Mechanism of arsenic immobilization and biotransformation in the biological aqua crust of mine drainage

Biological aqua crust (BAC), as a novel biological crust with high arsenic (As) immobilization capacity, might be an ideal nature-based solution for As removal in mine drainage. This study examined the As speciation, binding fraction and biotransformation genes in the BACs to find out the underlying mechanism of As immobilization and biotransfor-mation. Results showed that the BACs could immobilize As from mine drainage up to 55.8 g/kg, and their As immo-bilization concentrations were 1.3-6.9 times higher than that of sediments. Extremely high As immobilization capacity was attributed to the processes of bioadsorption/absorption and biomineralization driven by Cyanobacteria. The high abundance of As(III) oxidation genes (27.0 %) enhanced microbial As(III) oxidation, resulting in >90.0 % of As(V) with low toxicity and mobility in the BACs. The increase in abundances of aioB, arsP, acr3, arsB, arsC and arsI with As was the key process for microbiota in the BACs for resistance to the As toxicity. In conclusion, our findings innovatively confirmed the potential mechanism of As immobilization and biotransformation mediated by the micro-biota in the BACs and highlighted the important role of BACs for As remediation in mine drainage.

Automated summary

This study examined the mechanisms of As immobilization and biotransformation in Biological Aqua Crusts (BACs). The results showed that BACs could immobilize As through bioadsorption/absorption and biomineralization processes driven by Cyanobacteria. The high abundance of As(III) oxidation genes enhanced microbial As(III) oxidation, resulting in the conversion of As(V) into a less toxic form. The findings highlight the important role of BACs in As remediation in mine drainage.