In early December, teams of Puget Soundkeeper volunteers bundled up and headed to Seattle-area beaches to hammer in 9 cages of native mussels at a late night low tide. Why? Because mussels are a great tool for figuring out what’s in our water. These cages, which stay at their sites for two months, are part of the Puget Sound Mussel Monitoring program coordinated by the Washington Department of Fish and Wildlife. This program is sponsored by the Stormwater Action Monitoring program along with a network of state, county, and city agencies, tribes, marine resource committees, and other groups. In total, 94 cages of mussels were installed throughout the Puget Sound region in December and collected in late February for tissue analysis.

A map of sites where Soundkeeper placed mussel monitoring cages in 2017.

This program is a model of governments, non-profits, business, and the public collaborating to gain a better understanding of the sources, fate, and transport of contaminants in the Puget Sound nearshore, and what impacts they have on the marine food web.  This information will improve our ability to make cost-effective decisions to mitigate the harm pollution causes in the nearshore environment of Puget Sound.  In addition, the mussel sites help track regional progress in reducing pollution associated with urbanization and polluted stormwater runoff.

Mussels are prolific filter feeders that can filter anywhere from 20-50 gallons 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 and 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 accumulate contaminants until they reach equilibrium with their environment (this generally takes 60-90 days, the same amount of time our mussel cages were placed). Because of this, 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 sample on one particular day, when conditions may be variable, and is more sensitive to low levels of contaminants that may otherwise go undetected.

A Soundkeeper volunteer holds up a net bag of mussels. She is wearing a headlamp and behind her is the Seattle skyline. Photo by Hannah Letinich.

The results from these mussels will not be available until 2019, but the cages placed during the last round of sampling in 2015/2016 yielded interesting results. The most abundant organic contaminants measured were PAHs, PCBs, PBDEs, and DDTs. These contaminants are all known to be either carcinogenic or endocrine disrupting. PAHs and PCBs were detected in mussels from every site and the concentration of these contaminants was significantly higher in the most urbanized areas. Full results are available online here.

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’s 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 by contacting us at any time.


Photo: Hannah Letinich