Freshwater Mussel Soft Tissue Incorporates Strontium Isotopic Signatures of Oil and Gas Produced Water

In many basins across the United States, oil and gas (O&G) wastewater high in alkaline earth metals (such as Ba, Sr, and Ca) and radioactivity is discharged to surface waters. Freshwater mussels have experienced high mortality rates downstream of O&G discharges despite significant dilution. ⁸⁷Sr/⁸⁶Sr and Sr/Ca measured in mussel soft tissue could prove to be an inexpensive, efficient biomonitoring tool if tissue concentrations show O&G produced water signatures similar to those of shells. O&G-derived ²²⁶Ra/²²⁸Ra has not previously been studied in freshwater mussels. Additionally, accumulation of O&G-derived metals in mussel tissue may impact bioaccumulation in higher-trophic level organisms. A tank study using freshwater mussels (Elliptio complanata) was completed using Marcellus Shale-produced water diluted with regional surface water to realistic dilution levels (100−600-fold dilution). Results from the three-month study suggest Sr/Ca and ⁸⁷Sr/⁸⁶Sr robustly trace O&G pollution in mussel soft tissue. The high-dose tank soft tissue average ⁸⁷Sr/⁸⁶Sr [0.709502 ± (7.68 × 10⁻⁵)] was significantly more radiogenic than average control tank soft tissue [0.706808 ± (4.23 × 10⁻⁵)]. Radium concentrations in soft tissue were not significantly different between tanks. Changes in the soft tissue chemistry of mussel species from relatively low doses of O&G wastewater suggest surface water disposal volumes may require re-evaluation to prevent further impacts.