Heavy metal accumulation and its spatial distribution in agricultural soils: evidence from Hunan province, China

The issue of heavy metal pollution in Hunan province, China, has attracted substantial attention. Current studies of heavy metal soil pollution in Hunan province mainly focus on medium and small scales, thus heavy metal pollution is rarely considered at the province scale in Hunan. In order to investigate the heavy metal pollution status in agricultural soils in Hunan province, literature related to heavy metal soil pollution in Hunan province was reviewed and organized from the following databases: Web of Science, China national knowledge infrastructure (CNKI), Wanfang Data, and China Science and Technology Journal Database (CQVIP). The literature data for the contents of Pb (122 soil sampling sites), Zn (103 sites), Cu (102 sites), Cd (105 sites), As (100 sites), Hg (85 sites), Cr (95 sites), and Ni (62 sites) in agricultural soils were obtained at the province scale. The spatial auto-correlation method was applied to reveal the spatial distribution of heavy metal accumulation. The average contents of the 8 heavy metals in agricultural soils of Hunan were all significantly (P < 0.05) higher than their background values and they were not distributed evenly across the Hunan province; the content of each heavy metal in eastern Hunan (including the cities of Yueyang, Changsha, Zhuzhou, and Chenzhou) was higher than that of other regions. The exceeding standard rate (the ratio of surveyed content to the background value) for Cu, Cd, As, and Hg had strongly positive spatial correlation, whereas Zn and Ni presented a negative spatial correlation. Overall, the higher exceeding standard rates of the 8 heavy metals were mainly distributed in the highly industrialized cities such as Changsha, Zhuzhou, Xiangtan, Chenzhou, and Hengyang, thus more attention should be paid to such areas to manage soil pollution.