Comment on Caprolactam Study

Abstract

There is evidence that adult lead exposure increases cancer risk. IARC has classified lead as a ‘probable’ carcinogen, primarily based on stomach and lung cancer associations.We studied mortality among men in a lead surveillance program in 11 states,. categorized by their highest blood lead (BL) test (0–<5 µg/dl, 5–<25 µg/dl, 25–<40 µg/dl and 40+ µg/dl).There were 58,368 men with a median 12 years of follow-up (6 to 17 years from lowest to higher BL category), and 3337 deaths. Half of the men had only one BL test. There was a strong healthy worker effect (all cause SMR=0.69, 95% CI: 0.66–0.71). The highest BL category had elevated lung and larynx cancer SMRs (1.20, 95% CI: 1.03–1.39, n=174, and 2.11, 95% CI: 1.05–3.77, n=11, respectively); there were no significant excesses of any other cause-specific SMR. Lung cancer RRs by increasing BL category were 1.0, 1.34, 1.88, and 2.79 (test for trend p=<0.0001), unchanged by adjustment for follow-up time. The lung cancer SMR in the highest BL category with 20+ years follow-up was 1.35 (95% CI: 0.92–1.90).We found an association of blood lead level with lung cancer mortality. Our data are limited by lack of work history (precluding analyses by duration of exposure), and smoking data, although the strong positive trend in RRs by increasing blood lead category in internal analysis is unlikely to be caused by smoking differences. Other limitations include different lengths of follow-up in different lead categories, reliance on few blood lead tests to characterize exposure, and few deaths for some causes.