[Chlorination of drinking water in Spain and bladder cancer]

Drinking water chlorination generates trihalomethanes and other by-products with mutagenic and carcinogenic properties in animal experiments. Epidemiological studies have associated trihalomethanes to an increased risk of bladder cancer. We evaluate trihalomethane levels in four Spanish areas and calculate the bladder cancer risk attributable to this exposure.

Trihalomethanes have been analysed in 111 drinking water samples from four Spanish areas using gas chromatography. Water utilities were contacted and information on drinking water consumption in Spain has been collected. We reviewed the epidemiological studies that assess the association between bladder cancer risk and exposure to chlorination by-products. Attributable risk was calculated on the basis of these levels, mortality data per area and risk estimates obtained from the literature.

Mediterranean areas present the highest levels of trihalomethanes with 81, 80, 61 and 52 µg/l in Sabadell, Alicante, Barcelona and Manresa respectively. Lower levels are found in Tenerife and Asturias with 7 and 20 µg/l respectively. The bladder cancer attributable risk in high trihalomethane exposure areas may be, on average, around 20%.

The trihalomethane levels found are high compared to those of other European Union countries. In the high exposure areas, drinking water chlorination may generate a considerable number of bladder cancer cases. These estimations have to be carefully interpreted and verified with more extensive studies.