CHLORMEQUAT
First draft prepared by
M. Watson,
Pesticides Safety Directorate,
Ministry of Agriculture, Fisheries and Food,
York, United Kingdom
Explanation
Evaluation for acceptable daily intake
Biochemical aspects
Absorption, distribution and excretion
Biotransformation
Effects on enzymes and other biochemical parameters
Toxicological studies
Acute toxicity
Short-term toxicity
Long-term toxicity and carcinogenicity
Reproductive toxicity
Embryotoxicity and teratogenicity
Genotoxicity
Special studies
Skin and eye irritation and skin sensitization
Observations in humans
Comments
Toxicological evaluation
References
Explanation
Chlormequat (2-chloroethyltrimethylammonium chloride) was
evaluated by the Joint Meeting in 1970 and 1972 (Annex I, references
14 and 18). In 1972, an ADI of 0.05 mg/kg bw was established on the
basis of the NOAEL in a study of reproductive toxicity in rats. The
compound was reviewed at the present Meeting as a result of the CCPR
periodic review programme. This monograph summarizes new data on
chlormequat and studies that were not reviewed previously; it also
includes relevant data from the previous monograph and monograph
addendum on this pesticide (Annex I, references 15 and 19).
Evaluation for acceptable daily intake
1. Biochemical aspects
(a) Absorption, distribution and excretion
Experiments are described in articles published in the open
literature in which the absorption, distribution and excretion of
chlormequat were investigated. The level of detail in these papers
did not permit a complete evaluation by the present Meeting. In the
first study, the bulk (60.6%) of an oral dose of 14C-chlormequat
administered to male rats was excreted in the urine within 4 h, and
96% was eliminated within 46.5 h; faecal excretion accounted for
2.3%, and less than 1% was expired as 14C-carbon dioxide. The
remainder was found in the tissues, with the largest amounts in the
carcass (0.25%), intestines (0.11%) and liver (0.08%). Analysis of
urine samples by four different thin-layer and paper chromatographic
systems showed that all of the radiolabel was in chlormequat (Blinn,
1967).
In a second study, rats were administered a single (60 mg) oral
dose of 15N-chlormequat or received 2 mg of the labelled compound
daily for 100 days. After the single dose, the amount of compound in
the brain decreased quickly, but there was considerable accumulation
in the kidneys over the 20 days of the investigation. After
continuous administration, chlormequat was found particularly in
active muscles such as those of the heart and diaphragm (Bier &
Ackermann, 1970).
In a third study, a lactating cow received a single oral dose
of 1000 mg of 15N-chlormequat. The compound was found in the milk
and urine 3 h after administration; most (489 mg) was found 15-39 h
after administration. Only 22 mg were excreted in the milk, and the
concentration never exceeded 1 ppm; the peak concentration was found
12-60 h after administration (Lampeter & Bier, 1970).
(b) Biotransformation
It was reported in a short published article that only
chlormequat and two other compounds, which may have been other salts
of chlorcholine, occurred in the urine of rats that had received 200
mg/kg bw of chlormequat orally. Choline itself was not identified
(Bronisz & Romanowski, 1968).
(c) Effects on enzymes and other biochemical parameters
General pharmacological tests were carried out to determine the
physiological effects of chlormequat injected intravenously.
Oligopnoea, salivation and a tendency to inhibition of intestinal
propulsion were observed in mice immediately after they were dosed
with 7.4 mg/kg bw. In cats, there was mild inhibition of the
vasopressor effect of norepinephrine 30 min after administration of
1 mg/kg bw. In rabbits, neuromuscular junctions were blocked by
doses of 1 mg/kg bw and more; this effect was counteracted by
administration of 10 mg/kg bw of D-tubocurarine and potentiated by
administration of 1 mg/kg bw neostigmine. Coagulation of rat blood
was unaffected by concentrations of up to 3 mg/ml. In dogs, doses of
3 mg/kg bw and more caused a drop in blood pressure; at higher
doses, increased respiratory and heart rates were observed. These
effects were mitigated by prior intravenous administration of 1
mg/kg bw atropine (Mutoh et al., 1987).
The action of chlormequat was tested in vitro with the patch
clamp technique for electrophysiological measurements described by
Hamill et al. (1981). Muscles were excised from the feet of adult
NMRI mice and dissociated enzymatically to obtain individual muscle
cells. Chlormequat (purity, 95.6%) activated the nicotinic
acetylcholine receptor channel at all concentrations between 10 and
100 mmol/l (Franke & Mellert, 1991).
The affinity of chlormequat for subtypes of muscarinic
acetylcholine receptors was investigated in vitro on membranes
from bovine cerebral cortex, from rat heart and from rat
submaxillary gland. The results were compared with those obtained
for subtype-specific reference substances, and atropine was included
as a high-affinity reference compound with no subtype selectivity.
Chlormequat had low affinity for the muscarinic receptors in
comparison with the reference substances (Weifenbach, 1991).
2. Toxicological studies
(a) Acute toxicity
Clinical signs of toxicity seen after treatment with
chlormequat (Table 1) generally consisted of salivation, writhing,
chromodaccryorrhoea, decreased activity, tremors, diuresis and
piloerection. Mortality generally occurred within 24 h of treatment;
animals that survived recovered within 48 h. The findings at autopsy
were not consistent or related to treatment.
Rabbits and dogs may be more sensitive to the toxic effects of
chlormequat than rats and mice. The acute toxicity in monkeys was
similar to that seen in rats and mice.
Table 1. Acute toxicity of chlormequat
Species Route LD50 or LC50 Purity Reference
(mg/kg bw or (%)
mg/l air)
Mouse Oral 215-1020 NR Oettel, 1965
NR Levinskas & Shaffer, 1966
NR Ignatiev, 1967
98.0 Hattori, 1981
Mouse Intraperitoneal 60-68 NR Shaffer, 1970
98.0 Hattori, 1981
Mouse Subcutaneous 88-92 98.0 Hattori, 1981
Rat Oral 330-750 NR Oettel, 1965
NR Levinskas & Shaffer, 1966
NR Ignatiev, 1967
NR Stefaniek, 1969
98.1 Hattori, 1981
Rat Oral 522 66.1a Fischer & Lowe, 1990
Rat Intraperitoneal 53-75 98.1 Hattori, 1981
Rat Subcutaneous 113-118 98.1 Hattori, 1981
Rat Dermal > 4000 NR Gelbke & Freisberg, 1978
Rat Dermal > 5000 98.1 Hattori, 1981
Rat Inhalation > 5.2 99 Zeller & Klimisch, 1979
Rat Inhalation > 4.6 66.1 Hershman, 1990
Hamster Oral 1070 NR Levinskas & Shaffer, 1966
Guinea-pig Oral 215-620 NR Oettel, 1965
NR Levinskas & Shaffer, 1966
Table 1 (contd)
Species Route LD50 or LC50 Purity Reference
(mg/kg bw or (%)
mg/l air)
Rabbit Oral 60-81 NR Oettel, 1965
NR Levinskas & Shaffer, 1966
Rabbit Dermal 1250 66.1a Fischer et al., 1990a
Cat Oral 7-50 NR Oettel, 1965
NR Levinskas & Shaffer, 1966
Dog Oral < 50 NR Levinskas & Shaffer, 1966
Sheep Oral 150-200 NR Schulz et al., 1970
Monkey Oral > 800 NR Costa et al., 1967
NR, not reported
a Technical material consisting of 66.1% aqueous solution
(b) Short-term toxicity
Rats
Two studies of short-term toxicity are described in the 1972
JMPR monograph addendum (Annex I, reference 19), but detailed
reports were not available for evaluation at the present Meeting.
The summary of the first study states that groups of 10 male rats
were fed chlormequat at dietary levels of 0, 500, 1000 or 2000 ppm
(equivalent to 25, 50 or 100 mg/kg bw per day) for 29 days. There
was no mortality and no clinical signs of reaction to treatment;
body-weight gain and food intake remained undisturbed by treatment,
and no gross pathological changes were observed at termination of
the study (Levinskas & Shaffer, 1962).
In the second study, groups of 20 male and 20 female rats were
fed chlormequat at dietary levels of 0, 200, 600 or 1800 ppm
(equivalent to 10, 30 or 90 mg/kg bw per day) for 90 days. There was
no mortality and no clinical signs of reaction to treatment, and no
treatment-related changes in blood chemistry were seen. Body-weight
gain of males fed 1800 ppm was slightly depressed in comparison with
that of controls. Slightly increased kidney weights were recorded in
treated female rats and slightly increased liver weights in treated
males, particularly at 1800 ppm; however, histopathological
examination of major organs revealed no treatment-related changes
(Levinskas, 1965).
In a recent experiment of acceptable scientific quality, groups
of five male and five female Wistar rats were fed chlormequat at
dietary levels of 0, 500, 1500, 3000 or 4500 ppm (equal to 46, 137,
274 or 411 mg/kg bw per day) for four weeks. The test material was a
66.7% technical formulation, but the dietary levels were expressed
as pure chlormequat. Clinical signs of general deterioration in
health were seen in males and females receiving 4500 ppm and,
temporarily, in one male and one female receiving 3000 ppm. Reduced
body-weight gain and food intake were seen in animals fed 4500 ppm,
and slightly reduced weight gain was seen among those fed 3000 ppm.
Serum creatinine levels in males and females receiving 4500 ppm and
in females receiving 3000 ppm were lower than those of controls.
Decreased serum concentrations of total protein (in males) and of
urea (in females) were also seen at the high dietary level.
Examinations of locomotor activity, swimming tests, gross
pathological examinations, organ weight analysis and
histopathological examination revealed no reaction to treatment. The
NOAEL was 1500 ppm, equal to 137 mg/kg bw per day (Schilling et
al., 1990).
Rabbits
In a recent experiment of acceptable scientific quality, groups
of 10 male and 10 female New Zealand white rabbits received
chlormequat (purity, 99%) by repeated, occluded dermal applications
on shaven skin, five days per week for three weeks at doses of 0,
20, 50 or 150 mg/kg bw per day. Possible reactions to treatment at
the application site were limited to erythema during the first two
weeks of the study; however, these reactions, were no more severe
than reactions frequently seen after repeated, dermal, occluded
applications of control compounds. There were no other clinical
signs of reaction to treatment, and body-weight gain and food intake
remained undisturbed by treatment. Investigations of haematological
parameters and blood chemistry, gross pathology, organ weight
analysis and histopathology revealed no reaction to treatment (Buch
& Finn, 1981).
Dogs
In an experiment for which no detailed report was available to
the Meeting for evaluation (Annex I, reference 19), groups of two
male and two female dogs were fed chlormequat at dietary levels of
0, 20, 60 or 180 ppm (equivalent to 0.5, 1.5 or 4.5 mg/kg bw per
day) for 106-108 days. There were no deaths and no clinical signs of
reaction to treatment, and body-weight gain and food intake were
unaffected. Organ weight analysis and histopathology at termination
of the experiment revealed no treatment-related changes (Levinskas,
1965).
In a study reported in 1967, which was not conducted to
currently acceptable scientific standards, groups of three male and
three female beagle dogs were fed chlormequat (technical grade
purified twice by recrystallization) at dietary levels of 100, 300
or 1000 ppm (equivalent to 2.5, 7.5 or 25 mg/kg bw per day) for two
years; groups of 10 males and 10 females served as controls.
Excessive salivation and hind limb weakness were seen in some
animals receiving 1000 ppm; in this group, one male died after 22
days, and one female died after 38 days. The deaths were considered
by the authors of the report to be secondary to the clinical signs
of hind-limb weakness. Analysis of blood chemistry and urinalysis
revealed no treatment-related changes, other than the presence of
chlormequat in the urine of treated animals. At termination, gross
pathology, organ weight analysis and histopathology revealed no
changes attributable to treatment. The NOAEL was probably 300 ppm
(equivalent to 7.5 mg/kg bw per day), but the lack of further
investigation into the signs of hind-limb weakness precluded
establishment of a definitive NOAEL (Oettel & Sachsse, 1967).
(c) Long-term toxicity and carcinogenicity
Mice
In a study reported in 1971, the design of which was clearly
not in accordance with currently acceptable scientific standards,
groups of 52 male and 52 female CFLP mice were fed chlormequat
(purity, about 98.5%) at dietary levels of 0 or 1000 ppm (equivalent
to 150 mg/kg bw per day) for 78 weeks. Survival was unaffected, and
there were no clinical signs of reaction to treatment, except that
treated animals gained less weight than controls. Histopathological
examination was initially restricted to 10 males and 10 females from
each group but was extended to all animals with respect to tissues
in which a treatment-related effect was seen. The incidence of
benign lung tumours was higher (20 out of 52) in treated males than
in controls (10 out of 51), but the incidence was considered to be
within the normal range in untreated mice. The incidences of lung
tumours in females and of tumours in all other organs examined in
animals of each sex were not significantly higher in the treated
group than in controls (Weldon et al., 1971).
Groups of 50 male and 50 female B6C3F1 mice were administered
diets containing chlormequat (purity, 97-98%) at 500 or 2000 ppm
(equal to 70 or 286 mg/kg bw per day) for 102 weeks. The dietary
levels were set on the basis of the results of an eight-week
subchronic study with 1200-20 000 ppm designed to provide a
statistical estimate of the dose that would depress body-weight gain
by 10%. The control group consisted of 20 males and 20 females.
Body-weight gain remained largely unaffected by treatment, and there
were no treatment-related clinical signs. Survival was unaffected by
treatment and was adequate for assessment of carcinogenicity, as at
least 80% of animals in each group survived until termination of the
experiment. The incidence of haemangiomas and haemangiosarcomas was
slightly increased in treated females (1/20 in controls, 4/50 at 500
ppm and 5/50 at 2000 ppm), but the authors of the report concluded
that there was no clear evidence for the carcinogenicity of
chlormequat in these mice (National Cancer Institute, 1979).
Rats
The Meeting reviewed a short summary of a two-year study
reported in 1967, the design of which was not in accordance with
contemporary scientific standards. Groups of 50 male and 50 female
Sprague-Dawley rats were fed chlormequat (technical grade, purified
twice by recrystallization) at dietary levels of 0, 500 or 1000 ppm
(equivalant to 25 or 50 mg/kg bw per day) for two years. The authors
reported that survival was unaffected, there were no clinical signs
of reaction to treatment and food intake and body-weight gain
remained undisturbed by treatment. Haematological examinations,
analysis of blood chemistry and urinalysis carried out after three
and 12 months and before termination revealed no reaction to
treatment. Gross pathological examination, analyses of liver and
kidney weights and histopathological examination revealed no
abnormalities attributable to treatment. Normal, age-related
pathological changes were seen; in particular, the tumour profile in
treated and control animals was indistinguishable. Detailed
evaluation of this report was not possible (Oettel & Froberg, 1967).
A similar summary was available of another long-term study in
which groups of 50 male and 50 female Sprague-Dawley rats were fed
diets containing chlormequat (technical grade purified twice by
recrystallization) and choline chloride in a ratio of 10:7 for two
years. The dietary levels of chlormequat were 0, 500, 1000 or 5000
ppm (equivalent to 25, 50 or 250 mg/kg bw per day). The control
group consisted of 100 male and 100 female rats. Survival was
unaffected by treatment; the survival rates after two years were
72-82% in male rats and 48-64% in females. There were no clinical
signs of reaction to treatment, and body-weight gain and food intake
remained undisturbed. Haematological examination, limited analyses
of blood chemistry and urinalysis carried out after three and 12
months and before termination revealed no indication of any reaction
to treatment. Gross pathological examination, analysis of liver and
kidney weights and histopathological examination of a range of
organs and tissues revealed no abnormalities attributable to
treatment. Normal, age-related pathological changes were seen; in
particular, the tumour profile in treated and control animals was
indistinguishable (Oettel & Sachsse, 1974).
In a study designed to assess the tumorigenicity of chlormequat
in rats, groups of 50 male and 50 female Fischer 344 rats were
administered diets containing chlormequat (purity, 97-98%) at 1500
or 3000 ppm (equivalent to 75 or 150 mg/kg bw per day) for 108
weeks. The dietary levels were set on the basis of the results of an
eight-week subchronic study with 3150-14 700 ppm designed to provide
a statistical estimate of the dose that would depress body-weight
gain by 10%. The control group consisted of 20 males and 20 females.
Body-weight gain of treated rats was slightly lower than that of
controls, but there were no treatment-related clinical signs.
Survival was unaffected by treatment and was adequate for assessment
of carcinogenicity, as at least 64% of animals in each group
survived until termination of the experiment. The incidence of
leukaemia or malignant lymphoma was slightly increased in treated
females (3/20 in controls, 11/50 at 1500 ppm and 14/50 at 3000 ppm),
and there was an apparently dose-related increase in the incidence
of islet-cell adenomas of the pancreas in treated males (0/18 in
controls, 1/47 at 1500 ppm and 7/45 at 3000 ppm), but the authors of
the report concluded that there was no clear evidence for the
carcinogenicity of chlormequat in these rats (National Cancer
Institute, 1979).
(d) Reproductive toxicity
In a study conducted between 1965 and 1967 which was not in
accordance with currently acceptable scientific standards, groups of
20 male and 20 female rats received diets containing chlormequat at
0, 100, 300 or 900 ppm (equivalent to 5, 15 or 45 mg/kg bw per day)
throughout three generations. No abnormalities were seen in the
appearance, behaviour, food intake, body-weight gain, fertility,
gestation, lactation or viability of the offspring, and no fetal
malformations occurred that could be attributed to treatment.
Histopathological examination of 10 rats of each sex of the F3
generation in each dose group after nine weeks of treatment revealed
the presence of giant cells in the testicular tubules of four rats
treated with 900 ppm and two treated with 300 ppm. The authors
suggested that the cells were an expression of delayed maturation
during spermatogenesis; however, the Meeting found it difficult to
assess the significance of the finding and concluded that the NOAEL
was 100 ppm, equivalent to 5 mg/kg bw per day (Leuschner et al.,
1967).
(e) Embryotoxicity and teratogenicity
Mice
The results of three experiments in mice were summarized in the
1972 monograph addendum (Annex I, reference 19), but detailed
reports were not available for evaluation by the present Meeting. In
the first experiment, groups of pregnant mice received
intraperitoneal injections of chlormequat at 30 mg/kg bw on days 14
and 15 or days 11-15 of gestation. Another group of mice received
200 mg/kg bw per day by gavage on days 11-15 of gestation. All mice
were sacrificed on day 19. The number of fetuses per dam, fetal
size, frequency of resorptions and incidence of malformations were
similar in the test and control groups. In the second experiment,
pregnant mice were fed chlormequat at dietary levels of 0, 1000 or
10 000 ppm (equivalent to 150 or 1500 mg/kg bw per day) on days 1-15
of gestation or 25 000 ppm (equivalant to 3750 mg/kg bw per day) on
days 11-15. All animals were sacrificed on day 19. The number of
fetuses per dam, fetal size and frequency of resorptions were
similar in the test and control groups. Dams fed 10 000 or 25 000
ppm had a slightly greater number of malformed fetuses than
controls. In the third experiment, groups of mature male and female
mice were fed chlormequat at dietary levels of 0, 1000 or 5000 ppm
(equivalent to 150 or 750 mg/kg bw per day) and mated after 1, 3, 4
and 10 weeks. All mice were killed on day 19 of gestation. Feeding
of chlormequat was found to have no effect on the fertility of the
mice, and no evidence of teratogenicity was seen in the offspring
(Shaffer, 1970).
Rats
In a study described in the 1972 monograph addendum (Annex I,
reference 19), groups of pregnant rats were fed chlormequat at
dietary levels of 0, 1000 or 5000 ppm (equivalent to 50 or 250 mg/kg
bw per day) on days 1-21 of gestation. When the animals were
sacrificed the day before parturition, no teratogenic effects were
observed (Shaffer, 1970).
Hamsters
In a report published in the literature, groups of eight
pregnant Syrian golden hamsters were given chlormequat (purity
unspecified) by gavage at levels of 0, 25, 50, 100, 200, 300 or 400
mg/kg bw once on day 8 of gestation. Another group received 100
mg/kg bw daily on days 7, 8 and 9 of gestation. The control group
consisted of 15 animals. Clinical signs of toxicity were seen in the
groups receiving the higher doses. All animals were sacrificed on
day 14 of gestation. Animals fed 100 mg/kg bw or more had fewer
fetuses than controls and more fetal resorptions. In animals fed 200
mg/kg bw or more, fetal size and weight were reduced. No
abnormalities were observed in animals treated with a single dose of
0, 25, 50 or 100 mg/kg bw. Malformations (including anophthalmia,
microphthalmia, cleft palate and polydactylism) and evidence of
developmental retardation were seen in the offspring of dams treated
with three doses of 100 mg/kg bw or a single dose of 200, 300 or 400
mg/kg bw. The limited details presented in the publication make it
difficult to assess the occurrence of maternal toxicity; historical
data on the occurrence of malformations in controls were not
presented (Juszkiewicz et al., 1970).
Rabbits
In a study described in the 1972 monograph addendum (Annex I,
reference 19), groups of pregnant rabbits were fed diets containing
chlormequat at 0 or 1000 ppm (equivalent to 30 mg/kg bw per day) on
days 1-28 of pregnancy and were killed two days before parturition.
No evidence of teratogenicity was seen (Shaffer, 1970).
In a study of acceptable design, groups of 15 inseminated
female Himalayan rabbits were given chlormequat at 0, 1.5, 3, 6 or
12 mg/kg bw per day by gavage on days 6-18 of gestation. Fetuses
were delivered by caesarian section after sacrifice of the dams on
day 28 of gestation and were examined for abnormalities
macroscopically and by X-ray. In addition, the heads of all fetuses
were fixed in Bouin's solution, and transverse sections were
assessed. Treatment did not affect mortality. Rapid breathing,
salivation and apathy were seen on single occasions in single
animals receiving 6 or 12 mg/kg bw per day; body-weight gain of
animals given 12 mg/kg bw per day was reduced temporarily, and food
intake was temporarily depressed in all treated groups. Treatment
had no effect on the number of fetuses, conception rate, resorption
rate, size or weight of the fetuses or placental weights. No
teratogenic effect was seen. Minor variations and developmental
retardation were seen to the same extent in all groups, including
controls. The NOAEL for maternal toxicity was thus 6 mg/kg bw per
day, while there was no evidence of fetotoxicity or teratogenicity
at the highest dose tested, 12 mg/kg bw per day (BASF, 1979).
(f) Genotoxicity
The results of tests for the genotoxicity of chlormequat are
summarized in Table 2.
All of the assays for gene mutation carried out in bacteria and
mammalian cells gave negative results. No cytogenetic anomalies were
found in human lymphocytes in vitro, and unscheduled DNA synthesis
was not seen in rat hepatocytes. Neither dominant lethal mutation
nor micronuclei were seen in mice in vivo, and no chromosomal
aberrations occurred in rats.
(g) Special studies
Skin and eye irritation and skin sensitization
The irritancy of chlormequat chloride to the skin was tested in
Vienna white rabbits. About 0.5 ml of the test material (purity
unspecified) was applied to intact and abraded sites on each of six
rabbits and left in place for 24 h under an occlusive dressing. At
the intact sites, erythema and oedema were observed at the end of
the application period, but these signs were almost fully reversed
within two days. More severe signs were observed at the abraded
sites; the signs were only partly reversible, and superficial
necrosis was seen in three animals after three days (Gelbke, 1978).
About 500 mg of the same material were tested in the same way
in New Zealand white rabbits. Dermal reaction at the treatment sites
was limited to very slight or well-defined erythema, which was
evident only at the end of the application period. All reaction had
resolved completely within 72 h of treatment (Buch & Gardner, 1980).
In another experiment in New Zealand white rabbits, about 0.5
ml of chlormequat chloride (a technical material consisting of a
66.1% aqueous solution) was applied to intact sites on each of six
rabbits and left in place for 4 h under an occlusive dressing.
Dermal reaction at the treatment sites was limited to barely
perceptible or slight erythema, which was evident in three animals 1
h after treatment and in one animal at 24 h. All reaction had
resolved completely within 48 h of treatment (Fischer et al.,
1990b).
Table 2. Results of tests for the genotoxicity of chlormequat
End-point Test system Concentration Purity Results Reference
of chlormequat (%)
In vitro
Reverse S. typhimurium TA98, Up to 5000 µg/plate 66.1b Negative Traul & Mulligan, 1990
mutationa 100,1535, 1537, 1538
E. coli WP2uvr A-
Reverse S. typhimurium TA98, Up to 2500 µg/plate 92.4 Negative Zeller & Engelhardt, 1979
mutationa 100, 1535, 1537, 1538
Reverse Chinese hamster ovary Up to 5000 µg/ml 66.1b Negative Traul & Johnson, 1990
mutationa cells, hprt locus
Reverse Chinese hamster V79 Up to 5000 µg/ml 94.5-98.9 Negative Debets et al., 1986
mutationa cells, hprt locus
Chromosomal Human lymphocytes Up to 5000 µg/ml 94.5-98.9 Negative Enninga et al., 1987
aberrationsa
Unscheduled Rat hepatocytes Up to 7.5 µl/ml 66.1b Negative Pant & Law, 1990
DNA synthesis
Unscheduled Rat hepatocytes Up to 10 000 nl/ml 72c Negative Cifone & Myhr, 1987
DNA synthesis
Table 2 (contd)
End-point Test system Concentration Purity Results Reference
of chlormequat (%)
In vivo
Dominant lethal Male NMRI mice 1 x 261 mg/kg bw 99.6 Negative Gelbke & Engelhardt,
mutation 1979
Micronucleus Male and female Up to 2 x 202.5 94.5-98.9 Negative Geunard et al., 1983
formation NMRI mice mg/kg bw
Chromosomal Male and female Up to 1 x 500 66.1 Negative Sharma & Caterson, 1991
aberration Sprague-Dawley mg/kg bw
rats
a With and without metabolic activation
b Technical material consisting of 66.1% aqueous solution
c Technical material consisting of 72% aqueous solution
The irritancy of chlormequat chloride to the eye was tested in
Vienna white rabbits by applying about 0.1 ml of the test material
(purity unspecified) to the conjunctival sac of the right eyelids of
six rabbits. Conjunctival redness was seen in five rabbits 24 h
after treatment. After 48 h, conjunctival redness was seen in two
rabbits, one of which had a conjunctival discharge. All reactions
had resolved 72 h after treatment (Gelbke & Grundler, 1981).
The irritancy of chlormequat chloride (a technical material
consisting of a 66.1% aqueous solution) was also tested in New
Zealand white rabbits. About 0.1 ml was applied to the conjunctival
sac of the left eyelids of six rabbits and left for 24 h. One hour
after treatment, slight reactions were seen in all the rabbits.
These signs had resolved by 48 h in two animals and by four days in
all rabbits (Lowe & Boczon, 1990).
The potential of chlormequat to cause delayed contact
hypersensitivity was tested in albino guinea-pigs by the method of
Buehler. Induction was performed by applying 0.4 ml of the test
material to a shaven flank and leaving it for 6 h under an occlusive
dressing. This process was repeated three times per week for a total
of nine applications. After a two-week rest period, challenge was
performed by applying the test material to the opposite flank. No
erythema or oedema was observed after the challenge, whereas a
positive control compound (dinitrochlorobenzene) included in the
study gave the expected results. It was concluded that chlormequat
is not a skin sensitizer (Ventura & Moore, 1990).
3. Observations in humans
No information was available.
Comments
In experiments with 14C-labelled chlormequat in rats, which
were reported only in summary form, absorption was rapid and
elimination was essentially complete within 48 h, occurring almost
entirely via the urine; less than 1% of the administered dose
remained in the tissues. Accumulation of 15N-labelled material in
the kidneys was reported, but the experimental details were
incomplete and detailed evaluation was not possible. The
biotransformation of chlormequat has been little studied; it was
suggested that the only metabolites found in rat urine may have been
other salts of chlorcholine.
Pharmacological tests in mice, rats, rabbits and cats
administered chlormequat intravenously revealed a stimulatory effect
on the parasympathetic nervous system and a myoneural blocking
action. Further work revealed that chlormequat is a partial agonist
of the nicotinic acetylcholine receptor; the affinity for muscarinic
receptors was low and rather unselective.
Chlormequat was of moderate acute oral toxicity in rats, mice,
hamsters and guinea-pigs (LD50 = 200-1000 mg/kg bw), but there was
some indication that rabbits and dogs are more sensitive (LD50 =
50-80 mg/kg bw). Signs of toxicity may have been associated with
pharmacological action, and there were no consistent
treatment-related findings at autopsy. WHO (1992) classified
chlormequat as slightly hazardous.
In a recently completed four-week study of dietary toxicity in
rats, the NOAEL was 1500 ppm, equal to 137 mg/kg bw per day, on the
basis of reduced body-weight gain and depression of serum creatinine
concentration. These results are largely in agreement with those of
older studies in rats of up to 90 days' duration. In dogs, the NOAEL
in an unsatisfactory two-year study was 300 ppm, equal to 7.5 mg/kg
bw per day.
The potential carcinogenicity of chlormequat was investigated
in dietary studies in rats and mice carried out in the early 1970s.
Those experiments do not comply with contemporary standards. In
studies of carcinogenicity in rats and mice reported by the National
Cancer Institute in the USA in 1979, rats were fed dietary levels of
0, 1500 or 3000 ppm for 108 weeks and mice were fed dietary levels
of 0, 500 or 2000 ppm for 102 weeks. There were no signs of reaction
to treatment and chlormequat was not carcinogenic in either species.
In a multigeneration study in rats, which was not conducted
according to currently acceptable scientific standards, chlormequat
had no effect on reproductive performance at dietary levels up to
900 ppm; however, histopathological examination revealed giant cells
in the testicular tubules in 4 of 10 rats of the F3 generation
treated with 900 ppm and 2 of 10 rats of the F3 generation treated
with 300 ppm. The report suggests that this finding may be an
expression of delayed maturation during spermatogenesis; the Meeting
found the significance of this finding difficult to assess, but the
NOAEL may thus be 100 ppm, equivalent to 5 mg/kg bw per day.
The teratogenic potential of chlormequat has been investigated
in mice (following administration by intraperitoneal injection,
gavage and via the diet), in rats by dietary administration and in
hamsters and rabbits by gavage. Many of the study reports were
available only in summary form, and detailed evaluation was not
possible. In a dietary study in mice, the number of malformations in
animals fed 10 000 ppm on days 1-15 of gestation or 25 000 ppm on
days 11-15 was reported to be slightly higher than that seen in
controls; however, the exact significance of this observation was
difficult to assess. In hamsters, malformations and evidence of
delayed development were seen following three doses of 100 mg/kg bw
per day (on days 7-9 of gestation) or a single dose of 200, 300 or
400 mg/kg bw on day 8. Evidence of maternal and fetal toxicity was
also obtained at these doses. Further evaluation of these data in
hamsters was not possible, owing to lack of detail in the
publication. A well-conducted study in which rabbits were dosed
orally with up to 12 mg/kg bw per day was available for detailed
review. Signs of maternal toxicity were seen at the highest dose
level, but there was no evidence of teratogenicity or fetotoxicity.
Chlormequat has been adequately tested for genotoxicity in
vitro and in vivo in a range of assays. The Meeting concluded
that it was not genotoxic.
Although review of the available information raised no
suspicion of significant toxicological concern, the Meeting
concluded that in view of the inadequacy of the database in
comparison with acceptable contemporary standards, it was impossible
to maintain the ADI for chlormequat.
Toxicological evaluation
Levels that cause no toxic effect
Mouse: 2000 ppm, equal to 286 mg/kg bw per day (102-week
study of carcinogenicity)
Rat: 1500 ppm, equal to 137 mg/kg bw per day (four-week
study of toxicity)
3000 ppm, equivalent to 150 mg/kg bw per day
(108-week study of carcinogenicity)
Rabbit: 6 mg/kg bw per day (maternal toxicity in a study of
teratogenicity)
12 mg/kg bw per day (fetotoxicity and teratogenicity
in a study of teratogenicity)
Studies that would provide information useful for continued
evaluation of the compound
Updating of the database to acceptable standards
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See Also:
Toxicological Abbreviations
Chlormequat (AGP:1970/M/12/1)
Chlormequat (WHO Pesticide Residues Series 2)
Chlormequat (Pesticide residues in food: 1976 evaluations)
Chlormequat (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)
Chlormequat (JMPR Evaluations 1999 Part II Toxicological)