N,N-dimethylacetamide

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The study is comparable to Guideline study with acceptable restrictions (no details about the test substance; problems in analytical methodology of DMAC in drinking water; limited data on test animals and conditions; limited parameters in clinical chemistry; low number of rats in hematology, urinalysis and clinical chemistry; some organs not included in histopathology; histopathology not extended to low and mid dose groups concerning organs with effects in high dose group).

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

(no details about the test substance; problems in analytical methodology of DMAC in drinking water; limited data on test animals and conditions; some organs not included in histopathology of high dose group and controls; no documentation of details on incidences in the reevaluation [Monsanto 1990])

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

no

Specific details on test material used for the study:

- Name of test material: dimethylacetamide (DMAC)
- Source: Monsanto
no further details available

Species:

rat

Strain:

Long-Evans

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Blues Sruce Farms, New York
- Age at study initiation: 6-7 weeks
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: individually
- certified died and distilled water (plus DMAC) ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Photoperiod: 12 hrs dark/12 hrs light

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

Distilled water used as vehicle/drinking water; test solution prepared weekly and concentration in drinking water adjusted by body weight and drinking bevaviour.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

DMAC concentration in drinking water measured weekly by GC methods. Only 68 out of 114 samples were within 20 % of the nominal concentration. Authors assumed problems with analytical methodology rather than preparations errors. Decreased values in high dose males only during the 1st weeks (see doses).

Duration of treatment / exposure:

2 years

Frequency of treatment:

daily ad libitum

Post exposure period:

no

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

in water. Range of measured mean intake in females and males: 64-122 and 64-129mg/kg bw/day, respectively.

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

in water. Range of measured mean intake in females and males: 190-399 and 177-392 mg/kg bw/day, respectively.

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Remarks:

in water. Range of measured mean intake in females and males: 598-1227 and 267-1172 mg/kg bw/day, respectively.

No. of animals per sex per dose:

70

Control animals:

yes, concurrent vehicle

Details on study design:

At the end of six or twelve months of treatment, ten animals/sex/group (n=9 at 300 mg/kg bw/day) were randomly selected and sacrificed for examinations; at the end of 24 months on test, all of the survivors were killed; immediately after death, the external surface, all orifices, the thoracic, abdominal and pelvic cavities and their associated tissues and organs, the neck and its tissues and organs and the remaining carcass were examined for the presence of gross morphologic abnormalities; rats which died unscheduled deaths during the course of the study were examined similarly.

Post exposure period: no

Histopathology: in the first report (Monsanto 1979) it was stated that a complete histopathology at termination (after 24 months) was performed only in 10 rats/sex of the high dose group and all surviving control rats. In such a case the validity of the study would be limited. Therefore, a reevaluation of histopathology data was started and reported in Monsanto (1990). In this reevaluation all male and female rats of the control and the high dose were examined in complete histopathology (10 rats each at 6 and 12 months interim sacrifice and all survivors at terminatiion of each sex). However, only a description of non-neoplastic effects were given without detailed, tabulated results and without documentation of incidences.

Positive control:

no

Observations and examinations performed and frequency:

Clinical signs and mortality recorded once daily the 1st 3 months thereafter twice daily.
Detailed physical examination once weekly.

Ophthalmology
Parameters measured pretest and 3, 12, and 24 months after initiation in all rats (lids, lacrimal apparatus, cornea, conjunctiva, anterior chamber, lens, humor, retina, optic disc)

Body weight
Measured twice pretest and once weekly during the 1st 14 weeks of exposure, thereafter once monthly and at termination (after fasting).

Food consumption
Measured pretest, once weekly at week 1-14, twice weekly at week 15-26, and thereafter once monthly.

Drinking water consumption
Determined for 10 rats per dose per sex; pretest value, once weekly at week 1-59, once monthly thereafter; test substance intake calculated from water intake data.

Blood sampling 3, 6, 12, 18, 24 months after initiation; 6 rats per dose per sex.
Hematology: hemoglobin, hematocrit, erythrocyte counts, erythrocyte morphology, clotting time, total and differential leukocytes (n=20/sex/dose recommended).
Clinical chemistry: serum GPT, alkaline phosphatase, blood urea nitrogen (BUN), fasting glucose, gamma GT (no data on total protein or albumin).

Urinalysis
In 6 rats per dose per sex parameters were measured 3, 6 and 12 months after initiation in the high dose and control group; after 18 and 24 months urinalysis was performed in all groups (n=6 per sex per dose); parameters: gross appearance, pH, glucose, specific gravity, protein, ketone, bilirubin, occult blood.

Sacrifice and pathology:

Complete necropsy of all rats performed.
Organs weights measured from adrenal glands, brain, testes, ovaries, kidneys, spleen, liver, pituitary gland; n=10 per dose per sex at the 6 and 12 months interim sacrifice; at termination all survivors.

Histopathology of the following organs:
adrenal glands
bone marrow (sternal )
brain (medulia/pons, cerebellar cortex and cerebral cortex)
eye
testes
ovaries
heart (with coronary vessels )
intestine
colon
duodenum
ileum
kidneys
liver
lung
lymph node (mesenteric)
mammary gland (female)
pancreas
pituitary gland
prostate
salivary gland
skeletal muscle
skin
spinal cord (cervical)
spleen
stomach
thyroid/parathyroid glands
urinary bladder
uterus
gross lesions tissue masses

nose, larynx & pharynx, oesophagus, accessory genital organs, muscle, peripheral nerve not included.

Other examinations:

no

Statistics:

Yes, statistically significant differences were calculated by F-test, Students t-test, Cochran test, Dunnett test, level of significance: p<0.05.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

slightly increased incidence of alopecia at 1000 mg/kg bw/day in males and females and slightly increased incidence in yellow staining of anogenital area in females of this dose.

Mortality:

no mortality observed

Description (incidence):

no effects

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Significant decrease at 1000 mg/kg bw/day in males and females and at 300 mg/kg bw/day in males.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

no statistically significant effects

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

effects observed, non-treatment-related

Description (incidence and severity):

technical problems during the first weeks (see also dose range) and decreased palatability (pronounced in high dose males); high variability but no test substance-related pattern.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

no treatment related effects

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

at >= 100 mg/kg bw/day the hemoglobin concentrations and erythrocyte counts were reduced in females after 6 months of exposure (no effects after 3, 12, 18, or 24 months);
at >=300 mg/kg bw erythrocyte counts in males were increased (only at termination)
at 1000 mg/kg bw/day blood clotting time reduced in males (only at termination)
see comments below under - Any other information on results incl. tables.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

significant effects compared with the concurrent control
at 100 & 300 mg/kg bw/day alkaline phosphatase reduced in males after 6 and 18 months
at 1000 mg/kg bw/day reduced alkaline phosphatase activity in males at all intervals
at 1000 mg/kg bw/day serum GPT elevated in males and females after 6 months (no effects at other time points)
at >=100 mg/kg bw/day BUN elevated in males at all intervals
at 1000 mg/kg bw/day in females reduced glucose only after 12 months
see comments below under - Any other information on results incl. tables.

Urinalysis findings:

no effects observed

Description (incidence and severity):

no effects

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

>=100 mg/kg bw/day: rel. and absolute liver weight was increased after 6, 12, and 24 months in males and females
>=300 mg/kg bw/day: rel & abs. kidney weight increased in males and females after 12 months and in females after 6 months (no effects after 24 months, no effects in histopathology)
1000 mg/kg bw/day: rel & abs. kidney weight increased in males after 6 months (see above)
>=100 mg/kg bw/day: rel. and abs. adrenal weight increased in males after 6 months, no effects after 12 or 24 months (no histopathological effects)
1000 mg/kg bw/day testis weight was reduced (not statistically significant) after 12 months, significant at termination.

Gross pathological findings:

no effects observed

Description (incidence and severity):

no treatment related effects

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

at 1000 mg/kg bw/day in comparison to control group (no data about low and mid dose level; no details about incidences available):

- hypertrophy/hyperplasia of the central lobular hepatocytes (minimal to moderate in severity) was seen in numerous males and females but not in controls
- the incidence of liver cell vacuolisation and liver cell degeneration was increased in males and females; no data was given on statistical significance or toxicological relevance; no data about low and mid dose level is available
- pigmentation (brown) of liver cells and reticuloendothelial cells in males and females which was not seen in controls
- incidence of small flaccid testis increased as well as degeneration/atrophy of the germinal epithelium (minimal to marked in severity) in comparison to control
- secondary to effects in testis atrophy of prostate
- hemosiderosis of the spleen in females (but no anemia)
- increased incidence of lymphoid depletion/atrophy in males (questionable relevance)

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

at 1000 mg/kg bw/day in comparison to control group (no data about low and mid dose level; no details about incidences available):

-The incidence of thymomas in females was slightly increased: 0/50 in the control group, 1/50 (2 %) in the 100 mg/kg group, 0/50 in the 300 mg/kg group and 3/50 (6 %) in the high-dose group . These tumours, which occur spontaneously in Long-Evans rats with a somewhat variable incidence, showed no dose-response relationship and are not thought to be related to treatment

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: no treatment related increase in the incidences of neoplasms in any organ

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Sex:

male

Basis for effect level:

other: based on reduced body weight observed at 300 mg/kg bw/day (nominal)

Dose descriptor:

NOAEL

Effect level:

300 mg/kg bw/day (nominal)

Sex:

female

Basis for effect level:

other: based on reduced body weight, liver cell degeneration, observed at 300 mg/kg bw/day (nominal)

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

LOAEL

Effect level:

300 mg/kg bw/day (nominal)

Sex:

male

Basis for effect level:

other: reduced body weight

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

LOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Sex:

female

Basis for effect level:

other: reduced body weight, liver cell degeneration

Remarks on result:

other: Effect type: toxicity (migrated information)

The results were not discussed by the authors.

Comment: statistically significant effects in hematology and clinical chemistry were not evaluated concerning the toxicological relevance. No data were given on the range of historical value for this rat strain in this or other laboratories. Furthermore, only 6 rats per dose per sex were evaluated concerning clinical chemistry (n=10 recommended) and hematology (n=20 recommended) for some time points only 4 -5 blood samples were assessed (e.g. clinical chemistry 12 months, males, control or n=5 for hematology 12 months, males, control). In summary, the relevance of these effects is questionable.

Comments on histopathology: Hypertrophy of the liver (correlated with increased liver weight) seems to be related to increased metabolism of the test substance and is considered not to be an adverse effect, however, increased incidences in liver cell degeneration and vacuolisation as well as increased pigmentation might be adverse in view on the increased liver weight. Unfortunately, the liver was not histopathologically examined at the low and mid dose level complicating the derivation of an NOAEL. This problem is also unsolved concerning the effects in the testes (atrophy, degeneration, reduced organ weight). The other effects reported in histopathology are not considered to be of toxicological relevance. In the reevaluation of the histopathology (Monsanto 1990) the authors did not present data on statistical significance.

Conclusions:

Conclusion: In a chronic drinking water study no carcinogenic activity was detected but toxic effects like reduced body weight gain at >= 300 mg/kg bw/day in males and at 1000 mg/kg bw/day in females; the high dose induced liver cell degeneration in males and females and testis atrophy in males; the NOAEL was 100 mg/kg bw/day in males and 300 mg/kg bw/day in females. No carcinogenic activity was observd in this long-term drinking water study.

Executive summary:

Monsanto (1979) performed a 2-year oral drinking water study (equivalent to OECD 453, non-GLP) in male and female rats. Seventy animals were exposed to the test substance diluted in water daily for two years at concentrations of 100, 300, and 1000 mg/kg bw/day. The water was available ad libitum. A concurrent vehicle control was included. Animals were examined at least once daily for clinical signs and mortality. Complete necropsy was conducted of all animals at the end of the study. Clinical signs, effects on body weight, hematology, clinical biochemistry, organ weights, and non-neoplastic histopathological findings were reported to be treatment related. Non-treatment related effect included changes in water consumption and neoplastic histopathological findings. The NOAEC for carcinogenicity based on the results obtained in this study was concluded to be 1000 mg/kg bw/day.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1979

Report date:

1979

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1990

Report date:

1990

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

no

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

N,N-dimethylacetamide

EC Number:

204-826-4

EC Name:

N,N-dimethylacetamide

Cas Number:

127-19-5

Molecular formula:

C4H9NO

IUPAC Name:

N,N-dimethylacetamide

Test material form:

liquid

Specific details on test material used for the study:

- Name of test material: dimethylacetamide (DMAC)
- Source: Monsanto
No details available.

Test animals

Species:

rat

Strain:

Long-Evans

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Blues Sruce Farms, New York
- Age at study initiation: 6-7 weeks old
- Housing: individually
- Certified died and distilled water (plus DMAC) ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Photoperiod: 12 hours dark / 12 hours light

No further details available.

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
Distilled water was used as vehicle/drinking water; the test solution was prepared weekly and the concentration in drinking water was adjusted by body weight and drinking behaviour.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

DMAC concentration in drinking water was measured weekly by GC methods. Only 68 out of 114 samples were within 20 % of the nominal concentration. Authors assumed problems with analytical methodology rather than preparation errors. Decreased values were noted in high dose males only during the first weeks (see doses).

Duration of treatment / exposure:

2 years

Frequency of treatment:

daily ad libitum

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

nominal in water,
range of measured mean intake in males: 64-129 mg/kg bw/day,
range of measured mean intake in females: 62-122 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

nominal in water,
range of measured mean intake in males: 177-392 mg/kg bw/day,
range of measured mean intake in females: 190-399 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Remarks:

nominal in water,
range of measured mean intake in males: 267-1172 mg/kg bw/day,
range of measured mean intake in females: 598-1227 mg/kg bw/day

No. of animals per sex per dose:

70 rats

Control animals:

yes, concurrent vehicle

Details on study design:

At the end of 6 or 12 months of treatment, 10 rats/sex/group (n=9 at 300 mg/kg bw/day) were randomly selected and sacrificed for examinations; at the end of 24 months on test, all of the survivors were killed; immediately after death, the external surface, all orifices, the thoracic, abdominal and pelvic cavities and their associated tissues and organs, the neck and its tissues and organs and the remaining carcass were examined for the presence of gross morphologic abnormalities; rats which died unscheduled deaths during the course of the study were examined similarly.

- Post-exposure recovery period in satellite groups: No

Histopathology: In the first report (Monsanto, 1979) it was stated that a complete histopathology at termination (after 24 months) was performed only in 10 rats/sex of the high dose group and all surviving control rats. In such a case the validity of the study would be limited. Therefore, a reevaluation of histopathology data was started and reported by Monsanto in 1990. In this reevaluation all male and female rats of the control and the high dose group were examined in complete histopathology (10 rats each at 6 and 12 months interim sacrifice and all survivors at termination of each sex). However, only a description of non-neoplastic effects was given without detailed tabulated results and without documentation of incidences.

Positive control:

No

Examinations

Observations and examinations performed and frequency:

CLINICAL OBSERVATIONS, MORTALITY:
Clinical signs and mortality were recorded once daily and the first three months thereafter twice daily.

DETAILED CLINICAL OBSERVATIONS:
Measured once weekly.

OPHTHALMOLOGY:
Parameters were measured pretest and 3, 12, and 24 months after initiation in all rats (lids, lacrimal apparatus, cornea, conjunctiva, anterior chamber, lens, humor, retina, optic disc).

BODY WEIGHT:
Measured twice pretest and once weekly during the first 14 weeks of exposure, thereafter once monthly and at termination (after fasting).

FOOD CONSUMPTION:
Measured during the pretest, once weekly at weeks 1-14, twice weekly at weeks 15-26, thereafter once monthly.

DRINKING WATER CONSUMPTION:
Determined for 10 rats per dose per sex; pretest value, once weekly at weeks 1-59, once monthly thereafter; test substance intake was calculated from water intake data.

HEMATOLOGY, CLINICAL CHEMISTRY:
Determined 3, 6, 12, 18, 24 months after initiation in 6 rats per dose per sex.
Hematology: hemoglobin, hematocrit, erythrocyte counts, erythrocyte morphology, clotting time, total and differential leukocytes (20 rats/dose/sex recommended)
Clinical chemistry: serum GPT, alkaline phosphatase, blood urea nitrogen (BUN), fasting glucose, gamma GT (no data on total protein or albumin)

URINALYSIS:
In 6 rats per dose per sex parameters were measured 3, 6 and 12 months after initiation in the high dose and control groups; after 18 and 24 months urinalysis was performed in all groups (6 rats per dose per sex); parameters: gross appearance, pH, glucose, specific gravity, protein, ketone, bilirubin, occult blood.

Sacrifice and pathology:

GROSS PATHOLOGY:
A complete necropsy was performed.
Organ weights were measured from adrenal glands, brain, testes, ovaries, kidneys, spleen, liver, pituitary gland in 10 rats per dose per sex at the 6 and 12 months interim sacrifice and at termination in all survivors.

HISTOPATHOLOGY:
A histopathological assessment was conducted in the following organs and tissues:
adrenal glands, bone marrow (sternal), brain (medulia/pons, cerebellar cortex and cerebral cortex), eye, testes, ovaries, heart (with coronary vessels ), intestine, colon, duodenum, ileum, kidneys, liver, lung, lymph node (mesenteric), mammary gland (female), pancreas, pituitary gland, prostate, salivary gland, skeletal muscle, skin, spinal cord (cervical), spleen, stomach, thyroid/parathyroid glands, urinary bladder, uterus, gross lesions, tissue masses, nose, larynx, pharynx, oesophagus, accessory genital organs, muscle; peripheral nerve not included.

Other examinations:

No

Statistics:

Statistically significant differences were calculated by F-test, Student t-test, Cochran test, Dunnett test; level of significance: p<0.05.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

There was a slightly increased incidence of alopecia at 1000 mg/kg bw/day in males and females and a slightly increased incidence in yellow staining of the ano-genital area in females of this dose.

Mortality:

no mortality observed

Description (incidence):

There were no effects.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

There was a significant decrease in body weight at 1000 mg/kg bw/day in males and females and at 300 mg/kg bw/day in males.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

There were no statistically significant effects.

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

effects observed, treatment-related

Description (incidence and severity):

There were technical problems during the first weeks (see also dose range) and decreased palatability (pronounced in high dose males); there was high variability but no test substance-related pattern.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

There were no treatment related effects.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At >= 100 mg/kg bw/day the hemoglobin concentrations and erythrocyte counts were reduced in females after 6 months of exposure (no effects after 3, 12, 18, or 24 months).
At >=300 mg/kg bw erythrocyte counts in males were increased (only at termination).
At 1000 mg/kg bw/day blood clotting time was reduced in males (only at termination).
See comments below.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

There were significant effects compared with the concurrent control:
At 100 and 300 mg/kg bw/day alkaline phosphatase activity was reduced in males after 6 and 18 months.
At 1000 mg/kg bw/day reduced alkaline phosphatase activity was noted in males at all intervals.
At 1000 mg/kg bw/day serum GPT was elevated in males and females after 6 months (no effects at other time points).
At >=100 mg/kg bw/day BUN was elevated in males at all intervals.
At 1000 mg/kg bw/day in females there was reduced glucose only after 12 months.
See comments below.

Urinalysis findings:

no effects observed

Description (incidence and severity):

There were no effects.

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

There were significant effects on organ weights:
At >= 100 mg/kg bw/day relative and absolute liver weight was increased after 6, 12, and 24 months in males and females.
At >= 300 mg/kg bw/day relative and absolute kidney weight was increased in males and females after 12 months and in females after 6 months (no effects after 24 months, no effects in histopathology).
At 1000 mg/kg bw/day relative and absolute kidney weight was increased in males after 6 months (see above).
At >= 100 mg/kg bw/day relative and absolute adrenal weight was increased in males after 6 months; there were no effects after 12 or 24 months (no histopathological effects).
At 1000 mg/kg bw/day testis weight was reduced (not statistically significant) after 12 months, significant at termination.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No treatment related effects were noted at necropsy.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day the following effects were noted in comparison to the control group (no data about low and mid dose level; no details about incidences available):
- Hypertrophy/hyperplasia of the central lobular hepatocytes (minimal to moderate in severity) was seen in numerous males and females but not in controls
- The incidence of liver cell vacuolisation and liver cell degeneration was increased in males and females; no data was given on statistical significance or toxicological relevance; no data about low and mid dose level available.
- Pigmentation (brown) of liver cells and reticuloendothelial cells were noted in males and females which was not seen in controls.
- The incidence of small flaccid testis was increased as well as degeneration/atrophy of the germinal epithelium (minimal to marked in severity) in comparison to control.
- Secondary to effects in testis atrophy of prostate was noted.
- Hemosiderosis of the spleen was observed in females (but no anemia).
- There was an increased incidence of lymphoid depletion/atrophy in males (questionable relevance).

Effect levels

1

Dose descriptor:

LOAEL

Effect level:

300 mg/kg bw/day (nominal)

Sex:

male

Basis for effect level:

body weight and weight gain

2

Dose descriptor:

LOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Sex:

female

Basis for effect level:

body weight and weight gain

histopathology: non-neoplastic

3

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Sex:

male

Remarks on result:

other: no adverse effects observed at this dose level

4

Dose descriptor:

NOAEL

Effect level:

300 mg/kg bw/day (nominal)

Sex:

female

Remarks on result:

other: no adverse effects observed at this dose level

Target system / organ toxicity

1

Critical effects observed:

yes

Lowest effective dose / conc.:

1 000 other: mg/kg bw/day (night be lower; histopathology only on control and high dose animals)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

not specified

Relevant for humans:

yes

2

Critical effects observed:

yes

Lowest effective dose / conc.:

1 000 other: mg/kg bw/day (night be lower; histopathology only on control and high dose animals)

System:

male reproductive system

Organ:

testes

Treatment related:

yes

Dose response relationship:

not specified

Relevant for humans:

yes

Applicant's summary and conclusion

Conclusions:

In a chronic drinking water study reduced body weight gain was reported at >=300 mg/kg bw/day in males and at 1000 mg/kg bw/day in females; the high dose induced liver cell degeneration in males and females and testis atrophy in males; the (provisional) NOAEL was 100 mg/kg bw/day in males and 300 mg/kg bw/day in females.

Executive summary:

In a chronic drinking water study comparable to OECD TG 453 70 Long-Evans rats per dose per sex were treated with 0, 100, 300, or 1000 mg/kg bw/day. At the end of six or twelve months of treatment, 10 animals/sex/group were randomly selected and sacrificed for examinations; at the end of 24 months on test, all of the survivors were killed.

Except alopecia in high dose rats no relevant clinical signs were observed. The body weight was reduced in males at >=300 mg/kg bw/day and in females at the high dose level of 1000 mg/kg bw/day. No effects were detected on food and water consumption. The toxicological relevance of effects in hematology and clinical chemistry was questionable. Urinalysis and ophthalmology parameters were unremarkable. At 1000 mg/kg bw/day reduced testes weight and atrophy/degeneration were seen. In males and females of the high dose group increased incidence of liver cell degeneration, pigmentation and vacuolisation were found. The derivation of the NOAEL is questionable due to limitation of the histopathological assessment (only control and high dose).

Conclusion: In a chronic drinking water study reduced body weight gain was reported at >=300 mg/kg bw/day in males and at 1000 mg/kg bw/day in females; the high dose induced liver cell degeneration in males and females and testis atrophy in males; the (provisional) NOAEL was 100 mg/kg bw/day in males and 300 mg/kg bw/day in females.