Red mud-modified biochar reduces soil arsenic availability and changes bacterial composition

Worldwide arsenic (As) contamination in soils induces pollution of surface and ground waters, reduces crop quality and yield, and threatens human health. Biochar-based material has been proposed as ameliorants for contaminated soils. Here soil incubations were conducted to investigate the effects of biochar, red mud and red mud-modified biochar on the pH, total organic carbon content, sodium bicarbonate (NaHCO 3 )-extractable As concentration and microbial community composition of As-contaminated soils. Results show red mud-modified biochar reduces the concentration of NaHCO 3 -extractable As by 27%, whereas this concentration increases by 23% using biochar alone and 6% using red mud alone. Similar trends are observed for HCl-extractable As. The red mud and red mud-modified biochar treatments increased the relative abundance of Proteobacteria and its affiliated genera, such as Kaistobacter , Rhodanobacter and Rhodoplanes .