Sulfolane, an industrial solvent used in oil and natural gas refineries, has a high affinity for water and is associated with one of the largest groundwater contaminant plumes in the state of Alaska (~17.6 km2). Due to the size of the contaminant plume we questioned if there was any potential for sulfolane biodegradation to occur in subarctic aquifer substrate, and if so, what factors limit biodegradation. Another goal was to identify the sulfolane-degrading microorganisms and determine their distribution throughout the site. Linking bacterial identity to ecosystem function is a great challenge in microbial ecology since less than 1% can be cultured in the lab. We used stable isotope probing (SIP) with 13C- labeled sulfolane in combination with 16S rRNA gene sequencing to identify members of the microbial community actively involved in sulfolane biodegradation. Combining SIP with taxonomic gene sequencing allows for environmentally relevant organisms to be identified without culture bias. SIP results were compared to microbial community data information from >150 groundwater monitoring wells to determine the distribution of degraders throughout the site. Environmental metadata is being assessed to determine environmental drivers of the distribution of sulfolane degrading microorganisms throughout this contaminated aquifer.
Results/Conclusions
Laboratory studies we conducted using aquifer substrate revealed aerobic sulfolane biodegradation as the only possible degradation mechanism, with no detectable losses occurring in sterile controls or in anaerobic incubations. Hydrocarbon co-contamination retarded the rate of sulfolane biodegradation. The addition of a mineral nutrient solution significantly stimulated biodegradation at sulfolane concentrations far above those present in situ, but had no effect at site-relevant sulfolane concentrations. However, in microcosms containing only groundwater in the absence of aquifer solids the addition of a nutrient solution was crucial for sulfolane biodegradation to occur at all. SIP revealed that the dominant sulfolane degrading microorganism in aquifer substrate is closely related to an Albidiferax sp. Although we are still in the process of comparing the SIP and plume-wide microbial community datasets, preliminary results will be presented. This research indicates that sulfolane-degradation potential exists in the aquifer but oxygen limits biodegradation in situ. Nutrient limitations would need to be addressed if attempting to bioremediate extracted groundwater. Understanding the microbial ecology of contaminated sites is crucial for accurately estimating contaminant longevity, migration, and extent. We demonstrate a systematic and comprehensive ecological approach that can be applied to site assessments for sulfolane and other emerging environmental contaminants.