Geochemical assessment of agricultural soil: A case study in Songnen-Plain (Northeastern China)

Agricultural soil pollution is a serious problem that can endanger ecology, food safety, and human health. The study evaluated the accumulation and distribution of major and trace elements in the agricultural soil of the Gannan area in the northwest Songnen-Plain, a very important base of grain production in northeastern China. To identify the concentrations and sources of pollutants and also to assess the soil environmental quality, a total of 2400 topsoil (0–20 cm) samples and 10 subsoil (180–200 cm) samples were collected. Then 6 major elements (CaO, Fe2O3, K2O, MgO, Na2O, SiO2), 18 trace elements (As, B, Cd, Co, Cr, Cu, F, Hg, I, Mo, Mn, N, Ni, P, Pb, Se, S, and Zn), pH, and Corg (organic carbon) were analyzed. The accumulation of Cd, Cu, Pb, Zn, Hg, and F was apparent in the agricultural soils. Correlation coefficient analysis showed that most major and trace elements, as well as pH and Corg, were significantly positive correlated in agricultural soil. Principal component analysis (PCA) indicated two main anthropogenic sources for trace elements in agricultural topsoil. The first component including B, Cr, Cu, Mg, Ni, and Zn, represented a mixture of atmospheric deposition and livestock manures; whereas the second component, relating to Ca, F, Cd, Hg, Se, and P, suggested the inorganic fertilizers and lime, as well as agrochemicals. Spatial distribution patterns using GIS contour maps and an integrated soil pollution index were established for the selected metal concentrations. In general, the range of RI (the potential ecological risk index) was from 43.6 to 556, with a mean value of 106, indicating low ecological risk in this study area. This study indicated that more attention should be paid to metal pollution of agricultural soil in the rural area to safeguard both soil and food safety.