Heavy Metals Contamination in a Soil-Rice System: Identification of Spatial Dependence in Relation to Soil Properties of Paddy Fields.

Elevated levels of heavy metals in soils and crops is of environmental and health concerns.  To assess the extent of heavy metal contamination of paddy soils grown to rice in Wenling city in Zhejiang Province, China, extensive sampling was carried to identify spatial patterns and bioavailability to rice grown on these soils at the regional scale. The results showed that some areas in the paddy fields were contaminated by heavy metals, and rice grains in such areas may post potential risk for Cd. Sources of contamination are mainly due to various industries in the surrounding area of Wenling city as well applied agricultural chemicals. Except for Ni, spatial patterns for Cd and Pb, Cu and Zn in soil were similar. The spatial correlation of heavy metal in soil-rice was further observed by means of spatial distribution of enrichment index, indicating that the transfer of heavy metals in the paddy soil–rice system was related to intrinsic and extrinsic factors. The availability or uptake of heavy metal by rice was significantly affected by rice genotype. The bioavailability of metals was positively spatial correlated with soil organic matter (OM) and sand; negatively correlated with pH, electrical conductivity (EC), silt and clay. Soil pH and OM had strongest correlation with accumulation of Cd, Ni and Zn in rice grains; with little effect on Cu. Based on multiple regression analyses, heavy metal concentrations in rice grains were well described based on soil heavy metal concentrations and soil properties in paddy fields.