Spatio-temporal variations of trihalomethanes and haloacetic acids in water distribution systems with multi-pathway health risk and toxicological assessment

Abstract

Abstract This study investigated the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) across 16 distribution areas in Zonguldak Province (Türkiye). We analyzed their seasonal variations and public health risks in the surface water-supplied Ulutan (UDS) system in comparison with the groundwater-sourced Çaycuma (CGS) and Devrek (DGS) systems. Analyses were executed using USEPA methods 551.1 and 552.3, which revealed that total trihalomethanes (THM 4 ) and five regulated haloacetic acids (HAA 5 ) peaked in the UDS during winter, reaching 75.4 $$\:{\upmu\:}\text{g}\:$$ / L and 38.4 $$\:{\upmu\:}\text{g}\:$$ / L, respectively. The Kruskal-Wallis test was used to confirm significant seasonal variations, while Pearson and Spearman correlations were utilized to identify total organic carbon (TOC) and UV absorbance at 254 nm (UV 254 ) as the primary factors for DBP formation. The results of long-term exposure models demonstrated that ingestion is the dominant carcinogenic pathway across all networks, accounting for over 99% of the cumulative risk. Furthermore, non-carcinogenic Hazard Index (HI) values for UDS, CGS, and DGS remained below the USEPA threshold of 1. HAAs exhibited higher toxicity and genotoxicity than THMs. Monobromoacetic acid (MBAA) was the most significant contributor to the overall toxicity observed in all three systems. These findings provide a robust basis for the updating of regional drinking water safety policies and public health strategies.