Assessment of carcinogenic risk and non-carcinogenic hazard index associated with trihalomethanes exposure in indoor swimming pools in Shenzhen, China

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Trihalomethanes (THMs), a class of disinfection by-products (DBPs) formed during the chlorination of swimming pool water, have raised substantial public health concerns owing to their potential genotoxicity and carcinogenicity. This study assessed the multi-pathway lifetime cancer risks and non-cancer hazard indices of THMs in indoor swimming pools in Shenzhen, China. THMs were quantified in water (30 cm depth) and air (1.2 m height) using headspace gas chromatography (HS-GC-ECD) and thermal desorption gas chromatography (TD-GC), respectively, across six geographically distributed pools. Swimmer exposure parameters were determined through questionnaire surveys and Monte Carlo simulations, with risks evaluated under central tendency exposure (CTE) and reasonable maximum exposure (RME) scenarios according to the Risk Assessment Guidance for Superfund, Part A, E, and F. Median THM concentrations were 48.85 μg/L (IQR: 39.91–63.06) in water and 35.32 µg/m³ (IQR: 18.22–98.27) in air. Inhalation was the dominant exposure pathway, contributing 82% of cancer risk and 73% of non-cancer hazard index. Lifetime cancer risks reached 3.62 × 10−6 (CTE) and 1.10 × 10−5 (RME), between the USEPA’s tolerable risk range (10−6 to 10−4), and the non-cancer hazard indices were 6.35 × 10−3 (CTE) and 1.91 × 10−2 (RME), below the unacceptable level (1.0). The present study indicates that carcinogenic risks and non-cancer hazard index from chronic THM exposure in Shenzhen’s indoor swimming pools remain within acceptable limits as defined by regulatory guidelines.