Cleaner waters, healthier fish: Science leads to improved ecosystem health
Washington Department of Fish and Wildlife (WDFW) scientists identified a major source of toxic contaminants affecting salmon in the Snohomish River, leading to stricter wastewater controls and monitoring to improve water quality.
A 2016 analysis of salmon in the Snohomish River system by WDFW’s Toxics Biological Observation System (TBiOS) team revealed that juvenile Chinook salmon were being exposed to high levels of a type of toxic flame retardants known as polybrominated diphenyl ethers (PBDEs), with the primary source of these harmful PBDEs traced to the Everett Water Pollution Control Facility (WPCF).
The Everett WPCF is one of the largest wastewater treatment plants in the state, and a portion of the wastewater it treats is discharged near the mouth of the Snohomish River, a critical salmon-bearing river system. The Skykomish and Snoqualmie rivers converge inland to form the Snohomish River. Together they support many species of salmonids, including five species of Pacific salmon (Chinook, coho, pink, sockeye, and chum) and steelhead trout.
The Snohomish River is one of the largest contributors to Puget Sound Chinook salmon, which are listed as threatened under the federal Endangered Species Act. The Chinook populations of both the Skykomish and Snoqualmie rivers are below 10% of their estimated historical numbers.
Clean waterways are crucial for salmon and their recovery. Toxic contaminants can harm salmon at all life stages, impairing growth and development, increasing susceptibility to disease, and decreasing reproductivity. In developed areas, toxic contaminants enter waterways from stormwater runoff and wastewater outfall. Many toxic contaminants, including PBDEs, persist in the environment. These chemicals are difficult to remove, making them especially harmful to ecologically and culturally important species like threatened Chinook salmon.
Because anadromous salmon hatch and rear in freshwater streams and rivers before migrating to the ocean, TBiOS studied juvenile Chinook at different locations along their migratory route to measure PBDE levels. This confirmed that the salmon with the greatest concentrations of PBDEs — as much as ten times that found in upstream salmon — were located near a wastewater outfall from the Everett WPCF.
Despite the health risks to people and wildlife, wastewater monitoring and removal of many toxic contaminants is not required. While Everett wastewater managers have worked to reduce the amount of PBDEs released through wastewater, more can be done. After being alerted to the harmful levels of PBDEs found in juvenile Chinook, Everett WPCF voluntarily reduced the flow of wastewater into the Snohomish River during the migratory period for juvenile Chinook. When the Everett WPCF’s water quality permit came up for renewal, environmental and community groups submitted comments to the Department of Ecology in support of stringent water quality monitoring and plans to reduce PBDEs and other pollutants.
In response, Ecology issued new permit requirements for managing PBDEs at the Everett WPCF. Beginning in 2025, the City of Everett must identify businesses releasing PBDEs into wastewater to control and reduce PBDEs entering the wastewater system and, in 2027, Everett WPCF must begin monitoring PBDEs entering wastewater treatment as well as in outflow. During salmon migration they must also discharge treated wastewater in deeper water away from the migratory path instead of through the river when feasible. These actions aim to reduce a significant source of PBDE exposure for juvenile Chinook to support salmon recovery and improve ecosystem health.
TBiOS monitors toxic contaminants in indicator species throughout Puget Sound and conducts tracing studies to identify contaminant sources. Assessing the effects of toxic contaminants helps guide efforts to protect fish and shellfish health, ensure seafood safety, and promote ecosystem recovery.
