Arsenic in drinking-water and risk for cancer in Denmark.

Background: Arsenic is a well-known carcinogen, which is often found in drinking-water. Epidemiologic studies have shown increased cancer risks among individuals exposed to high concentrations of arsenic in drinking-water, whereas studies of the carcinogenic effect of low doses have had inconsistent results.

Objective: Our aim was to determine if exposure to low levels of arsenic in drinking-water in Denmark is associated with an increased risk for cancer.

Methods: The study was based on a prospective Danish cohort of 57,053 persons in the Copenhagen and Aarhus areas. Cancer cases were identified in the Danish Cancer Registry, and the Danish civil registration system was used to trace and geocode residential addresses of the cohort members. We used a geographic information system to link addresses with water supply areas, then estimated individual exposure to arsenic using residential addresses back to 1970. Average exposure for the cohort ranged between 0.05 and 25.3 microg/L (mean = 1.2 microg/L). Cox's regression models were used to analyze possible relationships between arsenic and cancer.

Results: We found no significant association between exposure to arsenic and risk for cancers of the lung, bladder, liver, kidney, prostate, or colorectum, or melanoma skin cancer; however, the risk for non-melanoma skin cancer decreased with increasing exposure (incidence rate ratio = 0.88/microg/L average exposure; 95% confidence interval, 0.84-0.94). Results adjusted for enrollment area showed no association with non-melanoma skin cancer.

Conclusions: The results indicate that exposure to low doses of arsenic might be associated with a reduced risk for skin cancer.