Redox Conditions Alter Biodegradation Rates and Microbial Community Dynamics of Hydraulic Fracturing Fluid Organic Additives in Soil–Groundwater Microcosms

One of the environmental risks associated with use of hydraulic fracturing stimulation technologies for oil and natural gas recovery is the potential release of used fluids into surface waters, soils, and groundwater that could contaminate drinking water resources. To better characterize biodegradability of organic additives, we developed a synthetic fracturing fluid (SFF) based on industry-disclosed formulas, compared its organic carbon composition to fluids used in Pennsylvania's Marcellus shale, and amended agricultural soil–groundwater microcosms with three different SFF concentrations to determine organic carbon degradation rates, changes in system biogeochemistry, and microbial community dynamics under aerobic and anaerobic conditions. Microorganisms indigenous to soils and groundwater were able to degrade between 70% and 92% of the amended dissolved organic carbon within 39 days, suggesting significant mineralization, transformation, or biomass assimilation of organic additives across anaerobic and aerobic redox conditions. Sequencing analysis of the 16S rRNA gene revealed a greater abundance of Pseudomonas in aerobic treatments and a higher relative portion of Desulfovibrio in anaerobic treatments amended with SFF, indicating that these taxa may be involved in SFF biodegradation processes under specific redox conditions. Results provide insight into biodegradability of hydraulic fracturing fluid organic additives in shallow agricultural soils and groundwater and biogeochemical processes that may attenuate their migration if accidentally released or spilled at the surface during hydraulic fracturing activities.