Pollution accumulation, sources, and risk assessment of potentially toxic elements in the soil-walnut system: insights from over 50 years of wastewater irrigation in a lead/zinc smelting region.
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Pollution from potentially toxic elements (PTEs) in farmland soil poses significant risks to food safety and human health. Accurately identifying and assessing the health risks of PTEs in farmland soil is crucial. In this study, we apply the pollution index to evaluate soil pollution levels, employ positive matrix factorization- principal component analysis to identify pollution sources, and quantify health risks through four exposure pathways associated with walnut kernel consumption. The results revealed that mercury (Hg) and cadmium exhibited the highest soil enrichment factor and very high contamination (pollution index > 6). Agricultural activities (6.6%), industrial production (6.2%), coal combustion (12.7%), and natural sources (74.5%) were identified as the major sources of these pollutants. Notably, the hazard index for adults (1.05) exceeded the recommended value, while the total cancer risk (TCR) index for children (2.84E-03) was lower than that for adults (2.04E-03), indicating that there are non-carcinogenic health risks, and the cumulative carcinogenic risk value of residents is not within the acceptable range. It is worth highlighting that Hg emerged as a priority pollutant originating from agricultural activities, with a higher bioconcentration factor observed in walnut kernels (0.511). Additionally, coal combustion contributed 31.3-35.3% to the total cancer risk, emerging as the second-largest contributor after natural sources. Furthermore, a significant correlation was observed between diagenetic elements and the enrichment of PTEs, emphasizing the importance of characterizing the content and composition of diagenetic elements in specific polluted areas to enhance our understanding of PTE sources. This study highlights the accumulation of PTEs in Baiyin City's environment, which presents significant challenges to long-term sustainability, particularly in regions severely affected by environmental degradation. Therefore, urgent measures are required to mitigate PTEs pollution and safeguard both farmland and public health.