Annual and Seasonal Variability of Trichloromethane in Drinking Water of Kunshan City 2016–2022 and Associated Health Risks

This study aimed to evaluate the annual pollution characteristics of trichloromethane (TCM) in Kunshan City's tap water from 2016 to 2022. This research analyzed 566 tap water samples from centralized water supply units, utilizing the GB 5749-2006 Sanitary Standard for Drinking Water as the evaluation benchmark. Data analysis employed non-parametric tests and Spearman's correlation analysis using Excel 2017 and SPSS 26.0. The results indicated a 100% compliance rate with the TCM limit (0.06 mg/L), with median annual concentrations ranging from 0.1 to 6.4 μg/L. Significant inter-annual variations were observed (H = 222.5, <i>p</i> < 0.01), with the lowest levels in 2019 and the highest in 2020. Quarterly analysis revealed significant seasonal differences (H = 94.0, <i>p</i> < 0.01), peaking in the third quarter (8.0 μg/L) and bottoming in the first quarter (3.5 μg/L). TCM concentrations showed significant correlations with annual and quarterly trends, turbidity, and chlorides (|rs| > 0.3, <i>p</i> < 0.01) but not with pH (rs = -0.0025, <i>p</i> = 0.55). While Kunshan City's drinking water demonstrates satisfactory TCM levels, an increasing annual trend and higher concentrations in the latter half of the year warrant continued monitoring and investigation. In this study, we assessed the health risks for households in Kunshan, China, due to trichloromethane (TCM) in drinking water. The overall carcinogenic risk from multiple exposure pathways was slightly above the ideal level, while the non-carcinogenic risk was within an acceptable range.