Evaluation and Source Identification of Heavy Metal Pollution in Black Soils, Central-Eastern Changchun, China

Black soils are vital agricultural resources, and assessing heavy metal contamination in black soils is of great significance to the sustainable development of agriculture and the environment. In this study, 1246 surface soil samples were collected from the central-eastern part of Changchun, where phaeozems and chernozems are widely distributed, and the As, Hg, Cr, Cd, and Pb concentrations were determined to investigate the pollution status in the black soils by the geoaccumulation index ( I geo ). To eliminate the influence of background variation and improve the calculation accuracy of the I geo values, the local background values of these five elements were estimated after classifying the samples into three clusters with the k -means clustering method. The I geo calculated with the local background values not only identified the pollution that is difficult to recognize in the low-background areas but also eliminated the easily misidentified pollution in the high-background areas. The I geo results show that the black soils are mainly contaminated with Hg, followed by Cd and Pb, and are almost free from the pollution of As and Cr. The further the sampling sites are from urban areas, the milder the soil pollution is. A positive matrix factorization (PMF) analysis shows that industrial activities and coal burning contributed the most to the heavy metal pollution in the black soils, followed by agricultural activities, which should be paid more attention to.