Karst water quality, source of pollution, and health risk assessment in China

Karst areas cover approximately 15 % of the world's non-frozen terrestrial surface area and contain lots of freshwater resources. Nearly one-third of China's territory comprises karst regions, where karst water plays an crucial role as the primary water source for local residents due to its good quality and abundance. However, being an open and semi-open ecosystem, the karst water system is highly vulnerable to external influences, including climate change and human activities, leading to a noticeable deterioration in water quality. By conducting a comprehensive literature review, this paper collects a large amount hydrochemical and isotope data related to karst water in China. The analysis of this data reveals significant disparity between karst water chemistry in North and South China, primarily stemming from distinct geological and climatic conditions. Karst waters are generally contaminated with sulfate, nitrate, heavy metals, and organic matter, all of which can cause harm to human health. The decline in karst water quality within China is mainly attributed to human activities, such as urban development, agricultural fertilizer, and industrial activities. The pollutants can directly or indirectly enter the karst water aquifers through various pathways, such as runoff and infiltration, thereby degrading the quality of karst water. This study reviews the chemical characteristics and pollution sources of karst water in China and assess human health risk of the nitrate in karst water, offering some insights for the future protection of karst water.