Shedding light on the effects of hydraulic fracturing flowback and produced water on phototactic behavior in Daphnia magna

The effluent produced during hydraulic fracturing (i.e. flowback and produced water; FPW), is a complex hyper-saline solution that is known to negatively impact the survival and the fitness of the water flea Daphnia magna, but to date effects on behavior are unstudied. In the current study, the effects of FPW on phototactic behavior of D. magna were examined. Exposure of naive animals to FPW resulted in a dose-dependent increase in the speed of appearance of daphnids in the illuminated zone of the test apparatus (i.e. a faster positive phototaxis response). A similar dose-dependent response was observed in a test solution where the salt content of FPW was recreated in the absence of other components, suggesting that the effect was largely driven by salinity. The effect of FPW was significant when the raw FPW sample was diluted to 20% of its initial strength, while the effect of salt-matched solution was significant at a 10% dilution. A distinct effect was observed following FPW pre-exposure. After a 24 h pre-exposure to 1.5% FPW, Daphnia displayed a significantly inhibited positive phototaxis response when examined in control water, relative to control animals that were not pre-exposed to FPW. This effect was not observed in salinity pre-exposed animals, however these daphnids displayed a significantly reduced phototactic response when tested in saline waters, indicating a loss of the positive phototaxis seen in naive organisms. These data indicate that FPW can induce perturbations in the behavior of aquatic invertebrates, an effect that may influence processes such as feeding and predation rates.