Enrichment characteristics of potential risk elements in the black soil region of Northeast China

Heavy metals in topsoil mainly originate from the natural geological background and human activities, and once the soil is contaminated with heavy metals, it is difficult to restore it to its original natural state. Therefore, it is important to assess the level of influence of heavy metals in soil to provide information for agricultural production. To clarify the intensity of anthropogenic impact on the soil environment in the black soils region (BSR), we used the geochemical data of 0–20cm topsoil (anthropogenic impact depth) and 150–180cm subsoil(natural background) to analyze the topsoil heavy metal enrichment coefficient for cadmium, mercury, lead, arsenic, zinc, nickel, copper, chromium, and their spatial distribution characteristics in BSR . The analysis showed that the heavy metal enrichment coefficients of lead, arsenic, zinc, nickel, copper and chromium are basically less than 2.0 in BSR, and there are only localized points with enrichment coefficients of greater than 2.0. Cadmium and mercury are more obviously enriched in the black soils area, and the enrichment areas are mainly distributed south of Harbin. The mercury enrichment area is distributed in a north–eastward strip along Shenyang, Changchun, and Harbin, and the cadmium enrichment areas are mainly distributed south of Changchun, with a continuous distribution to Tieling City. the enrichment of heavy metals in the topsoil is closely related to the population density by comparing spatial distribution patterns of the geological background, topography and land use, and the obvious enrichment areas for heavy metals are located in and around cities, especially in industrial cities and their surrounding areas. The enrichment depth of 40 cm is further evidence that the heavy metals in topsoil mainly originate from human activities.