Controlling mechanism and water quality assessment of arsenic in China's Yellow River Basin

Arsenic (As) is a well-known toxic and carcinogen element, and As contamination has gained public concerns worldwide. Mechanisms, sources, and potential health risks of high As in the China's Yellow River Basin (CYRB), a water-deficient area and the largest loess deposition area in the world, remain largely unknown. Hydrogen and oxygen isotopes, major ions, and As were analyzed in 409 river water and 164 groundwater samples in dry season to decipher these problems. Samples were alkaline (pH = 8.0 ± 0.4), and As concentrations (5.29 ± 10.5 μg/L) in the CYRB were above the world average, especially in upstream and midstream. About 9.1% and 13.0% of samples in river water and groundwater had As concentrations above the permissible limit of WHO, respectively. Based on self-organizing map (SOM) analysis, about 50.6% of samples with high As were SO₄–Cl–Na type while about 46.4% of samples with low As were HCO₃–Ca–Mg type. The δD (−62.5 ± 11.3‰) and δ¹⁸O (−8.5 ± 2.1‰) values of river water were higher than the groundwater (δD = −69.7 ± 10.2‰, δ¹⁸O = −9.9 ± 1.4‰), and most samples with As >10 μg/L were below the local and global meteoric water lines, indicating the evaporation effect on As enrichment, especially for river water. Evaporites dissolution of loess and ion exchange increased water salinity, accelerated desorption of As and enriched As in CYRB. Meanwhile, oil and coal exploitation contributed to the high As in the northwestern Loess Plateau. Health risk assessment indicated that 41.6% and 59.8% of groundwater samples posed high carcinogenic risk for adults and children, respectively. Therefore, corresponding measures must be implemented in these areas. In the future, As geochemistry in wet seasons in the CYRB and the characteristics among different seasons will be explored. These results highlight the impact of dry climate and anthropogenic activity on As enrichment in arid/semi-arid regions.