Nickel(2+) propionate

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.4200 (Carcinogenicity)

Qualifier:

according to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

GLP compliance:

yes

Species:

rat

Strain:

other: Fischer CDF(344)/CrlBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Raleigh, North Carolina
- Age at study initiation: 6 weeks
- Weight at study initiation: 118 to 147 g for males and 93 to 112 g for females
- Housing: housed individually in suspended stainless steel cages that were rotated in a regular fashion
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: acclimated to the laboratory conditions prior to in-life initiation
- Other: The results of the pretest health screen (gross necropsy and serological analyses) conducted prior to in-life initiation indicated that the population of animals was suitable for study use. Serological analyses of blood samples fromfive male and five female sentinel animals conducted by BioReliance Corporation, Rockville, Maryland, during weeks 25, 51, 77 and 103 did not reveal the presence of any viral infections that would negatively impact the results of this study.


ENVIRONMENTAL CONDITIONS
- Temperature: 70 to 76 °F
- Humidity (%): 29 to 73 %
- Air changes (per hr): 10 to 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12-h light/12-h dark cycle

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
A specified amount of the test article and vehicle was mixed weekly. The mixtures were stirred continuously throughout each exposure period. The appearance of each test article preparation was determined and documented as a clear colorless solution for groups 2 and 3 (10 and 30 mg/kg bw/day) and a clear pale blue solution for group 4 (50 mg/kg bw/day).

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were conducted by KAR Laboratories, Inc. (Kalamazoo, Michigan) prior to study initiation, during week 51, and following study completion to confirm the stability and purity of the test substance. Reverse osmosis deionized tap water was used for administration to control animals and in the preparation of the test article mixtures. Analytical concentration verification analyses conducted throughout the study demonstrated that the exposure solutions were stable and properly prepared. All analyses were within ±10% of the nominal concentration.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

daily

Dose / conc.:

0 mg/kg bw/day

Remarks:

referred to as group 1

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

referred to as group 2

Dose / conc.:

30 mg/kg bw/day (nominal)

Remarks:

referred to as group 3

Dose / conc.:

50 mg/kg bw/day (nominal)

Remarks:

referred to as group 4

No. of animals per sex per dose:

60

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale:
Exposures for the 90-day range finding study were selected based on previous gavage studies of nickel sulfate hexahydrate in rats. Two reproductive studies using Sprague–Dawley rats indicated that graded daily exposures from 5 to 125 mg/kg bw/day for one and two generations (>90 days in two generation study) resulted in few overt signs of toxicity. These studies also demonstrated the onset of lethality from administration of nickel sulfate hexahydrate at 150 mg/kg bw/d.
The 90-day range-finding study of nickel sulfate hexahydrate administered by gavage was conducted using exposures of 0, 50, 75, 100, 125, and 150 mg/kg bw/d. Based on the data from the 90-day range-finding study, exposure levels of 10, 30 and 50 mg/kg bw/day were selected for the 2 year oral gavage carcinogenicity study.

-Rationale for animal assignment: Sixty female and sixty male animals were assigned to each exposure group using a computer randomization program.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: General health/mortality/moribundity checks were performed twice daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed clinical observations were performed weekly and on the day of scheduled euthanasia (weeks 104–105). Beginning on week 25, detailed clinical observations included a palpable mass examination (including the occurrence, size, location and description of any palpable masses) followed by persistence or disappearance of these masses being documented at the next weekly clinical observation.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were recorded prior to randomization (day −3), on day 0 (i.e., the start of exposure), weekly during the first 13 weeks, once every 4 weeks thereafter and during week 103.

FOOD CONSUMPTION AND COMPOUND INTAKE
- Individual food consumption (grams/animal/day) was recorded on day 0, weekly during the first 13 weeks and once every 4 weeks thereafter, with the final food consumption measurement during week 103.

HAEMATOLOGY: Yes
- Selected hematological parameters were measured in blood samples collected from 10 animals/sex/group during week 54 (via tail vein) and prior to scheduled euthanasia during week 104/105 (via orbital plexus). Hematology and clinical chemistry parameters were measured according to the OECD 451 protocol.

Sacrifice and pathology:

GROSS PATHOLOGY/HISTOPATHOLOGY:
All animals were subjected to a complete gross necropsy examination at the time of death or euthanasia. Tissues collected at necropsy from all animals were processed for histopathological evaluation. Slides were prepared by Histo Techniques (Powell, Ohio) and Charles River Laboratories-Pathology Associates (Frederick, Maryland) and were examined microscopically by a Charles River Laboratories board-certified veterinary pathologist.

Other examinations:

Near the end of the study (week 103), additional biological sampling was performed to provide data on nickel in urine, feces and blood. Immediately following exposure on 1 day during week 103, five females and five males from each exposure group were placed in urine collection cages equipped with fecal collection screens, and an ice bath for cooling collected urine samples. Blood was collected from the orbital plexus of each animal approximately 30 min and 24 h post-exposure and sent to WIL Research Laboratories, Inc. (Ashland, Ohio) for analysis of blood nickel concentration. Urine and fecal samples were collected from each cage approximately 24 h post-exposure and sent to KAR Laboratories, Inc. for urine and fecal analysis of nickel concentrations. Urine was analyzed also for creatinine and albumin concentrations. Other standard hematology and clinical chemistry parameters for blood as well as other standard urinalysis parameters for urine were measured by Charles River Laboratories.

Statistics:

In-life data: The data were initially tested for normality using Levene's test for equality of variance followed by the Shapiro–Wilks test for normality.
A p≤0.001 level of significance was required for either test to reject the assumptions. If both assumptions were fulfilled, a singlefactor ANOVA was applied, with animal grouping as the factor, utilizing a p≤0.05 level of significance. If the parametric ANOVA was significant at p≤0.05, Dunnett's test was used to identify statistically significant differences between the control group and each nickel sulfate-treated group at the 0.05, 0.01 and 0.001 levels of significance. If either of the parametric assumptions was not satisfied, then the Kruskal–Wallis nonparametric ANOVA procedure was used to evaluate intergroup differences (p≤0.05). The Dunn's multiple comparison test was applied if this ANOVA was significant, again utilizing significance levels of p≤0.05, 0.01 and 0.001.


Survival Data: Kaplan–Meier estimates of group survival rates were calculated, by sex, and shown graphically. A log-rank dose response trend test of survival rates was performed utilizing dose coefficients. In addition, a log-rank test for survival was used to make pairwise comparisons of each treated group with the control group. Both the trend test and pairwise comparisons were conducted at the 0.05 significance level.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

The type and incidence of clinical signs observed in the treated groups were generally comparable to those observed in the control group.

Mortality:

mortality observed, treatment-related

Description (incidence):

There was a higher rate of mortality in groups 2–4 treated males and females during the first 24 weeks of this study which appeared to b treatment-related. Nickel induced pulmonary toxicity secondary to aspiration of the nickel sulfate solution was a potential cause. A later exposure time after week 24 (since rats are nocturnal feeders and 10 mL/kg exposure volume early in the morning to animals with relatively full stomachs may have produced sufficient gastric back pressure to force a portion of the administered dose to the opening of the trachea where it was aspirated) was effective in increasing survival, possibly by reducing aspiration of the test substance.
Mortality during week 24-48: only one death in nickel sulfate-treated group 3.
For the entire 104 weeks period there was no apparent treatment-related effect on mortality in males. In females, there was an increasing exposure–response trend in mortality relative to the controls (p<0.008).

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Body weights decreased in a exposure-dependent manner, with significantly decreased body weights observed in the two highest exposure groups for males and females (groups 3–4) Reductions in weight gain relative to controls at study week 103 reached the level of biological significance (i.e., >10% decrease) in the group 3 and 4 males and the group 4 females. This significant weight reduction indicates that the Maximum Tolerated Dose was reached in this study for both males and females.

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

A few statistically significant differences in the hematology data were observed in the treated males and females. For example, there were increases in red blood cells, hematocrit and/or hemoglobin in some of the animals in the 30 and 50 mg/kg bw/day groups. These changes may be associated with dehydration or could be related to nickel effects on gene expression of erytropoetin (HIF-inducible factor). However, none of these differences was suggestive of a hyperplastic (i.e., leukemia) response and none of these changes was considered toxicologically meaningful since they were small and did not follow a consistent exposure-related pattern.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Numerous gross necropsy findings were observed for animals in the control and nickel sulfate-treated groups but the type and incidence of these findings observed for the treated animals were comparable to those observed in the control group, and were consistent with findings commonly seen in aging rats in a longterm study. None of the neoplastic or non-neoplastic microscopic findings was considered to be related to the experimental exposures. The non-neoplastic findings were either considered to be secondary to toxicity or incidental background occurrences rather than a direct effect of nickel sulfate. Some examples of non-neoplastic findings in the 50mg/kg bw/day males include: increases in yperplasia of pars distalis of the pituitary gland, bronchial inflammation, lymphoid follicle atrophy of spleen, mandibular lymph node cystic degeneration, histiocytes infiltration of mesenteric lymph nodes, hyperkeratosis of the tail, eye mineralization and vacuolization of adrenal cortex. In the stomach, there was an increase in the erosion of glands, but a decrease in epithelial erosion. Decreases in atrophy of pancreatic acinus, mineralization of aorta, hyperplasia of thymus and presence of renal tubule pigment were also observed. Most of these effects were not observed in the 50 mg/kg bw/day female animals with the exception of the increases in bronchial inflammation, spleen and mandibular lymph node effects and the decreases seen for kidney pigmentation, eye effects and erosion of stomach glands. The increased bronchial inflammation seen in 50 mg/kg bw/day male and female rats was considered to be the indirect result of minor aspirations during gavage exposure.

Histopathological findings: neoplastic:

no effects observed

Details on results:

The pathology report, pathology peer-review and the pathology working group concurred that nickel sulfate hexahydrate did not cause any carcinogenic effects in this study. Analysis of the tumor data revealed only one statistically significant (p<0.001) increase in tumors corresponding to keratoacanthoma (tail) in the group 2 males. However, this finding is of questionable toxicologic significance since there was no exposure–response relationship, the incidence rate in the group 2 males (15%) was only slightly higher than the upper end of Haseman's historical control incidence for this tumor type (0–14%) and the incidence rate in the remaining control and treated groups (0–7%) was within the range of the CRL-Ohio historical incidence (0–2%) and the Haseman historical incidence (0–14%). No other tumor finding in this study was statistically significant.
No notable differences were observed between controls and treated animals for the hematology, biochemistry and urinalysis parameters measured during the toxicokinetic satellite study.
Nickel levels in feces increased in an exposure-dependent manner in the treated males and females. The relatively high fecal levels compared to the blood and urinary nickel levels demonstrated that the majority of the nickel the animals were exposed to was not systemically absorbed, but was excreted in the feces.

Relevance of carcinogenic effects / potential:

The treatment did not produce an exposure-related increase in tumorigenicity. Only one tumor type in one exposure group was statistically different from the study controls (keratoacanthoma in the 10 mg/kg/day males), but no exposure–response relationship was observed and this is a common tumor type. Therefore, results of this study indicate that nickel sulfate hexahydrate does not cause
carcinogenicity to rats when administered orally.

Dose descriptor:

LOAEL

Effect level:

6.7 other: Ni/kg bw/d

Sex:

male/female

Basis for effect level:

body weight and weight gain

Dose descriptor:

LOAEL

Effect level:

30 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

Dose descriptor:

NOAEL

Effect level:

2.2 other: Ni/kg bw/d

Sex:

male/female

Basis for effect level:

other: overall effects

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: overall effects

Key result

Critical effects observed:

no

Conclusions:

The NOAEL of the test substance was determined to be 10 mg/kg bw/d. The test substance does not cause carcinogenicity to rats when administered orally.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2007

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: EPA OPPTS 870.4200

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 451

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

nickel(2+);sulfate;hexahydrate

EC Number:

600-152-3

Cas Number:

10101-97-0

Molecular formula:

H12NiO10S

IUPAC Name:

nickel(2+);sulfate;hexahydrate

Test animals

Species:

rat

Strain:

other: CDF(344)/CrlBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Raleigh, North Carolina
- Age at study initiation: 6 weeks
- Weight at study initiation: 118 to 147 g for males and 93 to 112 g for females
- Housing: housed individually in suspended stainless steel cages that were rotated in a regular fashion
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: acclimated to the laboratory conditions prior to in-life initiation
- Other: The results of the pretest health screen (gross necropsy and serological analyses) conducted prior to in-life initiation indicated that the population of animals was suitable for study use. Serological analyses of blood samples fromfive male and five female sentinel animals conducted by BioReliance Corporation, Rockville, Maryland, during weeks 25, 51, 77 and 103 did not reveal the presence of any viral infections that would negatively impact the results of this study.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 70 to 76 °F
- Humidity (%): 29 to 73%
- Air changes (per hr): 10 to 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12-h light/12-h dark cycle

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: a specified amount of the test article and vehicle was mixed weekly. The mixtures were stirred continuously throughout each exposure period. The appearance of each test article preparation was determined and documented as a clear colorless solution for groups 2 and 3 (10 and 30 mg/kg bw/day) and a clear pale blue solution for group 4 (50 mg/kg bw/day).

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were conducted by KAR Laboratories, Inc. (Kalamazoo, Michigan) prior to study initiation, during week 51, and following study completion to confirm the stability and purity of the test substance. Reverse osmosis deionized tap water was used for administration to control animals and in the preparation of the test article mixtures. Analytical concentration verification analyses conducted throughout the study demonstrated that the exposure solutions were stable and properly prepared. All analyses were within ±10% of the nominal concentration.

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

referred to as group 1

Doses / concentrations 2

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

referred to as group 2

Doses / concentrations 3

Dose / conc.:

30 mg/kg bw/day (nominal)

Remarks:

referred to as group 3

Doses / concentrations 4

Dose / conc.:

50 mg/kg bw/day (nominal)

Remarks:

referred to as group 4

No. of animals per sex per dose:

60

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale:
Exposures for the 90-day range finding study were selected based on previous gavage studies of nickel sulfate hexahydrate in rats. Two reproductive studies using Sprague–Dawley rats indicated that graded daily exposures from 5 to 125 mg/kg bw/day for one and two generations (>90 days in two generation study) resulted in few overt signs of toxicity. These studies also demonstrated the onset of lethality from administration of nickel sulfate hexahydrate at 150 mg/kg bw/d.
The 90-day range-finding study of nickel sulfate hexahydrate administered by gavage was conducted using exposures of 0, 50, 75, 100, 125, and 150 mg/kg bw/d. Based on the data from the 90-day range-finding study, exposure levels of 10, 30 and 50 mg/kg bw/day were selected for the 2 year oral gavage carcinogenicity study.

-Rationale for animal assignment: Sixty female and sixty male animals were assigned to each exposure group using a computer randomization program.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: General health/mortality/moribundity checks were performed twice daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed clinical observations were performed weekly and on the day of scheduled euthanasia (weeks 104–105). Beginning on week 25, detailed clinical observations included a palpable mass examination (including the occurrence, size, location and description of any palpable masses) followed by persistence or disappearance of these masses being documented at the next weekly clinical observation.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were recorded prior to randomization (day −3), on day 0 (i.e., the start of exposure), weekly during the first 13 weeks, once every 4 weeks thereafter and during week 103.

FOOD CONSUMPTION AND COMPOUND INTAKE:
- Individual food consumption (grams/animal/day) was recorded on day 0, weekly during the first 13 weeks and once every 4 weeks thereafter, with the final food consumption measurement during week 103.

HAEMATOLOGY: Yes
- Selected hematological parameters were measured in blood samples collected from 10 animals/sex/group during week 54 (via tail vein) and prior to scheduled euthanasia during week 104/105 (via orbital plexus). Hematology and clinical chemistry parameters were measured according to the OECD 451 protocol.

Sacrifice and pathology:

GROSS PATHOLOGY/HISTOPATHOLOGY:
All animals were subjected to a complete gross necropsy examination at the time of death or euthanasia. Tissues collected at necropsy from all animals were processed for histopathological evaluation. Slides were prepared by Histo Techniques (Powell, Ohio) and Charles River Laboratories-Pathology Associates (Frederick, Maryland) and were examined microscopically by a Charles River Laboratories board-certified veterinary pathologist.

Other examinations:

Near the end of the study (week 103), additional biological sampling was performed to provide data on nickel in urine, feces and blood. Immediately following exposure on 1 day during week 103, five females and five males from each exposure group were placed in urine collection cages equipped with fecal collection screens, and an ice bath for cooling collected urine samples. Blood was collected from the orbital plexus of each animal approximately 30 min and 24 h post-exposure and sent to WIL Research Laboratories, Inc. (Ashland, Ohio) for analysis of blood nickel concentration. Urine and fecal samples were collected from each cage approximately 24 h post-exposure and sent to KAR Laboratories, Inc. for urine and fecal analysis of nickel concentrations. Urine was analyzed also for creatinine and albumin concentrations. Other standard hematology and clinical chemistry parameters for blood as well as other standard urinalysis parameters for urine were measured by Charles River Laboratories.

Statistics:

In-life data: The data were initially tested for normality using Levene's test for equality of variance followed by the Shapiro–Wilks test for normality.
A p≤0.001 level of significance was required for either test to reject the assumptions. If both assumptions were fulfilled, a singlefactor ANOVA was applied, with animal grouping as the factor, utilizing a p≤0.05 level of significance. If the parametric ANOVA was significant at p≤0.05, Dunnett's test was used to identify statistically significant differences between the control group and each nickel sulfate-treated group at the 0.05, 0.01 and 0.001 levels of significance. If either of the parametric assumptions was not satisfied, then the Kruskal–Wallis nonparametric ANOVA procedure was used to evaluate intergroup differences (p≤0.05). The Dunn's multiple comparison test was applied if this ANOVA was significant, again utilizing significance levels of p≤0.05, 0.01 and 0.001.

Survival Data: Kaplan–Meier estimates of group survival rates were calculated, by sex, and shown graphically. A log-rank dose response trend test of survival rates was performed utilizing dose coefficients. In addition, a log-rank test for survival was used to make pairwise comparisons of each treated group with the control group. Both the trend test and pairwise comparisons were conducted at the 0.05 significance level.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

The type and incidence of clinical signs observed in the treated groups were generally comparable to those observed in the control group.

Mortality:

mortality observed, treatment-related

Description (incidence):

There was a higher rate of mortality in groups 2–4 treated males and females during the first 24 weeks of this study which appeared to be nickel sulfate-related. Nickelinduced pulmonary toxicity secondary to aspiration of the nickel sulfate solution was a potential cause. A later exposure time after week 24 (since rats are nocturnal feeders and 10 mL/kg exposure volume early in the morning to animals with relatively full stomachs may have produced sufficient gastric back pressure to force a portion of the administered dose to the opening of the trachea where it was aspirated) was effective in increasing survival, possibly by reducing aspiration of the nickel sulfate.
Mortality during week 24-48: only one death in nickel sulfate-treated group 3.
For the entire 104 weeks period there was no apparent treatment-related effect on mortality in males. In females, there was an increasing exposure–response trend in mortality relative to the controls (p<0.008).

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Body weights decreased in a exposure-dependent manner, with significantly decreased body weights observed in the two highest exposure groups for males and females (groups 3–4) Reductions in weight gain relative to controls at study week 103 reached the level of biological significance (i.e., >10% decrease) in the group 3 and 4 males and the group 4 females. This significant weight reduction indicates that the Maximum Tolerated Dose was reached in this study for both males and females.

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

no effects observed

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

A few statistically significant differences in the hematology data were observed in the nickel sulfate-treated males and females. For example, there were increases in red blood cells, hematocrit and/or hemoglobin in some of the animals in the 30 and 50 mg/kg bw/day groups. These changes may be associated with dehydration or could be related to nickel effects on gene expression of erytropoetin (HIF-inducible factor). However, none of these differences was suggestive of a hyperplastic (i.e., leukemia) response and none of these changes was considered toxicologically meaningful since they were small and did not follow a consistent exposure-related pattern.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Numerous gross necropsy findings were observed for animals in the control and nickel sulfate-treated groups but the type and incidence of these findings observed for the treated animals were comparable to those observed in the control group, and were consistent with findings commonly seen in aging rats in a longterm study. None of the neoplastic or non-neoplastic microscopic findings was considered to be related to the experimental exposures. The non-neoplastic findings were either considered to be secondary to toxicity or incidental background occurrences rather than a direct effect of nickel sulfate. Some examples of non-neoplastic findings in the 50mg/kg bw/day males include: increases in yperplasia of pars distalis of the pituitary gland, bronchial inflammation, lymphoid follicle atrophy of spleen, mandibular lymph node cystic degeneration, histiocytes infiltration of mesenteric lymph nodes, hyperkeratosis of the tail, eye mineralization and vacuolization of adrenal cortex. In the stomach, there was an increase in the erosion of glands, but a decrease in epithelial erosion. Decreases in atrophy of pancreatic acinus, mineralization of aorta, hyperplasia of thymus and presence of renal tubule pigment were also observed. Most of these effects were not observed in the 50 mg/kg bw/day female animals with the exception of the increases in bronchial inflammation, spleen and mandibular lymph node effects and the decreases seen for kidney pigmentation, eye effects and erosion of stomach glands. The increased bronchial inflammation seen in 50 mg/kg bw/day male and female rats was considered to be the indirect result of minor aspirations during gavage exposure.

Histopathological findings: neoplastic:

no effects observed

Details on results:

The pathology report, pathology peer-review and the pathology working group concurred that nickel sulfate hexahydrate did not cause any carcinogenic effects in this study. Analysis of the tumor data revealed only one statistically significant (p<0.001) increase in tumors corresponding to keratoacanthoma (tail) in the group 2 males. However, this finding is of questionable toxicologic significance since there was no exposure–response relationship, the incidence rate in the group 2 males (15%) was only slightly higher than the upper end of Haseman's historical control incidence for this tumor type (0–14%) and the incidence rate in the remaining control and treated groups (0–7%) was within the range of the CRL-Ohio historical incidence (0–2%) and the Haseman historical incidence (0–14%). No other tumor finding in this study was statistically significant.
No notable differences were observed between controls and treated animals for the hematology, biochemistry and urinalysis parameters measured during the toxicokinetic satellite study.
Nickel levels in feces increased in an exposure-dependent manner in the treated males and females. The relatively high fecal levels compared to the blood and urinary nickel levels demonstrated that the majority of the nickel the animals were exposed to was not systemically absorbed, but was excreted in the feces.

Effect levels

1

Dose descriptor:

LOAEL

Effect level:

6.7 other: Ni/kg bw/d

Sex:

male/female

Basis for effect level:

body weight and weight gain

2

Dose descriptor:

LOAEL

Effect level:

30 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

3

Dose descriptor:

NOAEL

Effect level:

2.2 other: Ni/kg bw/d

Sex:

male/female

Basis for effect level:

other: overall effects

4

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: overall effects

Target system / organ toxicity

Key result

Critical effects observed:

no

Applicant's summary and conclusion

Conclusions:

The NOAEL of the test substance was determined to be 10 mg/kg bw/d.