The Acute Toxicity of Salinity in Onshore Unconventional Gas Waters to Freshwater Invertebrates in Receiving Environments: A Systematic Review

Abstract

Industries such as unconventional natural gas have seen increased global expansion to meet the increasing energy needs of our increasing global population. Unconventional gas uses hydraulic fracturing that produces significant volumes of produced waters, which can be highly saline and pose a toxic threat to freshwater invertebrates if exposure via discharges, spills, leaks, or runoff were to occur. The primary aim of the present review was to determine the sodium (Na + ) and chloride (Cl − ) content of these waters as an approximate measure of salinity and how these values compare to the NaCl or synthetic marine salt acute toxicity values of freshwater invertebrate taxa. Shale gas produced waters are much more saline with 78 900 ± 10 200 NaCl mg/L and total dissolved solids (TDS) of 83 200 ± 12 200 mg/L compared to coal bed methane (CBM) produced waters with 4300 ± 1100 NaCl mg/L and TDS of 5900 ± 1300 mg/L and pose a far greater toxicity risk from NaCl to freshwater invertebrates. In addition, the toxicity of other major ions (Ca 2+ , K + , Mg 2+ , CO 3 2− , HCO 3 − , and SO 4 2−) and their influence on the toxicity of Na + and Cl − were evaluated. Exposure of untreated and undiluted shale gas produced waters to freshwater invertebrates is likely to result in significant or complete mortality. Shale gas produced waters have higher concentrations of various metals compared with CBM produced waters and are more acidic. We recommend future research to increase the reporting and consistency of water quality parameters, metals, and particularly organics of produced waters to provide a better baseline and help in further investigations.

Mixture Toxicity of Three Unconventional Gas Fracking Chemicals, Barium, O‐Cresol, and Sodium Chloride, to the Freshwater Shrimp Paratya australiensis

“…Particular flowback‐produced waters are likely to have greater Ba toxicity risk. These include more saline waters (i.e., shale gas), which typically correspond with higher Ba concentrations (Willems et al, 2022 ), in combination with low SO 4 concentrations in both flowback‐produced water and surface waters, which would reduce BaSO 4 precipitation. The freshwater alga Chlorella sp.…”

“…For binary and ternary combinations for Ba 2+ and o ‐cresol, LC10 and LC50 values were derived from the single (definitive) chemical tests. Sodium chloride was assessed at three selected concentrations of 1 025, 2 050, and 3 075 mg/L NaCl, which are representative of the lower range of Na + and Cl − in coal bed methane and shale gas waters (Willems et al, 2022 ). The concentrations of each of the toxicants used in the three binary tests and one ternary test and the respective 96‐h survivability rates will be outlined in (Figure 1 ).…”

“…High salinity is a widespread issue, where Cl − and Na + are typically the two most abundant ions associated with salinity in flowback‐produced water, particularly from shale gas (Liden et al, 2022 ; Willems et al, 2022 ). In Australian groundwater reservoirs associated with unconventional gas extraction, total dissolved salt concentrations range from 40 to 200 000 mg/L (Hall et al, 2018 ), whereas mean Na + and Cl − concentrations of coal bed methane waters in Australia are approximately 1300 mg/L each or total 2600 mg/L NaCl content (Willems et al, 2022 ). Though both Na + and Cl − ions are essential for life on earth, they can become toxic at sufficiently elevated concentrations with prolonged exposures or fluctuations.…”

“…Though both Na + and Cl − ions are essential for life on earth, they can become toxic at sufficiently elevated concentrations with prolonged exposures or fluctuations. For freshwater organisms like Paratya australiensis , exposure to elevated concentrations of Na + and Cl − as in shale gas flowback‐produced water (Willems et al, 2022 ) beyond physiologically tolerable thresholds can interfere with osmoregulation. Other studies investigating salinity toxicity with P. australiensis have all used a synthetic marine salt with resulting 72–96‐h 50% lethal concentration (LC50) values ranging from 6600 to 39844 μS cm −1 (≈3693–22312 mg/L), as summarized in Paradise ( 2009 ).…”

“…In North America flowback‐produced waters can enter surface water environments through permitted discharges via the National Pollutant Discharge Elimination System, spills, leaks, or runoffs, as summarized in Willems et al ( 2022 ). In Australia, which is still dominated by coal bed methane production of natural gas, 80% of flowback‐produced water from coal bed methane is beneficially reused in the agriculture industry and by reinjection into aquifers (Australian Petroleum Production and Exploration Association, 2022 ).…”