Evaluation of centralized drinking water supply systems for reducing N-nitrosamine-associated carcinogenic risks in karst regions

Le résumé fourni par la source

Providing safe drinking water in remote karst regions requires balancing microbial protection with control of disinfection byproducts under highly heterogeneous hydrogeological conditions. Against a background of intensive agriculture, widespread livestock farming, and vulnerable karst hydrogeology in rural Southwest China, centralized supply systems have progressively replaced private wells through the implementation of Drinking Water Safety Projects. However, the behavior of N -nitrosamines in these decentralized treatment systems remains poorly constrained. Here, nine N -nitrosamines were investigated across 52 rural sites to quantify their occurrence, distribution patterns and associated carcinogenic risks. Total concentrations ranged from 3.5–16.1 ng/L in source water and 3.5–40.8 ng/L in finished drinking water. N -nitrosodimethylamine (NDMA) and N -nitrosopyrrolidine (NPYR) dominated across sites, while N -nitrosodibutylamine (NDBA) was more frequently detected after treatment. Despite detectable formation during disinfection, centralized tap water exhibited significantly lower median concentrations and reduced estimated lifetime carcinogenic risks compared to private wells. Process-level analysis suggested that N -nitrosamine occurrence was associated with both source-water characteristics and disinfectant type. Chloramine disinfection was associated with elevated concentrations, whereas free chlorine disinfection using calcium hypochlorite was not associated with a significant increase under current operational conditions. These findings clarify N -nitrosamine behavior in rural karst water systems and provide a basis for optimizing disinfection strategies to minimize chemical risks while maintaining microbial safety.

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