Mussels downstream of sewage treatment plant contain radium, study finds

Buried in streambeds and rarely moving because of their decades-long lifespan, freshwater mussels are biomonitors, meaning they show how clean their environment is, according to Penn State researchers. As bivalves feed on organic matter and filter the water around them, their internal tissues and hard shells begin to reflect everything in their environment—including radioactive particles.

A pair of researchers from Penn State’s Department of Civil and Environmental Engineering (CEE) analyzed the composition of mussels downstream of a centralized treatment facility in western Pennsylvania that has received and treated fracking wastewater from the oil and gas industry for at least two decades. The now decommissioned facility stopped receiving oil and gas wastewater in 2019.

Scientists found that even years later, the tissue and shells of the mussels contained radium that could be traced back to wastewater from fracking in the Marcellus Shale. The rock formation stretches underground from West Virginia through New York and is the largest natural gas field in the country. Their findings are now available online and will appear in the June issue The science of the total environment.

Although most facilities in Pennsylvania do not now receive water from oil and gas, between 2008 and 2011 Pennsylvania’s rivers and streams saw a significant volume of treated wastewater that came from fracking in the Marcellus Shale. Wastewater treatment plants remove major contaminants, including radium, before discharging the water into surface waters such as rivers, according to the researchers. However, treated water still contains trace amounts of contaminants and is five to ten times saltier than ocean water.

“With a much higher salinity than the surrounding environment, the discharged water has a different chemical fingerprint than the mussels are used to,” said Nathaniel Warner, a professor in Central and Eastern Europe and corresponding author of the paper. “The mussels closest to the water outlets died. Further downstream, the mussels found a way to tolerate the salinity and radioactive materials and instead absorbed them into their shells and tissues.”

He explained that other types of wastewater generally don’t contain many radioactive particles, but oil and gas wastewater found deep in the earth and brought up by fracking often contains specific unique ratios of elements — a kind of signature that can be traced. The unique ratios of the radioactive elements allowed the team to identify that the source of the contaminants was likely treated Marcellus Shale wastewater.

Katharina Pankratz, a PhD student in CEE and the first author of this paper to collect samples for radium analysis, contacted the Pennsylvania Department of Environmental Protection (DEP) to obtain a permit to sample mussels in the Allegheny River. DEP biologists who offered to help with the collection identified the species present and then randomly collected 10 eastern spikes — a common type of mussel — from four designated locations along the river.

The researchers found that half a kilometer downstream from the release site, mussels had approximately double the total radium levels of those upstream from the release site. And mussels five kilometers downstream from the release site had less than mussels closer to the site, but still had measurable amounts of radium.

Radiation exposure is measured in dose units known as micro-Seiverts (μSv). The researchers compared the radioactivity of the harvested eastern cobs with brazil nuts, which absorb radiation from the soil in which they grow. A 28-gram serving of Brazil nuts contains 0.47 to 0.80 μSv, with the maximum value calculated for one shell collected by the researchers in the study being 63.42 μSv. The International Atomic Energy Agency recommends that individuals limit their annual exposure to no more than 1,000 μSv. Any further exposure can lead to health problems.

“Along with nutrients, mussels also filter contaminants present in the water column, such as metals, microplastics, synthetic chemical compounds and other emerging contaminants,” Pankratz said. “Depending on the contaminant and its chemistry, if it’s small enough to pass through the mussel’s gills, it has the potential to accumulate in their tissue or precipitate in the hard shell structure.”

While these mussels are not harvested for human consumption, larger species such as waterfowl, raccoons, muskrats and otters regularly eat freshwater mussels, meaning contamination could travel up the food chain, Pankratz said.

“It raises concerns about potential impacts on other aquatic life, particularly endangered species that are more susceptible to contaminants,” she said. “This information can help shape future regulations for wastewater disposal to surface waters, particularly in regions where mussels are harvested for food. I hope this study will inspire further research into the ecological consequences of these disposals around the world.”