Spatial distribution and risk assessment of heavy metal contamination in soil-crop systems near gold mining areas

Heavy metal contamination from mining activities presents significant risks to soil quality, crop safety, and human health. This study systematically evaluates the levels, spatial distribution, bioaccumulation, and health risks of cadmium (Cd), lead (Pb), mercury (Hg), arsenic (As), and chromium (Cr) in agricultural soils and staple crops (wheat and maize) near historical gold mining sites in Pingdu, China. A total of 91 soil and crop samples were analyzed using inductively coupled plasma mass spectrometry and atomic fluorescence spectrometry. Pollution indices (Igeo, Pi, PN, RI) identified Cd as the primary contaminant, with widespread exceedances of background levels and regulatory thresholds, particularly in the northwest mining-affected areas. Principal component analysis (PCA) further linked Cd, Pb, Hg, and As to industrial and mining sources, while Cr appeared to originate from natural soil materials. Bioaccumulation analysis revealed that wheat exhibited a higher bioconcentration factor (BCF) for Cd than maize, suggesting greater susceptibility to metal uptake. Health risk assessments, based on oral ingestion, dermal contact, and inhalation exposure pathways, showed that Cd and As posed significant non-carcinogenic and carcinogenic risks, particularly for children. Notably, Cd in both wheat and maize exceeded the acceptable carcinogenic risk threshold for adults, while only Cd in wheat posed a carcinogenic risk to children. Given these findings, urgent measures are needed to mitigate heavy metal contamination in agricultural lands, particularly through stricter controls on mining-related emissions and soil remediation strategies. This study provides critical insights for environmental risk management and policy development in mining-impacted regions.