Heavy metal pollution migration and its ecological impact on microbial communities in the karst region of Guangxi.

This study examines the factors driving heavy metal pollution in karst soils and assesses the associated environmental risks. Using a representative karst depression in Guangxi as a case study, we measured soil concentrations of arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn). These concentrations were analyzed in relation to soil physicochemical properties, morphology, and geological factors to understand pollution dynamics and migration patterns. The findings highlight As as the dominant contaminant, primarily existing in a highly mobile, reduced form. Further analysis shows that its mobility is strongly influenced by soil pH and available phosphorus (AP), emphasizing the interplay between soil chemistry and pollutant behavior. The study area, dominated by limestone strata, experiences changes in soil oxidative conditions due to rainfall, which significantly influence As accumulation and migration. The presence of abundant iron and manganese oxides further amplifies these effects. According to the Hakanson index, As contamination in surface soils presents a high ecological risk to the surrounding environment. Microbial analysis reveals a positive correlation between Proteobacteria and both the total concentration and chemical forms of As. These bacteria demonstrate resistance to As and contribute to increased residual As content, thereby reducing its toxicity and mobility. Additionally, Proteobacteria thrive in As-contaminated soils with high pH and low nutrient levels, highlighting their potential for bioremediation. This positions Proteobacteria as a promising microbial group for managing As pollution in the region.