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.

In this study, biochar (BC) was prepared from bagasse and then successfully loaded with nanoscale zerovalent iron (nZVI) to produce BC-supported nZVI, termed nZVI@BC. Satisfactory results were obtained using a nZVI@BC-activated persulfate (PS), termed nZVI@BC/PS, to remediate total petroleum hydrocarbons (TPH)-contaminated water. The effects of three influencing factors—the dosage of nZVI@BC, D_nZVI@BC, the concentration of PS, C_PS, and the initial pH, pH_i—on TPH removal were examined through single-factor and batch tests. The results show the following. Each factor considerably influenced the performance of the prepared nZVI@BC/PS reaction system in removing TPH. The TPH degradation process conformed to a first-order kinetic model. The response surface method (RSM) was used in tandem with a Box–Behnken design to optimise the variables involved in TPH degradation. The three influencing variables (i.e., D_nZVI@BC, C_PS, and pH_i) were set in the range of 0.4–1.0 g/L, 20–160 g/L, and 2.21–9.42, respectively, during the experiment. An optimised quadratic model used to fit the experimental data displayed a high level of significance (p < 0.0001) with a very high regression value (R² = 0.9906; adjusted R² = 0.9786). Analyses of regression and variance revealed that the quadratic model sufficiently explains the TPH degradation rate. An electron paramagnetic resonance (EPR) spectroscopic analysis of the nZVI@BC/PS system revealed that SO₄⁻·, ·OH, O₂⁻·, and ¹O₂ participated in the activation and degradation processes. The results of this study show that nZVI@BC-activated PS systems possess great potential for applications in TPH-contaminated wastewater treatment and environmentally sustainable development.

The aim of this study was to explore the feasible measurement of the control of cadmium (Cd) and arsenic (As) accumulation in rice grains. A field experiment was carried out to research the effect of different treatments, including spraying silicon (Si)/selenium (Se) foliar fertilizers, the application of lime (CaO), water management (continuous flooding), and the co-application of foliar fertilizers and flooding, on Cd and As accumulation in rice grains in Guangxi Province. The results indicate that Cd accumulation in rice grains decreased under different treatments and Cd content in rice grains reached the threshold of 0.2 mg kg⁻¹. In the single technical treatments, CaO application, flooding, spraying foliar Se fertilizer, and spraying foliar Si fertilizer decreased Cd content by 73.15%, 60.44%, 45.76%, and 36.07%, respectively. However, flooding and CaO amendment enhanced As accumulation in rice grains. The co-application of flooding and spraying foliar fertilizer can simultaneously reduce Cd and As in rice grains. In addition, they resulted in lower Cd content than the single technical treatments. Among the treatments, the lowest bioaccumulation factors of Cd and As were found after the co-application of flooding and Si foliar fertilizer, which decreased these factors by 74.02% and 22.72%, respectively. These results suggest that spraying foliar Si fertilizer combined with flooding may be a promising method to synchronously inhibit the accumulation of Cd and As in rice.