Exposure to Hydraulic Fracturing Flowback Water Impairs Mahi-Mahi (Coryphaena hippurus) Cardiomyocyte Contractile Function and Swimming Performance

Abstract

Publicly available toxicological studies on wastewaters associated with unconventional oil and gas (UOG) activities in offshore regions are nonexistent. The current study investigated the impact of hydraulic fracturing-generated flowback water (HF-FW) on whole organism swimming performance/respiration and cardiomyocyte contractility dynamics in mahi-mahi (Coryphaena hippurushereafter referred to as “mahi”), an organism which inhabits marine ecosystems where offshore hydraulic fracturing activity is intensifying. Following exposure to 2.75% HF-FW for 24 h, mahi displayed significantly reduced critical swimming speeds (U crit) and aerobic scopes (reductions of ∼40 and 61%, respectively) compared to control fish. Additionally, cardiomyocyte exposures to the same HF-FW sample at 2% dilutions reduced a multitude of mahi sarcomere contraction properties at various stimulation frequencies compared to all other treatment groups, including an approximate 40% decrease in sarcomere contraction size and a nearly 50% reduction in sarcomere relaxation velocity compared to controls. An approximate 8-fold change in expression of the cardiac contractile regulatory gene cmlc2 was also seen in ventricles from 2.75% HF-FW-exposed mahi. These results collectively identify cardiac function as a target for HF-FW toxicity and provide some of the first published data on UOG toxicity in a marine species.

Technological Developments Since the Deepwater Horizon Oil Spill

“…Results provided a link between electrophysiological parameters of oil-induced impairments with a functional consequence. This technique was used by Folkerts et al (2020) to investigate the impact of flowback water generated by hydraulic fracturing on those same functions in mahi-mahi. Tarnecki et al (2016) developed a marine food web matrix of 474 Gulf of Mexico fish species based on diet information obtained from stomach sampling and online information.…”

Use of complex physiological traits as ecotoxicological biomarkers in tropical freshwater fishes

“…Critical swimming speed has also been used to show impacts of exposure to water containing complex contaminant mixtures (e.g. Folkerts et al, 2020; Goertzen et al, 2012) including by exposing fishes in cages (McKenzie et al, 2007). The zebrafish is an important model vertebrate species for laboratory studies to demonstrate impacts of contaminants on swimming performance, to demonstrate toxic effects and their mechanisms (e.g., Folkerts et al, 2017; Gerger et al, 2015; Lucas et al, 2016; Thomas & Janz, 2011).…”

Hydraulic Fracturing Return Fluids from Offshore Hydrocarbon Extraction Present New Risks to Marine Ecosystems

“…Primarily used for terrestrial extractions, hydraulic fracturing has also been extended to offshore hydrocarbon extraction in estuarine, shallow, and deep-sea marine environments. Concerns now exist that the chemical composition of the resulting hydraulic fracturing–flowback and produced water (HF-FPW) may impact the marine ecosystem . Studies of HF-FPW produced from terrestrial hydrocarbon extractions show that it contains a wide variety of salts and metals (e.g., Sr, Ba, Cu, Zn, Cd, V), chemical additives (e.g., scale inhibitors, surfactants, biocides), petrogenic organic compounds (e.g., polycyclic aromatic hydrocarbons), and transformation compounds (e.g., halogenated methane and acetone derived from the chemical additives in injected HF fluid through both biotic and abiotic reactions) .…”

“…Publicly available studies of the direct impact of HF-FPW on marine ecosystems, including shallow marine and deep-sea environments, are limited. To the best of our knowledge and based on the growing literature of HF-FPW effects on freshwater and a limited number of seawater organisms, HF-FPW entering the marine environment is also likely to lead to adverse effects on the exposed ecosystem. For example, elevated dissolved metals and organic carbon concentrations in HF-FPW may change the bioavailability of metal species under marine conditions, in particular, for those that are redox-active, with ecotoxicological implications.…”

“…Despite the poor understanding of the composition of HF-FPW from offshore hydraulically fractured wells, this waste fluid is allowed to be directly released to the the marine environment after treatment with discharges permitted under the National Pollutant Discharge Elimination System (NPDES) in the United States., whereas in China, permits for HF-FPW discharge are allowed under the Effluent Standards for Oil-Bearing Wastewater from Offshore Petroleum Development Industry Guideline (GB 4914-85). These discharged wastewaters are not yet classified as hazardous waste in the U.S. or Canada and are therefore allowed, despite ample evidence of adverse effects on marine and freshwater biota due to the exposure to inorganic and organic components and synergetic effects. , Additional inputs to the marine ecosystem may also come from terrestrial inputs or offshore HF-FPW spills or infrastructure failures. Despite regulated releases already occurring, the current knowledge on the potential impacts of HF-FPW on deep-sea organisms and changes in biogeochemical cycling in the surrounding environment is scarce, making prediction difficult.…”