Groundwater health risks and water quality assessment in the sources of many mighty rivers in Asia: Ngari, Tibet

Abstract

The Ngari region (NR) in Tibet, hailed as the crown jewel of the "Asian Water Tower", is the origin of numerous major rivers that traverse extensive regions of Asia, as well as the source of severe chronic groundwater heavy metal poisoning in South and Southeast Asia. The well-being of its water ecosystem not only impacts local residents, agricultural activities, and industrial development but also exerts a vital role in modulating regional and global climate patterns. As a significant factor impacting groundwater quality in NR, trace metal(loid)s (TMs) have not yet been explored. In light of this, the study delivers a pioneering analysis of the sources, spatial distribution, and health risks of 17 TMs in the drinking groundwater of NR for residents. Under the combined influence of volcanic-geothermal activities, parent rock weathering, mining activities, and industrial processes, the levels of heavy metals exhibit significant spatial variability. The comprehensive water quality assessment revealed that over 60 % of the sampling points showed poor water quality, rendering them unsuitable for long-term potable use. Health risk evaluations have indicated that Sb, As, U, Tl, and V are the primary contributors to carcinogenic concerns. The Hazard Index (HI) and Hazard Quotient (HQ) values for As both exceed 1, while the pollution indices of Sb, As, U, Tl, and V all approach 1. This suggests that daily oral exposure to arsenic may have a severely adverse impact on the health of Ngari residents and potentially lead to cancer. This study establishes a scientific foundation for metal cycling within the groundwater environment and ecological management in NR, and also provides theoretical guidance for preventing long-term chronic TM poisoning and ensuring sustainable protection of the regional water supply.