FEASIBILITY OF USING FRESHWATER MUSSELS TO MONITOR BA AND SR CONTAMINATION DUE TO SHALE GAS FLOWBACK WATER IN PENNSYLVANIA STREAMS

With the extensive Marcellus Shale natural gas development, horizontal drilling, combined with hydraulic fracturing, produces large quantity of saline flowback water high in Ba and Sr content, raising health and ecological concerns in case of spills.

Freshwater mussels, as sedentary filter-feeders, could potentially take up Ba and Sr in the growth rings of their shells, reflecting the geochemistry of the aquatic environment over time. The experimental site mussels (E. complanata and L. cariosa) were obtained from the West Branch Susquehanna River near Williamsport PA; the control site is on Buffalo Creek, Union County. From 2010 to 2014, PA Department of Environmental Protection data, at two monitoring points near West Branch sample sites, show that the river water Ba concentrations (± 1σ) were 30 (5) and 34 (13) μg/L, Sr = 100 (44) and 98 (50) μg/L. In two tributaries, Ba concentrations were 19 (6) and 26 (6) μg/L, Sr = 23 (8) and 32 (8) μg/L. Cross-sectional thin sections (0.5 mm) were observed under transmitted light microscope and scanning electron microscope backscattered electron mode to identify possible growth rings. X-ray diffraction confirmed that the mineralogy of the shell is mostly aragonite (CaCO₃). Ba and Sr were analyzed along transects in shell layers using electron probe micro-analysis (EPMA). For experimental site samples, Ba and Sr concentrations showed significant variations with 95% confidence. Linear regression indicated no correlation between Ba and Sr concentrations in the shells. The control site sample is still being analyzed. The use of mussels has promise for monitoring stream water chemistry with time for possible contributions from flowback water. However, it is unlikely that chemistry within growth rings could be assigned unequivocally to particular years.