The researchers found that half a kilometer downstream of a discharge site, mussels had approximately double the total radium levels as those upstream of the discharge site. And mussels five kilometers downstream of a discharge site had less than the mussels closer to the site, but still had a measurable amount of radium.
Radiation exposure is measured in dose units known as micro-Seiverts (μSv). The researchers compared the radioactivity of the sampled eastern spikes to Brazil nuts, which take up radiation from the soil in which they grow. A 28-gram serving of Brazil nuts contain 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 more exposure can lead to health problems.
“Along with nutrients, mussels also filter contaminants present in the water column, like metals, microplastics, synthetic chemical compounds and other emerging contaminants of concern,” Pankratz said. “Depending on the contaminant and its chemistry, if it is small enough to pass through the gills of the mussel, it has the potential to accumulate in their tissue or precipitate within the hard-shell structure.”
While these mussels are not harvested for human consumption, larger species, like waterbirds, raccoons, muskrats and otters, regularly eat freshwater mussels, meaning the contamination could pass up the food chain, Pankratz said.
“It raises concerns about potential impacts on other aquatic life, particularly endangered species more vulnerable to contaminants,” she said. “This information may help shape future regulations for wastewater disposal to surface water, especially in regions where mussels are harvested for food. I hope this study will inspire further research into the ecological consequences of these disposals worldwide.”
The U.S. National Science Foundation supported this work.
Read More: Mussels downstream of wastewater treatment plant contain radium, study reports