Pollution characteristics and health risk assessment of heavy metals in the vegetable bases of northwest China

Highlights: • A comprehensive heavy metal pollution and health risk assessment of agricultural soil was conducted. • Soils of the examined vegetable bases were more seriously polluted by heavy metals than was groundwater. • Heavy metal pollution in soil leads to high health risks to the public, especially children. • Major pollution sources affecting the vegetable basessuch as transportation, agricultural activities and stock farming. The objective of this study was to investigate heavy metal contamination in four major vegetable bases and determine the health risks of residents in the vicinity of the highly urbanized city Urumqi in Xinjiang, China. In this paper, we determined the contents of six heavy metals (i.e., As, Zn, Cd, Cr, Hg, and Pb) in surface soil and groundwater to evaluate the levels of heavy metal pollution and human health risks using the pollution index (PI), the Nemerow integrated pollution index (NIPI), the ecological risk factor (Eⁱ_r), risk index (RI) and the health risk assessment model. The results showed that (1) The PI, NIPI, the ecological risk factor and risk index indicated that Cd and Hg were the primary pollutants in Sishihu village. These indices suggested moderate to slightly heavy potential ecological risks. In Anningqu town, Hg and Cd led to high levels of pollution and posed slightly heavy potential ecological risks. In Qinggedahu village, it was concluded that the metals Zn, Cr, Cd, Hg, and Pb caused moderate to heavy pollution. In Liushihu village, the pollution trends in the area were low. The results of the pollution level of the irrigation well water (i.e., groundwater) indicated that the well water was considerably safer than the soil, but Cr posed a slight pollution risk. (2) The non-carcinogenic risks for adults based on the HI values of these four vegetable bases were Sishihu village > Anningqu town. For children, the carcinogenic risks posed by As through trough inhalation and ingestion were the main exposure pathways. From the TCR results, it can be seen that in Sishihu village, Anningqu town, and Qinggedahu village, the TCR values for adults and children were >1 × 10⁻⁴ (unitless), and this degree of carcinogenic risk is unacceptable. (3) The identification of risk sources determined the main pollution sources affecting the vegetable bases were human activities and natural sources. Anthropogenic activities were most often related to traffic pollution sources and agricultural pollution sources, such as the irrational use of pesticides and fertilizers and stock farming. The results are important for designing remediation scenarios to control the spread of contamination as well as for serving as a reference point for soil environmental protection efforts in this region.