Health Risk of Heavy Metal and Implication for Ecological Threat in Soils Weathered from the Black Shale.

Heavy metals were analyzed in rhizosphere soils and rice grains collected from typical black shale areas. The concentrations of As, Cd, Cu, and Zn in the rhizosphere soil exceeded the current soil environmental quality standards. Cd exhibited the highest bioaccumulation capacity, with 45% of rice grains exceeding food safety limit. Structural equation modeling (SEM) revealed that soil organic matter indicated that 34.79% of rice Cd accumulation and approximately 10%-25% of other metals were inhibited. Multiple regression modelling showed that in areas with high geological background of black shales, the screening and intervention values for soil Cd were adjusted to 0.24 mg kg and 0.42 mg kg for pH ≤ 5.5 and 0.27 mg kg and 1.66 mg kg for pH 5.5 - 6.5 respectively. Primary exposure pathways for non-carcinogenic risks were identified as food ingestion and skin contact. This study provides fundamental information for land use application and development in region with high geological background.