Identifying heavy metal pollution hot spots in soil-rice systems: A case study in South of Yangtze River Delta, China.

The soil-rice system in China is subjected to increasing concentrations of heavy metals (HMs) which derived from various sources. It is very critical to investigate the concentrations, spatial characteristics and hot spots of HMs content in the soil-rice system. This study presents work completed on 915 soil-rice sample pairs collected from South of Yangtze River Delta, China. These samples were evaluated for HM concentrations. Ordinary Kriging and the Getis-Ord index were used to explore spatial distributions and pollution hot spots. Averaged HMs content in soil is shown to be Zn > Cr > Pb > Cu > Ni > As > Hg > Cd, and concentrations in rice arrange as Zn > Cu > Cr > Ni > As > Cd > Pb > Hg. Compared with Chinese maximum permissible limits, mean content of all HMs in farmland soil are at safe levels and averaged content of all HMs in rice were also at safe levels except As and Ni. Ni was most polluted HM in soil Most of and showed relatively high content in farmland soil in southeastern part. As and Ni are the most polluted in rice, with highest content distributed in the northwestern and southern area, respectively. The majority of HMs pollution hot spots in soil clustered in the central area. Pollution hot spots of Ni and As in rice are mainly concentrated in the central part and southeastern part, correspondingly. Our results found a weak link between content and spatial pattern of pollution status of HMs in soil and rice. The results are anticipated to contribute to more efficient and accurate control of HMs pollution in soil-rice system, and assist decision-makers achieve a balance between cost and regulation of HM pollution.