Hydraulic fracturing extracts oil and gas through the injection of water and proppants into subterranean formations. These injected fluids mix with the host rock formation and return to the surface as a complex wastewater containing salts, metals, and organic compounds, termed flowback and produced water (FPW). Previous research indicates that FPW is toxic to Daphnia magna (D. magna), impairing reproduction, molting, and maturation time; however, recovery from FPW has not been extensively studied. Species unable to recover have drastic impacts on populations on the ecological scale; thus, this study sought to understand if recovery from an acute 48 h FPW exposure was possible in the freshwater invertebrate, D. magna by using a combination of physiological and molecular analyses. FPW (0.75%) reduced reproduction by 30% and survivorship to 32% compared to controls. System-level quantitative proteomic analyses demonstrate extensive perturbation of metabolism and protein transport in both 0.25 and 0.75% FPW treatments after a 48 h FPW exposure. Collectively, our data indicate that D. magna are unable to recover from acute 48 h exposures to ≥0.25% FPW, as evidence of toxicity persists for at least 19 days post-exposure. This study highlights the importance of considering persisting effects following FPW remediation when modeling potential spill scenarios.

Treatment and reuse of unconventional oil and gas (UOG) produced water are important strategies that address the dual challenges of water scarcity and pollution posed by UOG production. Considering the high salinity and complex chemistry of UOG produced water, it is important to comprehensively analyze the water quality and potential ecological risk of treated produced water for reuse applications. In this study, we evaluated and compared the efficacy of pretreatment followed by nanofiltration (NF) and reverse osmosis (RO) using membranes of varied permselectivity in treating produced water from the Niobrara Shale play in Colorado. We determined the efficacy of each technology in removing inorganic and organic constituents as well as reducing toxicity on Daphnia magna. Our results show that the pretreatment step resulted in a minor reduction of chemical constituents and toxicity and that the NF permeates did not meet the water quality criteria for irrigation and livestock drinking water. Despite high removal rates for most contaminants in the produced water by RO, the concentrations of chloride and boron as well as the sodium adsorption rate (SAR) in the RO permeates exceeded irrigation guidelines. We observed the passage of surfactants with molecular weights much higher than the molecular weight cutoff of NF and RO membranes, suggesting that membranes are not an absolute barrier to organic contaminants. Our results demonstrate that thorough chemical and toxicological analyses are needed to understand the feasibility and potential risk of treating UOG produced water for beneficial reuse.