Lifetime exposure to arsenic in drinking water and bladder cancer: A population-based case-control study in Michigan

Background: Arsenic in drinking water has been linked with the risk of urinary bladder cancer; however, questions remain regarding risks from low-level exposure (<100 µg/L). The authors conducted a population-based case-control study in southeastern Michigan, USA, where approximately 230,000 people are exposed to arsenic concentrations between 10-100 µg/L. Methods: This study included 411 bladder cancer cases diagnosed between 2000 and 2004, and 566 controls recruited during the same time period. Individual lifetime exposure profiles were reconstructed, and residential water source histories, water consumption practices, and water arsenic measurements or modeled estimates were determined at all residences. Arsenic exposure was estimated for 99% of participants' person-years. Results: Overall, no increased risk of bladder cancer was identified for time-weighted average lifetime arsenic exposure >10 µg/L when compared with a reference group exposed to <1 µg/L (odds ratio (OR) = 1.14; 95% confidence interval (CI): 0.78, 1.74). However, increased risk of bladder cancer from >10 µg/L arsenic was observed among those individuals who drank >1 L/day of water from home and below-average amounts of other fluids (OR = 3.27; 95% CI: 1.13, 9.51). Exploratory temporal analyses suggest exposures between ages 45 and 52 are most critical for development of arsenic-related bladder cancer. Conclusions: These results suggest that bladder cancer risk may be increased for individuals consuming at least 1 L/day of water containing arsenic > 10 µg/L, coupled with below average amounts of other fluids. Selecting the appropriate exposure metric needs to be thoughtfully considered when investigating risk from low-level arsenic exposure.