ACEPHATE
EXPLANATION
Acephate was evaluated for acceptable daily intake by the Joint
Meeting in 1976 (Annex, 1, FAO/WHO, 1977a) at which time an ADI of
0-0.02 mg/kg b.w. was allocated. A toxicological monograph was
published after that Meeting (Annex 1, FAO/WHO, 1977b). The ADI was
based on no-effect levels taken from studies performed by Industrial
Bio-Test Laboratories (IBT), most of which were later found to be
invalid. Further data were evaluated in 1982, when a temporary ADI of
0-0.003 mg/kg bw was allocated (Annex 1, FAO/WHO, 1983a). The
temporary ADI was extended at a level of 0-0.0005 mg/kg bw in 1984
(Annex 1, FAO/WHO, 1985b). Monograph addenda were published after the
1982 and 1984 Meetings (Annex 1, FAO/WHO, 1983b and 1985c).
Multigeneration reproduction and delayed neurotoxicity studies
were required by 1987. These and a lifetime carcinogenicity study in
mice were submitted for consideration by the present Meeting and are
summarized in this monograph addendum.
EVALUATION FOR ACCEPTABLE INTAKE
BIOLOGICAL DATA
Toxicological Studies
Special study on carcinogenicity
Groups of Charles River CD-1 mice were fed acephate technical in
the diet at levels of 0, 50, 250, or 1000 ppm for 104 weeks.
Seventy-five males (22-26 gm) and 75 females (18-22 gm) comprised each
group. Replacement groups were maintained for a period of 4 weeks,
from which one male mouse was taken for use in the control group
(previous animal missing) and one high-dose female mouse was used to
replace an animal that was sacrificed in extremis. A 1-year interim
sacrifice of 10 mice/sex/group was made. The animals were maintained
under standard laboratory conditions with regular water and dietary
analyses. Test diets were prepared weekly.
The mice were observed three times each weekday and twice daily
on weekends and holidays. Individual weights and food consumption were
measured weekly for the first 8 weeks of the study and monthly
thereafter. Orbital venous blood was examined at termination for
standard hematological variables in 19 mice/group/sex. At the end of
the interim period and at termination of the study, animals were
killed by carbon dioxide asphyxia. Post-mortem examinations were made
and standard blocks examined.
There was a treatment-related effect on body weight. Similar
values for body weight were obtained for controls and the 50 ppm
group, but animals in the mid- and high-dose groups showed decreased
body-weight gain. In the mid-dose group this effect was apparent from
13 weeks from the beginning of treatment in males and from 39 weeks in
females. The effect was found in both sexes from 4 weeks after the
beginning of treatment in the high-dose group, where the decrease in
body weight compared to controls was most marked. Examination of food
consumption data showed modest and marked reductions in intake in the
250 and 1000 ppm groups, respectively.
Mortality in treated and control groups was comparable. Although
the hematological data are incomplete, no changes that might be
attributable to treatment were found.
At both the 12-month interim sacrifice and at terminal sacrifice
significant effects were observed in the lungs. Lung changes consisted
of clusters of pigmented macrophages, often associated with
eosinophilic crystalloid bodies, alveolar hyalinosis, and acute
rhinitis. This was clearly a compound-related effect, but it appears
to have been due to resolution of lung infections; further examination
showed the pigmented material in the macrophages to be hemosiderosis.
A major significant finding in this study was an increase in
treatment-related hyperplastic and neoplastic lesions in the liver in
the high dose females. Twelve hepatocellular carcinomas, 3
hepatocellular adenomas and 17 hyperplastic nodules were observed
compared to 1, 0 and 2 in the control group, respectively.
These figures represent cumulative values from all animals dying
or sacrificed during the study, and killed at terminal sacrifice. From
individual records it appears that some of these lesions are
proliferative.
The liver changes observed in this study occurred in a
dose-related manner and were maximal at doses that were clearly toxic.
An increase in liver to body-weight ratio also occurred that was
statistically significant in high-dose females. Hepatocyte hypertrophy
in response to enzyme induction with subsequent hyperplasia, adenoma
formation, and in some instances, to carcinoma, is not remarkable and
is of doubtful prognostic significance for man.
There was an increased incidence of splenic hemangiomas and
hemangiosarcomas in this study (0-1 in controls, a maximum of 3
hemangiomas in males at 1000 ppm).
If the compound induced these tumors, induction was limited to
the 1000 ppm dose-level, which is a toxic dose. Hence, this apparent
increase may be the result of excessively high dosing, and, therefore,
of minimal concern, a point reinforced by consideration of historical
control data for the CDI mouse.
The NOAEL in this study was determined to be 250 ppm (Spicer,
1982).
Special study on Reproduction
Acephate technical (98.7% purity) was administered in the feed to
Crl:COBS 'CD' (SD) BR male and female rats at levels of 0, 25, 50 or
500 ppm. Rats in each group of the first (F0), second (F1b), and third
(F2b) generations initially consisted of 30 males and 30 females. Each
rat was observed at least twice daily for evidence of clinical effects
and was weighed at least once weekly.
Animals in the first generation were given the test compound from
the age of approximately 6 weeks for 10 weeks (75 days) prior to a
three-week cohabitation period and throughout two subsequent gestation
and lactation periods, until terminal sacrifice. Necropsies were
performed on all control and high-dose animals in the F0, F1b, and F2b
generations.
Food consumption data showed that females consumed more test
material on a mg/kg bw basis than males in each generation. Both sexes
ate more during the first week of the study than later, with a gradual
decrease during the cohabitation period. In agreement with apparent
nutritional needs, mg/kg bw/day intakes of acephate by the females
were generally higher during pregnancy and lactation than during the
last week of the cohabitation period.
No deaths occurred in F0 animals. The only clinical effect noted
was a localized alopecia in male rats. Average body weight and
body-weight gain were comparable in the 10-week premating period,
although some decrease in gain was seen in the highest-dose females at
week 10. During the F1a gestation and lactation periods, these
variables were not affected by the test diet. However, during the F1b
gestation period the 500 ppm dosage appeared to reduce body weight and
body-weight gain in pregnancy and, to a lesser extent, in early
lactation.
The administration of the test compound had no effect on mating
index, fertility index (the percentage of mated rats which were
pregnant), or gestation index (the percentage of pregnancies resulting
in litters) in F0 or F1a litters, nor was the duration of gestation
affected. At 500 ppm acephate, a decrease in the number of liveborn
pups in the second litter was observed, which was possibly related to
maternal effects (decreased ovulation and increased resorption)
following the high food intake in the previous lactation period. The
only change noted in the pups was a small reduction in body weight
evident on days 14 and 21 post-partum due to supplementation of milk
by the diet, which was accessible to the pups as they developed.
Pregnancy rates (females pregnant/females mated) during the
second F1b and F2b cohabitation periods were low for all groups,
including the controls. The pregnancy rates during the first (F2a)
cohabitation period was reduced in a non-significant manner in treated
animals. Significantly fewer pups were delivered by the high-dose
females and fewer pups were alive on day 4 post-parturition in litters
from the high-dose F2a and F2b females.
The histopathological data in this study produced no significant
findings.
The NOAEL in this study was determined to be 50 ppm (Christian &
Hoberman, 1986, 1987).
Special study in Delayed Neurotoxicity
Acephate technical (98.8% purity) was administered to a total of
16 white Leghorn hens (48 weeks of age weighing 1162-1857 gms) by
canula into the crop or proventriculus at 758 mg/kg bw which was the
oral LD50 determined in aprevious study. Eight hens given distilled
water only were used as controls; 600 mg/kg bw tri-o-tolyl phosphate
was administered as a positive control to 6 hens. All birds were
fasted for at least 15 hrs prior to dosing.
After 21 days, birds in the treatment and negative control groups
were redosed and observed for a further 21 days. Birds treated with
tri-o-tolyl phosphate were killed at 21 days.
Locomotor impairment was assessed twice weekly. Hens were dropped
from a height of approximately 1 meter in order to evaluate landing
ability. They were then made to walk about 8 mters and to hop onto a
surface raised 10 cm above the floor, followed by a further hop of the
same height. The brids were scored on an "ataxia" points system.
There was no mortality, and no abnormalities of mobility were
seen in the negative controls. The positive control birds had
diarrhoea during the first day and ataxia appeared in three birds at
day 14. Neurotoxicity was more evident from days 14 to 21, when 2 hens
showed loss of coordination; 3 showed this change together with limb
weakness and 1 was severly incapacitiated. In the treated group, 4
hens died between 4 and 7 days after dosing and 5 died 3 or 4 days
after the second dose. Symptoms of acute poisoning (diarrhoea and
relative immobility) were noted but at no time was there evidence of
neurotoxicity as assessed clinically.
Histopathological assessment of the brain, sciatic nerve, and
upper cervical, mid-thoracic, and lumbosacral sections of the spinal
cord in acephate-treated animals showed no significant changes.
Positive controls showed clinical and pathological changes typical of
delayed neurotoxicity (Beavers & Jaber, 1985).
COMMENTS
A satisfactory multigeneration study in rats was reported in 1987
with a no effect level of 50 ppm (2.5 mg/kg bw/day). A satisfactory
delayed neurotoxicity study in Leghorn hens was negative at 785 mg/kg
bw/day. A mouse life-time carcinogenicity study showed a significant
increase in liver tumors at the highest dose in females with a
no-effect level of 36 mg/kg bw/day. An apparent increase in splenic
hemangioma/hemagiosarcoma was no considered significant when
historical control data were considered.
TOXICOLOGICAL EVALUATION
LEVEL CAUSING NO TOXICOLOGICAL EFFECT
Mouse: 250 ppm in the diet, equal to 36 mg/kg bw/day
Rat: 5 ppm in the diet, equivalent to 0.25 mg/kg bw/day
Dog 30 ppm in the diet, equivalent to 0.75 mg/kg bw/day
ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN
0-0.003 mg/kg bw.
STUDIES WHICH WILL PROVIDE INFORMATION VALUBLE IN THE CONTINUED
EVALUATION OF THE COMPOUND
Observations in man.
REFERENCES
Beavers, J.B. & Jaber, M., 1985. Acute delayed neurtoxic study in
chikens with Chevron acephate technical. Unpublished final report,
from Wildlife International Ltd., St. Michaels, MD, USA. Submitted to
WHO by the Chevron Chemical Company, Richmond, CA, USA.
Christian, M.S. & Hoberman, A.M., 1986. Two generation (two litter)
reproduction study in rats with Chevron acephate technical (Chevron
Protocol S-2497). Unpublished interim report from Argus Research
Laboratories Inc., Horsham, PA, USA. Submitted to WHO by the Chevron
Chemical Company, Richmond, CA, USA.
Christian, M.S. & Hoberman, A.M., 1987. Two generation (two litter)
reproduction study in rats with Chevron acephate technical (Chevron
Protocol S-2497). Unpublished final report from Argus Research
Laboratories Inc., Horsham, PA, USA. Submitted to WHO by the Chevron
Chemical Company, Richmond, CA, USA.
Spicer, E.J.F., 1982. Lifetime oral carcinogenicity study in mice,
ORTHENE Technical (RE-12420). Unpublished report No. 415-006 from
International Research and Development Corporation, Mattawan, MI, USA.
Submitted to WHO by the Chevron Chemical Company, Richmond, CA, USA.
See Also:
Toxicological Abbreviations
Acephate (ICSC)
Acephate (Pesticide residues in food: 1976 evaluations)
Acephate (Pesticide residues in food: 1979 evaluations)
Acephate (Pesticide residues in food: 1981 evaluations)
Acephate (Pesticide residues in food: 1982 evaluations)
Acephate (Pesticide residues in food: 1984 evaluations)
Acephate (Pesticide residues in food: 1984 evaluations)
Acephate (Pesticide residues in food: 1988 evaluations Part II Toxicology)
Acephate (Pesticide residues in food: 1990 evaluations Toxicology)
Acephate (JMPR Evaluations 2002 Part II Toxicological)
Acephate (JMPR Evaluations 2005 Part II Toxicological)