Frits, chemicals

Endpoint summary

Description of key information

Value used for CSA:

• NOAEL (oral, systemic, animal data): 2.2 mg Ni/kg bw/day read-across from Ni sulphate hexahydrate (Heim et al 2007)
• LOAEC (inhalation, local, animal data): 0.5 mg Ni/m3 (Dunnick et al, 1995)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

10 mg/kg bw/day

Study duration:

chronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

LOAEC

0.5 mg/m³

Study duration:

chronic

Species:

rat

Additional information

• Approximately fifteen studies evaluating the toxicity of nickel oxide following repeated exposure were identified in the literature. These studies all evaluated toxicity associated with inhalation; no repeated dose studies evaluating effects associated with oral, dermal, or other routes were identified.
• Data for repeated-dose toxicity via oral exposure are read-across from Ni sulphate.  In addition, a summary document on the chronic oral toxicity Ni compounds can be found in the attached background document entitled, "Background-Oral Chronic Exposure Effects" (Section 7.5.1 of IUCLID) and in Appendix B4 of this CSR.  
• In a 2-year OECD 451 carcinogenicity study, decreased body weight gain ranging from 4% to 12% was recorded (males and females combined) following oral gavage of 2.2 to 11 mg Ni/kg bw/day. A dose-related reduced survival achieving statistical significance at the two highest dose levels was seen in females (Heim et al., 2007). The LOAEL of 6.7 mg Ni/kg bw/day based on reduced body weight and increased mortality together with a NOAEL of 2.2 mg Ni/kg bw/day from the Heim et al. (2007) study is taken forward to the risk characterisation for oral repeated dose toxicity, taking differences in oral absorption between nickel oxide and nickel sulfate into account.
• Data for repeated-dose toxicity via inhalation exposure to nickel oxide described below.  The inhalation studies ranged in exposure duration from 12 days to lifetime exposures, including 1, 3, 4, 6, 12, 13, 24, and 24+ month durations of nickel oxide inhalation. Several studies evaluated toxicity at the end of exposure, and some also included evaluation of toxicity one to three months following the cessation of exposure. Both green (high calcining temperature) and black (low calcining temperature) nickel oxides were evaluated, though most studies focused on a single dose of green nickel oxide. Toxicity was evaluated in rats, mice and hamsters. Endpoints generally included evaluation of body and organ weight changes, assessment of tissue damage (primarily in lung), mortality and gross toxicity, and alterations in serum or bronchoalveolar lavage fluid (BALF) chemistry.
• The most robust data characterizing toxicity following repeated doses of nickel oxide was reported in a series of publications by Dunnick and colleagues (1988, 1989, 1995; Benson et al. 1989). These studies were associated with a comprehensive bioassay conducted by the National Toxicology Program (NTP) that compared the toxicity of NiO, nickel sulphate, and Ni3S2 (NTP, 1996a, b, c). Toxicity evaluations were conducted following 16 days, 3 months, and two years (exposure on weekdays only) of exposure to green NiO (0, 1.2, 2.5, 5.0, 10, or 30 mg NiO/m3) in F344/N rats and B6C3F1 mice. Endpoints examined included clinical signs of toxicity, body and organ weights, histopathology, and measurement of the concentration of nickel in lung tissue. Following 12-day and 3-month exposures, adverse effects in rodents were primarily limited to the lung (e.g., increased tissue weight, inflammation, macrophage hyperplasia); effects were noted to occur in a dose dependent fashion, and were generally more severe in rats than mice. Following two years of exposure, effects included dose-dependent occurrence of alveolar and bronchiolar hyperplasia, inflammation, fibrosis, lymphoid hyperplasia of the lung-associated lymph nodes, and increases in lung weight. No increased mortality was observed due to NiO exposure of any duration. Relative to the other nickel compounds evaluated, NiO was the least toxic, though it resulted in the highest lung burden of nickel. As such, the authors generally concluded that toxicity to the lung correlated with solubility of the nickel compound rather than the amount of nickel in the lung. The LOAEC for respiratory effects in the chronic study was 0.6 mg/m3.
• In a series of studies associated with, but not specifically included in the comprehensive NTP bioassay, Benson et al. (1989) evaluated biochemical and cytological changes in BALF in rats and mice following 13 weeks or 6 months of exposure to green NiO (0, 0.6, 2.5 or 10 mg/m3). Generally, dose-dependent changes were observed for the majority of endpoints evaluated, including changes in total protein, lactate dehydrogenase, total nucleated cells, the percent of neutrophils and macrophages, macrophage proliferation, interstitial pneumonia and chronic inflammation. The severity and incidence of histopathological findings were evaluated over time in the 6-month exposure study (Benson et al., 1995); effects were generally most severe two months following the initiation of exposure, remained steady until the cessation of exposure. However, the incidence of lesions continued to increase in mice for two months after the termination of exposure, whereas the incidence (but not severity) decreased during the 4-month recovery phase. Based on the findings that changes in biochemical indicators of lung lesions measured in BALF paralleled the nature and incidence of morphological changes (as reported by Dunnick and colleagues), the authors concluded that inhalation of occupationally relevant aerosol concentrations of green NiO can produce toxic effects in the lungs of rodents.
• Chronic exposure to multiple doses of nickel oxide was also investigated by a number of other groups. Weischer and colleagues (1980a, 1980b) evaluated clinical and clinico-chemical parameters in blood, serum and urine, along with body and organ weight changes and tissue damage associated with exposure to NiO aerosols (three doses) for 21-, 28-, or 120-days in female and male rats. Gender differences were observed in the severity of changes for a number of clinical chemistry endpoints, though data generally suggested that toxicities occurred in a dose-dependent fashion with some exceptions (e.g., organ weight changes). The authors concluded that subchronic NiO inhalation induced lesions in lungs, liver and kidneys in rats.
• Though most studies characterizing repeated inhalation toxicity associated with nickel oxide did not report increased mortality, Takenaka et al. (1985) observed dose-dependent, significant decreases in mean survival times following exposure to 60 μg/m3 or 200 μg/m3 in rats. Exposure-dependent decreases in body weight, increased lung weight, and histopathological signs of toxicity were also reported. Following a similar duration of exposure, Tanaka et al. (1988) did not see an exposure related effect on body weight gain or mortality following inhalation of NiO (200 μg/m3 or 1200 μg/m3) in rats, though significant increases in lung weight and pulmonary lesions were clearly associated with exposure. These authors also evaluated animals 8 months following the cessation of a 12-month exposure and did not note any significant toxicities following long-term exposure. Cho et al. (1992) also evaluated toxicity in rats immediately following a 12-month inhalation exposure, and 8 months following cessation of the exposure. Similarly, the authors reported increased lung tissue weight; these authors also reported that NiO exposure resulted in a significant increase in lung lipid concentration following chronic exposure.
• Several studies also evaluated the toxicity of repeated inhalation exposure to a single concentration of nickel oxide. Murthy et al. (1983) exposed rats to NiO (120 μg/m3) for 12 days, collected BALF, and documented a number of cellular toxicities in macrophages using transmission electron microscopy. In a study evaluating the potential co-carcinogenicity of inhaled NiO and cigarette smoke, Wehner et al. (1975) exposed hamsters over a lifetime (53.2 μg NiO/L) and reported that NiO exposure did not appear to effect survival. The authors concluded that while the hamsters eventually developed increasingly severe pneumocomiosis in response to the chronic NiO exposures (53.2 μg/L), they did not find a significant carcinogenic effect of the inhaled NiO or a co-carcinogenic effect if cigarette smoke.
• Collectively, the available studies demonstrate that repeated inhalation of nickel oxide in laboratory species results in dose-dependent, adverse toxicological responses, primarily in the lung. These responses include, but are not limited to, increased tissue weight and a variety of cellular lesions associated with inflammation and hyperplasia (typically observed in macrophages). Repeated inhalation exposure to nickel oxide typically did not significantly influence mortality rates, body weight changes, nor was it associated with significant adverse effects in tissues other than the lung. Given the robust nature of the available studies, the data were sufficient to characterize toxicity following repeated inhalation exposure; however, data were insufficient to characterize repeated dose toxicity from all other routes.

The following information is taken into account for any hazard / risk assessment:

• ORAL: Data are read-across from Ni sulphate. A 2-year oral carcinogenicity study reported a NOAEL of 10 mg/kg body weight/day (2.2 mg Ni/kg b. w. /day) and a LOAEL of 30 mg/kg body weight/day (6.7 mg Ni/kg b. w. /day) (Heim et al. 2007). The LOAEL of 6.7 mg Ni/kg bw/day based on reduced body weight and increased mortality together with a NOAEL of 2.2 mg Ni/kg bw/day is taken forward to the risk characterisation. A comprehensive summary document on this topic is provided as a backgound document in section 7.5.1 of IUCLID and in Appendix B4 of this CSR.
• INHALATION: Exposure related toxicities were noted following 13 weeks and two years of exposure to NiO (Dunnick et al. 1989, 1995; NTP, 1996a) in both rats and mice. Adverse effects in rodents were primarily limited to the lung (e.g., increased tissue weight, inflammation, macrophage hyperplasia).  The most sensitive LOAEC from the chronic study in rats was 0.6 mg NiO/m3 or 0.5 mg Ni/m3.  

Justification for classification or non-classification

• Ni oxide is classified for repeated dose toxicity (STOT-RE 1;H372), according to the 1st ATP to the CLP Regulation. Supporting information can be found in the discussion section for this endpoint.