March 12, 2020

Tracking Toxics in the Salish Sea

Salish Sea Model allows researchers to decipher trends in toxics data

A cage securing mussels sits on the beach at Appletree Cove, where waves from the Puget Sound wash over the shellfish for research.

Mussels were transplanted via cages in 18 locations around Puget Sound, including this one at Appletree Cove. They were then collected and tissues were sampled for 200 contaminants.

Photo by David Toth, volunteer for the Washington Department of Fish and Wildlife

With the help of a diagnostic tool called the Salish Sea Model, researchers found that toxic contaminant hotspots in the Puget Sound are tied to localized lack of water circulation and cumulative effects from multiple sources.

Pharmaceuticals such as opioids and the chemotherapy drug melphalan—along with a suite of 62 other contaminants—were detected by a team of researchers from the University of Washington (UW), Washington State Department of Fish and Wildlife (WDFW), and PNNL.

Contaminant concentrations varied by location, suggesting toxics tend to concentrate in certain enclosed waterbodies that receive wastewater from various outfalls, but undergo little flushing.

Concerning Contaminants

Environmental contaminants are a global problem. Some toxic chemicals are unregulated, and their environmental effects are not well understood. But pharmaceuticals, flame retardants, detergents, some industrial chemicals, and even fragrances from soap or lotion are what researchers call ”contaminants of emerging concern.”

The 99 wastewater outfalls that discharge into the Puget Sound are regularly tested and treated to protect human health and marine life. Despite this process, the research team found concentrations in mussels that were potentially concerning in some localized areas.

“There is a regulatory system in place already to manage pollutants from outfalls. But these data show there is still a suite of chemicals that are entering our surface waters that could bioaccumulate if they are not flushed away efficiently,” said PNNL scientist Tarang Khangaonkar, who is supporting UW and WDFW efforts with the Salish Sea Model.

Contaminants follow a pattern similar to leaves caught in a river eddy—they are transported to wherever water takes them and accumulate in regions with poor circulation. Runoff from parking lots and wastewater pipes all funnel contaminants into the Puget Sound. From there, toxics ride the current and are mixed, churned, and diluted by the pulsing tides. Manmade structures, such as ship canals, can restrict tidal pulses and cause water to stagnate. Contaminants settle out, accumulate, and can show up in marine animals that live there.  

Mussels Sounding an Early Warning

A researcher opens a mussel, showing the inside of the shellfish
Bay mussels are an indicator species and were used by researchers to determine what contaminants are in the water around Puget Sound. Photo provided by the Washington Department of Fish and Wildlife

Mussels are a canary in the coal mine—an indicator species—that help scientists better understand environmental issues. As filter feeders, mussels consume food from the surrounding water and can accumulate contaminants in their tissue. This accumulation helps researchers understand what contaminants are in the water. This makes mussels a great study subject in the search for toxic contaminants.

The UW and WDFW research team examined mussels from 18 rural and urban sites around the Puget Sound—spanning from Port Townsend, inland to Everett, south to Olympia—to evaluate whether urban mussels had more contaminants than rural mussels. If contaminants were present, the researchers wanted to determine the source of the toxics. In other words, were contaminants coming from wastewater outfalls or from urban runoff?

Although this study was limited in scope, they found that mussels near urban areas did not necessarily contain more contaminants in their tissues. Toxic buildup had more to do with how much tidal flushing occurred in different bays, inlets, and waterways. Enclosed waterbodies that undergo poor flushing tend to have more stagnant water, resulting in contaminant buildup over time. Urban runoff from concrete, asphalt, parking lots, and roads likely plays a role in toxics getting into the Salish Sea in the first place. Plus, the combined effects of multiple outfalls likely play a major role in contaminant accumulation in certain areas.


A map of the Puget Sound showing the 18 areas where research mussels were deployed. The areas with toxics are colored red.
Salish Sea Model shows where toxics are concentrated in Puget Sound waterways. Figure by Tarang Khangaonkar and Adi Nugraha, PNNL.

Tales of Toxic Transport Using the Salish Sea Model

PNNL’s Salish Sea Model is a powerful computational tool that has been used to show water circulation patterns throughout the greater Puget Sound region and along the Pacific Ocean’s continental shelf, stretching from British Columbia’s Vancouver Island south to Oregon’s Yaquina Bay. Since 2018, the model has been used to predict the effects of climate change, to evaluate the duration of hypoxia events, to simulate the effects of nutrient pollution, and now to help interpret observed data on accumulation of toxics in mussel tissues.

In these studies led by UW and WDFW, the Salish Sea Model was used in a supporting role to compute a Salish Sea-wide map of effluent concentration from 99 wastewater outfalls over a one-year period. It was used by the researchers to examine exposures from the combination of all 99 wastewater outfalls, Khangaonkar explained. Water movement patterns are at the core of understanding the biogeochemical cycles and toxics fate and transport in the Puget Sound.

“It’s difficult to see overall trends without taking into account circulation patterns,” Khangaonkar said. “The Salish Sea Model is now being used by various research groups who recognize the importance of tidal circulation but lack the in-house modeling expertise. This support to the Puget Sound research community was one of the original motivations for developing the Salish Sea Model.”

A Toxic-tackling Team

The Salish Sea Model was used in two recently published studies led by UW and WDFW researchers with support from Khangaonkar. One study examined what contaminants accumulate in mussels, and the other study looked at the chemistry of water samples.

WDFW has been tracking toxics in mussels for eight years but wanted to collaborate with an oceanographer to better understand toxic transport patterns, WDFW research scientist Jim West said.

“We’ve long had the desire to connect with a modeler to help us understand how toxics move through the water,” West said. “Tarang came to us and said, ‘We’re thinking about adding a toxics component to Salish Sea Model—are you interested?’ We said heck yeah!”

“Tarang came to us and said, ‘We’re thinking about adding a toxics component to Salish Sea Model—are you interested?’ We said heck yeah!” - Jim West, research scientist, Washington Department of Fish and Wildlife

The study’s lead author, C. Andrew James with UW’s Center for Urban Waters, seconded the importance of the collaboration with PNNL.

“The Salish Sea Model is a really valuable contribution,” James said. “There are 99 wastewater treatment plants whose discharges flow into the area and the currents go a lot of different ways. It’s hard to predict where things end up. We wanted to know if we can evaluate currents and tides to figure out where contaminants go.”

Combining Outfalls, Compounding Toxics

For the first time, researchers predicted the combined concentration from all wastewater outfalls simultaneously using the Salish Sea Model. They were able to anticipate the highest contaminant accumulation areas based on currents, likelihood of dilution, and the distance from wastewater outfalls. Researchers concluded that toxics get caught up in some areas and are not flushed out. These areas have a higher level of contaminant buildup, making them more prone to biological impacts.

Marine life in the Salish Sea region is regularly exposed to a variety of contaminants from multiple sources. More information is needed to better understand these pathways, interactions, and chemical changes.

“We want to get better at incorporating the transport chemicals via the Salish Sea Model,” James said. “For example, when toxics enter the Puget Sound, some will degrade or transform.”

Sharing the Salish Sea Model with the Community

Researcher Tarang Khangaonkar stands outside PNNL's Seattle Research Center with the Space Needle in the background.
Tarang Khangaonkar, Salish Sea Model program manager, is based in PNNL's Seattle Research Center. Photo by Andrea Starr, PNNL

PNNL conducts numerous applications of the Salish Sea Model to assist with nearshore habitat restoration planning and design, analysis in support of re-establishment of fish migration pathways, and assessment of basin-wide water quality impacts.

The methods, models, and procedures used in projections for the Salish Sea region could be applied for similar analysis in other regions. The Salish Sea Model application results and solution files are routinely made available to collaborators upon request.

The mussel research published in the March 2020 edition of Science of the Total Environment, “Evaluating exposures of bay mussels (Mytilus trossulus) to contaminants of emerging concern through environmental sampling and hydrodynamic modeling,” (DOI: 10.1016/j.scitotenv.2019.136098). Authors are Andrew James (UW); Jennifer Lanksbury, James West (WDFW); and Tarang Khangaonkar (PNNL).

The water quality research was published in January 2020 in Environmental Science and Technology, “Suspect and Nontarget Screening for Contaminants of Emerging Concern in an Urban Estuary,” (DOI: 10.1021/acs.est.9b06126). Authors are Zhenyu Tian, Katherine T. Peter, Alex Gipe, David Wark, Edward Kolodziej, and C. Andrew James (UW, Center for Urban Waters); Haoqui Zhao, Fan Hou (UW); and Tarang Khangaonkar (PNNL).

The Salish Sea Model was developed by PNNL in collaboration with the Washington State Department of Ecology and through U.S. Environmental Protection Agency grant support. 


About PNNL

Pacific Northwest National Laboratory draws on its distinguishing strengths in chemistry, Earth sciences, biology and data science to advance scientific knowledge and address challenges in sustainable energy and national security. Founded in 1965, PNNL is operated by Battelle for the Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit For more information on PNNL, visit PNNL's News Center. Follow us on Twitter, Facebook, LinkedIn and Instagram.