and
Drug Administration, 1968) for clean-up with various eluants. The
basic alumina column clean-up was preferred because of its more
consistent activity. Oily samples such as nuts, seeds and citrus
peel required an additional cleanup stage (partitioning with
acetonitrile) before column chromatography. The microcoulometric
detector was used with a column of 1 m X 4 m 5% G.E. XE60 on
Anakrom ABS 50-60 mesh or 2 ft x ¨ in 30% Carbowax 20M on 60/80
Gaschrom Q (FAO/WHO, 1969). A 6 ft column packed with 3% XE60 on
80/100 Gaschrom Q and an electron capture detector has been found
to be the more efficient system (U.S. Food and Drug
Administration, 1968). Interferences from DDT and TDE were
eliminated by the clean-up procedure. These materials were eluted
in the benzene fraction using the Florisil column and in the
hexane fraction with the alumina column. Delley et al. (1964)
used glass columns packed with 2.5% Reoplex 400 on Anakrom ABS
maintained at 170°C with a hydrogen flame detector, which gave a
detection limit of 0.1 µg. These gas chromatographic procedures
are suitable for use for regulatory purposes.
Details of gas chromatographic procedures for determining
residues of chlorobenzilate and its metabolites in milk have been
described by Formica et al. (1972). The milk sample is mixed
with anhydrous sodium sulphate and extracted with benzene in a
Soxhlet apparatus. The benzene extract is evaporated to dryness,
redissolved in hexane and partitioned against acetonitrile to
separate chlorobenzilate and 4,4'-dichlorobenzophenone from milk
fats. The acetonitrile phase is concentrated and further cleaned
by thin-layer chromatography on silica gel developed with
benzene. Chlorobenzilate and 4,4'-dichlorobenzophenone are
finally determined by gas chromatography, using microcoulometric
and electron capture detection, respectively.
To test for 4,4'-dichlorobenzilic acid, acetone is added to the
milk and after filtration and evaporation of the acetone, ammonia
is added to the aqueous extract. The fats are separated by
partitioning with hexane, and the remaining water extract is
acidified with hydrochloric acid. The 4,4'-dichlorobenzilic acid
is extracted with ether and oxidized with acid potassium
dichromate to 4,4'-dichlorobenzophenone which is then determined
by gas chromatography with electron capture detection. By the
methods stated, the limits of detection are quoted as
chlorobenzilate, 0.025 ppm (5 mg); 4,4'-dichlorobenzophenone,
0.02 ppm (0.1 mg); 4,4'-dichlorobenzilic acid, 0.02 ppm (0.1 mg).
The Coulson electrolytic conductivity detector system, normally
used for nitrogen detection has been used to determine
halogenated compounds such as chlorobenzilate. The quartz
reduction tube was packed with a platinum gauze and the glass
column with 5% SE30 on Chromosorb W.S. (Coulson, 1966). Bartsch
et al. (1971) give a detailed review of residue methods.
Information has been supplied which fulfills five of the seven
requirements listed by the 1968 Joint Meeting. No information was
available regarding disappearance from soils or carry-over of residues
into wine as a result of treating grapes. The following tolerances are
Apples, pears, grapes 2
Citrus fruits 1
Melons, cantaloupes 1
Almonds and walnuts (shelled), tomatoes 0.2
Milk (from the feeding of treated forage) 0.05*
* at or about the limit of determination
FURTHER WORK OR INFORMATION
1. Data on the possible carry-over of residues into wine as a result
of the treatment of grapes.
2. Further data on the disappearance of residues in soils.
3. Further data on residues occurring from usage on tea.
Bartsch, E., Eberle, D., Ramsteiner, K., Tomann, A. and Spindler, M.
(1971) The carbinole acaricides: chlorobenzilate and chloropropylate.
Residue Reviews 39: 1-93.
Benfield, C.A. and Richardson, D. (1965) Report No. CP/64/Anal/21.
Fisons Pest Control Ltd., Chesterfield Park Research Station.
Bourke, J.B., Broderick, E.J. and Stoewsand, G.S. (1970) Elimination
rate and tissue residues of chloropropylate and chlorobenzilate in
rats. Bull. Environ. Contam. Toxicol., 5: 509-514.
Ciba-Geigy. (1972a) Composition of chlorobenzilate technical.
Ciba-Geigy. (1972b) Residue data on chlorobenzilate. Report 1960, RAR
40/71, RVA 53/72, RVA 54/72, RVA 55/72 and RVA 58/72. (unpublished)
Ciba-Geigy. (1972c) Residues of chlorobenzilate and two of its
metabolites in milk of Swiss cows. Report RVA 63/72. (unpublished)
Coulson, D.M. (1966) Selective detection of nitrogen compounds in
electrolytic conductivity gas chromatography. J. Gas Chromatog., 4:
Delley, R., Friedrich, K. and Geiser, A. (1964) Report of Geigy method
ROS No. 2526. (unpublished)
FAO/WHO. (1965) Evaluation of the toxicity of pesticide residues in
food. FAO PL/1965/10/1: WHO/Food Add./27.65.
FAO/WHO. (1969) 1968 Evaluations of some pesticide residues in food.
FAO/PL: 1968/M/9/1; WHO/Food Add./69.35.
Formica, G., Gabrielova, M. and Magnin, B. (1972) Gas chromatographic
residue determinations of chlorobenzilate and two of its metabolites
in milk. Ciba-Geigy report REM 13/72. (unpublished)
Hassan, T.K. and Knowles, C.O. (1969) Behaviour of three 14C-labelled
benzilate acaricides when applied topically to soybean leaves. J.
Econ. Entomol., 62: 618-619.
Knowles, C.O. and Ahmad, S. (1971) Comparative metabolism of
chlorobenzilate, chloropropylate and bromopropylate acaricides by rat
hepatic enzymes. Can. J. Physiol. Pharmacol., 49: 590-597.
U.S. Food and Drug Administration. (1968) The determination of
chlorobenzilate and chloropropylate in plant materials. Pesticide
Analytical Manual. Vol.II, Section 120 p. 218.