BLADDER CANCER AND EXPOSURE TO DISINFECTION BYPRODUCTS IN WATER THROUGH INGESTION, BATHING, SHOWERING AND SWIMMING IN POOLS: FINDINGS FROM THE SPANISH BLADDER CANCER STUDY

Abstract

ISEE-241 Introduction: Exposure to disinfection by-products (DBP) in drinking water has been associated with increased bladder cancer risk. At high doses, several byproducts are mutagens and animal carcinogens. Trihalomethanes (THM), the most prevalent DBP, are highly volatile. Previous epidemiological studies focused on exposure through ingestion of drinking water, although recent studies have shown the relevance of other routes. We evaluated the association between increased bladder cancer risk and DBP exposure through ingestion of drinking water as well as inhalation and dermal absorption during showering, bathing and swimming pool use, employing THM level as a marker of DBP exposure. Methods: We conducted a hospital-based case-control study in Spain between June, 1998 and June, 2001, including 1,226 cases and 1,271 controls (87% males). Lifetime residential history, source and amount of drinking water, as well as adult habits for bathing, showering and swimming pool use, were recorded. This information was linked with current measures of THM levels in drinking water and with extensive historical data from local authorities and water treatment plants. Odds ratios (OR) and 95% confidence intervals (CI) were calculated through logistic regression adjusting for age, gender, region, smoking status, education, urbanicity of residence, fruit and vegetable intake and overall quality of interview. Results: Average household THM level, an index evaluating all routes of exposure, was associated with an increased bladder cancer risk. OR=1.99 (95% CI=1.03–3.86) for average residential THM level >49 □g/l relative to ≤8 □g/l (p value for linear trend=0.012). For exposure to THM via ingestion, OR for the highest quartile (<35 □g/day), relative to non-exposure, was 1.38 (95% CI=0.9–2.0). Duration of showering and bathing, weighted by average residential THM level, was associated with an OR of 1.89 (95% CI=1.2–3.0) for ≥333 compared with >50 minutes/day x □g/L (p-value for linear trend=0.006). Ever attending a swimming pool was associated with increased risk, OR=1.59, 95% CI=1.2–2.1. Discussion: This is the first study to evaluate non-ingestion exposure routes to DBP and bladder cancer. Exposure misclassification due to the considerable temporal and spatial variability of THM levels within municipality, and the difficulties in recalling lifetime habits, probably resulted in non-differential misclassification and underestimation of the point estimates. These results support the hypothesis that long-term exposure to THM at levels currently observed in many industrialized countries is associated with an increased bladder cancer risk and are the first epidemiologic data suggesting the importance of inhalation and dermal absorption of THM.