After the spill: The mechanisms behind recovery and exposure to flowback and produced waters in Daphnia magna
Creators: Luu, Ivy
Publisher: name: University of Alberta Library
Year: 2022

<p>Hydraulic fracturing for unconventional oil and gas extraction produces a complex wastewater known as flowback and produced water (FPW). FPW effluents contain inorganic constituents (e.g., Na, Ca, Mg, Zn, Cu, Cl) and organic constituents (e.g., surfactants, proppants, polycyclic aromatic hydrocarbons). These FPW effluents are often transported away from their well of origin for reuse or disposal, creating the possibility of large FPW spills. The possibility of FPW spills entering freshwater environments is of particular concern, with the potential to cause long term damage to exposed organisms. Previous research has shown that FPW can cause impairments in reproduction and molting in Daphnia magna, a freshwater invertebrate, after a chronic sublethal exposure to FPW. However, recovery from FPW in this species has not been extensively studied and a species unable to return to pre-stressor conditions can have drastic impacts on a population and the ecological scale. <br>
Thus, this thesis investigated recovery within a single generation after an acute 48-hour FPW spill and in multiple generations after a chronic 21-day spill. Recovery was evaluated by endpoints including time to first brood, neonate output, and molt production returning to control pre-exposure levels. It was hypothesized that recovery can occur in Daphnia magna but full recovery from initial FPW exposure would require more than a single generation.<br>
The first objective of my thesis was to understand if a 19-day period in clean water resulted in sufficient recovery from an acute 48-h FPW spill by pairing physiological endpoints with molecular analyses. We found reproduction and molting significantly impaired, with a mean value of 12.4 ± 4.6 neonates and 2.5 ± 0.6 molts produced per daphnid after exposure to 0.75% FPW, compared to the control daphnids that produced 66.2 ± 4.9 neonates and 7.5 ± 0.3 molts per replicate. Systems-level quantitative proteomic analyses demonstrated 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 even an acute 48-h exposure renders recovery of Daphnia magna impossible in the first generation.<br>
The second objective of my thesis was to investigate if recovery from a chronic 21-day exposure to FPW was possible in four generations of Daphnia magna. Four generations were studied as the F3 generation was the first unexposed germ line to the F0 FPW exposure. To understand recovery, F0 Daphnia magna were exposed to 0.1% FPW for 21-day and then placed in clean water for the F1-F3 generations (recovery group). This treatment group was compared to a chronic FPW exposure group where all four generations were exposed to 0.1% FPW. Overall, time to first brood was delayed initially in the FPW exposed F0 (recovery and chronic). The time to first brood was 12.3 ± 0.5 days for the chronic group and 12.0 ± 0.4 days for the recovery group, ~2.5 days later than the control group at 9.6 ± 0.2 days, but no differences between neonate and molt production were found. No differences were found in the F1 and F2 generations between any of the three treatments. Meanwhile, the chronic F3 generation had a time to first brood of 11.7 ± 0.7 days compared to the control at 9.8 ± 0.3 days. <br>
This thesis gives insight into the potential recovery from FPW exposure in the key indicator species, Daphnia magna. After as little as 48 hours of FPW exposure, Daphnia were unable to recover, likely due to latent mortality. This emphasizes the importance of preventing spills, rather than reactive cleanup measures to best protect freshwater ecosystems. Notably, after a chronic exposure to FPW, Daphnia were able to recover by the F1 generation, but will face delayed maturation time if the spill is not remediated by the F3 generation. This indicates that spill remediation should be completed as soon as possible to prevent future organisms from having an adverse response to continued FPW exposure, after an initial spill.</p>