ETHEPHON
First draft prepared by
J-J. Larsen
National Food Agency of Denmark, Soborg, Denmark
EXPLANATION
Ethephon was evaluated at the 1978 JMPR, but an ADI was not
allocated since the available toxicological data were insufficient
(Annex 1, reference 30). It is a plant growth regulator that acts by
release of ethylene, influencing directly several physiological
processes such as ripening and maturation and stimulating the
production of endogenous ethylene. Since the compound in high
concentration (> 87%) is a waxy solid and difficult to handle, a
technical product that contains 71% ethephon and 21% water is
marketed and also used for most toxicological studies. Although
ethephon is a dibasic phosphonic acid, its commercial formulation
exhibits some anticholinesterase activity.
EVALUATION FOR ACCEPTABLE DAILY INTAKE
BIOLOGICAL DATA
Biochemical aspects
Absorption, distribution, and excretion
Rats
The absorption, distribution, metabolism, and elimination of
14C-ethephon was studied by single and multiple dose regimens in
male and female Crl:CD(SD)BR rats. Unlabelled ethephon (purity
96.1%) and 14C-ethephon (radiochemical purity > 96%,) dissolved
in methanol, soluted with a 0.9% (w/v) sodium chloride, and adjusted
to a pH of 3-4 with lactic acid were used. The compound was
administered orally to 5 male and 5 female rats in a single dose of
50 or 1000 mg/kg bw (dose volume 5 ml/kg bw, radioactivity 10
µCi/g), multiple oral doses of 50 mg/kg bw (non-radiolabelled
ethephon administered daily for 14 days followed 24 hours later by a
single dose of 14C-ethephon), or intravenously to 5 male and 5
female rats in a dose of 50 mg/kg bw (dose volume 1 ml/kg bw,
radioactivity 60 µCi/g). Urine and faeces were collected in
individual all-glass metabolism cages for 7 days. Expired
radioactivity was captured by a mercuric perchlorate and 2-ethoxy
ethanol: ethanolamine-containing trapping system. Urine, faeces, and
volatile trap solutions were collected at intervals up to 120 hours
after dosing, after which the rats were sacrificed and tissues taken
at necropsy for radioactivity measurement. In a parallel
pharmacokinetic study using a single dose of 50 or 1000 mg/kg bw,
blood was sampled from the lateral tail vein at intervals up to 168
hours and the concentration of radioactivity in whole blood was
determined.
Blood levels of radioactivity (50 or 1000 mg/kg bw) peaked at
0.5-2 hours post-dose and declined exponentially with levels near
background by 12-24 hours post-dose. Following a single oral dose of
14C-ethephon (50 mg/kg bw), about 90% of the administered
radioactivity was recovered, principally in urine (55%), expired air
(20%), and faeces (5%) during 120 hours after dosing. Most of the
dose was recovered within 24 hours post-dose. Pretreatment with non-
radiolabelled ethephon did not significantly alter tissue residues
at 120 hours post-dose over those animals receiving a single
administration only. Following a single oral dose of 14C-ethephon
(1000 mg/kg bw) about 86% of the administered radioactivity was
recovered, principally in urine (48%), expired air (19%), and faeces
(6%) at 120 hours post-dose. Most of the dose was recovered within
24 hours post-dose. No major sex difference in pharmacokinetics was
observed (Savage, 1990).
Dogs
The disposition of ethephon was studied in 3 male beagle dogs.
The animals, weighing 6.1-6.3 kg, were placed for 72 hours
acclimatization in individual metabolism cages the week before
dosing. A single oral dose of 180 mg/kg bw made up of 1.5 ml of a
methanolic 14C-ethephon solution (362.6 µCi/5 ml) and 2.0 ml of a
5 normal citric acid non-radiolabelled ethephon solution (purity
88%) was given in a 4 ml gelatin capsule. Ethylene and carbon
dioxide were collected from the expired air by a carbon dioxide and
ethylene-trapping system, and blood samples, urine, and faeces were
collected at intervals for scintillation counting. Blood samples
were also used for determination of RBC and plasma cholinesterase
levels. The animals were sacrificed 72 hours after dosing and
tissues removed for scintillation counting. Two of the three dogs
vomited 15-30 min after dosing thus questioning the dosing.
About 35% of the dose appeared in the urine of two dogs within
24 hours after dosing. The radioactivity in urine dropped within 72
hours to levels below 1%. In one dog receiving the full dosage, 4,
0.1, and 0.03% of the dose was found in faeces at 24, 48, and 72
hours after dosing, respectively. In this dog, 30% of the dose was
recovered as ethylene in the expired air and only traces of
14CO2 were recovered. Total selected organs retained at
sacrifice a maximum of 0.25% of the administered dose. Peak plasma
and blood cell concentrations were observed 2 hours after dosing.
Only traces were observed after 22 hours. Plasma cholinesterase
levels were reduced at 2 hours with recovery starting within a few
hours. Erythrocyte cholinesterase levels responded more slowly with
signs of recovery at 72 hours (Stephen & Walker, 1971).
Biotransformation
Rats
The mono- and di-sodium salts of ethephon, and some
unidentified metabolites were present in urine and faeces of male
and female Crl:CD(SD)BR rats dosed with single (50 or 1000 mg/kg bw)
or multiple dosages (50 mg/kg bw) of 14C-ethephon (Savage, 1990).
Ethylene was eliminated in the expired air. No significant sex,
route or dose differences in metabolism were observed (Hardy et
al., 1990).
Dogs
The urine of 3 beagle dogs was examined by thin layer and gas
chromatography following a single oral dose of 180 mg/kg bw 14C-
ethephon made up of 1.5 ml of a methanolic 14C-ethephon solution
(362.6 µCi/5 ml) and 2.0 ml of a 5 normal citric acid non-
radiolabelled ethephon solution (purity 88%) (Stephen & Walker,
1971). Ethephon was partly excreted unchanged in the urine and also
metabolized to ethylene and eliminated in the expired air (Stephen &
Stanovick 1971).
Effects on enzymes and other biochemical parameters
In beagle dogs dosed with 180 mg/kg bw ethephon, plasma
cholinesterase activity was inhibited at 2 hours with recovery
starting within a few hours. Erythrocyte cholinesterase levels
responded more slowly with signs of recovery at 72 hours. Very
sparse information on the test procedures, including time schedule
for sampling and measurements, was available (Stephen & Walker,
1971).
Toxicological studies
Acute toxicity studies
Ethephon has a low oral acute toxicity in mice, rats, and
rabbits. The LD50 or LC50 values are given in Table 1. WHO has
classified ethephon as unlikely to represent acute hazard in normal
use (WHO, 1992).
Table 1. Acute toxicity of ethephon
Species Sex Route Purity LD50 LC50 Reference
(%) (mg/kg bw) (mg/m3)
Mouse M oral 90 1920 Holsing, 1969
Rat M oral 71 3730 Myers, 1984
Rat M oral 71 2210 Myers, 1984
Rat F inh. (4 h) 72 4500 Nachreiner & Klonne, 1989
Rat F inh. (4h) 72 4500 Nachreiner & Klonne, 1989
Rabbit F oral 90 > 560 Weatherholtz, 1989
Rabbit M dermal 71 1700 Meyers, 1989
Rabbit F dermal 71 1400 Meyers, 1989
Short-term toxicity studies
Mice
A 4-week dietary study in mice was carried out with ethephon.
After 2 weeks' acclimatization, groups of 10 CD-1 mice/sex received
in the diet 0, 30, 100, 300, 1000, or 3000 ppm ethephon (purity
71%), equal to 0, 5.3, 18, 51, 181, or 546 mg/kg bw/day in males and
0, 6.5, 22, 69, 210, or 635 mg/kg bw/day in females. An additional 5
animals/sex were included in the 0, 300, and 1000 ppm groups for 2-
week cholinesterase activity determinations. The mice were 7 weeks
of age at initiation of dosing. Stability and homogeneity of the
test substance in the diet was not examined. No effects were
observed in the incidence of clinical signs or mortality, food
consumption, body weight, organ weights or ASAT, SDH, ALP, ALT or
brain ChE activity at any dose level. Biologically significant (>
20%) inhibition of plasma ChE activity was observed at 300 ppm (18-
22% in males and 23-29% in females), 1000 ppm (43-44% in males and
46-49% in females) and 3000 ppm (63% in males and 55% in females).
Significant inhibition of RBC was observed at 1000 ppm (29-34% in
males and 38-41% in females) and 3000 ppm (62% in males and 56% in
females). A statistically significant decrease (26%) in SDH was seen
in the female high-dose group, and a statistically significant
increase (24%) was seen in ALP in males of the high-dose group.
Based on erythrocyte cholinesterase inhibition, the NOAEL was 300
ppm equal to 51 and 69 mg/kg bw/day in male and female mice,
respectively (Miller & Troup, 1986a).
In order to establish an MTD for ethephon in mice, a 4-week
dietary study was carried out. After 2 weeks' acclimatization,
groups of 15 CD-1 mice/sex received in the diet 0, 3000, 10 000,
25 000, or 50 000 ppm ethephon (purity 71%), equal to 0, 530, 1800,
4500, or 10 000 mg/kg bw/day in males and 0, 630, 2200, 5900, or
15 000 mg/kg bw/day in females. No effects were observed in the
incidence of clinical signs or mortality. Food consumption reduction
in the 50 000 ppm group at week 1 and body-weight reductions in the
same group throughout the study for both sexes were; attributed
primarily to initial aversion to the test diets. For male mice,
organ weight changes at 28 days were consistent with the decreased
body weights. In females, a larger than expected reduction in spleen
weight, which was reflected in a decreased spleen to final body
weight and spleen to brain weight ratios, was observed in the 50 000
ppm group. The significance of this finding could not be determined.
Dose-related inhibition of plasma (54-82%) and erythrocyte (54-92%)
ChE activity was observed in both sexes at 2 and 4 weeks. Brain ChE
activity was not inhibited. Based on the finding that only plasma
and erythrocyte ChE activities were inhibited and only minimal
additional biological responses were observed, an initial high dose
of 50 000 ppm was established for oncogenicity testing of ethephon
in mice (Miller & Troup, 1986b).
Rats
A 4-week dietary toxicity study was carried out with ethephon
in rats. After 2 weeks' acclimatization, groups of 10 Sprague-Dawley
CD rats/sex received in the diet 0, 625, 1250, 2500, 5000, or 10 000
ppm ethephon (purity 71%), equal to 0, 52, 106, 214, 430, or 830
mg/kg bw/day in males and 0, 59, 120, 251, 487, or 980 mg/kg bw/day
in females. An additional 5 animals/sex were included in the 0,
1250, and 2500 ppm groups for 2-week cholinesterase activity
determinations.
No clinical signs of toxicity and no statistically significant
effect on food consumption, body weight, haematology, or clinical
chemistry were observed in either sex at any dosage level.
Inhibition of plasma ChE activity was 21-27% at 1250 ppm, 16-18% at
2500 ppm, 30% at 5000 ppm and 35% at 10 000 ppm in males and 29% at
625 ppm, 44-50% at 1250 ppm, 45-50% at 2500 ppm, 49% at 5000 ppm and
63% at 10 000 ppm in females. The inhibition of erythrocyte ChE
activity was 16-22% at 1250 ppm, 36-41% at 2500 ppm, 58% at 5000 ppm
and 73% at 10 000 ppm in males and 14-35% at 1250 ppm, 32-50% at
2500 ppm, 67% at 5000 ppm and 78% at 10 000 ppm in females. Brain
ChE activity was not inhibited at any dose level. The NOAEL for
ethephon in this study, based on erythrocyte ChE inhibition, was 625
ppm, equal to 52 and 59 mg/kg bw/day in males and females,
respectively (Miller & Troup, 1986c).
In order to establish an MTD for ethephon in rats, a 4-week
dietary toxicity study was carried out. After 2 weeks'
acclimatization, groups of 15 Sprague-Dawley CD rats/sex received in
the diet 0, 10 000, 25 000, or 50 000, ppm ethephon (purity 71%),
equal to 0, 962, 2300, or 4673 mg/kg bw/day in males and 0, 996,
2488, or 4900 mg/kg bw/day in females. Initial aversion to the test
diets, resulting in decreased body weight was observed in both sexes
in the 25 000 and 50 000 ppm groups. Inhibition of erythrocyte ChE
activity (69-91%) and plasma ChE activity (23-74%) was cumulative
and dose-related in both sexes. Brain ChE activity was not inhibited
at any dose level. Diarrhoea, associated with cholinesterase
inhibition, was observed from day 10 in the 50 000 ppm group. Based
on the rapid development of diarrhoea in the 50 000 ppm group, an
initial high dose of 30 000 ppm was established for chronic toxicity
and oncogenicity testing of ethephon in rats (Miller & Troup,
1986d).
Rabbits
A 21-day toxicity test was carried out with dermal application
of ethephon in rabbits. Groups of 5-10 male and female adult New
Zeeland white rabbits weighing 2.0-2.9 kg, received five days a
week, for three weeks, on the abdominal skin clipped free of hair 0,
300, or 600 mg/kg bw/day ethephon (purity 39.5%, stability and
compound verification data not given). After 6-8 hours' exposure,
the abdomen was washed with water. The general appearance,
behaviour, body weight, clinical chemistry, signs of dermal
irritation, gross pathology and histopathology were studied. No
systemic toxicity of ethephon was demonstrated at the two dose
levels apart from a severe dermal irritation characterized by
subepidermal fibrosis, acanthosis, hyperkeratosis, and ulceration of
the epidermis (Holsing, 1969).
Dogs
A one-year dietary toxicity study in dogs was carried out with
ethephon. After 10 weeks' acclimatization, groups of 5 beagle
dogs/sex received in the diet 0, 100, 300, 1000, or 2000 ppm
ethephon (purity 71%), equal to 0, 2.8, 8.1, 27, or 54 mg/kg bw/day
in males and 0, 2.6, 8.4, 30, or 50 mg/kg bw/day in females. Mean
values for homogeneity and stability assays were within acceptable
ranges.
The methodology for diet analyses of ethephon was initially
unsatisfactory and was changed during the study. During the first 10
weeks of dosing, examples of great variation (e.g., 260% and 60%)
between duplicate samples were seen. These initial problems were
solved. After week 11, all diets analyzed were generally within 10%
of the target levels. There was a higher incidence of soft stools in
the ethephon-treated groups, and there was a significant decrease in
terminal body weights, absolute and relative spleen weight (spleen-
to-body-weight ratio, and spleen-to-brain weight ratio), absolute
heart and thyroid/parathyroids weights for the 2000 ppm males when
compared to control values. For the 2000 ppm females, a significant
decrease in relative spleen weight and a significant increase in
kidney/brain weight ratio was seen. Based on the findings of soft
stools and changes in body weight and spleen weight, the NOAEL was
1000 ppm, equal to 27 mg/kg bw/day in males and 30 mg/kg bw/day in
females (Hamada, 1989).
In a 2-year study, groups of 6 beagle dogs/sex received in the
diet 0, 30, 300, or 1500 ppm ethephon (purity 75.6%), equal to 0,
0.86, 7.6, or 42 mg/kg bw/day in males and 0, 0.86, 8.4, or 47.8
mg/kg bw/day in females.
Treatment-related findings included an increased incidence of
soft stools in the 300 and 1500 ppm groups. Statistically
significant erythrocyte ChE inhibition occurred in the 300 ppm group
(42-56% in males and 36-56% in females) and in the 1500 ppm group
(68-79% in males and 59-79% in females), and a statistically
significant plasma ChE inhibition occurred in the 30 ppm (22-31% in
males and 24-38% in females), 300 ppm (46-62% in males and 51-58% in
females), and 1500 ppm (45-67% in males and 59-66% in females)
groups. In treated groups, brain ChE values ranged from 3.7-52%
above the control values. Compound-related gross pathology findings
included thickened stomach and intestinal walls in dogs from all
groups and compound-related histopathology consisted of smooth
muscle hypertrophy in the stomach and small intestine in the 300 and
1500 ppm groups. Based on the inhibition of erythrocyte ChE activity
and smooth muscle hypertrophy in the stomach and small intestine,
the NOAEL in this study was 30 ppm, equal to 0.86 mg/kg bw in both
males and females (Reno & Voelker, 1977).
Long-term toxicity/carcinogenicity studies
Mice
Male and female Swiss Albino mice (85/sex/group) were fed diets
containing ethephon (purity 75%) at concentrations of 0, 30, 300, or
1000 ppm for 78 weeks, equivalent to 0, 4.5, 45, or 150 mg/kg
bw/day. Statistically significant decreases in survival were noted
among 300 and 1000 ppm males. The increased mortality was considered
related to genitourinary infections, dermatitis and haematopoietic
tumours and not compound-related. Ethephon caused a dose-related
inhibition of plasma ChE activity in both sexes (9-34% in the 300
ppm group, and 37-64% in the 1000 ppm group). Similar results were
observed in erythrocyte ChE activity measurements (11-56% at 300 ppm
and 13-51% at 1000 ppm). Ethephon treatment did not cause
biologically significant inhibition of brain ChE at any dietary
concentration (0-9%). The incidences of haematopoietic tumours were
4, 3, 13, and 11% in males and 22, 18, 39 and 29% in females at 0,
30, 300, and 1000 ppm, respectively. The major contributing factor
to the increase of 39% in the 300 ppm females was the incidence of
thymic lymphoma involving the thymus itself (incidence of 5, 5, 19,
and 13% at dose levels of 0, 30, 300, and 1000 ppm, respectively).
Since the incidence of haematopoietic tumours was not significantly
increased in females at the 1000 ppm level, the increased incidence
in the 300 ppm females was considered as random variation and
unrelated to ethephon administration. Based on inhibition of
erythrocyte ChE activity, the NOAEL was 30 ppm, equivalent to 4.5
mg/kg bw/day. There was no evidence of carcinogenicity (Voss &
Becci, 1985).
Male and female CD-1 mice (70/sex/group) were fed diets
containing ethephon (purity 71.6%) at concentrations of 0, 100,
1000, or 10 000 ppm for 78 weeks, equal to 0, 14, 140, or 1480 mg/kg
bw/day (males) and 0, 17, 170, or 1780 mg/kg bw/day (females). An
additional group (70 males and 70 females), that received 50 000
ppm, were sacrificed in the first week of the study due to extensive
morbidity and mortality after several days of dosing. An interim
sacrifice (20 mice/sex per group) was performed at 52 weeks of
treatment. Data on homogeneity and stability were acceptable.
Concentration verifications of the diets gave analytical values
ranging from 88-111% of nominal concentrations. No treatment-related
changes were observed in the incidence of abnormal clinical signs,
mortality, food consumption, efficiency of food utilization, water
consumption, or incidence of ophthalmic findings during the study.
Body weight and weight gain for males were not affected throughout
the study. No altered haematology measurements, serum chemistry
measurements (except ChE inhibition), organ weights, gross
pathological observations, or histopathological observations were
related to ethephon exposure at the 52-week or 78-week evaluation
periods. Potentially treatment-related findings included depressed
body weights and weight gains in females from the 10 000 ppm dose
group that were evident starting at approximately 39 weeks. In
addition, decreased urine pH, presumably resulting from the highly
acidic nature of the test material, was observed in male mice from
the 10 000 ppm group at 52 and 77 weeks and from the 1000 ppm group
at 77 weeks. No other effects on urinalysis measurements were
observed in either sex at any dose level, and the decrease in pH was
not considered to be a toxic effect of ethephon treatment.
Ethephon was determined to be a potent inhibitor of plasma ChE
activity with dose-related inhibition (35-41 and 65-71% in the 1000
and 10 000 ppm male dose groups, respectively, and 18-24, 41-61, and
74-76% in the 100, 1000, and 10 000 ppm female dose groups,
respectively). Similar results were observed in erythrocyte ChE
activity measurements (35-36 and 70-72% in the 1000 and 10 000 ppm
male dose groups, respectively, and 21-36 and 60-74% in the 1000 and
10 000 ppm female dose groups, respectively). This inhibition was,
however, not considered to be detrimental to the animals based on
the lack of other findings consistent with ChE inhibition. Ethephon
treatment did not cause biologically significant inhibition of brain
ChE at any dietary concentration used in this study (4-18%).
Ethephon was not considered to be carcinogenic since no neoplasms
resulted from the treatment. Two tumour types in males and two types
in females were observed at a frequency greater than 5% (males:
hepatocellular adenoma 6/69, 10/69, 4/70, 8/70 and lung adenoma
2/69, 5/70, 14/70, 6/70; females: thymic region lymphosarcoma 1/68,
2/19, 3/16, 5/68 and lung adenoma 7/70, 4/69, 7/69, 7/70 at dose
levels of 0, 100, 1000, or 10 000 ppm, respectively). Only lung
adenomas incidences in the 1000 ppm males were statistically
increased over the controls. Based on no dose relation, common
occurrence of lung adenomas in this mouse strain and that the
adenomas were neither larger nor tended toward malignancy more than
in other groups, it was concluded that the increase in lung adenomas
in males was not treatment-related. Based on inhibition of
erythrocyte ChE activity, the NOAEL was 100 ppm equal to 14 and 17
mg/kg bw/day in males and females, respectively (Miller, 1988).
Rats
Male and female Sprague-Dawley CD rats (55/sex/group), received
diets containing ethephon (purity 75.6%) at concentrations of 0, 30,
300, or 3000 ppm for 104 weeks, equal to 0, 1.2, 12.5, or 129 mg/kg
bw/day (males) and 0, 1.6, 16, or 171 mg/kg bw/day (females).
Cholinesterase activity was consistently inhibited in plasma
(22-31% at 30 ppm, 46-62% at 300 ppm and 45-67% at 3000 ppm in males
and 29-38% at 30 ppm, 51-58% at 300 ppm and 59-66% at 3000 ppm in
females). Similar results were obtained on erythrocytes (42-56% at
300 ppm and 68-80% at 3000 ppm in males and 47-56% at 300 ppm and
59-79% at 3000 ppm in females). Brain cholinesterase activity was
not affected by ethephon (0-10%). Evaluation of all other parameters
did not reveal any findings which could be attributed to the test
material. Ethephon was not found to be carcinogenic in doses up to
3000 ppm equal to 129 and 171 mg/kg bw/day in males and females,
Based on inhibition of erythrocyte ChE activity, the NOAEL was 30
ppm equal to 1.2 and 1.6 mg/kg bw/day in males and females,
respectively (Reno et al., 1978).
Four groups of 90-100 Sprague-Dawley CD rats/sex/dose were fed
diets containing ethephon (purity 71%) at concentrations of 0, 300,
3000, 10 000, or 30 000 ppm for 97 weeks (males) or 104 weeks
(females), equal to 0, 13, 131, 446, or 1420 mg/kg bw/day (males)
and 0, 16, 161, 543, or 1790 mg/kg bw/day (females). The additional
10 animals/sex in the 0, 10 000, and 30 000 ppm groups were
maintained on control diet for 4 weeks following a 12-month exposure
period to determine recovery of altered measurements. Data on
homogeneity and stability of the diet were within acceptable ranges.
Treatment-related alterations were observed at dietary
concentrations of 10 000 and 30 000 ppm. These changes included an
increased incidence of semi-solid faeces (males, 30 000 ppm),
depressed body weight and weight gain, decreased efficiency of food
utilization, decreased serum glucose (30 000 ppm group only), dose-
related alterations in urinalysis measurements, particularly
decreased urine pH (attributed to the highly acidic nature of the
test material), and an increase in absolute (15% in females, 30 000
ppm) and relative kidney weight (31% in females, 30 000 ppm). For
animals treated with 3000 ppm ethephon or lower, no signs of
toxicity were seen. Plasma and erythrocyte ChE activities were
statistically and dose-dependently inhibited at all dose levels. In
plasma from males, the inhibition ranged from 17-44, 27-47, 38-67,
and 45-56% at 300, 3000, 10 000, and 30 000 ppm, respectively, and
in plasma from females from 15-27, 37-59, 47-65, and 56-72% at 300,
3000, 10 000, and 30 000 ppm, respectively. In erythrocytes from
males, the inhibition ranged from 4-10, 39-47, 65-81, and 83-87% at
300, 3000, 10 000, and 30 000 ppm, respectively, and in erythrocytes
from females from 9-19, 43-63, 72-79, and 82-86% at 300, 3000,
10 000, and 30 000 ppm, respectively. Inhibition of brain
cholinesterase activity (< 9%) was not considered biologically
significant. Carcinogenicity was not demonstrated. Animals from the
10 000 and 30 000 ppm dose groups, maintained under control
conditions for 4 weeks following 52-week exposure, showed recovery
of all altered measurements. Complete recovery to control values
was, however, not observed for body weight and plasma and
erythrocyte ChE activity.
Based on decreased body weight, weight gain, efficiency of food
utilization, and increased absolute and relative kidney weight, the
author concluded that the NOAEL was 3000 ppm, equal to 131 and 161
mg/kg bw/day in males and females, respectively. The ChE inhibition
was not considered detrimental to the animals based on the lack of
other findings in both sexes consistent with ChE inhibition (Miller,
1989). However, based on inhibition of erythrocyte ChE activity, the
Meeting concluded that the NOAEL was 300 ppm, equal to 13 and 16
mg/kg bw/day in males and females, respectively.
Reproduction studies
Rats
Male and female Crl:CD(SD)BR Sprague-Dawley weanling rats
(28/sex/group in the F0 generation) were exposed for 10 weeks to
ethephon (purity 71.3%) at dietary concentrations of 0, 300, 3000,
or 30 000 ppm, equal to 0, 22, 220, or 2260 mg/kg bw/day in F0
males and 0, 25, 260, or 2570 mg/kg bw/day in F0 females and 0,
20, 200, or 2220 mg/kg bw/day in F1b males and 0, 24, 245, or 2520
mg/kg bw/day in F1b females. The animals were randomly paired
within dose groups for a 3-week mating period to produce the F1a
generation. Exposures continued through mating, gestation,
parturition and lactation. At weaning on lactational day 21, 28
F1a weanlings/sex/group were randomly selected to produce the F2
generation and were exposed to the same dietary concentration of
ethephon as their parents for 10 weeks. In addition, 10 F1a
weanlings/sex/dose were randomly selected for necropsy and
examination of gross lesions. At least 10 days after weaning of the
F1a litters, the F0 parents were paired again for 3 weeks to
produce the F1b generation. Exposures continued through mating,
gestation, parturition and lactation. After the F1b pups were
weaned, the F0 parental animals were necropsied and high-dose and
control animals examined for histopathologic lesions. At the time of
weaning of the F1b litters, the decision was made to use the F1b
generation to produce the F2 generation and the F1a animals (who
had completed a 10-week exposure) were euthanized and discarded.
Twenty-eight F1b weanlings/sex per group were randomly selected
and exposed to the same dietary concentrations of ethephon as their
parents for 10 weeks. In addition, 10 randomly selected F1b
weanlings/sex/dose were necropsied and examined for gross lesions.
After their pre-breed exposure, F1b parental animals were paired
as described above to produce the F2a and F2b generations.
Mating, gestation, lactation, necropsy of the F1b parents and
selected F2a and F2b weanlings were performed as described above
except that no F2 animals were selected as parents. Non-selected
F1a, F1b, F2a and F2b pups were euthanized and discarded
after the necropsy of their selected littermates.
During the 10-week pre-breed exposure, F0 males and females
at 30 000 ppm exhibited consistently reduction of body weight and
weight gain and increased incidence of loose faeces. Females at 3000
ppm showed reduced food consumption during the 1st, 3rd and 6th
weeks of exposure. At the F0 breed to produce F1a litters,
gestational parameters were unaffected by treatment. Significant
reductions in gestational body weights and lactational body weights
were observed at 30 000 ppm. The F1a litters exhibited reduced
body weights per litter at 30 000 ppm. During the second breeding of
the F0 animals to produce F1b litters, gestational and
lactational body weights were reduced at 30 000 ppm. An increased
number of stillborn pups was observed at 30 000 ppm. F1b pup body
weights per litter were reduced at 30 000 ppm and F1b pup deaths
were increased at 3000 and 30 000 ppm.
There were no treatment-related lesions observed in the
necropsy of F1a and F1b pups which died during lactation, of
randomly selected F1a and F1b pups or of F0 adults. There were
also no treatment-related lesions observed in the histopathologic
examination of selected organs from high-dose and control F0
adults. While terminal body weight was reduced in F0 males and
females at 30 000 ppm, absolute organ weights were unaffected by
treatment. Brain weight relative to body weight was increased for
F0 males and females at 30 000 ppm.
During the 10-week exposure of the F1a animals, males at 3000
and 30 000 ppm exhibited reductions in body weight, weight gain and
food consumption. F1a females at 300, 3000, and 30 000 ppm
exhibited significantly reduced body weight throughout the 10-week
exposure, and significantly reduced body-weight gain at 3000 and
30 000 ppm. Both males and females at 30 000 ppm exhibited increased
incidences of loose faeces. Since the F1b generation was selected
to produce the F2 generation, selected F1b animals were also
subjected to a 10-week pre-breed exposure and F1a animals were
euthanized and discarded after their 10-week exposure. During this
period, F1b males and females at 30 000 ppm exhibited reduced body
weight, weight gain and food consumption as well as increased
incidences of loose faeces. Weight gain was reduced in F1b males
and females at 3000 ppm as well. In F1b males, an increased
incidence of loose faeces was observed at 3000 ppm.
At the F1b breeding to produce F2a litters, gestational
parameters were unaffected by treatment. Maternal gestational body
weight and lactational body weight at 30 000 ppm was reduced. F2a
pup body weights per litter were reduced at 30 000 ppm. Perinatal
deaths and lactational survival were unaffected by treatment. During
the second breeding of the F1b animals to produce F2b litters,
maternal F1b gestational body weight and lactational body weight
at 30 000 ppm were reduced. The number of stillborn F2b pups and
perinatal deaths were increased at 30 000 ppm. F2b pup body
weights per litter were reduced at 3000 and 30 000 ppm.
There were no treatment-related lesions observed in the
necropsy of F2a and F2b pups which died during lactation, of
randomly selected F2a and F2b pups (10/sex/dose) or of F1b
adults. There were also no treatment-related lesions observed in the
histopathologic examination of selected organs from high-dose and
control F1b adults. Terminal body weight was reduced in F1b
males and females at 30 000 ppm. Brain weight relative to body
weight and ovaries/testes weight relative to body weight were
increased for F1b males and females at 30 000 ppm; brain weight
relative to body weight was also increased in F1b parental adults
at 3000 ppm.
Based on reduced food intake, body weight and body weight gain,
the NOAEL for maternal toxicity and for filial toxicity was 300 ppm,
equal to 22 and 25 mg/kg bw/day in males and females, respectively.
There was no adverse effect on reproduction at the highest dose
tested of 30 000 ppm, equal to 2220 and 2520 mg/kg bw/day in males
and females, respectively (Neeper-Bradley & Tyl, 1990).
Special studies on delayed cutaneous hypersensitivity
Evaluation of the delayed cutaneous hypersensitivity of
ethephon (purity 72%) was performed in young adult albino Dunkin-
Hartley guinea-pigs (10 animals/sex/group), allocated in one test
article-control group (induction with vehicle and challenge with
test article), one treated group (induction and challenge with test
article) and one positive control group (induction and challenge
with DNCB). Induction was performed by 3 series of 2 x 0.1 ml
intradermal injections (Freund's complete adjuvant (50% V/V in
water), ethephon (0.75 V/V in water), and a 1:1 mixture of the two
solutions), or by topical occlusive route for 48 hours with 0.5 ml
of ethephon (50% V/V in water). During challenge, the topical
occlusive application was performed with 0.5 ml ethephon (35% V/V in
water) or 0.5 ml of 1-chloro-2,4-dinitrobenzene (DNCB) (0.05% W/W in
1.2 propylene glycol). The cutaneous macroscopic examinations were
performed according to the scale of Magnusson & Kligman after 24 and
48 hours followed by histopathological examinations.
Doubtful macroscopic reactions were observed in 15 out of 20
ethephon-treated animals. Histopathological examination of these
lesions showed images of orthoergic irritation in 9 animals.
No reactions of cutaneous sensitization were observed in the 20
ethephon-treated guinea-pigs but the lesions of orthoergic
irritation noted in 9 of them may hide possible reactions of
cutaneous sensitization (Clement, 1989).
Special studies on delayed neurotoxicity
Groups of 10 white Vantress chickens received by intubation
1000 mg/kg bw/day ethephon (purity 88%) on days 1 through 5, or 1000
mg ethephon/kg bw on day 1 and thereafter 500 mg/kg bw/day on days 2
through 10. Two positive control groups received 60 mg/kg bw/day
tri-o-cresyl phosphate. Two negative control groups received 300
mg/kg bw/day of olive oil.
Fifteen out of 40 animals died in the test groups and 8 out of
20 in the positive control groups. Only the deaths which occurred in
the positive control group were considered to be due to
neurotoxicity. No clinical signs of neurotoxicity and no gross
pathology was observed in any of the necropsied chickens.
Microscopic examination showed no cytopathologic changes in the
spinal cord or sciatic nerve of the animals receiving ethephon.
Administration of tri-o-cresyl phosphate caused clinical signs of
neurotoxicity and some spinal axonal dystrophy in 10 chickens and
sciatic neuropathy in one chicken. The Meeting concluded that there
was no evidence of delayed neurotoxicity at doses up to 1500 mg/kg
bw/day (Weatherholtz & Shott, 1970).
Groups of 15-30 white leghorn chickens received a single oral
dose of 0, 3160, or 3850 mg/kg bw ethephon (purity 71%). A positive
control group received 500 mg/kg bw tri-o-tolyl phosphate orally.
Twenty-one days following dosing, all surviving birds (21) were
treated orally with a single dose of 2370 mg/kg bw ethephon.
Twenty-eight of thirty birds in the 3850 mg/kg group were found
dead within 24 hours after the first dose. One additional mortality
was recorded in this group on test day 8. Ten of thirty birds in the
3160 mg/kg group were found dead within 24 hours after the first
dose. One bird from this group was found dead within 48 hours after
the second dose. Signs of lethargy and anorexia were present
following dosing. Complete recovery of all surviving birds was seen
during both 21-day test periods. There were no signs of locomotor
disturbances or other clinical signs of delayed neurotoxicity among
any of the ethephon-treated chickens during the 42-day test period.
Ethephon-treated birds exhibited decreased food intake and body
weight loss during the test period. The positive control birds lost
weight and exhibited behavioural signs of neurotoxicity by day 9 of
the investigation. All positive control birds were sacrificed in
extremis on test day 17 or 18. Gross pathologic examination of
birds found dead within 24 hours after dosing revealed diffuse red
discoloration with severe dilation of the vessels in the intestinal
tract and diffuse light grey discoloration with transparent gel
circumscribing the crop area in all birds. Histopathology of neural
tissues from the ethephon-treated birds revealed no changes.
Treatment-related lesions were noted with respect to the positive
control birds. No evidence of delayed neurotoxicity was observed in
this study at 3160 mg/kg bw. The 3850 mg/kg bw dose could not be
evaluated since at this high level only one bird survived the
observation period (Fletcher, 1983).
Special studies on embryotoxicity/teratogenicity
Sexually mature, virgin female Charles River COBS(R) CD rats
were acclimated for 10 days before being mated with males of the
same strain at an age of 15 weeks. Groups of pregnant rats (25
rats/group) were dosed orally by garage (10 ml 0.5% aqueous
Methocel(R) suspension/kg bw) with 0, 200, 600, or 1800 mg/kg
bw/day ethephon (purity not given) on days 6 through 19 of
gestation.
There were no biologically significant differences in maternal
appearance, behaviour and body-weight gain, and there were no signs
of fetotoxicity or teratogenicity in the 200 and 600 mg/kg bw/day
group when compared to the control group. At 1800 mg/kg bw/day, 14
of the 25 dams died during the treatment period and only nine
litters with viable fetuses were available for evaluation. The NOAEL
was 600 mg/kg bw/day, based on maternal toxicity (Rodwell, 1980).
Male and female Crl:CD(SD)BR rats were used for breeding. Mated
females (25/group) were treated with ethephon (purity 71.7%) by oral
gavage at 0, 125, 250, or 500 mg/kg bw/day on days 6 through 115 of
gestation.
Survival rates were 100% at all dose levels and there were no
test material-related clinical observations. There were no
statistically significant differences in body weights of treated
animals when compared with those of controls and no test material-
related parental necropsy observations.
The pregnancy rates were 92%, 84%, 88%, and 88% at 0, 125, 250,
and 500 mg/kg bw/day, respectively. There were no significant
differences in the number of corpora lutea or implantations,
implantation efficiency, the number or percentage of live or
resorbed fetuses, or mean fetal weights and no test material-related
fetal external, soft tissue, or skeletal abnormalities.
There was a significant increase in the total number of fetuses
at 125 and 250 mg/kg bw/day with skeletal abnormalities such as
reduced vertebral arches; however, there was no statistical
difference in the percent of total fetal skeletal abnormalities.
This observation was not considered toxicologically important
because there was no dose-response and no increase in the total
number or percent of fetuses in the high dose. The NOAEL for
maternal toxicity was 500 mg/kg bw/day. There was no teratogenicity
at the dose levels tested (Henwood, 1989).
Rabbits
Ethephon (purity unknown) at 0, 50, 100, or 250 mg/kg bw/day in
water was administered orally by intubation to groups of 17 pregnant
New Zeeland white rabbits from day 6 through day 19 of gestation.
An increased incidence of inactive animals was noted in the
maternal 250 mg/kg bw/day group during the treatment and post-
treatment phases. Lower food consumption values during the treatment
and a significantly lower maternal survival rate were also noted in
this group. No other significant findings were noted in the maternal
animals.
The mean number of resorptions was higher at 100 and 250 mg/kg
bw/day and on a per litter basis, a significantly higher incidence
of resorption was noted in the 250 mg/kg bw/day animals. The mean
number of live fetuses and fetal viability was lower at 100 and 250
mg/kg bw/day. However, no statistically significant differences were
noted. All other fetal data were comparable between the control and
treated groups.
The NOAEL for maternal and embryo/fetotoxicity was 50 mg/kg
bw/day based on the lower survival rate and higher resorptions.
There were no teratogenic effects (Weatherholtz et al., 1981).
Ethephon (purity 72.2%) was administered by oral gavage to
pregnant New Zeeland white rabbits on days 7 through 19 of gestation
at dosages of 0, 63, 125, or 250 mg/kg bw/day. The control animals
received deionized water.
The percent of females surviving to the scheduled necropsy was
95, 91, 95 and 14%, for the control, 63, 125, and 250 mg/kg bw/day
group, respectively. Test material-related clinical observations
were seen for 17/22 females at 250 mg/kg bw/day including ataxia and
prostration. There were no test material-related clinical
observations at 63 or 125 mg/kg bw/day. At 250 mg/kg bw/day, but not
at the two lower dose levels, the body weight and weight gain were
significantly lower than those of controls.
Parental necropsy findings, such as erosions in the stomach,
were more frequent among the 250 mg/kg bw/day does (8 does compared
with 2 control does).
Pregnancy rates were 95, 95, 91, and 82% for the control, 63,
125, and 250 mg/kg group, respectively. Post-implantation loss and
the percent of early resorptions were considerably higher and the
percent of live fetuses was lower at 250 mg/kg bw/day. There were no
statistical differences in fetal body weight and no test material-
related fetal external, soft tissue, or skeletal variations or
malformations. The NOAEL for maternal and embryo/fetotoxicity was
125 mg/kg bw/day. There were no teratogenic effects (Henwood, 1990).
Special studies on genotoxicity
Ethephon was not considered genotoxic since it was negative in
several in vitro and in vivo test systems except when tested in
the Ames test with Salmonella typhimurium, strain TA1535. Data are
shown in Table 2.
Special studies on skin irritation
In a skin irritation test, 0.5 ml of an aqueous ethephon (70%
active ingredient) solution was placed on one intact site of the
dorsal area of the trunk of each of 6 New Zeeland white rabbits,
clipped a few days before dosing and trimmed just before application
of the test material. Contact periods were 1 or 4 hours. Ethephon
was found to be corrosive after the 4-hour contact period since
spots of necrosis and edema were observed in 4 rabbits and contact
erythema in 6 rabbits. After the 1-hour procedure, erythema, but no
edema or necrosis, was observed (Myers, 1983).
Special studies on skin sensitization
Groups of Hartley-derived albino guinea-pigs (5/sex), received
a patch containing 0.4 ml 25% w/v ethephon (72% active ingredient)
water solution. The patch was applied to each animal and occluded
for 6 hours once weekly for three consecutive weeks.
Dinitrochlorobenzene in 100% alcohol was used as the control.
Following a 2-week rest period, the guinea-pigs were topically
challenged with ethephon (10% w/v in distilled water). No evidence
of contact sensitization was observed following challenge with
ethephon (Rush, 1989).
Observations in humans
A preliminary dose range study with ethephon was carried out in
2 human volunteers. They received 5.4-120 rag/day ethephon (purity
88%) in propylene glycol (by oral capsule, in 3 divided doses, one
immediately after each meal) over a 7-week period. The approximate
dosage ranged from 0.06-1.25 mg/kg bw/day.
Table 2. Results of genotoxicity assays on ethephon
Test system Test object Concentration Purity Results Reference
of ethephon
In vitro
Ames test (with and Salmonella typhimurium 0.1-50 72.3% Jagannath, 1987
without metabolic TA1535 µg/plate +(±S9)
activation) TA1537 -(±S9)
TA1538 -(±S9)
TA98 -(±S9)
TA100 -(+S9)
DNA repair test Rat hepatocyte primary 10-1000 71.0% - Barfknecht et al.,
culture µg/ml - 1984
Unscheduled DNA Rat hepatocyte 25-1000 71.3% - Cifone, 1988
synthesis assay µg/ml
Chromosomal aberration Chinese hamster ovary 502-2010 71.3% - Murli, 1988
(± activat.) cell µg/ml
CHO/HGPRT mutation Mammalian CHO-KI- 500-2500 71.0% - Godek et al.,
assay (+ activat.) BH4 cells µg/ml 1983
CHO/HGPRT mutation Mammalian CHO-KI- 166-5000 71,0% - Godek et al.,
assay (+ activat.) BH4 cells µg/ml 1984
CHO/HGPRT mutation Mammalian CHO-KI- 500-2600 72.3% - Young, 1988
assay (+ activat.) BH4 cells µg/ml
Table 2 (contd)
Test system Test object Concentration Purity Results Reference
of ethephon
In vivo
Micronucleus test Mice 200 mg/kg >90% - Sorg et al., 1981
bw
Dominant lethal Rats 250-1000 ? - Naismith &
mg/kg bw (>707) Matthews, 1979
The compound had no inhibitory activity on human plasma or
erythrocyte ChE activity. No persistent side effects were observed
during the course of the study. However, transient, subjective
feelings of urinary urgency were experienced by both volunteers. A
slight elevation in serum GPT was also observed from the 26-46th day
of study. Laboratory studies performed two weeks following the last
compound administration gave test results within normal biological
limits (Reese, 1971).
Sixteen human volunteers in good health received orally by
capsule 0 (3 males and 3 females) or approximately 120 mg/day (5
males and 5 females) of ethephon (divided into 3 doses) for 28 days
(purity 10% in a powdered formulation), followed by a 14-day dose-
free period. Based on average substance consumption and average body
weight for the subjects, the approximate dosage was 1.5 mg/kg bw/day
in makes and 2.2 mg/kg bw/day in females. The results indicated that
the compound had no inhibitory effect on human plasma or erythrocyte
cholinesterase activity. No persistent side effects were observed
during the course of the study. However, transient subjective
complaints of urinary urgency, sudden "onset of diarrhoea", effect
on appetite and dyspepsia were recorded. Laboratory studies
performed during the study and two weeks following the last dose of
test material were, in general, within normal biological limits.
Based on clinical symptoms, a NOAEL could not be determined (Reese,
1972).
Thirty human volunteers in good health received orally by
capsule, without knowing to which group they were assigned, 0 (6
males and 4 females) or 0.5 mg/kg bw/day (10 males and 10 females)
of ethephon (purity 2.5% in a powdered formulation), divided into 3
doses, for 16 days, followed by a 29-day dose-free period. Plasma
cholinesterase activity was significantly inhibited and in a
reversible manner (54-62% of pre-dose levels). No gross symptoms nor
changes in haematology, clinical chemistry, or urinalysis were
associated with the test substance administration. The NOAEL was 0.5
mg/kg bw/day in both males and females, based on lack of inhibition
of erythrocyte cholinesterase (Weir, 1977a).
Twenty human volunteers in good health received orally by
capsule, without knowing to which group they were assigned, 0 (3
males and 3 females), 0.17 (3 males and 4 females) or 0.33 mg/kg
bw/day (4 males and 3 females) of ethephon (purity 22% in a powdered
formulation), divided into 3 doses, for 22 days, followed by a 14-
day dose-free period. Plasma ChE activity was significantly and
irreversibly inhibited (59-74% of pre-dose values). No gross
symptoms nor changes in haematology, clinical chemistry, or
urinalysis were associated with the test substance administration.
The NOAEL was 0.33 mg/kg bw/day in both males and females, based on
lack of inhibition of erythrocyte cholinesterase (Weir, 1977b).
COMMENTS
Following oral administration of ethephon to rats, about 90% of
the administered radioactivity was recovered, principally in urine
(50%), expired air (19%), and faeces (6%) during 120 hours post-
dose. Most of the dose was recovered within 24 hours post-dose.
After oral administration of ethephon to dogs, radioactivity
was found in urine (40%), expired air (30%) and faeces (5%). Total
body retention was 1%. Peak plasma and red blood cell concentrations
were observed 2 hours after dosing. Only traces were observed after
22 hours.
After oral administration to rats, ethephon was excreted in
urine and faeces as the mono- and disodium salts and some
unidentified metabolites and metabolized to ethylene and eliminated
in the expired air. In dogs, ethephon is partly metabolized to
ethylene and eliminated in expired air and also excreted unchanged
in the urine.
In dogs dosed orally with ethephon, plasma cholinesterase
activity was inhibited at 2 hours with recovery starting within a
few hours. Erythrocyte cholinesterase levels responded more slowly
with signs of recovery at 72 hours.
Ethephon has a low oral acute toxicity in mice, rats, and
rabbits. WHO has classified ethephon as unlikely to represent acute
hazard in normal use. Ethephon is corrosive to the skin of rabbits.
In a four-week study in mice at dietary concentrations of 0,
30, 100, 300, 1000 or 3000 ppm, the NOAEL was 300 ppm (equal to 51
mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
activity.
In a four-week study in rats at dietary concentrations of 0,
625, 1250, 2500, 5000 or 10 000 ppm, the NOAEL was 625 ppm (equal to
52 mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
activity.
In a one-year study in dogs at dietary concentrations of 0,
100, 300, 1000 or 2000 ppm, the NOAEL was 1000 ppm (equal to 27
mg/kg bw/day), based on soft stools and changes in body and spleen
weight. However, cholinesterase activities were not determined.
In a two-year study in dogs at dietary concentrations of 0, 30,
300, or 1500 ppm, the NOAEL was 30 ppm (equal to 0.86 mg/kg bw/day),
based on inhibition of erythrocyte cholinesterase activity and
smooth muscle hypertrophy in the stomach and small intestine.
In two 78-week studies in mice at dietary concentrations of 0,
30, 100, 300, 1000 or 10 000 ppm, the NOAEL was 100 ppm (equal to 14
mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
activity. There was no evidence of carcinogenicity.
In two 104-week studies in rats at dietary concentrations of 0,
30, 300, 3000, 10 000 or 30 000 ppm, the NOAEL was 30 ppm (equal to
1.2 mg/kg bw/day), based on inhibition of erythrocyte cholinesterase
activity. There was no evidence of carcinogenicity.
Brain cholinesterase was not depressed in any study.
In a two-generation reproduction study in rats at dietary
concentrations of 0, 300, 3000 or 30 000 ppm, the NOAEL for maternal
and filial toxicity was 300 ppm (equal to 22 mg/kg bw/day), based on
reduced food intake, body weight and weight gain. There was no
adverse effect on reproduction.
In two studies in hens for delayed neurotoxicity, no evidence
of delayed neurotoxicity was observed.
In two oral teratogenicity studies in rats at dose levels of 0,
125, 200, 250, 500, 600, or 1800 mg/kg bw/day, the NOAEL was 600
mg/kg bw/day, based on maternal toxicity. There were no teratogenic
effects.
In two teratogenicity studies in rabbits at oral dose levels of
0, 50, 63, 100, 125, or 250 mg/kg bw/day, the NOAEL was 50 mg/kg
bw/day, based on maternal and embryo/fetotoxicity. There were no
teratogenic effects.
After reviewing the in vitro and in vivo genotoxicity data,
the Meeting concluded that there was no evidence of genotoxicity.
In 16 male and female human volunteers treated orally with 0 or
120 mg/day (divided into 3 doses) of ethephon (approximately 1.5 and
2.2 mg/kg bw/day in males and females, respectively) for 28
consecutive days, no significant inhibitory effect on human plasma
or erythrocyte cholinesterase activity was observed. Subjective
complaints of urinary urgency, sudden onset of diarrhoea, effect on
appetite and dyspepsia were recorded. Based on clinical symptoms, a
NOAEL could not be determined.
In 30 male and female human volunteers treated orally with 0 or
0.5 mg/kg bw/day of ethephon (divided into 3 doses) for 16
consecutive days, plasma cholinesterase activity was inhibited but
recovered within the recovery period of 29 days. The NOAEL was 0.5
mg/kg bw/day in both males and females, based upon the lack of
inhibition of erythrocyte cholinesterase.
In 20 male and female human volunteers receiving 0, 0.17 or
0.33 mg/kg bw/day of ethephon orally (divided into 3 doses) for 22
consecutive days, plasma cholinesterase activity was inhibited and
did not recover within the recovery period of 14 days. The NOAEL was
0.33 mg/kg bw/day in both males and females, based upon the lack of
inhibition of erythrocyte cholinesterase.
An ADI of 0-0.05 mg/kg bw was established, based on the NOAEL
in the 16-day study in humans of 0.5 mg/kg bw/day, using a 10-fold
safety factor.
TOXICOLOGICAL EVALUATION
Level causing no toxicological effect
Mouse: 100 ppm, equal to 14 mg/kg bw/day (78-week study)
Rat: 30 ppm, equal to 1.2 mg/kg bw/day (104-week study)
Dog: 30 ppm, equal to 0.86 mg/kg bw/day (two-year study)
Humans: 0.5 mg/kg bw/day (16-day study).
Estimate of acceptable daily intake for humans
0-0.05 mg/kg bw.
Studies which will provide information valuable in the continued
evaluation of the compound
The Meeting noted that ethephon is a dibasic phosphonic acid
and therefore not able to phosphorylate hydrolases at the serine
residue. However, in vivo data showed inhibition of plasma and
erythrocyte, but not brain, cholinesterase. Neither data with the
pure compound nor in vitro studies were available. The Meeting
considered that these effects on cholinesterases need clarification
and recommended re-evaluation of the compound in 1995.
Further observations in humans.
REFERENCES
Barfknecht, T.R., Naismith, R.W. & Matthews, R.J. (1984). Rat
hepatocyte primary culture/DNA repair test. Unpublished report No.
PH 311-UC-002-84 from Pharmacon Research International, Inc.,
Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc,
Secteur Agro, Lyon, France.
Cifone, M.A. (1988). Mutagenicity test on ethephon in the rat
primary hepatocyte unscheduled DNA synthesis assay. Unpublished
Report No. 10065-0-447 from Hazleton Laboratories America, Inc.,
5516 Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Clement, C. (1989). Test to evaluate the sensitizing potential in
the guinea-pig. Guinea-pig maximization test. Unpublished report No.
903326 from Hazleton France, Les Oncins, B.P. 118 -69210 L'Arbresle,
France. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
France.
Fletcher, D.W. (1983). 42-Day neurotoxicity study with ethephon in
mature white leghorn chickens. Unpublished and unnumbered report
(project No. 83 DN 102) from Bio-life Associates, Ltd. Route 3, Box
156, Neilisville, Wisconsin 54456, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
Godek, E.G., Naismith, R.W. & Matthews, R.J. (1983). CHO/HGPRT,
mammalian cell forward gene mutation assay. Unpublished report No.
PH-314-UC-003-83 from Pharmacon Research International, Inc.,
Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc
Secteur Agro, 14, 20, Rue Pierre Baizet, BP 9163 - 69263 Lyon Cedex
09, France.
Godek, E.G., Naismith, R.W. & Matthews, R.J. (1984). CHO/HGPRT,
mammalian cell forward gene mutation assay. Unpublished report No.
PH-314-UC-001-84 from Pharmakon Research International, Inc.,
Waverly, Pennsylvania 18471, USA. Submitted to WHO by Rhône-Poulenc
Secteur Agro, 14, 20, Rue Pierre Baizet, BP 9163 - 69263 Lyon Cedex
09, France.
Hamada, N.N. (1989). One-year oral toxicity study in Beagle dogs
with ethephon(R). Unpublished and unnumbered report (Project No.
HLA 400-722) from Hazleton Laboratories America Inc., 9200 Leesburg
Turnpike, Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
Hardy, I.A.J., Chem, C., Marshall, I.R. & Outram, J.R. (1990). Plant
growth regulators: ethephon. Spectroscopic identification of
metabolites from a 14C-ethephon ADME study in the rat. Unpublished
report No. D. Ag. 1523 from Rhône-Poulenc Agriculture Limited,
Fyfied Road, Ongar, Essex, United Kingdom. Submitted to WHO by
Rhône-Poulenc, Secteur Agro, Lyon, France.
Henwood, S.M. (1989). Teratology study with ethephon technical-base
250 in rats. Unpublished and unnumbered report (Project No. HLA
6224-125) from Hazleton Laboratories America Inc., 3301 Kinsman
Boulevard., P.O. Box 7545, Madison, Wisconsin 53707, USA. Submitted
to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Henwood, S.M. (1990). Teratology study with ethephon technical-base
250 in rabbits. Unpublished and unnumbered report (Project No. HLA
6224-158) from Hazleton Laboratories America Inc., 3301 Kinsman
Boulevard., P.O. Box 7545, Madison, Wisconsin 53707, USA. Submitted
to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Holsing, G.C. (1969). Acute oral - Mice, five compounds. Unpublished
and unnumbered report (Project No. 141-197) from Hazleton
Laboratories, Inc., TRW Life Sciences Center, P.O. Box 30, Falls
Church, Virginia 22046, USA. Submitted to WHO by Rhône-Poulenc,
Secteur Agro, Lyon, France.
Holsing, G.C. (1969). Three-week repeated dermal application -
rabbits. Unpublished and unnumbered report (Project No. 141-171)
from Hazleton Laboratories, Inc., TRW Life Sciences Center, P.O. Box
30, Falls Church, Virginia 22046, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
Jagannath, D.R. (1987). Mutagenicity test on ethephon Base 250 in
the Ames Salmonella/microsome reverse mutation assay. Unpublished
report No. 10065-0-401 from Hazleton Laboratories America, Inc.,
5518 Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
Submitted to WHO by Rhône-Poulenc Secteur Agro, 14, 20, Rue Pierre
Baizet, BP 9163 - 69263 Lyon Cedex 09, France.
Miller, J.P. Van & Troup, C.M. (1986a). Twenty-eight day dietary
toxicity study with ethephon in mice. Unpublished report No. 48-139
from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Miller, J.P. Van & Troup, C.M. (1986b). Twenty-eight day dietary
toxicity study with ethephon in mice study II. Unpublished report
No. 49-4 from Busily Run Research Center, R.D. 4, Mellon Road,
Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc,
Secteur Agro, Lyon, France.
Miller, J.P. Van & Troup, C.M. (1986c). Twenty-eight day dietary
toxicity study with ethephon in rats. Unpublished report No. 48-123
from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Miller, J.P. Van & Troup, C.M. (1986d). Twenty-eight day dietary
toxicity study with ethephon in rats Study No. II. Unpublished
report No. 49-3 from Bushy Run Research Center, R.D. 4, Mellon Road,
Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc,
Secteur Agro, Lyon, France.
Miller, J.P. Van (1988). Lifetime dietary oncogenicity study with
ethephon in albino mice. Unpublished report No. 51-502 from Bushy
Run Research Center, R.D. 4, Mellon Road, Export, Pennsylvania
15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
France.
Miller, J.P. Van (1989). Lifetime dietary combined chronic toxicity
and oncogenicity study with ethephon in albino rats. Unpublished
report No. 51-501 from Bushy Run Research Center, R.D. 4, Mellon
Road, Export, Pennsylvania 15632, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
Murli, H. (1988). Mutagenicity test on ethephon base 250 in an in
vitro cytogenetic assay measuring chromosomal aberration
frequencies in Chinese hamster ovary (CHO) cells. Unpublished report
No. 10065-0-437 from Hazleton Laboratories America, Inc., 5516
Nicholson Lane, Suite 400, Kensington, Maryland 20895, USA.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Myers, R.C. (1983). Ethephon base 250, primary skin irritancy
(D.O.T.). Unpublished report No. 46-11 from Bushy Run Research
Center, R.D. 4, Mellon Road, Export, Pennsylvania 15632, USA.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Myers, R.C. (1984). Ethephon base 250, acute peroral toxicity study.
Unpublished report No. 47-49 from Bushy Run Research Center, R.D. 4,
Mellon Road, Export, Pennsylvania 15632, USA. Submitted to WHO by
Rhône-Poulenc, Secteur Agro, Lyon, France.
Myers, R.C. (1989). Ethephon base 250, acute percutaneous toxicity
study. Unpublished report No. 46-122 from Bushy Run Research Center,
R.D. 4, Mellon Road, Pennsylvania 15632, USA. Submitted to WHO by
Rhône-Poulenc, Secteur Agro, Lyon, France.
Nachreiner, D.J. & Klonne, D.R. (1989). Ethephon base 250, acute
aerosol inhalation toxicity test in rats. Unpublished report No. 52-
580 from Bushy Run Research Center, R.D. 4, Mellon Road, Export,
Pennsylvania 15632, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Naismith, R.W. & Matthews, R.J. (1979). Dominant lethal study.
Unpublished report No. 56375 from Pharmakon Laboratories, 1140
Quincy Avenue, Scranton, Pennsylvania 18510, USA. Submitted to WHO
by Rhône-Poulenc, Secteur Agro, Lyon, France.
Neeper-Bradley, T.L. & Tyl, R.W. (1990). Two-generation reproduction
study in CD albino rats exposed to ethephon by dietary inclusion.
Unpublished report No. 51-539 from Bushy Run Research Center, 6702
Mellon Road, Export, Pennsylvania 15632-8902, USA. Submitted to WHO
by Rhône-Poulenc, Secteur Agro, Lyon, France.
Reno, F.E & Voelker, R.W. (1977). A two-year dietary study in dogs,
ethrel. Unpublished and unnumbered report (Project No. 141-260) from
Hazleton Laboratories America Inc., 9200 Leesburg Turnpike, Vienna,
Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Reno, F.E, Serota, D.G., & Voelker R.W. (1978). 104-Week chronic
toxicity study in rats. Unpublished and unnumbered report (Project
No. 141-263) from Hazleton Laboratories America Inc., 9200 Leesburg
Turnpike, Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
Reese, W.H. (1971). Preliminary dose range study in two human
volunteers. Unpublished and unnumbered report (project No. 1223)
from Bionetics Research Laboratories, Division of Litton Industries,
Bionetics Research Laboratories, Inc. 7300 Pearl Street, Bethesda,
Maryland 20014, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Reese, W.H. (1972). Evaluation of ethrel in human volunteers.
Unpublished and unnumbered report (project No. 7223) from Bionetics
Research Laboratories, Division of Litton Industries, Bionetics
Research Laboratories, Inc. 7300 Pearl Street, Bethesda, Maryland
20014, USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon,
France.
Rodwell, D.E. (1980). Teratology study in rats. Unpublished report
No. 369-042 from International Research and Developmental
Corporation, Mattawan, Michigan 49071, USA. Submitted to WHO by
Rhône-Poulenc, Secteur Agro, Lyon, France.
Rush, R.E. (1989). Dermal sensitization study in guinea-pigs with
Base A-250. Unpublished and unnumbered report (study No. SLS
3147.44) from Springborn Laboratories, Inc. Mammalian Toxicology
Division, 553 North Broadway, Spencerville, Ohio 45887, USA.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Savage, E.A. (1990). 14C-ethephon: absorption, distribution,
metabolism, and excretion in the rat. Unpublished report No. 68/103
& P89/366 from Hazleton UK, North Yorkshire HG3 1PY, United Kingdom.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Sorg, R.M., Naismith, R.W. & Matthews, R.J. (1981). Genetic
toxicology micronucleus test (MNT). Unpublished report No. PH 309A-
UC-001-81 from Pharmakon Laboratories, Waverly, Pennsylvania 18471,
USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Stephen, W. & Walker D. (1971). Metabolism of 14C-ethephon in the
dog. Unpublished and unnumbered report from Hazleton Laboratories
America Inc., 9200 Leesburg Turnpike, Vienna, Virginia 22180, USA.
Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Stephen, W. & Stanovick, R.P. (1971). Identification of 14C-
ethephon metabolites in the dog. Unpublished and unnumbered report
from Hazleton Laboratories America Inc., 9200 Leesburg Turnpike,
Vienna, Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc,
Secteur Agro, Lyon, France.
Voss, K.A. & Becci, P.J. (1985). 78-Week oncogenic evaluation in
Swiss albino mice. Unpublished and unnumbered report (study no.
5754) from Food and Drug Research Laboratories, Inc, Route 17C, P.O.
Box 107, Waverly, NY 14892-0107 607 565-8131, USA. Submitted to WHO
by Rhône-Poulenc, Secteur Agro, Lyon, France.
Weatherholtz, W.M. (1980). Acute oral toxicity study in rabbits.
Unpublished and unnumbered report (Project No. 400-630) from
Hazleton Laboratories America, Inc., 9200 Leesburg Turnpike, Vienna,
Virginia 22180, USA. Submitted to WHO by Rhône-Poulenc, Secteur
Agro, Lyon, France.
Weatherholtz, W.M. & Shott, L.D. (1970). Neurotoxicity Study - Hens,
Ethrel, formulated, Etrel, technical. Unpublished and unnumbered
report (Project No. 141-218) from Hazleton Laboratories, Inc., TRW
Life Sciences Center, P.O. Box 30, Falls Church, Virginia 22046,
USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Weatherholtz, W.M, Wolfe, G.W. & Durloo, R.S. (1981). Teratology
study in rabbits, technical ethephon. Unpublished and unnumbered
report (Project No. 400-635) from Hazleton Laboratories America,
Inc., 9200 Leesburg Turnpike, Vienna, Virginia 22180, USA. Submitted
to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Weir, R.J. (1977a). Evaluation of ethephon in human volunteers.
Unpublished and unnumbered report (project No. 2416) from Litton
Bionetics, Inc. 5516 Nicholson Lane, Kensington, Maryland 20795,
USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
Weir, R.J. (1977b). Evaluation of ethephon in human volunteers.
Unpublished and unnumbered report (project No. 2476) from Litton
Bionetics, Inc. 5516 Nicholson Lane, Kensington, Maryland 20795,
USA. Submitted to WHO by Rhône-Poulenc, Secteur Agro, Lyon, France.
WHO (1992). The WHO recommended classification of pesticides by
hazard and guidelines to classification 1992-1993 (WHO/PCS/92.14).
Available from the International Programme on Chemical Safety, World
Health Organization, Geneva, Switzerland.
Young, R.R. (1988). Mutagenicity test on ethephon base 250 in the
CHO/HGPRT forward mutation assay. Unpublished report No. 10065-0-435
from Hazleton Laboratories America, Inc. 5516 Nicholson Lane, Suite
400, Kensington, Maryland 20895, USA. Submitted to WHO by Rhône-
Poulenc, Secteur Agro, Lyon, France.
See Also:
Toxicological Abbreviations
Ethephon (Pesticide residues in food: 1977 evaluations)
Ethephon (Pesticide residues in food: 1978 evaluations)
Ethephon (Pesticide residues in food: 1983 evaluations)
Ethephon (JMPR Evaluations 2002 Part II Toxicological)