Evaluating RadiumExposure in E. dilatata: Insights fromControlled Laboratory Studies of Oil and Gas ProducedWater

Radium maypose a risk to aquatic organisms, such as freshwater mussels, living downstream of facilities that discharge oil and gas produced water (OGPW). Exposed freshwater mussels incorporate radium as a calcium substitute, accumulating it in their soft tissue or carbonate shell. Here, in a 25 day controlled laboratory setting, Eurynia dilatata were dosed with radium-laden Marcellus OGPW to mimic exposures that occurred in river systems downstream of the OGPW discharges. Soft tissue from dosed mussels produced distinct ²²⁶Ra activities (mean = 2.22 pCi/g) and ²²⁸Ra/²²⁸Ra isotopic signatures (mean = 0.33) when compared to control samples (0.73 pCi/g; 0.73) with a strong linear correlation with water ²²⁶Ra activities, a direct indicator of the volume of OGPW to which freshwater mussels were exposed. Shell from dosed tanks produced similar results with distinct ²²⁶Ra activities (mean = 0.16 pCi/g) and ²²⁸Ra/²²⁸Ra isotopic signatures (mean = 0.29) when compared to control samples (0.09 pCi/g; 0.54); however, no linear trend was observed, indicating adsorption mechanisms over a short duration study. Bioconcentration factors in both the tissue and shell produced a strong negative correlation (<i>R</i>² = 0.82; 0.80 respectively) with water ²²⁶Ra/Ca ratios indicating high calcium concentrations in OGPW may inhibit excessive radium bioaccumulation.