BROMOPROPYLATE JMPR 1973
IDENTITY
Chemical name
isopropyl-4,4'-dibromobenzilate
Synonyms
NEORON(R), ACAROL(R)
Ciba/Geigy GS-19851
Structural formula
Other information on properties
Physical state: White crystalline powder
Melting point: 77°C
Vapour pressure: 5.5 x 10-7 mm Hg at 20°C
5.25 x 10-3mm Hg at 100°C
Density: 1.59 g/cm3 at 20°C
Solubility: <0.5 ppm in water at
20°C, soluble in organic solvents
Stability: Fairly stable in neutral or
slightly acid media;
half-life periods in aqueous 10%
methanol at PH O (IN HCI) 50 days;
at PH 6-7 (water) >3 years;
at pH 9 (0.05 M borax buffer)
15 days;
Purity:
(technical material) Minimum 88% isopropyl-4,4-dibromobenzilate
Maximum 12% by-products of manufacture
isopropyl-4-bromobenzoate
isopropyl ether of isopropyl-4,4
dibromobenzilate
isopropyl-4-bromobenzilate
isopropyl-alpha,alpha-bis (4 bromophenyl)
acetate
toluene
Details of concentration of individual
impurities filed with FAO as
confidential information were
considered by the meeting.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
Biochemical aspects
Absorption, distribution and excretion
Two male and two female rats were each administered by gavage 1.6
mg 14C-labelled bromopropylate. Expired CO2, urine and faeces were
collected for the next 120 hours in periods of 24 hours following
which blood and other tissues were taken for analysis. Less than 0.2%
of activity was found in respired CO2. In males, 90% of activity was
found in faeces and 6% in urine while in females 55% appeared in
faeces and 33% in urine. About 75% activity was eliminated in 48 hours
but after 120 hours 2.6% (males) and 1.5% (females) of the
administered dose remained in tissues, mainly kidneys, liver and fat.
(Cassidy and Min, 1968).
One cow received 0.33 mg/kg/day of 14C-labelled bromopropylate
in the diet for five days. After a further 13 days without treatment
the animal was killed. In the 20 days 94.9% of the administered
activity was recovered, 0.96% in the milk, 20.5% in the urine and
73.4% in the faeces. No activity was detectable in tissues other than
adipose tissue which contained 0.06-0.17 ppm at the time of autopsy
(Murchison, 1968; Cassidy et al., 1968).
Biodegradation
Only the parent compound was detected in the adipose tissue and
the milk of a cow which had received 0.33 mg/kg/day of 14C-labelled
bromopropylate for five days. Most of the activity found in the faeces
was the parent compound as shown by analysis of the first
post-treatment day sample which contained 92% parent compound, the
remainder being unidentified metabolites. The majority of activity in
urine consisted of 4,4'-dibromobenzilic acid and a more polar
unidentified metabolite. Other possible metabolites,
4,4'-dibromobenzohydrol, 4,4'-dibromobenzophenone and 4-bromobenzoic
acid were not found (Cassidy et al., 1968). In the faeces of rats
administered bromopropylate 60% of activity was parent compound and
20% 4,4'-dibromobenzilic acid (Cassidy et al., 1968).
Three groups of three beef calves were each fed diets containing
0, 5 and 50 ppm bromopropylate. Fat biopsies were taken after two and
eight weeks of feeding and one animal from each group was killed after
four and six weeks. After 10 weeks feeding the remaining animal which
had been fed on the 5 ppm diet was killed; the one on 50 ppm was
maintained on control diet for a further two weeks before it was
killed. After four, six and 10 weeks the 5 ppm diet produced
respectively levels of 1.5, 1.5 and 2.8 ppm of bromopropylate in the
fat. The 50 ppm diet produced fat levels of 7.3 ppm after four, and
8.0 ppm after six weeks. After two weeks an control diet the
concentration of bromopropylate in fat had fallen to 0.3 ppm. Muscle
tissue contained low residues of unchanged bromopropylate while liver
and kidneys also contained 4,4'-dibromobenzilic acid during the
feeding period. (Cullen and Mattson, 1968; Fancher et al., 1968, b and
c.)
TOXICOLOGICAL STUDIES
Special studies on reproduction
Rat. Groups of 20 male and 20 female rats in the first generation
and groups of 25 male and 25 female rats in the second and third
generations were used in a three-generation test (two litters being
produced in each generation) and fed on diets containing 0, 2.5 and 5
ppm bromopropylate. In a second test, groups of 25 male and 25 female
rats received diets containing 0, 30 and 100 ppm bromopropylate.
Through out the tests no abnormalities attributable to bromopropylate
were found in the reproductive physiology of male or female rats and
there was no evidence of gross abnormalities in the offspring
throughout the studies. The number of young in each litter and their
growth and survival were normal. The weights of liver, kidneys and
spleen were comparable with controls in the rats of the F 3b
generation whose parents received 2.5 and 5 ppm diets while spleen and
liver weights of F 3b young of parents fed on 30 and 100 ppm diets
were slightly higher than controls. No histological abnormalities were
found in these animals at any dosage level (Coulston, et al. 1970c;
Coulston et al., 1971).
Dog. Groups of three male and three female dogs were fed on diets
containing 0, 30 and 100 ppm bromopropylate in their diet. After an
unstated time the females were mated with males of the same group. All
matings resulted in pregnancy and delivery of normally sized litters.
The only deformed pup was found in a control litter. All others were
normal in appearance, behaviour and development. Increases in the body
weight of the pups in most of the litters of groups receiving
bromopropylate were similar to those of control pups. The reduced
growth rate of one litter of the 100 ppm group was attributed to the
results of poor maternal care (Coulston et al., 1970b; Coulston and
Benitz, 1972).
Acute toxicity
The results of tests to investigate the acute toxic action of the
compound are summarized in Table 1.
TABLE 1. THE ACUTE TOXICITY OF BROMOPROPYLATE
LD50
Species Sex Route Purity (mg/kg) Reference
Mouse M O Tech 8 000 (Ueda and Kondo,
1968)
Rat M+F O Tech >5 000 (Stenger, 1967)
Rat M+F O Formulation 6 000 (Drake, 1970)
Rat O Formulation >23 100 (Fencher et al.,
1968a and b)
Short-term studies
Rat. Groups of 10 male and 10 female rats received 0, 40, 200, 1000
and 5000 mg bromopropylate/kg bw by gavage as a suspension in 0.5%
aqueous tragacanth on six days each week for four weeks. The highest
dosage level produced polyuria throughout the 21 days before the
animals were killed and for the first eight days pale mucoid faeces
were produced. The rate of body weight gain and food intake were
reduced in this and the 1000 and 200 mg/kg groups. Rats of the 5000
mg/kg group developed a relative neutrophilia but the results of
haematological analyses in all groups were normal. The absolute and
relative liver weights were increased in the three highest dosage
groups and cytoplasmic swelling and periportal infiltration were seen.
Hepatic necrosis occurred at the highest dosage level. At the 40 mg/kg
dosage level the one animal which died during the test showed similar
abnormalities in the liver; others of the group appeared normal.
(Paterson, 1967a).
Groups of 12 male and 12 female rats were fed for 90 days on
diets containing 0, 100, 300 and 1000 ppm bromopropylate. Another
group received diet containing 3000 ppm for 55 days and 4000 ppm for a
further 35 days. In the highest dosage level group the food intake and
rate of weight gain were below normal and at autopsy the liver, kidney
and testes weights were heavier than in controls relative to body
weight, and loss of basophil material, pigmentation (possibly
lipofuscin) and fatty infiltration were present in hepatocytes. Mild
to severe regressive changes were seen in testes on histological
examination. At the 1000 ppm level food intake was slightly less than
in controls although weight gain was similar. Testes were lighter than
in controls and similar histological changes were seen in the liver.
At the two lower levels smaller numbers of rats showed loss of
basophil material and cytoplasmic swelling with focal vacuolation.
These changes were considered to be physiological being attributed to
SER hypertrophy, but no EM studies were carried out to confirm this.
The results of haematological and blood biochemistry studies and of
urine analyses were similar in all groups. (Paterson and Drake, 1967.)
Dog. A group of two male and two female dogs received orally, by
capsule, lg/kg/bw/day of bromopropylate for 30 days. A second group
received 2 g/kg/day for four days, then 0.5 g/kg for a further 26
days. Diarrhoea and vomiting occurred in dogs of both groups. During
the first week the food intake was decreased and body weight was lost
or the gain in weight was below normal. The results of a
haematological examination were normal. Determination of organ weights
did not indicate any dose-related changes. In both groups serum
transaminase and alkaline phosphatase levels were increased by
treatment and cytoplasmic swelling and fine vacuolation of hepatocytes
was found. No mature spermatoza were found in male animals but this
may have been due to the age of the animals. (Paterson, 1967b.)
Four groups of eight male and eight female dogs were fed for two
years on diets containing 30, 100, 250 and 1000 ppm bromopropylate. A
fifth group received 4000 ppm in the diet for three months.
A group of 10 males and 10 females acted as controls. The highest
dosage level produced light coloured soft stools after one week and
semi-fluid stools thereafter. Food intake was reduced and weight was
lost. Two dogs died (after four and six weeks) and two others were
killed because they became cachetic. In these four animals increased
serum alkaline phosphatase, diminished serum cholesterol and mild
anaemia were found. Haemosiderosis of Kupfer cells, proximal tubular
cells of the kidney, the spleen and the bone marrow, degenerative
changes in the distal convoluted tubules of the kidney, hyperplasia of
bone marrow and extramedullary haematopoiesis were seen in these
animals at autopsy. In the other animals of the 4000 ppm group killed
at three months, accumulation of haemosiderin in the macrophages of
the spleen and bone marrow and in Kupfer cells was observed.
Examination of liver by EM showed S.E.R. hypertrophy and an increase
in numbers of lysosomes, many of which contained lamellar structures.
Two male and two female animals were fed for nine months on control
diets following three months on 4000 ppm diet. Stools returned to
normal consistency within a week and weight was gained normally.
Biochemical and haematological parameters also returned to normal in a
short time; animals were indistinguishable from controls at the time
of autopsy. The 1000 ppm diet also produced softening of stools.
Although weight gain by males was normal, females failed to gain
weight. Some females showed slight anaemia on some occasions. The
microsomal enzymes, biphenyl hydroxylases, showed increased activity
and this was associated with an increase in liver weight relative to
body weight at six months and at two years (in females only). SER
hypertrophy was marked at three months and numerous myelin bodies were
also seen. Although at two years the SER hypertrophy was not different
from controls, myelin bodies were still present.
An increase in microsomal enzymes was found in the 250 ppm group
together with an enlarged liver (relative to body weight) at six
months but not at two years. No adverse effects were observed in dogs
fed on 100 and 30 ppm diets (Coulston et al., 1970b).
Long-term studies
Rat. Groups of 50 male and 50 female rats were fed for two years on
diets containing 0, 15, 30 and 100 ppm bromopropylate. Five male and
five female rats from each group were killed after six months and one
year and autopsies performed. No changes in appearance or behaviour
occurred. Food consumption and weight gain were similar in test and
control animals throughout the test and survival rates were similar
for the first 18 months. Approximately half of these control female
animals alive at 18 months survived to 24 months while only a third of
test animals on 30 and 100 ppm levels survived over this period. No
alterations attributable to bromopropylate were observed in the
results of haematological examinations or serum analyses in test
animals. No changes in organ weights of gross or microscopic
abnormalities attributable to ingestion of the pesticide were observed
in animals examined at any time. However, EM studies on the livers of
animals of the 100 ppm group surviving two years showed slightly less
glycogen, focal enlargement of intracrestal space in the mitochondria,
focal dilatation of SER and more prominent lipid accumulations than
livers of control animals. These differences were not considered to be
significant pathological alterations in cell ultrastructure. The
number of tumours and their location were similar in control and test
groups (Coulston et al., 1970a).
Comments
Bromopropylate is absorbed rapidly and eliminated in both faeces
and urine. Faeces contain a high proportion of parent compound while
4,4'-dibromobenzilic acid and a more polar (unidentified) metabolite
are found in urine. A larger proportion of ingested compound was found
in the faeces of male than of female rats. Although the elimination of
a single dose was not complete by 120 hours in rats and about 2% of
the dose was detectable in tissues, mainly in the kidneys, liver and
fat at that time, there was no evidence that bromopropylate or its
metabolites are likely to accumulate in tissues.
Studies in rats and dogs show no ill-effect on reproductive
function and no teratogenic effect was seen in response to diets
containing 100 ppm bromobenzilate. The no-effect level in a two-year
rat study was 15 ppm in the diet. In female rats exposed to 30 or 100
ppm survival rates were reduced, but only during the last few months
of the test. Some abnormalities were observed in the EM appearance of
hepatic cells of rats receiving 100 ppm bromopropylate but the
toxicological significance of these is doubtful. Rats exposed to more
than 100 ppm showed a reduced rate of weight gain, reduced food intake
and increased weight of liver and kidneys. The increased liver weight
found in dog studies was accompanied by SER hypertrophy and an
increase in the activity of microsomal enzymes. Liver enlargement in
rats was also associated with histological appearance suggestive of
enzyme induction. Dietary levels of about 3000 ppm produced
pigmentation and marked fatty infiltration of hepatocytes and
degenerative changes in the kidneys and testes of rats. The no-effect
level in a two-year dog study was 100 ppm in the diet. The two-year
rat study did not indicate that bromopropylate has carcinogenic
activity.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Rat: 15 ppm in the diet equivalent to 0.75 mg/kg bw
Dog: 100 ppm in the diet equivalent to 2.5 mg/kg bw
Estimate of acceptable daily intake for man
0-0.008 mg/kg bw.
RESIDUES IN FOOD AND THEIR EVALUATION
Use pattern
Bromopropylate was first tested in the field for control of mites in
1966. The product is officially approved or in the process of
registration in the following countries:
Australia France Portugal
Austria Iran South Africa
Belgium Israel Spain
Bulgaria Italy Switzerland
Chile Japan Turkey
Cyprus Netherlands USSR
Yugoslavia
Commercial formulations are emulsifiable solutions containing 25%
and 50% active ingredient.
Pre-harvest treatments
Use recommendations.
Bromopropylate is a contact miticide effective against all stages
of mites such as Eriophyidae (eriphyid mites), Tenuipalpidae
(false spider mites) and Tetranychidae (spider mites) (Vial et al.,
1971).
Although the chemical does not have a pronounced ovicidal action,
it displays some activity on the early egg development stages, Newly
hatched larvae are killed by contact with the araricidal deposit on
the foliage.
Bromopropylate kills mites in all postembryonal stages, whether
they are susceptible or resistant to chlorinated hydrocarbons and/or
organic phosphate compounds (Westigard and Barry, 1970).
The main fields of application are in pome fruit citrus,
grapevines, hops and cotton. The recommended application rates in the
various crops are given in the following table.
The effective dosage rate per unit area depends on the amount of
foliage and on the size of the plants being treated: consideration
should be given to the foliage surface increase during the growing
period of the developing crop. Normally only one treatment would be
required if applied before mite populations build up and if climatic
conditions were unfavourable to mites. Under some circumstances it is
necessary to provide for a second treatment.
Post-harvest treatment
Bromopropylate is only recommended for application to growing
crops.
Other uses
Bromopropylate is also used on ornamental plants (dosage rate:
37.5-50 g ai/100 l).
Residues resulting from supervised trials
Pome fruits, stone fruits, grapevines, citrus, bananas,
strawberries, vegetables, cotton, tea and hops were treated in field
trials with the 25% and 50% ES formulations at recommended
concentrations of 25-60 g ai/100 l spray mixture. Residues were
determined by gas chromatography with an electron capture detector as
well as with a microcoulometric detector. The limits of detection
varied from 0.01-0.05 ppm. Data from residue trials conducted in
Australia, Canada, Germany, India, Indonesia, Israel, Japan, South
Africa, Switzerland and the United States of America are compiled in
Table 1.
TABLE 1. RECOMMENDED APPLICATION RATES OF BROMOPROPYLATE FOR
VARIOUS CROPS
Crop g ai/100 l g ai/ha
Pome fruit 37.5-50 500-750
Stonefruit 37.5-50 500-750
Citrus 37.5-50 500-750
Grapevines 37.5-50
Hops 37.5-50
Cotton 37.5-50 500-750
Soybeans 500-750
Vegetables 400-600
Tea 37.5
Fruits
Bromopropylate is a non-systemic and non-penetrating acaricide.
It remains on the peel and does not migrate into the pulp of the
fruits. Various experiments with labelled and non-labelled
bromopropylate in apples, citrus and bananas showed clearly that the
pulp of treated fruits contained none or only minute traces of
residues.
Higher dosages or multiple applications generally yield higher
residues, i.e. the quantity of residues soon after application is
proportional to the amount of active ingredient applied.
The dissipation of residues is mainly due to weathering and
growth dilution (Cassidy, 1967). Table 2 shows the residues of
bromopropylate immediately and three weeks after treatment and the
estimated half-life periods on different crops.
It is most noticeable that the level and rate of disappearance of
residues on distinctly different varieties of fruit are exceptionally
uniform. There is adequate justification for extending the tolerance
to include fruits on which there are only limited data.
TABLE 2. RESIDUES OF BROMOPROPYLATE AT VARIOUS TIMES AFTER TREATMENT
AND ESTIMATED HALF-LIFE PERIODS ON DIFFERENT CROPS
Average residues in ppm Half-life
Crop Immediately Three weeks period
after treatment after treatment (weeks)
Apples 1.8 1.0 3-4
Pears 0.7 0.36 3
Plums 1.7 0.75 3
Grapes 1.1 0.70 3
Strawberries 8.3 0.5 1-2
Citrus 1.8 0.9 3
Hops 13-50 4.4-27.0 2
Tea > 20 - <1
Vegetables
Residues of bromopropylate in tomatoes and eggplants were 0.12
ppm or less 7-21 days after a single treatment at normal use rates.
Cotton
Seed and fibres of cotton were analysed separately; in the seeds
no residues could be detected three days after treatment of the plants
with 50 g bromopropylate/100 l.
Tea
In trials in Indonesia each sample taken from tea plants on the
first, fourth, seventh and ninth day after spraying was divided into
two halves. Before residue analysis, one-half of each sample was
submitted to the usual process of manufacture (made tea) consisting of
withering, rolling, fermentation and firing of tea leaves; the second
half of each sample was merely dried at 25°- 30°C (dried leaves).
Residues of bromopropylate decreased rapidly on made tea as well as on
dried tea (within nine days of application from levels of 22.5-55 ppm
to levels of 0.15-2.5 ppm). The estimated half-life period is less
than one week.
Hops
Generally, residue levels are higher in dried than in fresh hops
due to concentration during the drying. Practically no evaporation of
bromopropylate takes place during drying.
Fate of residues
In animals
A cow received 14C-bromopropylate by capsule for five days at a
rate of 0.33 mg/kg/day, corresponding to 9.7 ppm in feed. Within 20
days the radio-activity recovered in faeces, urine and milk amounted
to 73.4%, 20.5% and 0.66% respectively. After the last dose, the
concentration of 14C-bromopropylate equivalents in milk approached
0.09 ppm and declined rapidly reaching the limit of quantitative
determination five days post treatment. Radio-activity showed
corresponding behaviour indicating a level of 0.03 ppm at the end of
the treatment period. Radio-activity was no longer detected after
another four days.
When the animal was killed, 20 days after treatment, only fat
contained significant radio-activity averaging 0.13 ppm of
bromopropylate equivalents. In all other tissues and organs (muscle,
liver, kidney, heart, brain, ovary, spleen) radioactivity was below
the limit of detection, i.e. 0.01 ppm (Cassidy et al., 1968).
The compound was fed during 30 and 70 days to milk cows (Fancher
et al., 1968d; Mattson et al., 1968) and to beef calves (Fancher et
al., 1968c; Cullen and Mattson, 1968); and the residues followed up in
milk, fat tissues, liver, kidney and muscle (see Table 3).
The residues in milk were found to be proportional to the feeding
levels of bromopropylate in the diet (Mattson et al., 1968) and did
not exceed 0.1 ppm at the 5.3 ppm dosage rate. Residues are mainly
found in the fatty tissue where they mounted to 2.8 ppm after 70 days
at the 5 ppm feeding rate. Bromopropylate is, however, rapidly
eliminated from fatty tissues: after two weeks following a 70-day
feeding at 50 ppm, only 0.3 ppm of bromopropylate could be found. In
muscle 0.19 ppm and 0.42 ppm bromopropylate were detected after
feeding 70 days at 5 ppm and 28 days at 50 ppm, respectively. Again a
rapid excretion of the compound was observed after cessation of
administration (<0.04 ppm two weeks after feeding for 70 days at
50 ppm).
In liver and kidney, 4,4'-dibromobenzilic acid was found in
addition to small amounts of unchanged bromopropylate. The presence of
4,4'-dibromobenzilic acid indicated that these organs may be the site
of hydrolysis of bromopropylate. The presence of 4,4'-dibromobenzilic
acid in the kidney was expected since it had also been found to be
excreted in the urine (Cullen and Mattson, 1968).
TABLE 3. RESIDUES IN MILK OF COWS AND TISSUES OF CALVES PER BROMOPROPYLATE AT VARIOUS RATES
FOR 30 AND 70 DAYS, RESPECTIVELY
Duration Residues in ppm
Animal Bromopropylate of treatment
ppma (days) Bromopropylate DBBAb
Milk cows 3 30 Milk: 0.06
5.3 0.10
11.7 0.18
54.8 0.84
After: 28 70 28 70c
(days)
Calves 5 70 Fat: 1.5 2.8 n.d.d n.d.
Muscle: <0.04 0.19 n.d. n.d.
Liver: 0.16 0.50 0.03 0.14
Kidney: 0.17 0.07 0.03 0.10
After: 28 84 28 84c
(days)
Calves 50 70 Fat: 7.3 0.3 n.d. n.d.
Muscle: 0.42 <0.04 n.d. n.d.
Liver: 0.04 <0.04 0.14 n.d.
Kidney 0.05 <0.04 0.13 n.d.
a Concentration in food.
b DBBA = 4,4'-dibromobenzilic acid.
c Days after first administration,
d n.d. = not detectable (<0.02).
In a study with calves which were kept on a diet containing 5 and
50 ppm bromopropylate for 70 days (Cullen and Mattson, 1968) residues
were determined in various tissues. Residues in muscle, liver and
kidney were of the order of 0.5 ppm but decreased to below the limit
of determination two weeks after the compound was withdrawn from the
feed. Residues in fat reached 8 ppm but declined to 0.3 ppm in 14 days
(see Table 4).
TABLE 4. RESIDUES IN TISSUES OF CALVES FED BROMOPROPYLATE WITH
THEIR DIET AT TWO RATES FOR 10 WEEKS
Residues found (ppm)
Tissue Weeks Bromopropylate DBBAa
analysed
5 ppm 50 ppm 5 ppm 50 ppm
fed fed fed fed
Fat 4 1.5 7.3 n.d.b n.d.
6 1.5 8.0 n.d. n.d.
10 2.8 - n.d. n.d.
12 -c 0.3 n.d. n.d.
Muscle 4 <0.04 0.42 n.d n.d.
6 0.22 0.13 n.d. n.d.
10 0.19 - n.d. n.d.
12 - <0.04 n.d. n.d.
Liver 4 0.16 0.04 0.03 0.14
6 0.12 0.11 0.08 0.50
10 0.50 - 0.14 -
12 - <0.04 - <0.02
Kidney 4 0.17 0.05 0.03 0.13
6 0.30 1.04 0.02 0.50
10 0.07 - 0.10 -
12 - <0.04 - <0.02
a DBBA = 4,4'-dibromobenzilic acid.
b n.d. = not detectable (<0.02).
c not analysed.
TABLE 5. RECOVERY OF RADIO-ACTIVITY AFTER APPLICATION OF
14C-BROMOPROPYLATE TO SOYBEAN LEAVES
Days after treatment 0 8 16
Radio-activity recovered 95.5% 83.9% 62.6%
In plants
Only slight translocation of bromopropylate was observed in
soybeans after topical application of the 14C-labelled compound to
the leaves (Hassan and Knowles, 1969). In this study an auto-radiogram
of a leaf prepared 39 days after treatment revealed that the bulk of
the radio-activity was still confined to this leaf and that only a
minute translocation took place into the petiole. Table 5 shows that
95.5, 83.9 and 62.2% of the applied radio-activity was recoverable
from these leaves, 0, 8 and 16 days after application.
The behaviour of 14C-bromopropylate was followed on apples,
apple leaves and in soil after spraying apple trees to run-off with 60
g active ingredient per 100 l spray mixture (Cassidy, 1968; Cassidy et
al., 1968), For residue determination, samples were taken
periodically until harvest 40 days after treatment. The study showed
that bromopropylate remains in the surface waxes of the apple peel and
does not penetrate into the pulp). This is clearly documented by the
photograph of an apple radio-autogram, (Cassidy, 1968a). Residue
levels compiled in Table 6 show only an insignificant amount of
bromopropylate in the pulp.
These traces of bromopropylate might be due to contamination by
the paring knife during the peeling procedure rather than to true
penetration of the compound into the pulp.
To determine whether any metabolites were present in or on apples
at harvest time, aliquots of peel and pulp extracts were
chromotographed on TLC-plates and then autoradiographed. Ninety per
cent. of the radio-activity was intact bromopropylate, about 2% proved
to have the Rf-value of 4,4'-dibromobenzilic acid. About 9% of the
radio-activity was not extractable, corresponding to a residue value
below 0.1 ppm, expressed as bromopropylate. No bromobenzoic acid,
4,4'-dibromobenzophenone, or 4,4'-dibromobenzohydrol were detected.
No significant loss of radio-activity from the apples occurred
during 40 days. The decrease in residue concentration was mainly due
to growth dilution; the values were initially 1.0-1.5 ppm and about
0.5 ppm at harvest. In an experiment (Cassidy, 1967) with a wax
coated, flask, streaked with a solution of 14C-bromopropylate and
then placed in a wind chamber (turbulent air flow), it could be shown
that the loss in bromopropylate by volatilization is practically
negligible. To determine whether degradation occurred on or in the
apple leaves, random samples were taken after various intervals (Table
6) from two sprayed trees. The leaves were extracted with acidified
acetone and water. The acetone was removed and the extract partitioned
between chloroform and water. The radio-activity was determined in
each phase of the stripping solution and in the residue of the
extraction. To characterize the radio-activity in the chloroform
fractions, aliquots were chromatographed on TLC. Leaves representing
each sampling interval were radio-autographed (Cassidy, 1968b).
TABLE 6. RESIDUES OF 14C-BROMOPROPYLATE IN AND ON APPLE FRUITS
AND LEAVES AT VARIOUS INTERVALS AFTER TREATMENT
ppm values equivalent to 14C-bromopropylate
Interval (days) 0 1 ´ 5 12 19 40
Whole apple 1.25 0.5
Peel 8.2 2.3 2.1 5.8
Pulp 0.06 0.03 0.02 0.08
Leaves of tree I 89.9 47.4 49.5 47.3 25 26.1
Leaves of tree II 108.6 69.5 69.3 46.4 19.8 15.3
In these radio-autograms the leaves, especially the veins, were
well outlined and even 40 days after application the radioactivity was
mainly confined to individual spots indicating that practically no
distribution had occurred (Cassidy, 1968b).
Immediately after spraying, average ppm levels of
14C-bromopropylate on leaves were about 100, whereas after 40 days
they were from 15 and 26. The radio-activity on leaves decreased
considerably. However, rain during the fifteenth and sixteenth day
after treatment was a main cause of its removal (see Table 6).
14C-bromopropylate is evidently more tenaciously held by waxes on the
surface of apple fruits than by waxes on the surface of leaves, as the
loss from apple fruits is very slow.
At harvest, 40 days after treatment, 94% of the remaining
radio-activity on apples was extractable with chloroform. The only
transformation product identified was 4,4'-dibromobenzilic acid and
this amounted to approximately 7%.
In soil
Residue studies were conducted in various types of soil after
direct application as well as after spraying fruit trees. Residues
extracted from soils 40 days after treatment with 14C-bromopropylate
consisted of up to 95% unchanged bromopropylate. The half life in
sandy soil was found to be approximately 60 days and in silt loam
approximately 30 days (Kahrs, 1969e, 1970, 1971).
In soil samples collected under apple trees treated with
14C-bromopropylate (Cassidy, 1968b) a large variation in
radioactivity occurred. The initial level of bromopropylate was about
0.04 ppm. Following heavy rain 40 days after treatment the average was
0.6 ppm. About 1-3% of the extractable radioactive residues were
identified as 4,4'-dibromobenzilic acid; 4,4'-dibromobenzohydrol and
4,4'-dibromobenaophenone were not detected in soil as was the case in
plants and animals. The unextractable radio-activity in soil remained
small, about 6-9% (Cassidy, 1968b, 1969, 1970).
In storage and processing
Fruit cooking
Fortified and field-sprayed apple samples were cooked for 15 and
30 minutes (Blass, 1973c) to determine the effect of cooking on the
residues. The untreated samples were fortified with 5 ppm
bromopropylate. The field treated apples had residues of 0.69 and 0.41
ppm. As indicated in Table 7, cooking for 15 minutes removed 50% or
more bromopropylate in both the fortified and the field-sprayed
samples. After 30 minutes cooking only about 20% of the compound could
be detected.
TABLE 7. RESIDUES OF BROMOPROPYLATE IN APPLES AFTER COOKING THE
FORTIFIED AND TREATED SAMPLES
Sample ppm ppm before Time of cooking ppm found
added cooking (minutes)
15 2.5
Fortified 5.0 5.0
30 1.3
15 0.27
0.67
30 0.10
Sprayed -
15 0.20
0.41
30 0.07
Tea - manufacture and brewing
The tea manufacturing process consisting of withering, rolling,
fermentation and firing the tea leaves has considerable effect on the
level of residues of bromopropylate on tea. A series of trials in
Indonesia showed that the manufacturing process reduced the levels to
35-40% of the level found after air-drying alone (19.5 ppm declined to
8.3 ppm).
Experiments in India showed that little, if any, of the
bromopropylate in tea leaves was extracted by the hot water in the
brewing process. The wet leaves after brewing contained almost the
same amount of residue as the same leaves before brewing.
Methods of residue analysis
Residues of bromopropylate can be determined by specific methods
utilizing gas chromatography and thin-layer chromatography.
Electron-capture detectors, microconlometric detectors and flame
ionization detectors have been successfully used (Geigy, 1968, 1968a,
1969; Cannizzaro et al., 1968).
For the determination of bromopropylate in hops and beer a more
rigid clean-up was developed (Geigy, 1968b). Residues of
bromopropylate in milk and animal tissues were determined by GLC using
electron capture detector (Geigy, 1968c).
National tolerances
Tolerances and waiting periods for bromopropylate in different
countries are compiled in Table 8. The values for tolerances and
waiting periods vary considerably from country to country for the same
crop, as a result of different climatic conditions, and differences in
agricultural practices - both factors influencing the rate of
dissipation of the residue.
TABLE 8. NATIONAL TOLERANCES AND WAITING PERIODS FOR BROMOPROPYLATE
ON PLANT PRODUCTS
Countries Crops Tolerance Waiting
(ppm) period
(days)
Australia Pome & stone fruits 5 21
Austria Pome & stone fruits -
horticultural crops - 21
Bulgaria General - 7
France Pome & stone fruits - 15
grapevines
Israel Citrus, grapevines, - 7
apples, pears,
vegetables
Japan Fruits, citrus, hops - -
TABLE 8. (Cont'd.)
Countries Crops Tolerance Waiting
(ppm) period
(days)
Netherlands Apples & pears 2 21
South Africa Bananas, 5 14
citrus, cotton 5 10
Spain Fruits - 15
Switzerland Pome & stone fruits 1.5 21
USSR Cotton - 20
Yugoslavia Field crops, fruits, - 7
vegetables, strawberries - 10
Appraisal
Bromopropylate (isopropyl-4-4'-dibromobenzilate) is a contact
miticide active against all stages of a wide range of mites. The main
fields of application are in pome and stone fruits, citrus,
grapevines, hops and cotton where it is applied at the rate of 37.5-50
g/100 l. It is registered for sale in more than 15 countries. The
properties and uses are in many ways similar to those of
chlorobenzilate and chloropropylate (FAO/WHO 1965b, 1969b, 1973b).
Commercial formulations are only emulsifiable solutions. The technical
grade contains a minimum of 88% isopropyl-4, 4'-dibromobenzilate. The
impurities have been identified and quantified.
Bromopropylate is only recommended for application to growing
plants. Usually one treatment is sufficient but multiple applications
are necessary in some instances. No post-harvest treatments are
approved and to date there are no uses on animals.
Bromopropylate is non-systemic and non-penetrating. It shows
remarkable residual effect against mites on leaves. It remains on the
peel and does not migrate into the pulp of fruits. The concentration
of residues is proportional to the amount of active ingredient
applied. Multiple applications have an additive effect and result in
higher residues. The dissipation of residues is mainly due to
weathering and growth dilution. The half-life period on most fruits is
three weeks though on leafy crops such as hops and tea the rate of
dissipation is much greater.
Extensive data were available from supervised field trials on
pome fruits, stone fruits, grapes, citrus, strawberries, bananas,
vegetables, cotton, hops and tea in 11 countries.
TABLE 9.
Application Interval between last treatment and sampling
(days)
Country Commodity Residues of bromopropylate in ppm
(year) Number of Dose g a.i./ analysed
Formulation treatment 100 l 0 7 14 21 28 35 42
APPLES
Switzerland 25E 1 37.5 Whole fruit 2.0 1.1 1.2 0.8 0.9 0.8
(1966) Peel 9.0
Switzerland 50E 1 25 Whole fruit 2.2 1.4 1.0 0.5 0.08
(1967) 50E 1 37.5 Whole fruit 2.9 0.8 0.7 0.6 0.15
South Africa 25E 1 37.5 Whole fruit 2.0 1.3 1.5
(1969)
USA 25E 1 30 Whole fruit 1.2 0.48 0.73 0.88 0.31 0.36
(Washington) 25E 1 60 Whole fruit 1.8 1.3 0.94 0.67 0.49 0.67
(1968)
Australia 30E 2 37.5 Whole fruit 1.85 1.07 1.15 1.01 0.77 0.77
(1970) 30E 1 75 Whole fruit 1.76 1.46 1.3 1.21 1.16 1.17
30E 2 37.5 Whole fruit 1.59 1.42 1.04 0.8 0.8 0.75
30E 2 75 Whole fruit 3.58 2.44 2.45 2.06 1.93 1.87
30E 2 50 Whole fruit 2.23 1.81 1.43 1.38 1.37 1.28 1.27
30E 2 50 Whole fruit 2.73 2.73 2.27 2.25 2.10 1.9 1.97
PEARS
Switzerland 25E 1 25 Whole fruit 0.7 0.5 0.5 0.4 0.4
(1967) 25E 1 37.5 Whole fruit 0.85 0.65 0.65 0.5 0.3
50E 1 25 Whole fruit 0.5 0.5 0.35 0.25 0.4
50E 1 37.5 Whole fruit 0.85 0.55 0.3 0.3 0.6
TABLE 9. (Cont'd.)
Application Interval between last treatment and sampling
(days)
Country Commodity Residues of bromopropylate in ppm
(year) Number of Dose g a.i./ analysed
Formulation treatment 100 l 0 7 14 21 28 35 42
Switzerland 25E 1 37.5 Whole fruit
(1971)
South Africa 50E 1 75 Whole fruit 2.0 1.0 1.0
(1969)
BANANAS 50E 1 25 Peel 5.6
South Africa Pulp 0.19
(1968)
GRAPES
Switzerland 50E 1 25 Whole fruit 1.0 0.9 1.1 0.8 0.4 0.2 0.2
(1967) 37.5 Whole fruit 1.2 1.2 1.5 2.1 1.8 0.4 0.4
25E 1 25 Whole fruit 0.7 0.8 0.4 0.4 0.15
25E 1 37.5 Whole fruit 0.6 1.0 0.5 0.5 0.4
50 1 25 Whole fruit 0.7 0.8 0.4 0.3 0.2
50 1 37.5 Whole fruit 0.9 0.9 0.7 0.6 0.3
25E 1 25 Whole fruit 0.9 1.1 0.9 0.5 0.7 0.4 0.4
25E 1 37.5 Whole fruit 1.3 1.0 1.0 0.9 0.7 0.6 0.5
Israel 50E 1 75 3.4 1.5
(1972)
GRAPEFRUIT
USA 25E 1 30 Whole fruit 1.1 1.2 1.3 1.3
(California) 25E 1 60 Whole fruit 1.3
(1968)
LIMES
USA 25E 3 30 Whole fruit 0.96 1.5 1.4 0.96
TABLE 9. (Cont'd.)
Application Interval between last treatment and sampling
(days)
Country Commodity Residues of bromopropylate in ppm
(year) Number of Dose g a.i./ analysed
Formulation treatment 100 l 0 7 14 21 28 35 42
(Florida) 25E 3 60 Whole fruit 2.7 2.5 2.8
(1968) 25E 3 + oil 60 Whole fruit 3.0 3.3 2.9
ORANGES
Israel 50E 1 25 Peel 1.9 1.4 1.65 1.65
(1973) Pulp 0.05 0.055 <0.04 0.045
PEACHES
Australia 30ES 1 airblast 50 Whole fruit 3.1 2.02 1.36 1.21 1.13 0.5
(1970) 30ES 1 hand spray 50 Whole fruit 6.9 3.8 2.58 1.61 1.13 0.7
30ES 1 airblast 37.5 Whole fruit 2.86 1.35 0.70 0.66 0.79 0.3
30ES 1 airblast 37.5 Whole fruit 1.68 1.00 0.92 0.71 0.54 0.51
PLUMS
Switzerland 25E 1 25 Whole fruit 2.1 1.1 0.8 0.7 1.2 0.7
(1967) 25E 1 37.5 Whole fruit 1.9 2.3 1.4 1.0 1.4 0.6
50E 1 25 Whole fruit 1.4 0.4 0.8 0.6 0.4 0.3
50E 1 37.5 Whole fruit 1.7 1.4 0.8 0.7 0.5 0.3
25E 1 37.5 Whole fruit 1.5 1.2 0.7
STRAWBERRIES
USA - 2 60 Fruits 8.3
(Florida)
(1969)
TABLE 9. (Cont'd.)
Application Interval between last treatment and sampling
(days)
Country Commodity Residues of bromopropylate in ppm
(year) Number of Dose g a.i./ analysed
Formulation treatment 100 l 0 7 14 21 28 35 42
TOMATOES
Israel 50E 1 1 kg a.i./ha Whole fruit <0.10 0.11 <0.10
(1971) 0.12 <0.10 0.10
EGG-PLANTS
Israel 50E 1 1 kg a.i./ha Fruits <0.1 <0.1 <0.1
(1971) <0.1 <0.1 <0.1
3 9 14 16
COTTON
South Africa 50E 1 50 Seed <0.02 <0.02 <0.02
(1968) Fibres 0.22 0.06 0.11
0 1 4 7 9 14 15 21 26 37
TEA
Indonesia 50E 1 18.75 Dried leaves 22.5 19.5 1.7 0.15
(1968) Manufactured 30.0 8.3 3.8 2.5
50E 1 37.5 Dried leaves 55.0 20.5 19.5 0.5
Manufactured 7.8 4.9 0.36
TABLE 9. (Cont'd.)
Application Interval between last treatment and sampling
(days)
Country Commodity Residues of bromopropylate in ppm
(year) Number of Dose g a.i./ analysed
Formulation treatment 100 l 0 1 4 7 9 14 15 21 26 37
HOPS
Germany 25E 1 25 Fresh 12.8 10.7 6.0 3.9
(1967) 25E 1 25 Dried 56.5 38.0 27.0 27.4
25E 1 25 Fresh 13.0 8.6 5.8 4.8
25E 1 25 Dried 43.0 32.0 32.0 27.4
The rate of dissipation has been measured by chemical analysis as
well as with radio-labelled compound and it is evident that
volatilization is not significant. Rain is an important factor in
reducing residues but this affects leaves more than fruit, no doubt
due to the protective effect of the heavier wax layers on fruits.
The residues at harvest are principally the parent compound with
approximately 7% being 4,4'-dibromobenzilic acid. No bromobenzoic
acid, 4,4'-dibromobenzophenone or 4,4'-dibromobenzohydrol could be
detected.
Studies were available to show the fate of residues in soil,
animals, and in fruit, vegetables and plant materials subjected to
processing.
Following application to soil, bromopropylate is slowly leached
throughout the top 10 cm. After 40-60 days the residue extracted from
both sandy soil and loam consists of unchanged bromopropylate. The
half-life in arable soil is of the order of 60 days.
When fed to dairy cows at rates corresponding to 5-55 ppm in the
ration, bromopropylate residues were found in milk though even at the
highest level the residue did not exceed 1 ppm. Following withdrawal
of the chemical from the feed residues in milk declined below limit of
detection in seven days. Calves fed bromopropylate accumulated
significant amounts in fat but only small quantities in muscle, kidney
and liver. Accumulated residues disappeared within 14 days of
withdrawing the chemical from rations.
Cooking removed 50% of residues on apples in 15 minutes and 80%
in 30 minutes. No residues could be detected in brewed tea or beer
made from tea leaves and hops respectively containing residues at the
highest level likely to be encountered in practice.
Analytical methods specific to bromopropylate are available.
These use GLC with either electron capture, microcoulometric or flame
ionization detectors. In the hands of those who developed the methods,
the limit of determination was reported to be from 0.01 to 0.05 ppm.
National tolerances have been established in only three
countries.
RECOMMENDATIONS
Approved uses of bromopropylate will give rise to unavoidable
residues which will decline slowly between application and harvest.
However, following good agricultural practice, including waiting
periods of the following order, the residues at harvest will not
exceed the following limits which are recommended as maximum residue
limits for the specified commodities moving in trade. Where single
treatments are adequate to control mite infestations, residues will be
considerably less.
No significant loss of residues is expected during storage or
shipping. Preparation and processing will reduce residue levels
considerably so that food as consumed will contain only a fraction of
the amount of residues indicated.
Based on interval
Tolerances (days)
(ppm) from application
to harvest
Apples, bananas (whole), 5 21
cherries, citrus, grapes,
nectarines, peaches, pears,
plums, prunes
Strawberries 5 14
Hops (dried) 5 56
Tea (manufactured) 5 8
Vegetables, cotton seed 1 14
Banana (pulp), citrus pulp 0.2 21
FURTHER WORK OR INFORMATION
Desirable
1. Studies to elucidate the effects on survival rate of rats
on long-term feeding.
2. Long-term studies in a second species of animal.
3. Studies on the effects of bromopropylate on the liver.
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