Distribution, sources, and potential health risks of fluoride, total iodine, and nitrate in rural drinking water sources of North and East China

Small-scale water sources serving villages and towns are the main source of drinking water in rural areas. Compared to centralized water sources, rural water sources are less frequently monitored for water quality and have poor post-treatment facilities, making them vulnerable to drinking health risks. To reveal the hydrochemical characteristics, contaminant sources, and health risks in rural water sources, 189 water samples were collected from lakes and reservoirs, rivers, and groundwater in North and East China for major ions, nutrient salts, microelements, and stable isotope analysis. Statistical analysis and isotopic tracing were performed, as well as human health risk assessment. The exceeding threshold rates for fluoride (F-) and nitrate (NO3-) in surface water were 1.8 % and 9.1 %, respectively. For groundwater, the exceeding threshold rates were 20.9 % for F-, 15.7 % for total iodine (TI), and 4.5 % for NO3-. F- and TI were mainly derived from the leaching of fluoride- and iodine-containing minerals by cationic exchange, and NO3- is mainly derived from nitrogen in the soil (31.7-43.9 %), the use of ammonia fertilizers (24.3-36.1 %), and the discharge of manure and sewage (19.4-31.9 %). Nitrogen in the soil can be an important source of nitrate in the aquatic environment, and soils with higher clay content have a greater retention effect on the migration of nitrogen pollutants from the surface to the groundwater. F- in water sources contributes most to human health risks for drinking, followed by NO3- and TI, and a higher proportion of groundwater (37 %) present health risks for drinking than surface water (14 %) for children. Authorities should give high priority to optimizing the choice of water sources and technology for water treatment, and rational measures should be taken to protect water sources from the threats of anthropogenic pollution.