Inorganic-Organic Characteristics and Health Risk Assessment of Typical Underground River System in Southwest China

Karst groundwater provides drinking water for about 25% of the world's population. As the main type of karst groundwater, underground rivers are an important water supply source for karst areas in Southwest China. It is of great significance to master the water quality, pollution status and human health risk for water resources protection and safety use in southern karst areas.

To reveal the chemical compositions, pollution degree and health risk of underground river water.

22 groups of underground river water samples (half inorganic and half organic samples) from the underground river system of Shiziyan in Huixian, Guilin, Guangxi were collected. The concentrations and spatial distribution of 21 inorganic ions and 41 organic indices were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS), ion chromatography (IC) and gas chromatography-mass spectrometry (GC-MS).The single index pollution standard index method was used to evaluate the pollution of 17 inorganic ions and 15 detected organic compounds. The health risk assessment model recommended by the United States Environmental Protection Agency (US EPA) was used to study the human health risk of 10 major pollutants.

The results showed that: (1) Ca²⁺ and HCO₃^- were the dominant ions in the Shiziyan underground river. The concentrations of NH₄⁺, Fe, Al and Mn in the underground river exceeded the groundwater quality standard by 1.33, 1.2, 1.5 and 1.01 times, respectively, and the exceeding points were mostly located in the discharge area of the underground river. 18 organic compounds were detected, of which the detection rates of volatile organic compounds (VOCs), semi volatile organics (SVOCs) and organochlorine pesticides (OCPs) were 18.75%, 30.77% and 91.67% respectively. (2) Compared with the groundwater background values, the underground river water in the study area was slightly-moderately polluted by 10 inorganic indicators and 14 organic compounds. Some sampling points were seriously polluted by NO₃^-, Fe, Al and Mn, and one sampling point (UR8) was extremely polluted by benzo a pyrene. (3) According to the results of health risk assessment, the non-carcinogenic health risks of being exposed to drinking water and for skin exposure were 9.98×10^-3 per year for adults and 1.09×10^-2 per year for children, and carcinogenic health risks were 1.33×10^-7 per year for adults and 2.82×10^-7 per year for children, which were within acceptable levels.

There are various degrees of inorganic and organic pollution in the study area, but the pollutant indicators do not pose a non-carcinogenic or carcinogenic health risk to the population.