Accumulation of Marcellus Formation Oil and Gas Wastewater Metals in Freshwater Mussel Shells.

For several decades, high-salinity water brought to the surface during oil and gas (O&G) production has been treated and discharged to waterways under National Pollutant Discharge Elimination System (NPDES) permits. In Pennsylvania, USA, a portion of the treated O&G wastewater discharged to streams from 2008 to 2011 originated from unconventional (Marcellus) wells. We collected freshwater mussels, Elliptio dilatata and Elliptio complanata, both upstream and downstream of a NPDES-permitted facility, and for comparison, we also collected mussels from the Juniata and Delaware Rivers that have no reported O&G discharge. We observed changes in both the Sr/Ca and Sr/Sr in shell samples collected downstream of the facility that corresponded to the time period of greatest Marcellus wastewater disposal (2009-2011). Importantly, the changes in Sr/Ca and Sr/Sr shifted toward values characteristic of O&G wastewater produced from the Marcellus Formation. Conversely, shells collected upstream of the discharge and from waterways without treatment facilities showed lower variability and no trend in either Sr/Ca or Sr/Sr with time (2008-2015). These findings suggest that (1) freshwater mussels may be used to monitor changes in water chemistry through time and help identify specific pollutant sources and (2) O&G contaminants likely bioaccumulated in areas of surface water disposal.