Freshwater mussels, which burrow into streambeds and rarely move during their decades-long lifespans, serve as biomonitors that indicate environmental cleanliness, according to Penn State researchers. As these bivalves filter water and feed on organic matter, their tissues and shells reflect the surrounding environment, including radioactive particles.
Researchers from Penn State’s Department of Civil and Environmental Engineering (CEE) analyzed mussels downstream of a Western Pennsylvania treatment facility that had treated fracking wastewater from the oil and gas industry for at least two decades. This facility, now decommissioned, stopped accepting oil and gas wastewater in 2019.
The researchers discovered that even years after the facility ceased operations, mussels still contained radium traceable to fracking wastewater from the Marcellus Shale, a major natural gas field spanning from West Virginia to New York. Their findings, published online and in the June issue of *Science of the Total Environment*, highlight the persistence of these contaminants.
Despite most Pennsylvania facilities no longer accepting oil and gas wastewater, significant volumes of treated fracking wastewater were discharged into the state’s rivers and streams between 2008 and 2011. Although treatment processes remove major contaminants, including radium, the discharged water remains five to ten times saltier than ocean water and still contains trace contaminants.
Nathaniel Warner, a professor of CEE and corresponding author of the study, noted that mussels near discharge points often died due to high salinity, while those further downstream adapted by absorbing the salinity and radioactive materials into their shells and tissues. Unlike other wastewaters, fracking wastewater contains unique radioactive element ratios, allowing researchers to trace the contamination back to the Marcellus Shale.
To collect radium samples, Katharina Pankratz, a CEE doctoral candidate and first author of the study, obtained a permit from the Pennsylvania Department of Environmental Protection (DEP). DEP biologists helped collect 10 eastern spikes, a common mussel species, from four locations along the Allegheny River.
The study revealed that mussels half a kilometer downstream from a discharge site had double the radium levels compared to those upstream. Although radium levels decreased five kilometers downstream, they remained measurable. The radioactivity in the sampled mussels was compared to Brazil nuts, which naturally absorb radiation; a 28-gram serving of Brazil nuts contains 0.47 to 0.80 μSv, while the maximum value for a single mussel in the study was 63.42 μSv. The International Atomic Energy Agency recommends an annual exposure limit of 1,000 μSv to avoid health risks.
“Mussels filter not only nutrients but also contaminants such as metals, microplastics, and synthetic chemicals,” Pankratz explained. These contaminants can accumulate in mussels’ tissues or shells, potentially passing up the food chain to larger species like waterbirds, raccoons, muskrats, and otters.
Pankratz expressed concern about the impact on other aquatic life, particularly endangered species, and emphasized the need for future regulations on wastewater disposal to protect ecosystems. She hopes the study will inspire further research into the global ecological consequences of such disposals.
