Arsenic levels in ground water and cancer incidence in Idaho: an ecologic study

Abstract

Long-term exposure to arsenic above 50 microg/L in drinking water has been related to multiple types of cancers. Few epidemiologic studies conducted in the US have detected an association between regional exposures below this level in drinking water and corresponding cancer occurrence rates. This county-level ecologic study evaluates arsenic levels in ground water and its association with targeted cancer incidence in Idaho, where some regions have been found to contain higher arsenic levels. Using cancer incidence data (1991-2005) from the Cancer Data Registry of Idaho and arsenic data (1991-2005) from the Idaho Department of Environmental Quality, we calculated the age-adjusted incidence rate for cancers of the urinary bladder, kidney and renal pelvis, liver and bile duct, lung and bronchus, non-Hodgkin's lymphoma (NHL), and all malignant cancers according to arsenic levels in ground water. Multivariate regression analysis was applied to evaluate the relationship between arsenic levels in ground water and cancer incidence. For males, but not for females, age-adjusted incidence for lung cancer and all malignant cancers was significantly higher in the intermediate arsenic counties (2-9 microg/L, n = 16) and the high arsenic counties (>or=10 microg/L, n = 5) compared to the low arsenic counties (<2.0 microg/L, n = 23). When adjusted for race, gender, population density, smoking and body mass index (BMI), no relationship was found between arsenic levels in ground water and cancer incidence. In this ecological design, exposure to low-level arsenic in ground water is not associated with cancer incidence when adjusting for salient variables. For populations residing in southwestern Idaho, where arsenic has been found to exceed 10 microg/L in ground water, individual risk assessment is required in order to determine whether there is a link between long-term arsenic exposure at these levels and cancer risk.