Asbestos as a cofactor in carcinogenesis among nickel-processing workers.

It has been widely assumed, especially in the absence of other explanations, that lung cancer and nasal sinus cancers observed among nickel smelter workers are the result of the carcinogenicity of nickel. Although there may be such influence, supplementary hypotheses are also possible. The nickeliferous ores from at least one major smelter in New Caledonia (excess numbers of cancers have been found in these smelter workers) are derived from serpentinized host rocks which contain large amounts of chrysotile asbestos. Analysis indicates that nickel ores from this area are heavily contaminated by these fibers. The deposits are mined for their nickel content, but workers may be exposed to the asbestos fibers contained in the deposits. Hygiene measures limited to the avoidance of nickel may be inadequate under such circumstances and should be reevaluated so as to prevent the inhalation of asbestos-containing dusts.