Mobilization of As, Fe, and Mn from Contaminated Sediment in Aerobic and Anaerobic Conditions: Chemical or Microbiological Triggers?

We integrated aqueous chemistry, spectroscopy, and microbiology techniques to identify chemical and microbial processes affecting the release of arsenic (As), iron (Fe), and manganese (Mn) from contaminated sediments exposed to aerobic and anaerobic conditions. The sediments were collected from Cheyenne River Sioux Tribal lands in South Dakota, which has dealt with mining legacy for several decades. The range of concentrations of total As measured from contaminated sediments was 96 to 259 mg kg(-1), which co-occurs with Fe (21 000-22 005 mg kg(-1)) and Mn (682-703 mg kg(-1)). The transition from aerobic to anaerobic redox conditions yielded the highest microbial diversity, and the release of the highest concentrations of As, Fe, and Mn in batch experiments reacted with an exogenous electron donor (glucose). The reduction of As was confirmed by XANES analyses when transitioning from aerobic to anaerobic conditions. In contrast, the releases of As, Fe and Mn after a reaction with phosphate was at least 1 order of magnitude lower compared with experiments amended with glucose. Our results indicate that mine waste sediments amended with an exogenous electron donor trigger microbial reductive dissolution caused by anaerobic respiration. These dissolution processes can affect metal mobilization in systems transitioning from aerobic to anaerobic conditions in redox gradients. Our results are relevant for natural systems, for surface and groundwater exchange, or other systems in which metal cycling is influenced by chemical and biological processes.

Automated summary

We conducted an integrated study combining aqueous chemistry, spectroscopy, and microbiology techniques to investigate the release of arsenic, iron, and manganese from contaminated sediments under different aerobic and anaerobic conditions. Our results showed that the highest concentrations of these metals were released under anaerobic conditions with the addition of an exogenous electron donor. XANES analyses confirmed the reduction of arsenic under anaerobic conditions. Additionally, the release of these metals after a reaction with phosphate was significantly lower compared to experiments amended with glucose.