Abstract:

Selenium (Se)-rich soil is a valuable resource for the production of Se-rich agricultural products. Soil derived from black shales weathering is usually of high concentration of Se and heavy metals. To guide the similar safe use of Se-rich soil, a black shales area in the central part of Zhejiang Province was selected to identify possible risks of heavy metals in crop exceeding standards, through the investigation on the concentration and bioavailability of heavy metals and Se in soil and crop. The results showed that the Se-rich and Se-sufficient soil in the study area accounted for 38% and 62% coverage; the Se-rich rice and lotus seeds were 85.71% and 100%, respectively. 26% of soil samples is of cadmium (Cd) content over the soil pollution screening value and less the soil risk control value. The proportions of Cd active and potential active states were of 57% and 40%, respectively. Up to 31% of rice samples exceeds national cadmium limit. The risk assessment based on the total concentration of heavy metals and sequential extraction shows that the Cd risk areas for the development and utilization of Se-rich soil are mainly located in Xipishangang and Yaotangbian area,and the cultivation of agricultural products should be prohibited. Other Se-rich hilly areas overlying black shales should be protected and rationally developed and utilized as low risk of Cd in crops and low bioavailability of heavy metals in soil, although cadmium concentration in soil is high.

Key words: black shales, selenium-rich soil, heavy metal, risk assessment, central part of Zhejiang Province