Toxic contaminants in bay mussels (Mytilus trossulus) transplanted to Port Gamble Bay, Washington before cleanup and restoration (2015-2017)

Port Gamble Bay is located in Washington State on the north end of the Kitsap Peninsula. It is approximately two square miles in size and generally shallow, with depths up to 60 feet, and is connected at its north end to the Hood Canal. The former Pope & Talbot Inc. sawmill is located along the western shoreline of the mouth of Port Gamble Bay and manufactured forest products there from 1853 to 1995. Historic mill operations at Pope & Talbot Inc. included wood chipping, log rafting, wood burning, and storage activities, and resulted in contamination of Port Gamble Bay. Contaminants of most concern related to human health from these activities include carcinogenic polycyclic aromatic hydrocarbons (cPAHs), polychlorinated biphenyls (PCBs), dioxins/furans and metals (arsenic, cadmium, copper, and mercury). The Washington State Department of Ecology (Ecology) is currently managing a cleanup of contaminated sediments in the Port Gamble Bay, including removal of thousands of existing creosote-treated pilings, dredging of contaminated sediments, and capping with clean sediments employed as source control measures (Washington Department of Ecology, 2013).

In a study in 2000, caged mussels (Mytilus galloprovincialis) were deployed in Port Gamble Bay as part of a larger study to provide a Puget Sound-wide perspective on PAH exposures in documented herring spawning grounds (Applied Biomonitoring, 2002). Mussels were transplanted to two sites in Port Gamble, near the Saw Mill and at Little Boston Harbor, and at one site outside the bay at Teek Bluff for a two month period (April â€" June). At the end of the study the PAH tissue burdens in mussels were assessed. The Port Gamble mussels, especially those placed near the Saw Mill, showed consistently high PAH signals compared to most of the other sites and exhibited end-of-test total PAHs that were significantly higher than the beginning-of-test concentrations: Saw Mill mean = 427.03 µg/kg dry weight (dw) vs. T₀ mean = 87.18 µg/kg dw (Applied Biomonitoring, 2002). The authors concluded that more studies were needed in Port Gamble to determine if â€�"bioavailable PAHs are affecting herring egg development”.

The focus on potential effects of PAHs on herring egg development is linked to the fact that unusually high rates of herring embryo mortality (>20%) have been observed in Port Gamble Bay since the early 1980s (WDFW, unpublished data). Since that time efforts have been made to assess whether herring embryo mortality is linked to contamination (Kocan, 1987), and to compare PAH concentrations and herring embryo health with other spawning stocks (Hershberger et. al., 2005). These concerns are further motivated by the fact that prior to 2000, the Port Gamble Bay herring stock was considered one of the larger spawning stocks in Puget Sound, and since that time its spawning biomass has steadily declined from 2,459 tons to 208 tons in 2008 (Stick and Lindquist, 2009).

The most recent examination of PAHs in Port Gamble Bay mussels was conducted as part of a larger study in the winter of 2012-2013. In that study, mussels (M. trossulus) were transplanted to two locations in Port Gamble Bay (near the previous Saw Mill site and across the bay at Point Julia). Although the 2012/13 mussels exhibited lower total PAHs (205.2 and 180.3 µg/kg dw for Port Gamble, West and Point Julia respectively; Figure 1) than the M. galloprovincialis mussels from the 2000 study, the PAH content of the Port Gamble Bay mussels at the end of the 2012/13 study were higher than the starting condition (71.36 µg/kg dw; Figure 1) of mussels for that study, suggesting a biologically available source of PAHs still exists within the bay (Figure 1; Lanksbury et al., 2014).

Study purpose and objective

The purpose of this study was to synoptically evaluate the geographic extent and magnitude of contamination in bay mussels (Mytilus trossulus) during the winter of 2014-15, prior to a large-scale remediation project scheduled in Port Gamble Bay. The objective was to compare the extent, magnitude and pattern of contamination (specifically PAHs, PCBs, cadmium, and dioxins/furans) in M. trossulus mussels exposed to different locations within and outside of the Sediment Management Areas (SMAs; Figure 2) identified in the Port Gamble Bay Remedial Investigation (Ecology 2012). Specifically we will compare; 1) the extent of contamination across the bay before remediation, 2) the magnitude of contamination in the different areas, including a reference area, before remediation, and 3) the patterns of contamination (i.e. PAH analyte fingerprints) before remediation.