Spatiotemporal variability and source apportionment of soil heavy metals in an urban cluster of the Yangtze River Delta,China
In China,regional environmental protection is of increasing significance due to population growth and urbanisation.The study investigated heavy metal pollution in surface soil from a city in the Yangtze River Delta urban agglomeration.Based on 1∶250 000 and 1∶50 000 soil geochemical surveys,the soil contents of eight heavy metals were evaluated according to a soil geochemical classification system.Geostatistics was used to analyse the spatiotemporal variations in heavy metal contents,while correlation,cluster and principal component analyses were used to analyse their sources.The average contents of seven heavy metals(As being the exception)in the two phases exceeded the reported soil background values for Jiangsu Province and China overall,indicating widespread soil pollution.Compared with the 1∶250 000 survey,the coefficients of variation of all heavy metal contents(except Cd)were significantly higher.The ranges of variation in contents in the two periods were higher and the continuity was poor.While the specific difference was more obvious at the greater survey scale,human activities also had a greater impact on local soil.The soil geochemical classification results showed that the soil in the two stages showed different degrees of heavy metal pollution,especially of Cd and Hg,indicative of local accumulation due to point source pollution.Analysis of the spatiotemporal variations in heavy metal contents in the two phases showed that over the years,heavy metal accumulation in soil had become severe,mainly due to Cd,Cu and Hg pollution.Source analysis showed that As,Cr and Ni mainly came from a small number of agricultural activities superimposed on the parent material,Cd,Cu and Hg mainly came from industrial activities,and Pb and Zn mainly came from transportation and a small number of industrial activities superimposed on the parent material.
soil heavy metalscontamination evaluationspatial and temporal variability characteristicsmultivariate statistical analysissource apportionment