Characteristics and the possible origins of selenium in surface soil in Lanling County, Shandong Province, China

Soil selenium (Se) levels deeply affect the Se intake in the human body, and the origins of soil Se are significant for the utilization of Se-rich soils and local human health. The Se origins of Se-rich soils were detected by comparing surface soil Se levels and exogenous soil Se fluxes in two areas with different parent rocks. Soil Se levels in Kuangkeng Town (0.095–0.631 mg/kg) are higher than those in the Cangshan Subdistrict (0.044–0.526 mg/kg). However, the net flux of exogenous soil Se in Cangshan Subdistrict (0.793 g/ha/y) is observed to be 2.7 times that in Kuangkeng Town (0.294 g/ha/y). The geological background of Ordovician carbonate in Kuangkeng is confirmed to be responsible for the Se-rich soil. Se enriches in soil with the leaching of numerous CaMg(CO 3 ) 2 in Ordovician carbonates during weathering, which is the important Se origin of Se-rich soil. Soil Se levels overlying Ordovician are also significantly higher than those overlying Cambrian and Quaternary strata, and the geostatistical analysis also indicates a dominating Se source of parent rocks. The geochemical cycles of soil Se are forwarded. Therefore, Ordovician carbonates should be of concern for Se-rich soils although they have low-Se levels.