Characterization of contamination levels of heavy metals in agricultural soils using geochemical baseline concentrations

Abstract

It is currently very difficult to accurately evaluate the soil contamination by heavy metals (HMs) attributed to the unavailability of local geochemical background values (LGBVs). This study was performed to establish the geochemical baseline concentrations (GBCs), as an alternative for LGBVs to use for HM pollution assessment of agricultural soil. GBCs of the HMs selected were determined using the cumulative frequency distribution curves (CFDCs). GBCs were then used to pursue the HM soil pollution and associated ecological risks, via calculation of geo-accumulation indices (Igeo), pollution load indices (PLI), as well as potential ecological risk indices (RI). As to the soil investigated, the GBCs of Ni, Zn, Pb, and Cr were 29.34 mg/kg, 45.54 mg/kg, 21.81 mg/kg, and 33.65 mg/kg, respectively. Igeo values ranged from − 4.58 to 0.33 (Ni), from − 2.46 to 2.14 (Zn), from − 5.32 to 0.77 (Pb), and from − 3.83 to 0.96 (Cr), suggesting that the region was not polluted by these HMs. PLI values ranged from 0.08 to 2.45 with an average of 1.02. 49.6% of soil samples had the PLI values > 1.0, indicating that some of the soil may be moderately contaminated by HMs. The RI values of selected HMs were < 150, indicating a low potential ecological risk. Principal component analysis (PCA) implied Zn, Pb, and Cr were mainly sourced from parent (geological) materials, as well as agricultural activities, atmospheric deposition, etc., depending on the element. The present study illustrates the necessity of the characterization of GBCs at a regional scale, allowing for more accurate assessment of soil contamination by HMs. We hope that this will eventually lead to further development of better environmental management practices for agricultural soil polluted by HMs.