Characteristics and Source Analysis of Heavy Metals in Farmland Soil on the South of Dongting Lake

Abstract

Based on the grid distribution method, 1589 topsoil samples were collected from farmland on the south side of Dongting Lake from April to August 2020. The content, potential ecological risk, spatial distribution characteristics, and source analysis of heavy metals in the soil were studied. The concentrations and pH of As, Cd, Pb, Cu, Zn, Ni, Cr, and Hg in the soil were determined using ICP-MS, ICP-OES, HG-AFS, and ISE methods. The results showed that the average concentrations of Zn, Cr, Pb, Cu, Ni, As, Cd, and Hg were 118.18, 82.21, 52.1, 33.76, 32.81, 18.25, 0.42, and 0.13 mg·kg-1, respectively. All heavy metals had medium or high variability. The soil was mainly weakly acidic with a pH between 3.96 and 7.90. Hg and Cd had high ecological risks. The spatial distribution of heavy metals showed a tendency of being high in the southwest and low in the northeast. The PMF and PCA methods were used to analyze the sources and calculate the contribution rates of the eight types of heavy metals. The PMF results showed that the contribution rates of soil heavy metals in the study area were as follows:agricultural activity sources (36.98%), natural sources (32.94%), water and soil exchange sources (17.05%), and atmospheric dry and wet deposition sources (13.03%). The PCA results showed that the soil heavy metals in the study area mainly came from agricultural activity sources (68.04%), natural sources (31.02%), and atmospheric deposition sources (0.94%). The conclusions of the two source analysis methods tended to be consistent, that is, agricultural activities were the main source of soil heavy metals in the study area. The vertical profile analysis showed that the contents of Cd, Hg, and Pb elements were high in the surface layer and low in the deep layer, and the phenomenon of anthropogenic input was obvious. These results can provide a scientific basis for the formulation of prevention and control countermeasures of farmland soil heavy metal pollution around Dongting Lake.