TRACE AND MAJOR ELEMENT RATIOS IN ELLIPTIO DILATATUS SHELLS AS INDICATORS OF SURFACE WATER QUALITY IN WESTERN PENNSYLVANIA

Centralized waste treatment facilities in western Pennsylvania accept, treat, and discharge conventional oil and gas wastewaters. This wastewater contains elevated levels of Cl, Br, Ba, Sr, and Ra among other trace elements. Prior to 2012, these facilities also accepted unconventional flowback and produced water. While unit processes in these treatment plants are designed to remove many contaminants, some elevated loads of Cl, Br, Sr, and Ra are discharged into waterways. Previous research suggests that discharge from these facilities has led to accumulation of radium in sediments which may contribute to further decline of endangered mussel species native to the region. Mussels are used as a bio indicator species due to their ability to sequester and incorporate many trace metals into their biomass and shell. This work analyzes concentrations of metals in mussel shells to determine if accumulation of elements present in the discharge of brine treatment facilities are bioaccumulating in the nearby environment. We measured major and trace element ratios by laser ablation inductively coupled plasma mass spectroscopy (LA-ICPMS) in shells of Elliptio dilatatus, a common mussel species. Using ¹⁸O/¹⁶O ratios (δ¹⁸O) we can observe seasonal trends along the growth bands of the shells as well as date changes in concentration within the shells. We can also use ⁸⁷Sr/⁸⁶Sr ratios measured by multi-collector ICP-MS to indicate the likely origin of the strontium (e.g., mine drainage, oil and gas wastewater). Elevated ratios of Ba/Ca, Na/Ca, and Sr/Ca in shells collected downstream of one wastewater treatment facility correspond to periods of the highest reported discharge from that facility (2009-2012). We also plan to develop partitioning coefficients between shells and water at varying salinities by comparing shell concentrations to associated water concentrations in both recent and historic samples. We can then compare this data to mussels grown in controlled reactors to see how environmental factors may change these values. Concurrent work looking at sediment cores collected from a lake downstream of a similar facility has confirmed both elevated strontium concentrations in the sediment deposited during the time period of highest discharge as well as ⁸⁷Sr/⁸⁶Sr indicative of unconventional oil and gas activity.