Lithology and Human Activities Determine the Distribution and Pollution Level of Potentially Toxic Elements in the Topsoil of the Karst Region, Southwestern China

Abstract

Potentially toxic elements (PTE) pollution in soils has become a major global environmental problem, and their spatial distribution and risk assessment are essential issues of concern to human beings. To analyze the distribution characteristics and the pollution levels of arsenic, cadmium (Cd), chromium, copper, mercury, nickel, lead and zinc in soil, 573 surface soil samples were collected from the karst region (karst area, K; denudation monadnock with solutional cap rock, KSC; non-karst area, NK) in Mashan County, Guangxi Province. The pollution load index (PLI), potentially ecological risk index (RI) and Nemerow composite pollution index (NCPI) were employed to assess the pollution levels of PTE. The PLI and RI results revealed that the soils have undergone relatively low-moderate contamination due to the high geological background. The average concentration of PTE in different soils were in the following decreasing order, K>KSC>NK. The concentration of Cd in 75.74% of samples exceeded the risk screening values of GB 15618-2018. The relatively high pollution level of PTE was mainly distributed in K soil, rich in calcium, magnesium and an alkaline environment. Therefore, there is a higher risk of pollution in areas with high background of heavy metals in karst areas. The clean-precaution and light pollution levels in the NCPI risk assessment were distributed in NK and KSC areas, respectively. However, metal ores and human activities caused the deviation of the clean-low risk and lithological distribution in the NK and KSC areas.