Spatial Trends in the Concentration of Polychlorinated Biphenyls (PCBs) in Chinook (Oncorhynchus tshawytscha) and Coho Salmon (O. kisutch) in Puget Sound and Factors Affecting PCB Accumulation

Polychlorinated biphenyls (PCBs) are among the most ubiquitous and persistent contaminants in aquatic ecosystems worldwide. Even though only an estimated 1% of the total PCBs produced have reached the oceans so far (Stone 1992), PCBs are everywhere in aquatic systems (Phillips 1964) including remote polar aquatic ecosystems where PCBs are transported via atmospheric processes (Hammar 1989). PCBs were manufactured prior to 1975 and used extensively as industrial coolants and in electrical transformers, where they were frequently mixed with oils and greases. Since 1976, PCB manufacture has been banned in the U.S., but they persist in the aquatic environment and their high toxicity continues to cause concern for aquatic life, especially fish.

The Washington Department of Fish and Wildlife (WDFW) monitors concentrations of 101 contaminants in marine fishes in Puget Sound, including chinook (Oncorhynchus tshawytscha) and coho salmon (O. kisutch), as part of the Puget Sound Ambient Monitoring Program (PSAMP). This effort is implemented by a multi-agency consortium of scientists and natural resource managers who assess and monitor the environmental health of the Puget Sound ecosystem (Puget Sound Water Quality Authority 1995; Puget Sound Water Quality Action Team 1998). This monitoring has documented that PCBs are one on the few contaminants that accumulate in chinook and coho salmon from Puget Sound. WDFW continues to monitor PCB concentrations in adult chinook and coho salmon because of their importance in the Puget Sound ecosystem and in recreational and commercial fisheries. Prior to these PSAMP studies, PCB exposure and accumulation in chinook and coho salmon from Puget Sound were not well studied. The aim of PSAMP is to assess spatial and temporal trends in PCB exposure in these species by annually monitoring PCB concentrations in the edible muscle tissue of adult fish at various locations throughout Puget Sound.

Exposure to PCB-contaminated sediments and food are primary pathways for accumulation of PCBs in fish (Varanasi et al. 1992). However, various biotic and abiotic factors affect the degree of exposure and accumulation. Exposure to PCBs may be affected by the proximity of fish to contaminated sediments and prey, the magnitude of contamination in their habitats, fish movement patterns, trophic status, growth rates, duration of exposure (i.e., lifespan or fish age), and bioavailability of PCBs (Jensen et al. 1982; Hammar et al. 1993; Stow et al. 1994; Bentzen et al. 1996). Furthermore, although fish may be exposed to PCBs, speciesspecific metabolism and detoxification of PCBs, reproductive and maturational patterns (e.g., sex and age of first reproduction), and the level of body fat (i.e., percent lipids) can affect the degree to which these PCBs accumulate in tissues, and have adverse effects (Masnado 1987; Larsson et al. 1991; Varanasi et al. 1992; Loizeau and Abarnou 1994; Bentzen et al. 1996; Larsson et al. 1996).

In the Pacific Northwest PCBs have been detected in Pacific salmon from various locations in Alaska (NMFS unpublished data, John Stein, personal communication) and the Columbia River (Tetra Tech. Inc. 1996), suggesting a widespread source of PCBs in this areas. Pacific salmon are anadromous and throughout their lives may be exposed to PCBs in fresh water, estuarine, or marine areas. Although specific migratory patterns of these species vary, chinook and coho salmon are spawned in freshwater, live there for 3 to 15 months after emergence as embryos from gravel nests, and subsequently migrate to marine waters. PCB concentrations in prey consumed by salmon may vary in these habitats. In fresh water, young chinook and coho salmon consume aquatic insects and crustaceans but as these fish smolt and enter the estuary they consume a wider variety of invertebrates and larval fish (Higgs et al. 1995). Adult salmon in marine waters continue to eat invertebrates but they consume more epipelagic fish (Higgs et al. 1995), increasing the likelihood of PCB biomagnification in their tissues. The amount of time each species or population spends at sea varies widely, but for both species the majority of their growth occurs in marine waters (Groot and Margolis 1991) before they return to their natal streams to spawn.

PCBs are lipophilic, typically concentrating in the fatty tissues in fishes (Varanasi et al. 1992), and thus PCBs may readily accumulate in muscle tissue of adult chinook and coho salmon because of their relatively high lipid content. However, the lipid content in the muscle tissue in adult salmon in marine waters decreases rapidly as they approach fresh water and reach reproductive maturity, particularly in females (Hendry 1998). Thus, the lipid content of the muscle tissue, the sex of the fish, and the degree of maturation may all affect PCB accumulation in chinook and coho salmon.

One of the main objectives of PSAMP is to assess species-specific and location-specific differences in PCB accumulation in adult chinook and coho salmon. However, meaningful comparisons of PCB concentration in tissues of chinook and coho salmon from different Puget Sound locations can only be made after an accounting of the factors described above that could affect PCB accumulation at these locations. The purpose of this paper was to model the accumulation of PCBs in chinook and coho salmon from Puget Sound. In addition to unspecified location effects that may be associated with proximity to and magnitude of PCB contamination, we estimated the contribution of percent body weight as lipids, the gender and age of the fish, and the hatchery or wild origins of the fish. First, we compared differences in PCB concentrations between adult chinook and coho salmon sampled from marine areas of Puget Sound and from five Puget Sound rivers. Then, for coho salmon we evaluated the effects of tissue lipid content and sampling location on PCB accumulation. At a subset of the sampling locations we evaluated the effects of gender and the hatchery or wild origins on the PCB accumulation in coho salmon. An insufficient number of samples was collected to fully assess which aspects of the chinook salmon's complicated life history affect PCB accumulation in that species, and therefore only preliminary analysis on the effects of fish age and percent lipids are presented for that species in this paper.