Each type of nickel-containing alloy is a unique substance with its own special physico-chemical and biological properties that differ from those of its individual metal constituents. The potential toxicity of a nickel alloy (including carcinogenic effects) must, therefore, be considered separately from the potential toxicity of nickel metal itself and other nickel-containing alloys.
While there are no studies of nickel workers exposed solely to nickel alloys in the absence of metallic or oxidic nickel, studies on stainless steel and nickel alloy workers (who would likely have low level nickel alloy exposures) suggest an absence of nickel-related excess cancer risk. Intratracheal studies on animals have generally shown an absence of cancer risk in animals exposed to nickel alloys. Collectively, these studies suggest that nickel alloys do not act as respiratory carcinogens. For many alloys, this may be due to their corrosion resistance which results in reduced releases of metal ions to target tissues.
With respect to non-carcinogenic respiratory effects, no animal data are available for determining such effects, and the human studies that have looked at such endpoints have generally shown no increased mortality due to non-malignant respiratory disease.
Because alloys are specifically formulated to meet the need for manufactured products that are durable and corrosion resistant, an important property of all alloys and metals is that they be insoluble in aqueous solutions. They can, however, react (corrode) in the presence of other media. Of particular importance to dermal exposures is the potential of individual alloys to corrode in sweat. The potential for nickel alloys to elicit an allergic reaction in occupational settings will depend on both the sweat resistant properties of the alloy and the amount of time a worker is in direct and prolonged skin contact with an alloy. Alloys that release less than 0.5 µg/cm2/week are generally believed to be protective of the majority of nickel- sensitized individuals when in direct and prolonged skin contact. Alloys that release greater than 0.5 µg/cm2/week of nickel may not, in and of themselves, be harmful. They may be used safely when not in direct and prolonged contact with the skin or when appropriate protective clothing is worn.