Abstract

MWF mixtures vary across manufacturing process, facilities, enterprises and over time. The routes of exposure are dermal in liquid phase, and inhalation as dusts, mists and vapours. The challenge is to generalise from specific worker populations observed over many decades and from animal studies limited to few priority components. Cancer risks have been observed in both hazard identification and exposure-response studies. Respiratory disorders and performance deficits are other health effects of MWFs appearing as increased morbidity and mortality or reduced pulmonary function, as well as immune-mediated disorders: adult-onset asthma and hypersensitivity pneumonitis (HP). Dermatitis has been a constant associate of MWFs for more than two centuries. The goal here was to explore the development of a generic summary of MWF effects to determine exposure levels conferring an acceptable low level of risk in most metalworking environments. Only total gravimetric measures of airborne dusts or mists were considered, usually with restriction to the respirable fraction. Aggregate cancer excess risk was estimated from the few studies with adequate retrospective exposure assessments and work history. Lifetime risk was calculated. Annual proportional loss of respiratory capacity was evaluated, using a benchmark dose procedure. Incidence of asthma and hypersensitivity pneumonitis (HP) was examined as were aggregate symptoms focusing largely on respiratory complaints. For MWF exposure to 0.1 mg/m³ over 45 yr, the lifetime risk of attributable cancer was about 3.5% and attributable respiratory impairment would occur in 4.5% of workers. Lifetime risk of asthma or HP (under outbreak conditions) was 80% at 0.1 mg/m³. After 45 yr at 0.1 mg/m³ MWF, excess prevalence of primarily respiratory symptoms would be 9 percent based on published studies, and 20 percent from NIOSH investigations.