G360 PROJECT TEAM: Dr. Kari Dunfield, Dr. Ramon Aravena, Dr. Beth Parker, Dr. Philipp Wanner, Steven Chapman, Andrea Roebuck, Jeremy Fernandes & Michael Ben-Israel (PhD Candidate)
This study is being conducted at an urban pilot field system where 51 hybrid poplars were planted in 2008 to remediate toluene released 40 years ago into an underlying fractured bedrock aquifer. The phytoremediation system is now mature and ripe for performance evaluation and to investigate plant-mediated toluene attenuation processes. Biodegradation in the saturated and vadose zones was assessed by integrating metagenomic molecular approaches and compound-specific stable carbon isotope analysis (CSIA). Highly resolved contaminant and redox species concentrations, stable isotope ratio profiles, and bacterial degradation gene quantities were measured in groundwater that was sampled using multilevel monitoring wells.
Results show that biodegradation is occurring in groundwater under aerobic and anaerobic conditions, and the extent of biodegradation and its contribution to plume attenuation is controlled by temporally shifting redox conditions. Biodegradation gene quantities and activity measured in soil and roots and toluene stable isotope ratio profiles in soil vapour demonstrated that biodegradation is occurring in the vadose zone, and that it is being enhanced by the trees.
Toluene concentrations in tree sap were measured and provided the first demonstration that hybrid poplars actively phytoextract toluene from fractured bedrock systems. Furthermore, advanced gene sequencing of bacteria in roots of trees taking up toluene showed that significant mass is biodegraded after uptake. The combination of these techniques represents a powerful, novel site monitoring approach. This study has validated performance of the phytoremediation system by systematically quantifying toluene uptake, the potential for toluene degradation, and by demonstrating active toluene biodegradation across relevant environmental media in situ.