Pirimiphos-methyl

Carcinogenicity

Description of key information

- Oral: NOAEL for systemic toxicity (based on the inhibition of cholinesterase activity) is 10 ppm (0.4 mg/kg bw/day); NOAEL for carcinogenicity is 300 ppm (12.6 mg/kg bw/d, the highest dose tested) as the incidence of brain and pancreatic tumours are considered to be non-treatment related; male/female, rat, 104 weeks, equivalent to OECD 453, Gore 1979  

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

no

Remarks:

Study performed before GLP

Species:

rat

Strain:

other: SPF

Remarks:

Wistar-derived

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: young adult
- Weight: mean 315 g at the study initiation
- Housing: housed four per cage in Wilmslow type mobile rat units. The cages were constructed of 19 gauge galvanised wire mesh (1 cm2) on three sides and floor, with a solid panel at the back. The overall cage dimensions were 33 x 27.5 x 13.5 cm. The cages were suspended over collecting trays which were lined with absorbent paper.
- Acclimation period: 4 weeks

Route of administration:

oral: feed

Vehicle:

maize oil

Details on exposure:

DIET PREPARATION: All diets were prepared from a basic stock ration. The control diet contained 77 parts of stock ration, 18 parts of malt extract and 5 parts of maize oil with the test substance, all by weight. The ingredients were mixed mechanically for ten minutes and then extruded into pieces 3-6 cm long and 1 cm diameter. The diet was then dried under vacuum at a temperature not exceeding 40°C.

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

104

Frequency of treatment:

Continuous

Post exposure period:

4 to 8 weeks, no treatement (8 males and 8 females)

Dose / conc.:

10 ppm

Remarks:

Dietary equivalent to 0.4 mg/kg bw/day

Dose / conc.:

50 ppm

Remarks:

Dietary equivalent to 2.1 mg/kg bw/day

Dose / conc.:

300 ppm

Remarks:

Dietary equivalent to 12.6 mg/kg bw/day

No. of animals per sex per dose:

48

Control animals:

yes, plain diet

Details on study design:

In addition to the 40 animals in the main study, groups of 8 rats/sex/dose level were exposed and killed at interim periods of 12, 26 and 52 weeks. To assess recovery, additional groups of 8 rats/sex/dose group were maintained on control diet for 4-8 weeks post treatment after the 104 weeks exposure period. Each experimental group therefore comprised 72 rats/sex/dose at the start of the experiment.

Observations and examinations performed and frequency:

BODY WEIGHT:
- Time schedule for examinations: Individual body weights were recorded weekly throughout the pre-treatment period and during the first 12 weeks of test, then at four-weekly intervals until termination.

FOOD CONSUMPTION AND COMPOUND INTAKE:
- Time schedule: Weekly amounts of food consumed by each cage of four rats were measured during the first 12 weeks of test. Thereafter, measurements were made every fourth week

HAEMATOLOGY:
- Time schedule for collection of blood: Tail vein samples were taken from ten males and ten females in each group pre-experimentally and at 26, 52, 65, 87 weeks and terminally by cardiac puncture; Cardiac samples were taken from eight males and eight females in each subgroup at 52 weeks
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 males and 10 females in each group
- Parameters checked: general, repeated: haemoglobin concentration, packed ceil volume, mean corpuscular haemoglobin concentration, white cell counts, differential, reticulocytes, platelets and mean corpuscular diameter; 52 weeks, cardiac samples: clotting function evaluation, prothrombin and kaolin/cephalin

CLINICAL CHEMISTRY:
- Time schedule for collection of blood: plasma and erythrocyte cholinesterase: weekly throughout the pre-treatment period, then at weeks 2,4,6,8 and 12, and thereafter at approximately 12-weekly intervals throughout period of treatment. Assays were also carried out on remaining animals during the first, fourth and eighth weeks of the post-treatment recovery period; brain cholinesterase: 12, 26, 104 weeks and during the 8 weeks of recovery period
- Animals fasted: No data
- How many animals: eight males and eight females in each group; remaining animals (post-treatment recovery group)
- Parameters checked: Plasma, brain and erythrocyte cholinesterase activity

Sacrifice and pathology:

GROSS PATHOLOGY:
A full post-mortem examination was carried out on all animals which survived the full experimental term, and wherever possible on animals which died or had to be killed prematurely. Organ weights of liver, spleen, kidneys, adrenals, lungs and heart were recorded for all animals surviving the full term of treatment and those maintained for four and eight weeks post-treatment.

HISTOPATHOLOGY:
Sections of the following tissues were preserved in formol corrosive and examined histopathologically: liver, kidney, spleen, heart, lung, adrenal, ovary, uterus or testis, epididymis, prostate and seminal vesicle, thymus, thyroid, pancreas, stomach, duodenum, jejunum, ileum, caecum, colon, urinary bladder, salivary gland and pituitary.
Brain, spinal cord and peripheral nerve tissues were taken from 50% of the animals in each group and preserved in buffered formol saline. Other tissues showing macroscopic changes were taken as and when required.

Other examinations:

The weights of the following organs, liver, spleen, kidneys, adrenals, lungs and heart were recorded for all animals surviving the full term of treatment and those maintained for four and eight weeks post-treatment.

Clinical signs:

no effects observed

Description (incidence and severity):

For the greater part of the investigation the animals maintained a generally high standard of health and well being. There were two outbreaks of transient disease which affected some animals (See "Any other information on results incl tables" section). No other pathological syndromes, with the exception of those commonly associated with ageing were observed.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Deaths occurred sporadically among the groups until approximately 84th week. Thereafter, the incidence increased whereby the number of animals dying during the latter 20 weeks of test constituted 60% of total mortalities. The overall survival rate of around 50% is within the range established for the strain. The number of female deaths, 89, were possibly fewer than usual, but this was counterbalanced by a slightly higher than average incidence, 105 for males. This difference most probably reflects the slightly earlier onset of respiratory disease among males.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

There were no significant differences at any stage. Treated males generally showed slightly higher body weight gains that their controls. The body weight gains of treated females were comparable with controls. The withdrawal of the test substance from diet did not influence the values for any group (based on body weights for the eight week post-treatment recovery period).

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

The values indicate no marked differences in the amounts of food consumed nor in the rates of food utilisation. Calculated from these data, the average daily consumption of the test substance expressed in mg/kg body weight, was in the region of 0.4, 2.1 and 12.6 for groups receiving 10, 50 and 300 ppm, respectively.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

Apart from a very slight anaemia in the females in group receiving 300 ppm test substance there were no adverse effects attributable to the test substance either on haemopoiesis or blood clotting function.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

The plasma enzyme was most affected on the group receiving 300 ppm dose, showing >50% inhibition in males and >70% inhibition in females throughout the study. Erythrocyte and brain cholinesterase activity were not so markedly affected showing approximately 20-40% inhibition.

The enzyme activity in all cases returned to control value within four weeks of cessation of dosing with the test substance. Erythrocyte cholinesterase activity was not affected in group receiving 10 and 50 ppm, nor was brain activity apart from a small depression in the 50 ppm group males at 26 weeks and at termination. The only consistent effect on the 50 ppm group animals was therefore inhibition of plasma cholinesterase activity (50-65%) in the females throughout, and to some extent in the males from week 65 onwards. The 10 ppm group females showed a small depression of plasma cholinesterase throughout the study with the biologically acceptable decrease in activity (25%) being exceeded on only two isolated occasions, at 39 weeks (28%) and at 65 weeks (34%) The male plasma enzyme activity remained at control values.

Endocrine findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

All values were well within normal limits and there were also no differences between groups during the eight-week post-experimental recovery period.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Recurring macroscopic lesions such as subcutaneous tumours, pale and pitted kidneys and congested and grape-like lungs, were seen in control and treated animals alike and were not related to compound administration.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

Many animals showed characteristic old-age changes, the most marked of these being chronic nephropathy, moderate to severe fatty vacuolation and bile duct hyperplasia in the liver, degenerative myocarditis, thymic atrophy, and, mainly in the female animals, degenerative change and haemorrhage in the adrenal cortex. There was a high incidence of respiratory disease, a common finding in this colony of rats. Papillomatous hyperplasia and basal dysplasia of the epithelial mucosa of the stomach was encountered in a few animals. It was seen in both control and test animals and was not dose-related.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

The incidence of cerebral tumours encountered in this study was fairly high (4-5%), but the tumours also occurred in control animals. The tumours did not show a dose response and were not related to the administration of the test substance. The tumours were predominantly meningiomas, but glial tumours were also encountered. Other recurring tumours occurred in both control and treated animals and were not dose-related. Tumour incidence was analysed statistically and the analyses showed that the minor differences between the groups were not statistically significant.

The pathology data indicate marginally increased incidences of pancreatic tumours. The 4 males with pancreatic islet cell adenoma were old, including 2 animals from the recovery groups, one animal sacrificed at 104 weeks and the other sacrificed at week 92. The animal with pancreatic islet cell carcinoma was sacrificed at week 104 and found to have multiple tumours; the pathology description does not indicate whether there was a primary tumour giving rise to metastases. Both benign and malignant pancreatic islet cell tumours have been reported occasionally in historic control animals.

Other effects:

not examined

Key result

Dose descriptor:

NOAEL

Remarks:

Systemic

Effect level:

10 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical biochemistry

Remarks on result:

other:

Remarks:

Dietary equivalent to 0.4 mg/kg bw/day

Key result

Dose descriptor:

NOAEL

Remarks:

Carcinogenicity

Effect level:

300 ppm

Based on:

test mat.

Sex:

male/female

Key result

Critical effects observed:

no

Table 1. Lesion incidences in Wistar rats fed diets containing the test substance

	Males						Females
Dose (ppm)	0	10	50	300	HCR^#(%)	New HCD % studies^$¥∞	0	10	50	300	HCR^#(%)	New HCD % studies^$¥∞
Animals investigated	42	43	45	42			43	45	46	47
Pancreas, islet cell adenoma	0	0	0	4 (10%)	0-6	0-10 15/23	1 (2%)	0	0	0	0-4	0-4 9/23
Pancreas, islet cell carcinoma	0	0	0	1 (2%)	0-7	0-4^§ 5/23	0	0	0	0	0-2	0-2^§ 1/23
Brain, meningioma (B)	1 (2%)	1 (2%)	2 (4%)	2 (5%)	0-4	0-4 8/23	0	0	1 (2%)	0	0	0-2 6/23
Brain, ependymoma (B/M)	0	0	0	0	0-5	0-2 1/23	0	0	0	1 (2%)	0	0-2 1/23
Brain, ganglioneuroma (B)	0	0	0	0	0	0	0	0	0	1	0	0
Pituitary adenoma	5	6	8	4			17	22	19	23
Pituitary carcinoma	0	0	0	0			1	0	0	1
Adrenal cortex, diffuse vacuolation	1	3	2	3	2-28		1	1	2	3	0-2
Liver, severe fatty vacuolation	4	2	1	2	0-2		3	3	3	8	0-16
Epididymis, cystic vacuolation	0	1	0	4			-	-	-	-
Kidney, nephropathy, mild	16	11	5	10	33-59		11	18	8	17	14-68
Kidney, nephropathy, moderate	5	15*	13*	11	15-26		3	5	7	3	2-23
Kidney, nephropathy, severe	1	5	2	4	5-16		2	0	2	2	2-15

* p<0.05              B - benign            M - malignant    

^#HCR - Historic control range from 6 studies with varying terminology

^§reported as adenocarcinoma

^$rat Alpk:APfsd Wistar BABU

^¥ additional HCD from the applicant’s laboratory over a 20 year period from 1984-2004, showing a consistent low level of findings with no evidence of shift over time (Richards-Doran, 2015)

^∞incidence/number of studies

 Table 2. Cholinesterase activities (mean; absolute and % inhibition of control) in Wistar rats (~8/group) fed diets containing the test substance

Week	pre-	2	12	26	52	104	1 recovery	4 recovery
Dose (ppm)
Erythrocyte
Males      0^£	0.9	1.0	1.3	1.4	1.2	1.0	0.9	1.2
10 (%)	2	+7	+27	+9	10	2	+19	+24
50 (%)	+7	0	0	9	15	9	+1	+2
300 (%)	0	16	24	37	25	31	15	+3
Females      0^£	1.0	1.2	1.3	1.7	1.1	1.4	1.1	1.2
10 (%)	+5	+6	+8	11	+3	+13	0	6
50 (%)	+5	7	+2	13	10	4	12	+10
300 (%)	+14	37	30	43	38	27	32	0
Brain
Males     0^#	N.P.	N.P.	32.2	34.0	28.0	30.2	N.P.	25.5
10 (%)	N.P.	N.P.	3	2	5	9	N.P.	+7
50 (%)	N.P.	N.P.	3	22	4	29	N.P.	+2
300 (%)	N.P.	N.P.	17	31	9	38	N.P.	6
Females      0^#	N.P.	N.P.	32.8	26.2	24.3	26.1	N.P.	26.9
10 (%)	N.P.	N.P.	5	+2	+5	+3	N.P.	1
50 (%)	N.P.	N.P.	14	0	0	6	N.P.	4
300 (%)	N.P.	N.P.	34	36	30	19	N.P.	14

N.P. - not performed            

 ^£-mmoles/ml/min             

 ^#-DpH/g/h         

+increase in cholinesterase

Bold= > cut off values

 

Outbreaks of transient disease

The first outbreak occurred during the sixteenth week of test when several animals of either sex developed swellings in the area of the salivary glands. Palpation did not cause the animals discomfort and no other signs were apparent. There were no observable changes in general behaviour, appetite or overall condition. The number of animals affected were approximately equal in all groups. The duration of the swellings was very brief, no more than seventy two hours, after which time the animals appeared normal. The condition did not re-occur. The second outbreak of disease occurred during the latter weeks of test. Several animals in each group developed respiratory disease and had to be killed. In order to prevent further losses, all the animals were treated with 18 mg/kg oxytetracycline daily for five days during the eighty sixth week. The response to the treatment was good and there were only sporadic deaths due to respiratory failure in the ensuing period. At its peak, the numbers of animals dying of respiratory disease in one week were: 7 in Group 1, 3 in Group 2, 7 in Group 3, 6 in Group 4.

Conclusions:

The NOAEL for systemic toxicity is 10 ppm (0.4 mg/kg bw/day) based on depression of brain cholinesterase activity (>20%) at 50 and 300 ppm. A NOAEL for carcinogenicity is 300 ppm (12.6 mg/kg bw/d) (the highest dose tested) as the incidence of brain and pancreatic tumours are considered to be non-treatment related.

Executive summary:

In a non-GLP study which was similar to OECD guideline 453 (pre-GLP and pre-guideline), groups of 48 male and 48 female Wistar-derived rats were fed the test substance in diet at levels of 10, 50 and 300 ppm for 104 weeks (dietary equivalent to 0.4, 2.1, 12.6 mg/kg bw/day). Groups of 8 rats/sex/dose group were maintained on control diet for 4‑8 weeks post treatment with the test substance for 104 weeks, to assess recovery. An additional 8 rats/sex/dose level were fed the same diets and killed at interim periods of 12, 26 and 52 weeks, but did not receive pathology examinations. Investigations included body weight, food consumption, clinical signs and haematology (10/sex/group at 26, 52, 68, 87 and 104 weeks). Cholinesterase determinations were performed on plasma and erythrocyte samples (8/sex/group) obtained pre-test and on weeks 2, 4, 6, 8, 12 then 3 monthly to week 104 and on weeks 1, 4 and 8 of recovery. Brain cholinesterase assays were performed on animals identified for interim sacrifice, at week 104 (8/sex/group) and at the end of the recovery phase [no details of sample processing procedures are available]. Pathological examinations of all animals included a gross examination with microscopic examination of less than 30 organs, but including brain, spinal cord and peripheral nerve. Owing to a respiratory infection, all animals received oxytetracycline for 5 days during week 86. No tests for statistical significance were performed.

During these periods no adverse effects were seen apart from cholinesterase inhibition. Rats fed 300 ppm test substance showed marked plasma cholinesterase inhibition (50-80%) and some inhibition of erythrocyte and brain cholinesterase activity (30-40%). Apart from this there were no other adverse effects at the 300 ppm dose except for a slight anaemia in female rats. At the 50 ppm level, only female plasma cholinesterase activity was inhibited consistently (50-65%) throughout the study.

The incidence of cerebral tumours encountered in this study was fairly high (4-5%), but the tumours also occurred in control animals. The tumours did not show a dose response and were not related to the administration of the test substance. The tumours were predominantly meningiomas, but glial tumours were also encountered. Other recurring tumours occurred in both control and treated animals and were not dose-related. Tumour incidence was analysed statistically and the analyses showed that the minor differences between the groups were not statistically significant.

The pathology data indicate marginally increased incidences of pancreatic tumours. The 4 males with pancreatic islet cell adenoma were old, including 2 animals from the recovery groups, one animal sacrificed at 104 weeks and the other sacrificed at week 92. The animal with pancreatic islet cell carcinoma was sacrificed at week 104 and found to have multiple tumours; the pathology description does not indicate whether there was a primary tumour giving rise to metastases. Both benign and malignant pancreatic islet cell tumours have been reported occasionally in historic control animals.

The highest level of the test substance in diet which can be fed to rats over a two-year period without adverse effect is considered to be 10 ppm (0.4 mg/kg bw/day). A NOAEL for carcinogenicity is 300 ppm (12.6 mg/kg bw/day) (the highest dose tested) as the incidence of brain and pancreatic tumours are considered to be non-treatment related.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

12.6 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Study performed before GLP and guidelines, comparable to OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies) with restrictions.

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The tumours observed in the pancreas and brains of rats occurred spontaneously and were not related to treatment with the test substance. There were no pre-neoplastic lesions or any other toxicological findings that indicated these tissues were a target organ and no mechanistic basis for tumour formation, raising into question the biological plausibility of the findings. Furthermore, the test substance was found to be non-genotoxic in a battery of in vitro and in vivo tests.

Based on the available data classification for carcinogenicity is not warranted in accordance with EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation No. 1272/2008.

Additional information

Two-year feeding study in rats (Gore, 1979)

In a non-GLP study which was similar to OECD guideline 453 (pre-GLP and pre-guideline), groups of 48 male and 48 female Wistar-derived rats were fed the test substance in diet at levels of 10, 50 and 300 ppm for 104 weeks (dietary equivalent to 0.4, 2.1, 12.6 mg/kg bw/day). Groups of 8 rats/sex/dose group were maintained on control diet for 4‑8 weeks post treatment with the test substance for 104 weeks, to assess recovery. An additional 8 rats/sex/dose level were fed the same diets and killed at interim periods of 12, 26 and 52 weeks, but did not receive pathology examinations. Investigations included body weight, food consumption, clinical signs and haematology (10/sex/group at 26, 52, 68, 87 and 104 weeks). Cholinesterase determinations were performed on plasma and erythrocyte samples (8/sex/group) obtained pre-test and on weeks 2, 4, 6, 8, 12 then 3 monthly to week 104 and on weeks 1, 4 and 8 of recovery. Brain cholinesterase assays were performed on animals identified for interim sacrifice, at week 104 (8/sex/group) and at the end of the recovery phase [no details of sample processing procedures are available]. Pathological examinations of all animals included a gross examination with microscopic examination of less than 30 organs, but including brain, spinal cord and peripheral nerve. Owing to a respiratory infection, all animals received oxytetracycline for 5 days during week 86. No tests for statistical significance were performed.

During these periods no adverse effects were seen apart from cholinesterase inhibition. Rats fed 300 ppm test substance showed marked plasma cholinesterase inhibition (50-80%) and some inhibition of erythrocyte and brain cholinesterase activity (30-40%). Apart from this there were no other adverse effects at the 300 ppm dose except for a slight anaemia in female rats. At the 50 ppm level, only female plasma cholinesterase activity was inhibited consistently (50-65%) throughout the study.

The incidence of cerebral tumours encountered in this study was fairly high (4-5%), but the tumours also occurred in control animals. The tumours did not show a dose response and were not related to the administration of the test substance. The tumours were predominantly meningiomas, but glial tumours were also encountered. Other recurring tumours occurred in both control and treated animals and were not dose-related. Tumour incidence was analysed statistically and the analyses showed that the minor differences between the groups were not statistically significant.

The pathology data indicate marginally increased incidences of pancreatic tumours. The 4 males with pancreatic islet cell adenoma were old, including 2 animals from the recovery groups, one animal sacrificed at 104 weeks and the other sacrificed at week 92. The animal with pancreatic islet cell carcinoma was sacrificed at week 104 and found to have multiple tumours; the pathology description does not indicate whether there was a primary tumour giving rise to metastases. Both benign and malignant pancreatic islet cell tumours have been reported occasionally in historic control animals.

The highest level of the test substance in diet which can be fed to rats over a two-year period without adverse effect is considered to be 10 ppm (0.4 mg/kg bw/day). A NOAEL for carcinogenicity is 300 ppm (12.6 mg/kg bw/day) (the highest dose tested) as the incidence of brain and pancreatic tumours are considered to be non-treatment related.

78-weeks feeding study in mice

The carcinogenicity of the substance was investigated under GLP to a test protocol in accordance with the USA EPA Pesticide Assessment Guideline, Subdivision F, 83-2. Groups of 50 female and 50 male CD-1 mice were fed the test substance in the diet daily for a minimum of 78 weeks at concentrations of 0, 50, 200 and 400 ppm. Due to the severity of the treatment related effects in both sexes, the highest concentration in the diet was decreased to 300 ppm from day 8 of the study onwards. 

All surviving animals of the carcinogenicity study were subjected to a full post mortem examination, including detailed histological investigations. There was no evidence of carcinogenic effects at any treatment level in either sex over the full treatment period of 78 weeks. Thus, the NOEC for carcinogenicity is considered to be 300 ppm (equivalent to 57 mg/kg bw/day for both sexes).

CD-1 mice receiving the test substance via diet for a period of 78 weeks produced signs of toxicity in both sexes. At initially 400 ppm, this was evident as weight loss, a decrease in total food consumption, clinical signs and increased mortality (males). The reduction of the dietary concentration to 300 ppm from day 8 of treatment resulted in these effects subsiding. The remaining signs of toxicity at the end of 78 weeks of treatment were a decrease in the body weight of males compared to controls and an increase in overall mortality of males, primarily from the initial increase in mortality in week 1 of treatment. Other effects included statistically significant depressions in the cholinesterase activity in plasma, red blood cells and brain evident in most female and male groups receiving the test substance at weeks 52 and 78. With the exception of depressions in ChE activity, the only other effects at 200 ppm were a slight decrease in male body weight during the first two weeks of treatment when compared to controls, and an increase in overall male mortality compared to male controls, but not when compared to female controls. With the exception of the depressions in plasma ChE activity in bothe sexes and red blood cell ChE activity in females, there were no other effects at 50 ppm. 

The NOAEL in this study is considered to be 50 ppm in both sexes (equivalent to 9 mg/kg bw/day for both sexes) in the absence of any clinical signs, decreases in body weight and food consumption or an increase in mortality.