N-nitrosamines in karst groundwaters in southwestern China: Risks and implications for drinking water safety

Groundwater is a vital drinking water source for populations in remote karst regions. However, the highly developed karst tube systems facilitate the infiltration of surface wastewater containing N -nitrosamines, raising concerns about groundwater safety. To assess the safety of groundwater and identify which types are safer for consumption, this study investigated N -nitrosamines in various groundwater types, including ground river, karst cavern, well, and mountain spring waters, in Guangxi, a typical karst region in southwestern China. The total concentrations of eight N -nitrosamines in groundwater ranged from 5.1 to 70.3 ng/L, with N -nitrosodiethylamine (NDEA), N -nitrosodimethylamine (NDMA), and N -nitrosopyrrolidine (NPYR) being the dominant species. Ground river water exhibited significantly higher N -nitrosamine concentrations than karst cavern, well, and mountain spring waters. Significant correlations between N -nitrosamines and dissolved inorganic nitrogen suggested their co-emissions from domestic wastewater and the secondary formation potential of N -nitrosamines in groundwater. Redundancy analysis further identified domestic and swine wastewater as the primary sources. Ground river and mountain spring waters posed the highest risks among the four groundwater types, with 30 % and 20 % of sites, respectively, exceeding acceptable cancer risk thresholds. These findings underscore the importance of thorough water treatment before groundwater is used for drinking. Strict livestock farming and domestic wastewater discharge regulations are essential to mitigate contamination risks, particularly in karst areas. • N -nitrosamines are widespread in karst groundwater, dominated by NDEA, NDMA, and NPYR. • Ground river waters had higher N -nitrosamines than wells, springs, and caverns. • Domestic and swine wastewater were identified as the primary N -nitrosamine source. • The secondary formation potential of N -nitrosamines in groundwater was suggested. • Wells and caverns provided safer groundwater than mountain springs and ground rivers.