Health Stream Literature Summary - Issue 50 - June 2008

Arsenic in drinking-water and risk for cancer in Denmark.
Baastrup, R., Sorensen, M., Balstrom, T., Frederiksen, K., Larsen, C.L., Tjonneland, A., Overvad, K. and Raaschou-Nielsen, O. (2008) Environmental Health Perspectives, 116(2); 231-7.

High arsenic concentrations (up to several hundred micrograms per litre) in drinking water have been associated with various internal cancers and with skin cancer. The effects of exposure to low doses of arsenic have not been addressed in many studies and results have been inconsistent. This cohort study was conducted to determine if individual exposure to low levels of arsenic in drinking water in Denmark is associated with a risk of cancer.

This study was based on the prospective Danish cohort Diet, Cancer and Health study in which 57,053 persons were enrolled between 1993 and 1997 living in one of 23 municipalities in the Copenhagen or Aarhus area of Denmark. At enrolment information was collected on diet, beverages, smoking, education, medical conditions, occupations, reproductive factors, body mass index and skin reactions to sun. Cohort members were followed up for cancer incidence using the population-based Danish Cancer Registry from the time of enrolment until the date of first cancer diagnosis, emigration, death or 1st August 2003, whichever came first. Cancers of the lung, bladder and colorectum and non-melanoma and melanoma skin cancers were included. Residential histories of cohort members were traced between 1970 and 2003 by record linkage to the Central Population Registry. Arsenic concentrations in Danish drinking water were obtained and the average arsenic concentration for each water utility was calculated between 1987 and 2004. Geographic information systems were used to link addresses with water supply areas. For each cohort member two exposure measures were calculated, a time-weighted average exposure and a cumulated arsenic exposure.

Of the cohort members, 56,378 persons were included who filled in the questionnaire, reported daily intake of tap water and had not had a cancer diagnosis before enrolment. The time-weighted arsenic exposure of the cohort members calculated from 41 years of age up to the date of enrolment varied between 0.05 and 25.3 micro g/L with a median concentration of 0.7 micro g/L. The results with no adjustment for enrolment area showed no significant association between exposure to arsenic and risk for any type of cancer except for non-melanoma skin cancer, for which higher arsenic exposure was associated with lower risk. The incidence rate ratio (IRR) for non-melanoma skin cancer was 0.88 (95% CI, 0.84-0.94) per micrograms per litre increase in time-weighted average exposure. A similar pattern was seen for cumulated arsenic exposure with an IRR of 0.95 (95% CI, 0.92-0.97) for a 5-mg increase in exposure. Results adjusted for enrolment area showed virtually no effect for non-melanoma skin cancer, an insignificant inverse risk associated with melanoma skin cancer and a significantly increased risk for breast cancer in association with time-weighted average exposure to arsenic (IRR = 1.05; 95% CI, 1.01-1.10).

There were no statistical significant associations found between arsenic concentrations in Danish drinking water and the risk for cancers of the lung, bladder, kidney, liver prostate or colorectum. An inverse association was found between arsenic concentrations and risk for skin cancers, which suggests that arsenic might have a protective effect at low concentrations. The results also indicated that arsenic in drinking water might slightly increase the risk of breast cancer. The findings here should be interpreted with caution as more studies are required to confirm the results.