Source Identification and Superposition Effect of Heavy Metals (HMs) in Agricultural Soils at a High Geological Background Area of Karst: A Case Study in a Typical Watershed

Abstract

Exogenous sources and the superposition effect of HMs in agricultural soils made the idenfication of sources complicated in a karst area. Here, a typical watershed, a research unit of the karst area, was chosen as the study area. The smaller-scale study of watersheds allowed us to obtain more precise results and to guide local pollution control. In this study, sources of HMs in agricultural soil were traced by a CMB model. Superposition effects were studied by spatial analysis of HMs and enrichment factor (EF) and chemical fraction analysis. The average concentrations of Cd, Pb, Cr, Cu, Ni and Zn in surface soils were 8.71, 333, 154, 51.7, 61.5 and 676 mg∙kg−1, respectively, which exceeded their corresponding background values. The main sources of Cd, Pb and Zn in agricultural soil were rock weathering, atmospheric deposition and livestock manure, and their contributions were 47.7%, 31.0% and 21.2% for Cd; 7.63%, 78.7% and 13.4% for Pb; and 17.0%, 52.3% and 28.1% for Zn. Cr mainly derived from atmospheric deposition (73.8%) and rock weathering (20.0%). Cu and Ni mainly came from livestock manure (81.3%) and weathering (87.5%), respectively, whereas contributions of pesticides and fertilizers were relatively limited (no more than 1.04%). Cd, Pb, Zn and Cu were easily enriched in surface soils near the surrounding pollution sources, whereas Cr and Ni were easily enriched in the high-terrain area, where there was less of an impact of anthropogenic activities. The superposition of exogenous sources caused accumulation of Cd, Pb and Zn in topsoil, contaminated the subsoil through leaching and improved bioavailability of Cd and Pb, causing high ecological risk for agricultural production. Therefore, Cd and Pb should be paid more attention in future pollution control.

A review on adsorption characteristics and influencing mechanism of heavy metals in farmland soil

“…The adsorption sites on the soil surface are progressively saturated. 42 It was found that the electron effect of Cd, Pb, and Zn in the surface soil was significantly higher than that in the subsoil and increased with depth. Therefore, it is not difficult to see that the content of organic matter causes the difference of heavy metal adsorption in each layer of soil.…”

Effects of vegetation restoration on distribution characteristics of heavy metals in soil in Karst plateau area of Guizhou

“…At the same time, the soil seriously polluted by heavy metals may become a long-term pollution source of groundwater and ecosystem ( Konyshev et al, 2020 ; Li et al, 2009 ). Therefore, heavy metal pollution in soil is becoming an increasingly serious environmental problem ( Zhong et al, 2018 ; Yang, Wu & Yang, 2022 ; Zhang et al, 2022 ).…”

“…Among them, the status of soil heavy metals pollution in karst areas in different land and vegetation cover types appeared in karst areas ( Han et al, 2022 ; Liu et al, 2022 ; Sun et al, 2020 ). Such as natural background, agricultural activity area ( Zhang et al, 2021 ; Han et al, 2012 ; Zeng et al, 2019 ), mining area ( Zhou et al, 2022 ; Zhang et al, 2022 ; Wang et al, 2022b ; Qi et al, 2022 ) has become a major thrust of research. The research content is mainly based on the distribution characteristics of soil heavy metal content or how to reduce the heavy metal content in soil.…”

“…At present, the research on soil heavy metal pollution in karst areas of southwest China is mainly focused on two aspects: one is the changes of soil structure (aggregates), soil organic matter and other nutrients ( Xu et al, 2017 ; Sun et al, 2009 ) under the influence of heavy metal pollution. The second is the distribution characteristics of heavy metals in soil ( Zhang et al, 2021 , 2022 ) under different land use types such as farmland and mining area ( Zhu, Xiao & Guo, 2018 ), removal effect ( Zhou et al, 2022 ) and remediation technology exploration ( Li, 2020 ). However, research on the mechanism of phytoremediation technology for heavy metals in soil is limited.…”

Limited Role of Rhamnolipids on Cadmium Resistance for an Endogenous-Secretion Bacterium

“…Increasingly serious cadmium (Cd) pollution has been caused by industrialization and technological development with large amounts of waste released [1][2][3]. Heavy metals can cause non-biodegradable bioaccumulation and have remarkable toxicity to organisms, leading to severe damage to biology and ecosystems in low concentrations [4][5][6]. For example, cadmium (Cd) can accumulate in the food chain and be a cause of great public concern, such as the Cd-related disease (Itai-Itai disease) in Japan [7,8].…”