Estimating toxics loadings to the Lake Washington Watershed

Background

Fish can become contaminated with a class of chemicals called polychlorinated biphenyls (PCBs). Commercial products and industry used PCBs widely until they were banned in 1977. Despite bans, PCBs remain at toxic levels in the environment and especially in fish. Contaminated fish can pose a health risk to the people who eat them. Lake Washington is the largest freshwater lake in King County, Washington and fish in the lake have some of the highest concentrations of PCBs measured across the state. No one knows exactly where PCBs in Lake Washington fishes originate.

• The goal of this project was to help answer the following questions.
• What input pathways contribute PCBs to Lake Washington?
• Do we need to reduce the ongoing sources of PCBs entering the lake?
• Are fish accumulating PCBs only from historical pollution present in lake sediments?
• To what extent do PCBs exit the Ship Canal and contaminate Puget Sound?

Please refer to the EPA's PCB website for background information on PCBs.

Project objectives

This project developed numeric tools to understand how to reduce contaminant concentrations in Lake Washington fish. This project examined PCBs and polybrominated diphenyl ethers (PBDEs). The tools estimated how much each contaminant comes into Lake Washington and Elliott Bay and identified their routes or pathways. The results are helping water quality managers identify how to reach safe PCB and PBDE levels in fish.

The pathways we estimated include:

• combined sewer overflows (CSOs)
• stormwater discharges
• road runoff
• river input
• air deposition

The project's tools consist of:

• Annual loadings of PCBs and PBDEs. We estimated these loadings from existing and new data collected by this project.
• Fate and transport and bioaccumulation models. These models enabled us to test different PCB reduction scenarios.

Field study

The field study collected data to estimate PCB and PBDE loadings (total mass per year). We focused on loadings entering Lake Washington and Elliott Bay (via the Ship Canal). We collected data in 2012-2013. These data included:

• Total organic carbon
• PCB and PBDE congener concentrations
• Associated flow rates for each pathway
  
  • Tributaries
  • Atmospheric deposition
  • Stormwater runoff
  • CSO discharge
  • Road runoff

A map of the sampling locations is available for viewing.

Model development

We estimated the loadings for each pathway and the total for Lake Washington and Elliott Bay. We used historical and the new data for this estimation. We also developed a fate and transport model and a bioaccumulation model. We then simulated how fish tissues respond to different PCB reduction scenarios. Too little PBDE data were available for fish tissue and sediment. As a result, we did not simulate fish tissue response for PBDE reduction scenarios.

PCB reduction options

The project team and advisory panel selected a variety of PCB reduction scenarios. To select the scenarios, we used information on relative pathway contributions. Scenarios differed by the total reduction in PCB load. We then modelled the scenario outcomes by running various simulations. The results informed which reductions are the most important to pursue. Successful reductions will help reduce fish tissue concentrations until they are safe for human consumption.

Management Discussion

The results of this project identified the key PCB pathways needing reduction. Water quality managers and stakeholders can use these results to inform policy decisions. Successful reductions can help us reach safe levels in Lake Washington fish tissue. We shared the results with technical and policy groups and post the final report on this website.