Epidemiologic evidence on the carcinogenicity of metalworking fluids.

The purpose of this review is to organize and evaluate the epidemiologic evidence regarding the potential carcinogenicity of metalworking fluids. Published literature was initially examined to identify the key contributions, with a strong emphasis on the series of studies by Eisen et al. A key challenge to addressing the issue is the diversity of metalworking fluids, additives, and by-products produced in use, along with the notable changes in the composition and use of such agents over time. Although several smaller cohort studies provided useful data on this issue through the 1980s, the Eisen et al. studies offer unique information given the size of the cohort, sophistication in exposure assessment, and detailed analysis of cancer mortality risks within the cohort as a function of estimated exposure. The most notable associations, based on precision, magnitude, and evidence for increasing risk with increasing exposure are those between straight metalworking fluids and both rectal and laryngeal cancer, as well as soluble metalworking fluids and laryngeal cancer. Further progress will require additional studies of the scale of Eisen et al.'s as well as a more systematic approach to integrating information from toxicology and industrial hygiene into the interpretation of the epidemiologic literature.