Data relevant to characterizing the adverse health effects of nickel “sulfides” in humans arises almost exclusively from processes in the refining of nickel. Exposures in the refining sector should not be confused with those in mining, where the predominant mineral from sulfidic ores is pentlandite [(Ni, Fe)9S8]. Pentlandite is very different from the nickel subsulfides and sulfides found in refining. Although a modest lung cancer excess has been found in some miners (ICNCM, 1990), this excess has been consistent with that observed for other hard-rock miners of non-nickel ores (Muller et al., 1983). This, coupled with the fact that millers have not presented with statistically significant excess respiratory cancer risks, suggests that the lung cancer seen in miners is not nickel- related (ICNCM, 1990). Further, pentlandite has not been shown to be carcinogenic in rodents intratracheally instilled with the mineral over their lifetimes (Muhle et al., 1992). Therefore, for purposes of this document, it should be understood that any critical health effects discussed relative to “sulfidic nickel” pertains mainly to nickel sulfides (NiS) and subsulfide (Ni3S2).
As in the case of oxidic nickel, it is the inhalation of sulfidic nickel compounds that is the route of exposure of greatest concern in occupational settings. No relevant studies of dermal exposure have been conducted on workers exposed to sulfidic nickel. Because exposures to sulfidic and oxidic nickel compounds have often overlapped in refinery studies, it has sometimes been difficult to separate the effects of these two nickel species from each other. Overwhelming evidence of carcinogenicity from animal studies, however, has resulted in the consistent classification of sulfidic nickel as a “known carcinogen” by many scientific bodies (IARC, 1990; ACGIH, 1998; NTP, 1998). This evidence is discussed below.
Inhalation Exposure: Sulfidic Nickel