Freshwater mussels serve as biomonitors, reflecting the cleanliness of their environment by accumulating substances in their tissues and shells. A recent study by Penn State researchers examined mussels downstream of a former centralized treatment facility in Western Pennsylvania that accepted fracking wastewater from the Marcellus Shale. Even after the facility ceased operations in 2019, the mussels still contained radium originating from the fracking wastewater. The researchers found that the mussels closest to the discharge site died off due to high salinity levels, while those further downstream developed a tolerance to the contaminants.
Wastewater treatment facilities in Pennsylvania remove major contaminants like radium before discharging treated water into surface water. However, the water still contains trace amounts of contaminants and is significantly saltier than ocean water. The discharged water has a different chemical composition than what mussels are accustomed to, leading to an uptake of radioactive materials and increased salinity in their tissues and shells. The unique ratios of radioactive elements in Marcellus Shale wastewater allowed the researchers to identify the source of the contaminants in the mussels.
Radium analysis of mussel samples revealed higher levels of radium downstream of discharge sites, with mussels closest to the site containing double the radium levels compared to those further upstream. While mussels further downstream had lower radium levels, they still contained measurable amounts of the radioactive element. The researchers compared the radioactivity levels in mussels to Brazil nuts, finding that a single mussel collected in the study had a higher radiation exposure than the recommended annual limit for individuals.
Contaminants present in water, like metals, microplastics, and synthetic chemical compounds, can accumulate in mussel tissues and shells if they pass through the gills. While freshwater mussels are not consumed by humans, larger species like waterbirds and muskrats often eat them, potentially passing contamination up the food chain. This raises concerns about the impact on other aquatic life, particularly endangered species that are more vulnerable to contaminants. The researchers hope their study will inform future regulations on wastewater disposal to surface water and inspire further research into the ecological consequences of such practices worldwide.
The study was supported by the U.S. National Science Foundation and highlights the importance of monitoring freshwater ecosystems for contaminants like radium that can persist in organisms like mussels. By studying the effects of wastewater disposal on freshwater mussels, researchers can better understand the implications for other aquatic species and the environment as a whole. This research contributes to ongoing efforts to protect water quality and aquatic ecosystems from the potential harms of industrial activities like fracking.