Spring is here, and tiny, young Chinook salmon will begin their incredible journey from the Snohomish River to the ocean. The young salmon are making their way downstream, swimming fast, passing towns…they are ocean-bound. 

Their journey is not an easy one. They face many challenges, from natural causes like predation or competition for food to human causes like pollution, including toxic chemicals.

One group of toxic chemicals called polybrominated diphenyl ethers – or PBDEs – are known to affect the health and survival of juvenile Chinook salmon. 

PBDEs are a group of flame retardants used in furniture, car seats, electronics, plastics, and children’s toys to meet fire safety standards. These chemicals remain in the environment for a long time, eventually building up in food webs and making their way from Chinook salmon to endangered orca whales that eat salmon. 

But how do the chemicals make their way into the bodies of Chinook salmon?

To answer this question, we studied how PBDEs flow through and accumulate in the Snohomish River watershed. We published our findings in a report titled “Assessing Sources of Toxic Chemicals Impacting Juvenile Chinook Salmon.” 

Concerning effects of toxic exposure

Our study contributes to the growing scientific knowledge of toxic chemicals in Washington state’s rivers and streams.

In 2016, the Washington Department of Fish and Wildlife discovered that juvenile Chinook salmon in the Snohomish River had high concentrations of flame retardants, or PBDEs, in their bodies. The levels were high enough to cause damaging health effects, including a higher risk of diseases, reduced growth, and increased predation.

Further research pinpointed locations where salmon most likely encountered PBDEs – in the lower Snohomish estuary, particularly near a wastewater treatment plant outfall.

Other published studies have reported similar, concerning levels of PBDEs in juvenile Chinook throughout the Puget Sound region. 

To understand how widespread toxic chemicals are in Washington’s watersheds, we established a program to investigate sources of contamination in rivers and streams.

Finding sources of flame retardants

We uncovered how juvenile Chinook are exposed to PBDEs and identified sources of these chemicals in the Snohomish watershed by analysing data from 31 locations along the Snohomish, Skykomish, and Snoqualmie rivers. 

At each location, we collected four types of samples – water, sediment (river mud and particles in the water), slime growing on rocks, and macroinvertebrates (stream bugs) – anything the salmon were in contact with or could eat. We collected samples throughout the year to compare differences in PBDE levels across seasons and water flow events to determine how and when juvenile Chinook were exposed to the chemicals. 

Even though PBDE levels varied in water, sediment, biofilms, and invertebrates across the Snohomish watershed, there were three notable trends:

• Two areas in the watershed had higher concentrations of PBDEs, which indicates the source of chemical contamination is local and can be attributed to treated wastewater discharged to the river system. These areas were the lower mainstem of the Snohomish estuary and part of the Skykomish River near the town of Monroe. 
• PBDEs accumulated in sediment, biofilms, and invertebrates at a much higher concentration than the surrounding waters. This means flame retardants are adsorbed on to river mud and concnetrated in the food web, remaining there at high levels. 
• In invertebrate tissues, PBDE concentrations were highest in March and April when juvenile Chinook reside in the Snohomish estuary. The salmon eat the invertebrates, which is how they are likely exposed to PBDEs in the Snohomish watershed.

Knowing where and how Chinook salmon are exposed to toxic chemicals informs our work to reduce these chemicals in Washington’s waterbodies, support healthy salmon populations, and safeguard food sources for people and resident orca whales.

Reducing toxic pollution

Throughout this study, we worked with partners including Tribes, non-profits, federal and local government partners, and the City of Everett to reduce toxic PBDEs in the watershed. 

Last year, we updated the water quality permit for Everett’s Water Pollution Control Facility and included the scientific data collected during this study. The new permit has PBDE-related requirements, including diverting treated water away from migrating salmon, monitoring PBDE levels, and evaluating how the facility’s lagoon treatment system could reduce PBDE discharges.

We plan to conduct similar in-depth studies in other watersheds. Our research contributes to Puget Sound Vital Signs that measure the health of Puget Sound's ecosystem and progress made on recovery goals. 

Since flame retardants are found in everyday consumer products, you too can help by reducing your exposure to these chemicals. Protecting your health also helps Chinook salmon, orcas, and Puget Sound by limiting toxic chemicals that can wash into rivers and streams.