Naphthenic acid anaerobic biodegrading consortia enriched from pristine sediments underlying oil sands tailings ponds

Seepage from oil sands tailings ponds (OSTP), which contain toxic naphthenic acids (NAs), can infiltrate into groundwater. Clay sediment layer beneath is a critical barrier for reducing the infiltration of NAs into the sand sediment layer, where groundwater channels reside. Biodegradation has great potential as a strategy for NAs removal, but little is known about NAs biodegradability and potential functional microbes in these pristine sediments. This study investigated the potential for anaerobic biodegradation of NAs by microbial consortia enriched from clay and sand sediments underlying OSTP, amended with either acid extracted organics or Merichem NAs, under nitrate- and sulfate-reducing conditions. Degradation of NAs only be detected after DOC concentration reached to steady state after 163 days. Microbial community analysis shows that different electron acceptors, sediment types, and NAs sources associated with specific microbial taxa and can explain 14.8, 13.9 % and 5% of variation of microbial community structures, respectively. The DOC and methane were the most important geochemical properties for microbial community variations. This study approved the potential capability of indigenous microbial communities from the pristine sediments in NA degradation, demonstrating the barrier function of pristine clay sediments underlying OSTP in prohibiting organic contaminants from entering into groundwater.