Childhood cancer incidence and arsenic exposure in drinking water in Nevada.

Inorganic arsenic exposure through drinking water causes cancer in adults; however, the carcinogenic potential in children remains unknown. A recent leukemia cluster in Churchill County, Nevada, where arsenic levels in water supplies are relatively high, has prompted concern. The authors investigated the incidence of childhood cancer between 1979 and 1999 in all 17 Nevada counties, grouped by low (i.e., < 10 microg/l), medium (10-25 microg/l), and high (35-90 microg/l) population-weighted arsenic levels in public drinking water supplies. The standardized incidence ratios (SIRs) for all childhood cancers combined were 1.00 (95% confidence interval [CI] = 0.94, 1.06), 0.72 (95% CI = 0.43, 1.12), and 1.25 (95% CI = 0.91, 1.69) for low-, medium-, and high-exposure counties, respectively. There was no relationship between arsenic levels in water and childhood leukemia (SIRs = 1.02, 0.61, and 0.86, respectively [95% CIIs = 0.90, 1.15; 0.12, 1.79; and 0.37, 1.70, respectively]). For all childhood cancers, excluding leukemias, the SIRs were 0.99 (95% CI = 0.92, 1.07), 0.82 (95% CI = 0.42, 1.22), and 1.37 (0.92, 1.83), respectively. The excess in 5- to 9-yr-old children and 10- to 14-yr-old children was in bone cancers, and the excess in 15- to 19-yr-old young adults was primarily in lymphomas. The findings in this study are reassuring in that leukemia risks were not increased at the concentrations of arsenic in water found in this study. Nonetheless, the results raise the possibility that there are increased risks for nonleukemic childhood cancers that require confirmation in other studies, particularly those in which higher exposures are addressed.