Persisting Effects in Daphnia magna Following an Acute Exposure to Flowback and Produced Waters from the Montney Formation.

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.

A common well pad does not imply common toxicity: Assessing the acute and chronic toxicity of flowback and produced waters from four Montney Formation wells on the same well pad to the freshwater invertebrate Daphnia magna.

Large stores of previously inaccessible hydrocarbons have become available due to the development of hydraulic fracturing technologies. During the hydraulic fracturing process, a mixture of water and proprietary additives is injected into geologic formations to release trapped hydrocarbons. After fracturing, injected water and fluid from the target formation return to the surface as flowback and produced water (FPW), a potentially toxic byproduct of hydraulic fracturing activities. FPW is a complex mixture that contains chemical additives present in the initial injection fluid as well as salts, metals, and a variety of organic compounds. As a result, FPW composition can be highly variable across wells from different geological formations, methods of fracturing and well development, and well age. The present study sought to determine if FPW sourced from four wells (O, P, U, V) located on the same well pad within the Montney Formation have similar levels of acute and chronic toxicity to the freshwater invertebrate, Daphnia magna. Minimal differences in the estimated 48 h LC50 concentrations were observed among the studied wells. Long-term, 21 d exposures to ≤2% FPW revealed differences in the level of lethality between wells, including complete mortality in daphnids exposed to 2% well O by day 9. No sublethal effects were observed as a result of exposure to FPW from wells P, U or V; however, a large impairment of reproductive traits and molting behaviour were detected after exposure to 0.75% well O FPW. These results indicate that FPW sourced from wells on the same well pad cannot be considered the same in terms of chemical composition or toxicity, an important distinction to make for risk assessment practices.