Evaluation of Arsenic levels in ground water and cancer incidence in Idaho: An Ecologic Study

Objective: Long-term exposure to arsenic in drinking water has been related to multiple types of cancers. This ecologic study evaluates the relationship between arsenic level in ground water and cancer incidence in Idaho.

Method: Using cancer incidence data, 1990-2004, from the Cancer Data Registry of Idaho and arsenic data from the Idaho Department of Environmental Quality, we conducted spatial analysis to identify geographic patterns in incidence for cancers of the bladder, kidney, liver, lung, non-Hodgkin's lymphoma (NHL), and all sites combined. Spatial regression was applied to evaluate the relationship between arsenic level in ground water and cancer incidence.

Results: Spatial clustering of lung cancer incidence was demonstrated in males (p=0.006) and females (p=0.001). Higher incidence for lung cancer and all cancer sites combined were clustered in north Idaho, while lower rates clustered in southeastern Idaho. Incidence for all cancer combined and lung cancer was significantly higher in intermediate arsenic counties (2-9µg/l, n=5) and high arsenic counties (≥10µg/l, n=16) compared to low arsenic counties (≤210µg/l, n=23). No relationship was found between arsenic level in ground water and cancer incidence. However, smoking prevalence is significantly associated with cancer incidence for bladder, kidney, lung, and all sites combined.

Conclusion: Exposure to arsenic in ground water is not associated with cancer incidence in Idaho. To clarify relationship between arsenic exposure and cancer risk, individual risk assessment adjusted for smoking and occupation is crucial in southwest counties where ground water has been found to contain relatively higher levels of arsenic.