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 (Ca²⁺ , K⁺ , Mg²⁺ , ${\text{CO}}_3^{2-}$ , HCO₃ ^- , and ${\text{SO}}_4^{2-}$ ) 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. Environ Toxicol Chem 2022;41:2928-2949. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Keywords: Acute toxicity; freshwater invertebrates; hydraulic fracturing; produced water; salinity; unconventional gas.

Figure 1

Inclusion flowchart to screen literature containing salinity (Na⁺ and Cl⁻) concentrations in untreated onshore unconventional gas waters which formed Supporting Information, Table S1. Search 1 and 2 n values refer to the number of results that were obtainable/downloadable through Mendeley Desktop and the institutional library access. Flow diagrams were constructed following PRISMA systematic review guidelines (McInnes et al., 2018).

Figure 2

Inclusion flowchart to screen literature containing salinity (NaCl) and synthetic marine salt toxicity data for freshwater invertebrates which formed Supporting Information, Tables S2 and then S2.1. Search 1 and 2 n values refer to the number of results that were obtainable/downloadable through Mendeley Desktop and the institutional library access. Flow diagrams were constructed following PRISMA systematic review guidelines (McInnes et al., 2018).

Figure 3

Summary of major cations (Ca, K, Mg, Na), anions (Cl, ${\text{CO}}_3^2$, HCO₃, ${\text{SO}}_4^2$) total dissolved solids and sum of Na and Cl salinity in onshore unconventional gas waters by country (and basin coal bed methane and shale gas. Based on data compiled from Supporting Information, Tables S1.1 and S1.2. A statistical summary of Figure 3 can be found in Supporting Information, Table S5. AUS = Australia; CAN = Canada; CHN = China; USA = United States of America; CBM = coal bed methane; SG = shale gas; TDS = total dissolved solids.

Figure 4

Concentrations of elements in untreated onshore unconventional gas waters from Supporting Information, Table S1.2. Only elements that had n ≥ 4 entries were used. (A–E) Parts are organized by highest (left) to lowest (right) mean concentrations of each element and are tiered together. (A) ≥1000 mg/L, (B) ≥100 mg/L and <1000 mg/L, (C) ≥10 mg/L and <100 mg/L, (D) ≥1 mg/L and <10 mg/L, (E) <1 mg/L. Outliers were kept, highlighting the large variability in elemental concentrations in onshore unconventional gas waters.

Figure 5

Water quality parameters from onshore unconventional gas waters, based on the data compiled in Supporting Information, Table S1.1. Biochemical oxygen demand and oxidation‐reduction potential data have been omitted because n = 1. ALK = alkalinity; COD = chemical oxygen demand; DO = dissolved oxygen; DOC = dissolved organic carbon; EC = electrical conductivity; O&G = oil and grease; SAR = sodium adsorption ratio; TDS = total dissolved solids; TOC = total organic carbon; TH = total hardness; TSS = total suspended solids; NTU = nephelometric turbidity unit.

Figure 6

Log10 plot of mean (±SE) concentrations of the 10 most studied elements from Supporting Information, Table S1.2 by country: Australia (AUS), Canada (CAN), China, (CHN) and the United States (USA). Significant differences (α > 0.001 ≤ 0.05) between country unique combinations (n = 6) are as follows: a = AUS–CAN, b = AUS–CHN, c = AUS–USA, d = CAN–CHN, e = CAN–USA, f = CHN–USA. Capital letters (A–F) represent highly significant differences between pairs (α ≤ 0.001).

Figure 7

Log10 plot of mean (±SE) concentrations of the 10 most studied elements from Supporting Information, Table S1.2 by basin (coal bed methane [CBM] or shale gas [SG]). Highly significant differences between CBM and SG for each of the elements is denoted by a = significance (α ≤ 0.001), b = significance (α > 0.001 ≤ 0.05); no label represents no significance.

Figure 8

Acute toxicity of NaCl or synthetic marine salts in freshwater invertebrates worldwide, from laboratory‐based tests, categorized by the taxonomic rank of order. Outliers were kept, highlighting the variability of the acute toxicity data among orders.

Figure 9

Acute toxicity range of NaCl or synthetic marine salts in freshwater invertebrates worldwide, from laboratory‐based tests, categorized by the taxonomic rank of family. Outliers were kept, highlighting the variability of the acute toxicity data among families.