A nested case-control study of stomach cancer mortality among automobile machinists exposed to metalworking fluid

PURPOSE: In a nested case-control study of 140 stomach cancer deaths (1941–1984) among 46,384 automobile workers, we examined risk in relation to lifetime exposure to metalworking fluid (MWF) in machining and grinding operations. METHODS: Exposure was defined during varying windows of biologic time (<10 years before death, 10–20 years before death, and > 20 years before death) and evaluated using a nonparametric smoothing technique and conditional logistic regression. Exposure was measured by duration, intensity (mg/m3), and cumulative exposure (mg/m3-years) to each MWF type (straight, soluble, or synthetic), as well as by duration of exposure to selected metals, additives, and components of the fluids. RESULTS: When data from three plants were combined, grinding with water-based synthetic or soluble MWF increased the risk of stomach cancer mortality. Those grinding with synthetic MWF with more than 1.3 mg/m3–years exposure during the 10 years just prior to death experienced a 4.4-fold risk of stomach cancer (95% CI 1.5–13.1). Increased risk was also observed among those in the highest category of soluble grinding grading exposure (OR 1.9; 85% CI 1.0–3.6). In plant-specific analysis, there was evidence of increased risk of stomach cancer associated with exposure to straight MWF and iron, as well as the water-based fluids. CONCLUSIONS: Study findings suggest that stomach cancer mortality was associated with exposure to each MWF type. Results suggesting that synthetic MWF may act as a stomach cancer promoter are of particular concern because this MWF is widely used in todayʹs high speed grinding operations.