Trihalomethane Levels in Municipal Drinking Water of Madrid (Spain) and Health Risk Assessment for Oral Exposure

Abstract Trihalomethanes (THMs) are generated in the drinking water treatment plant, due to the reaction of the halogenated disinfection compounds with the natural organic matter (NOM). They are related to health problems both from the point of view of cancer development and other important diseases. This study aimed to assess the quality of tap water in Madrid in terms of prevention and control of THMs risks in the supply water treated by Canal de Isabel II (CYII) in a total of 108 samples throughout 2015 to 2020, to distinguish the problems of the different 21 districts or types of buildings, the seasonality and to estimate the risk of exposure to THMs from tap water in the population of Madrid. The variables considered include year, seasonality, district of Madrid and sampling point. The concentrations of THMs detected in all samples were within the current legal limit (100 µg/l). Chloroform was the compound with the highest contribution to the sum of THMs. A decreasing trend in THMs concentrations was observed over the years of the study related to the removal of NOM and the use of chloramines. THM levels were higher in the central area than in the peripheral districts and the lowest concentrations were detected in summer. Regarding risk assessment, the results of the non-carcinogenic risk indicate that there is no potential risk from tap water consumption for the adult population. For the carcinogenic risk, only water samples with THM concentrations between 50 and 75 µg/l could constitute a risk for high consumers.