Mussels downstream of wastewater treatment plant contain radium, study reports show

Buried in stream beds and rarely moving during their lives, freshwater mussels are biomonitors, meaning they indicate 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.

Two 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 had accepted and treated hydraulic fracturing wastewater from the he oil and gas industry for at least two decades. The facility, now decommissioned, stopped accepting oil and gas-generated wastewater in 2019.

Researchers found that, even years later, the mussels’ tissues and shells contained radium that could be traced to wastewater from hydraulic fracturing in the Marcellus Shale. The rock formation extends underground from West Virginia to New York and is the nation’s largest natural gas deposit. Their findings are available online now and will appear in the June issue of Total Environmental Science.

Although most Pennsylvania facilities do not currently accept oil and gas produced water, from 2008 to 2011, Pennsylvania’s rivers and streams saw a significant volume of treated wastewater from fracking hydraulics in the Marcellus shales. Wastewater treatment plants remove key contaminants, including radium, before discharging the water into surface waters, such as rivers, according to researchers. However, the treated water still contains traces of contaminants and is five to ten times saltier than ocean water.

“With salinity much higher than that of the surrounding environment, the released water has a different chemical fingerprint than the mussels are accustomed to,” said Nathaniel Warner, CEE professor and corresponding author of the paper. “The mussels closest to the water discharges died. Further downstream, the mussels found a way to tolerate the salinity and radioactive material and instead absorbed them into their shells and tissues.”

He explained that other types of wastewater generally do not contain many radioactive particles, but oil and gas wastewater found deep in the earth and extracted by hydraulic fracturing often contains proportions of specific unique elements – a kind signature that can be traced. The unique ratios of radioactive elements allowed the team to identify that the source of the contaminants is likely treated wastewater from the Marcellus Shale.

To collect the samples for radium analysis, Katharina Pankratz, a CEE doctoral student and first author of the paper, 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, then randomly collected 10 eastern cobs – a common type of mussel – from four designated locations along the river.

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

Radiation exposure is measured in dose units called micro-Seiverts (μSv). The researchers compared the radioactivity of the sampled eastern tips to that of 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, while the maximum value calculated for a single mussel collected by researchers in the study was 63.42 μSv. The International Atomic Energy Agency recommends that individuals limit their annual exposure to no more than 1,000 μSv. Any additional exposure may cause health problems.

“In addition to nutrients, mussels also filter contaminants found in the water column, such as metals, microplastics, synthetic chemical compounds and other emerging contaminants of concern,” Pankratz said. “Depending on the contaminant and its chemical composition, if it is small enough to pass through the mussels’ gills, it has the potential to accumulate in their tissues or precipitate in the hard shell structure.”

Although these mussels are not harvested for human consumption, larger species, such as waterbirds, raccoons, muskrats and otters, regularly eat freshwater mussels, meaning that the Contamination could move up the food chain, Pankratz said.

“This raises concerns about potential impacts on other forms of aquatic life, particularly threatened species more vulnerable to contaminants,” she said. “This information could help shape future regulations regarding wastewater discharge into surface waters, particularly in areas where mussels are harvested for food. I hope this study inspires further research into the ecological consequences of these eliminations throughout the world.”