Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea <i>Daphnia magna</i>

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean <i>Daphnia magna</i> was characterized utilizing acute (48 h median lethal concentrations; LC<sub>50</sub>) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC<sub>50</sub> of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC<sub>50</sub> value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (<i>cyp4</i>) and moulting (<i>cut</i>). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.