Objective To assess possible relationships between occupational exposure to metalworking fluid (MWF) mist and bladder cancer risk.

Methods A nested case-control study was conducted within a cohort of workers from 6 steel-producing factories. Cases were diagnosed with bladder cancer in 2006–2012. Three controls per case were randomly selected from the cohort, matched to cases by age at diagnostic and counter-matched according to 4 strata of surrogate measure of exposure to MWF mists, assessed using a job-exposure matrix. Cases (n = 84) and controls (n = 251) provided information during personal interviews on occupational history, including the type of MWF used (straight oils, soluble oils, synthetic fluids), and smoking habits. Experts estimated intensity, frequency and probability of exposure to each MWF mist. Conditional logistic regression, adapted to counter-matching, was used to calculate Odds-Ratios (OR) and 95% confidence intervals (95% CI), taking into account the 3 types of MWF mist, and adjusting for smoking and other occupational factors.

Results A statistically significant OR for bladder cancer was observed for workers exposed to MWF mist, for over 20 years during occupational history (OR 3.32, 95% CI: 1.48–7.46). ORs were statistically significant for workers ever exposed to straight oils (OR 2.14, 95% CI: 1.05–4.36), for over 20 years during occupational history (OR 5.49, 95% CI: 1.75–17.2). ORs statistically not greater than 1 were observed for workers ever exposed to soluble oils (OR 1.46, 95% CI: 0.71–3.02), for over 20 years during occupational history (OR 2.43, 95% CI: 0.88–6.70). OR was not statistically significant for workers ever exposed to synthetic fluids (OR 1.2, 95% CI: 0.31–3.30). Dose-response relationships were observed with cumulative exposure to MWF mist and straight oils in the last 20 years before diagnosis.

Conclusion This study highlighted association between recent exposure to straight oils and bladder cancer risk, but did not detect any relationship concerning soluble oils or synthetic fluids.