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The presence of residual Cr(VI) in soils causes groundwater contamination in aquifers, affecting the health of exposed populations. Initially, permeable reactive barriers(PRB) effectively removed Cr(VI) from groundwater. However, as PRB clogging increased and Cr(VI) was released from upstream soils, the contamination plume continued to spread downstream. By 2020, the level of contamination in the downstream was nearly identical to that in the upstream. The study results show that during normal operation, the PRB can successfully remove Cr(VI) from contaminated groundwater and reduce the carcinogenic and non-carcinogenic risks to humans from the downstream side of groundwater. However, the remediated groundwater still poses an unacceptable risk to human health. The sensitivity analysis revealed that the concentration of the pollutant was the most sensitive parameter and interacted significantly with other factors. Ultimately, it was determined that the residual Cr(VI) in the soil of the study region continues to contaminate the groundwater and constitutes a serious health danger to residents in the vicinity. As remediated groundwater still poses a severe threat to human health, PRB may not be as effective as people believe.

There is a certain connection between the microbial community and functional flora in rare earth mining areas, but the pollution characteristics and pollution metabolic pathways in the mining area are still unclear. The conditions of heavy metals, rare earth elements, and microorganisms after the mining of rare earth mines were studied in this paper. It was found that after mining, all the sampling areas showed low pH and low total organic carbon(TOC), accompanied by high iron and aluminum concentrations. The development of vegetation is closely related to the development level of microorganisms. In the complex environment of rare earth mining areas, the Proteobacteria showed an absolute competitive advantage. In the process of mine environmental recovery, the relative abundance of Acidobacteria will increase significantly, but with the further development of restoration, the relative abundance of Firmicutes in rare earth mining areas will gradually decrease. There are many genera of bacteria related to the N cycle and heavy metal metabolism in the study area, indicating important metabolic pathways of ammonia nitrogen and heavy metals in rare earth mining areas. At the same time, the study found that there are bacterial genera that promote plant nitrogen fixation in the area, further revealing the nitrogen cycle.