Possible enrichment process of Cd in the Se-rich soil area of Lanshan District, Shandong Province, China.

Abstract

High cadmium (Cd) concentrations widely occured in selenium (Se)-rich soils, which has been an important obstacle in the usage of Se-rich soils. There is still no special information detailing the enrichment process and mechanism of Cd in Se-rich soils. 4474 soils and 21 rocks in Lanshan District were sampled to detect its enrichment process. The surface soils have Cd concentrations of 0.01-9.41mg·kg-1 (an average of 0.16mg·kg-1). The soil Cd concentrations were significantly correlated with soil Se concentrations. The relatively higher-Cd surface soils are distributed in Lower-middle Ordovician carbonate areas with Se-rich soils and Quaternary areas with typical anthropic activities. Surface soils in Ordovician carbonate area have the highest Cd concentrations. Soil Cd concentrations are significantly correlated with sulfophil elements (Zinc (Zn), Copper (Cu), Molybdenum (Mo), Lead (Pb) and Arsenic (As) etc.), Ca (Calcium) concentrations and soil organic carbon (SOC). The soil and rock samples from different geological units also confirmed soil Cd concentrations developing from Ordovician carbonates were higher than those from other rocks. The results indicate the soil Cd concentrations were the complex consequences of bedrock, soil-forming processes and anthropogenic activities. Higher Ca concentrations and more reduction environments result in high-Cd bedrock. CaCO3 leaching and alkaline pH, which are the special soil-forming process of carbonates, enrich Cd in soils. Agricultural and industrial activities also affect soil Cd concentrations. An enrichment model of Cd in Se-rich soils is forwarded.