Nickel sulphide

Endpoint summary

Additional information

Manyin vitrogenetic toxicity studies, were identified characterizing the genetic toxicity of NiS. The primary cell types used in the studies included, Chinese Hamster Ovary (CHO) or Syrian hamster embryo (SHE) cells, though some assays also utilized mouse FM3A or C3H10T1/2 cells. Genotoxicity endpoints included chromosomal aberrations, morphological transformation, DNA strand breakage, and mutation frequency. Several studies evaluated cytotoxicity and/or cellular uptake of NiS along with genotoxicity. Most studies clarified the type of NiS (i. e., crystalline, amorphous) assessed in the study and several evaluated the comparative genotoxicity of multiple types.

The majority of studies identified reported findings of genotoxicity in CHO cells. Patierno and Costa (1985) reported that treatment of CHO cells with crystalline NiS induced single strand DNA breaks and DNA-protein crosslinks, but double stranded DNA breaks were not detected. Similar findings were reported by Sen and Costa (1985); in this assessment, crystalline NiS particles induced all four types of chromosome aberrations (gaps, breaks, exchanges, and dicentrics) at all doses and during all time points, and appeared to show a time-dependent, dose-response relationship. NiS also caused selective fragmentation of the heterochromatic long arms of the X-chromosomes. Sen and Costa (1986) further studied the genotoxicity of crystalline NiS and reported that exposure had minimal effect on cell cycle kinetics but caused a time-dependent (not dose-dependent) induction of sister chromatid exchanges. This group of investigators also demonstrated that NiS induced a significant, time-dependent number of chromosomal aberrations in heterochromatic regions in both CHO and C3H10T1/2 cells (Senet al. 1987).

Several studies compared genotoxicity of crystalline and amorphous NiS in CHO or SHE cells. Costaet al. (1982) reported that the reduced form of both crystalline or amorphous NiS (which allowed for an increased uptake into cells relative to the non-reduced form) increased morphological transformation. This study also demonstrated that treatment of CHO cells with crystalline NiS resulted in increased DNA strand breakage relative to untreated cells and cells exposed to amorphous NiS. The authors concluded that surface charge differences between the two forms affects phagocytosis into the cell and the ability to transform cells was correlated with the ability of cells to phagocytize NiS. The importance of the role of uptake of NiS was supported by data demonstrating a dose-dependent decrease in the number of surviving colonies treated with NiS or Ni₃S₂; however, transformed colonies were only observed with Ni₃S₂.

In a separate evaluation, Robisonet al. (1982) also reported DNA breakage following exposure to crystalline NiS but not amorphous NiS; DNA breakage did not initially slow the growth of CHO cells, but evidence that DNA breakage slowed cell proliferation was evident at 48 hours. The authors concluded that Ni²⁺ions liberated from phagocytized NiS particles were more accessible to the nucleus (relative to NiCl₂) to cause DNA damage. The relative importance of uptake was also reported in an assay using modified CHO cells (AS52 cells). A 24-hr exposure to NiS resulted in a significant dose-response correlation coefficient calculated for “amorphous NiS” based on the mutation frequencies for each dose (Fletcheret al. 1994). In comparing the administered doses to nickel levels in the cytosol and nucleus, the authors concluded that intracellular nickel (II) concentrations constituted an important determinant in cytotoxicity and mutagenicity responses by AS52 CHO cells to nickel compounds.

In FM3A cells from a mouse mammary carcinoma, NiS induced a dose-dependent (0.32 to 2 mM) increase in chromosomal aberrations – including gaps, breaks, and exchanges but no fragmentations (Umeda and Nishimura 1979; Nishimura and Umeda 1979). This group of authors also reported that the percent of aberrant metaphases decreased as recovery time increased.

Dose-dependent increases in cytotoxicity and mutation frequency were reported in Chinese hamster V79 cells and two V79 hprt deficient transgenic variants (G12 and G10) with the bacterial gpt gene integrated at different chromosome sites (Kargacinet al. 1993). Because mutation frequency varied between the cell types; the authors speculated that mechanisms of mutagenicity might differ across the transgenic cell lines. Positive results in G12 cells were later found to be due to epigenetic effects of nickel on DNA methylation rather than true mutagenic effects. Leeet al. (1993) reported that NiS caused dose-dependent (0.08 to 0.6 μg Ni/cm²) increases in cytotoxicity and reported a mutation frequency as high as 55-fold greater than the spontaneous mutation rate in G12 cells exposed to NiS for 24 hr.

The study published by Arrouijalet al. (1990) demonstrated positivein vitroclastogenic activity of α-Ni₃S₂in human lymphocytes. Statistically significant, dose-dependent increases in aberrations (generally ≥ 20 per 200 cells) were observed. Mutagenic effects were also assessed by Ames test in five strains; high toxicity (growth inhibition) was observed at concentrations of ≥ 500 μg/plate, though no mutagenic activity was observed in any of the strains. Mutagenic effects were also negative at the HPRT locus in V79 cells under the conditions tested. The authors of this study concluded that the soluble fraction was responsible for genetic toxicities observed.

As noin vivostudies with NiS were located, the study conducted by Arrouijalet al. (1990) can be used to read-across from Ni₃S₂. Following a single i. p. injection (a non physiological route of administration for a water insoluble nickel compound like nickel subsulphide), mice exhibited a significant increase of micronuclei frequency in polychromatic erythrocytes (PCEs) and a significant decrease in the number PCEs. Together within vitrofindings, the authors concluded that Ni₃S₂when injected as a suspension can causein vivoclastogenic effects.

Mayeret al.(1998) also conducted a multi-component study to evaluate the mutagenicity and genotoxicity of Ni₃S₂bothin vitroandin vivo. Results indicated that Ni₃S₂administration increased mutation frequency up to 4.5-fold duringin vitromutation studies using a BigBlueTM Rat 2 embryo fibroblast cell line (lac1 transgenic line). Assays were also conductedin vivoin transgenic rodent mutation models to investigate the DNA damaging effect and mutagenic potential of nickel subsulphide in target cells of carcinogenesis. CD2F1 mice and lacZ transgenic CD2F1 mice (MutaMouse mice), as well as F344 rats and lac1 transgenic F344 rats (Big Blue rats), exposed to Ni₃S₂via inhalation did not exhibit the same type of responses observedin vitro, and treatment-related genotoxic effects were generally limited to DNA damage in mice; no mutagenicity was observed. Thus, the authors suggested that the collective findings were supportive of a non-genotoxic model for nickel carcinogenesis. A repeated dose inhalation study with nickel subsulphide in rats can be read across to nickel sulphide (Bensonet al., 2002). This study found that inhalation exposuresto nickel sulphate and nickel subsulphide at toxic levels can cause genotoxicity in the respiratory tractin vivo.However, only Ni₃S₂exposure (0.6 mg/m³, 0.44 mg Ni/m³) significantly increased epithelial and nonepithelial cell proliferation after 3 and 13 weeks.

Collectively, NiS – both crystalline and amorphous - have demonstrated the potential to cause genotoxicity, including DNA damage, under laboratory conditions in a number of cell lines. However, in a number of these studies, negative and positive controls were not incorporated, nor were statistical analyses implemented to determine the significance of findings. Taken together with the results ofin vivostudies conducted with another sulfidic Ni compound, Ni₃S₂, the weight of the evidence evaluation indicates that a genotoxic potential should be considered for NiS.

 

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

Collectively, NiS – both crystalline and amorphous - have demonstrated the potential to cause genotoxicity, including DNA damage, under laboratory conditions in a number of cell lines. However, in a number of these studies, negative and positive controls were not incorporated, nor were statistical analyses implemented to determine the significance of findings. Taken together with the results ofin vivostudies conducted with another sulfidic Ni compound, Ni₃S₂, the weight of the evidence evaluation indicates that the genotoxic potential of NiS should be considered. Recently, nickel compounds have been recognized as genotoxic carcinogens with threshold mode of action in ECHA RAC opinion on nickel and nickel compounds OELs (see discussion of ECHA 2018 report inAppendix C2).

Justification for classification or non-classification

Ni sulfide is classified as Muta. 2;H341 according to the 1st ATP to the CLP Regulation. Background information can be found in the discussion section.