Risk assessment and source apportionment of heavy metals in the soil–water-grain system in a typical area of the central Qinghai–Tibet Plateau

Heavy metals (HMs) within the soil–water-grain system have substantial effects on both eco-environmental and human health. This study collected 232 samples (58 surface soil, 89 drinking water, and 85 highland barley) from the central Qinghai–Tibet Plateau (QTP) and analyzed the contamination characteristics, source apportionments, and associated risks of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb). The study employed geochemical normalization factors, biotoxicity assessment methods, ecological risk and health risk assessment models, and the Positive matrix factorization (PMF) model to assess the soil–water-grain system. The results showed no accumulation of HMs in highland barley, and no biotoxicity was observed. Soil was identified as the primary medium contributing to ecological and health risks, with overall risk levels ranging from slight to moderate, particularly higher in the northern and eastern regions of the study area. Cr posed non-carcinogenic risks to local children in 100% of cases and to adults in 27.27% of cases. Pb presented non-carcinogenic risks in 81.82% of cases for children and 36.36% for adults. Furthermore, As, Cd, and Cr were found to pose carcinogenic risks to both children and adults. Non-carcinogenic and carcinogenic risks were more pronounced in children than in adults. Children’s health risks were primarily driven by As concentrations in grains, with a sensitivity contribution exceeding 90%. The Monte Carlo simulation (MCS) indicated that ingestion rates were more sensitive for children, while body weight showed an inverse relationship. The PMF model identified three potential sources of HMs: anthropogenic, geogenic, and environmental. Therefore, to ensure the sustainable development of ecology and the health of residents, it is urgent to conduct routine soil remediation and maintain a balanced diet to mitigate the migration and transformation of HMs in the study area and improve the health level of residents.