Clams and mussels may be a more effective, less expensive way to clean harmful chemicals from streams, rivers, and lakes.
Pharmaceuticals, personal care products, herbicides, and flame retardants are increasingly showing up in waterways. The chemicals are found in some waters at trace levels and little is known about their health effects. But some have been implicated as potentially harmful to fish reproduction in waters receiving large amounts of wastewater.
In the right quantities, bivalves such as clams and mussels can remove some contaminants of emerging concern (CECs) from water in a matter of days, a new study shows.
The findings make a case for the conservation and restoration of freshwater bivalve habitats as a means of ensuring and amplifying the species’ capacity to naturally purify water.
“We would be doing two things here—restoring ecosystems and cleaning water,” says Richard Luthy, professor of civil and environmental engineering at Stanford University and coauthor of the paper published in the journal Environmental Science and Technology.
A way to save clams, too
Found in municipal wastewater, agricultural runoff, and animal wastes, CECs don’t break down easily when they reach streams and other waterways. Although much remains unknown about their effects, CECs are not considered a threat to tap water or water reuse for irrigation.
For the new study, researchers subjected native California floater mussels and invasive Asian clams to treated wastewater with various concentrations of CECs. Within 72 hours, the clams and mussels had removed up to 80 percent of some of the chemicals.
Luthy speculates that municipal water treatment facilities are unlikely to employ bivalves in their systems, due to the management and maintenance issues involved. But mussels and clams could be put to work in wetlands and managed natural water systems to further treat plant effluent, agricultural runoff, and other wastewater sources.
This arrangement could have the added benefit of saving bivalves themselves. More than 70 percent of native US freshwater mussels are at risk of extinction.
Just as engineered oyster beds and rafts in the Bronx River and Long Island Sound are bringing back the eastern oyster and helping control nutrients and excessive algae, freshwater clams and mussels could be managed to remove trace levels of CECs and improve water quality in streams dominated by effluent or urban runoff.
“Each native mussel filters about two liters of water a day, so it doesn’t take a whole lot to improve water quality,” Luthy says.
Luthy and the study’s lead author, Niveen Ismail, a Stanford graduate student in civil and environmental engineering, will next look at the creatures’ ability to absorb trace chemicals and pathogens, with an eye toward harnessing additional benefits from the re-introduction of native species in decline as well as invasive species that dominate some waterways.
They will demonstrate bivalves’ potential as water cleansers at San Francisco’s Mountain Lake, a body of water contaminated with harmful bacteria. By showing that mussels’ filtering processes can remove harmful bacteria as well as CECs, the work will support efforts to improve water quality and restore native species.
“While there is still considerable research needed to determine the best method to deploy these bivalves on a large scale, at Mountain Lake we are considering using a raft carrying caged native bivalves which will allow us to monitor the health of the bivalves and also protect them from predators,” Ismail says.
Claudia Müller, a former Stanford postdoctoral researcher in civil and environmental engineering and Rachel Morgan, a former Stanford undergraduate student in civil and environmental engineering are coauthors of the study.
This National Science Foundation, the Engineering Research Center for Re-inventing the Nation’s Water Infrastructure, a Ford Foundation predoctoral fellowship, and an NSF graduate research fellowship funded the study.
Source: Stanford University