by Kathryn Davis
What do mussels know about what’s in our water? A lot, as it turns out. In late October, teams of Puget Soundkeeper volunteers bundled up and headed to Seattle beaches ready to hammer in three cages of native mussels at a late night low tide. This work was part of the Regional Stormwater Monitoring Program’s Mussel Monitoring Project, coordinated by the Department of Fish and Wildlife. In total, 73 cages of mussels were installed throughout Puget Sound where they will stay for a total of 3 months. In February 2015, they will be collected and their tissues will be analyzed for accumulation of various pollutants.
Mussels have long been used to study water contamination, but this project focuses specifically on urban sample sites with high pollution loads. Less contaminated sites are also included for reference. Over the long term, this monitoring provides valuable information about improvements or declines in Puget Sound water quality.
Why are mussels used to study pollution? Mussels are prolific filter feeders that can filter anywhere from 20-50 gallon of water each day. Because of this, they perform an important ecosystem service- they clean our water! However, this also means they accumulate the chemicals present in their food and water in their tissues. Mussel digestive systems are relatively primitive: they lack a functioning liver. They cannot metabolize contaminants and, instead, accumulate them unchanged in their tissues. This is bad news for mussels, but good news for science. Mussels will bioaccumulate contaminants until they reach equilibrium with their environment (this generally takes 60-90 days, the same amount of time our mussel cages will be placed). Because these chemicals are not biotransformed, mussels provide a comprehensive look at what pollutants are present in a body of water over a period of time. This is a more robust measure than taking a water sample on one particular day, when conditions may be variable, and is more sensitive to low levels of contaminants that may otherwise go undetected.
Although the results from these mussels will not be available until 2017, the cages placed during the last round of sampling in 2012 yielded some interesting results. Four highly carcinogenic compounds (PAHs, PCBs, PBDEs, and DDTs) were the most abundant contaminants. All four carcinogens were found in every mussel sample, regardless of location. The highest concentrations of these compounds were found in the most urbanized areas (Elliott Bay, Salmon Bay, Commencement Bay, and Sinclair Inlet near Bremerton). Full results are available online.
These toxic contaminants enter Puget Sound through a variety of pathways including stormwater runoff, groundwater releases, air deposition, marinas and ferry terminals, as well as discharges from stormwater outfalls, wastewater treatment plants, combined sewer overflows, and permitted industrial sites. Although manufacture of PCBs was banned in the US in 1979, legacy PCBs are still found in significant large amounts in the Puget Sound basin.
It is important to continue work to stop the flow of these pollutants at their sources. Puget Soundkeeper legal actions, policy advocacy, outreach projects and business partnerships are focused on addressing stormwater pollution and finding creative solutions to the challenges facing Puget Sound today. Find out more about this work by browsing our website or contacting us at any time.
Photos: (1) Puget Soundkeeper (2) Leslie Seaton