Analysis of Trihalomethanes in Drinking Water Distribution Lines and Assessment of Their Carcinogenic Risk Potentials

This study examined the spatial and seasonal variations of trihalomethanes (THMs) and estimated the health risks associated with THM exposure in drinking water through various pathways. Water samples were collected from 14 distribution districts connected to the Ulutan Distribution System (UDS) and the Süleyman Bey Distribution System (SDS), which supply drinking water to Zonguldak Province, Türkiye. THMs were measured using the USEPA 551 method. The median total trihalomethanes (TTHMs) ranged from 41 μg/L to 71 μg/L, which is below the Turkish drinking water standard of 100 μg/L. Chloroform (TCM) was the most common trihalomethane in all distribution networks in UDS and SDS. On the other hand, pre-ozonation oxidation after chlorination in SDS disinfection caused the contribution of brominated THMs (62%) to THM formation to be higher than that of TCM (38%). The study on cancer risk reveals that ingestion (96%) poses the greatest risk of the investigated pathways, followed by dermal contact (3.95%), while inhalation has been found to have a negligible effect. The highest and lowest median TTHMs occurred during winter and summer. The findings of the study show that the distribution areas of Kozlu, Ömerli, Topçalı, and Uzunçayır, for both genders, exhibit an unacceptable cancer risk level according to the criteria established by the USEPA (˃10 −4 ). Bromodichloromethane (BDCM) and chlorodibromomethane (DBCM) are the main contributors to cancer risk for males and females in UDS and SDS. The hazard index (HI) data indicated that the HI value remained below one for both UDS and SDS. Sensitivity analysis of THMs demonstrated that exposure frequency (EF) was the primary parameter contributing to the maximum potential impact on the total cancer risk exposure frequency (EF), followed by body weight (BW) and exposure duration (ED). Further, the results provide valuable information for health departments and water management authorities, enabling the formulation of more specific and efficient policies to minimise THM levels in drinking water distribution networks.