Potential Effects of Contaminants on Fraser River Sockeye Salmon

The results <strong>of</strong> this analysis showed that iron and nickel in the Lower Fraser River Area <strong>of</strong>Interest and nickel in the South Thompson River Area <strong>of</strong> Interest occurred in sediments atconcentrations sufficient to adversely affect exposed sockeye salmon (Table 5.19). Thefrequency <strong>of</strong> exceedence <strong>of</strong> the selected toxicity thresholds for the two metals indicatesthat exposure to sediment-associated contaminants has likely increased in the LowerFraser River Area <strong>of</strong> Interest over the past 20 years (Figure 5.17).While the concentrations <strong>of</strong> certain metals exceeded the selected toxicity thresholds at upto 39% <strong>of</strong> the stations sampled, it is unlikely that exposure to contaminated sedimentsrepresents a significant factor in the decline <strong>of</strong> sockeye salmon over the past 20 years.Most importantly, interactions between sockeye salmon and contaminated sediments arelikely to be minimal under most circumstances. In some cases, sockeye salmon rearing inareas dominated by benthic productivity (e.g., freshwater sloughs) could be exposed tosediment-associated contaminants through consumption <strong>of</strong> contaminated prey. However,as nickel and iron are only minimally bioaccumulated, this exposure route is likely notsignificant for these metals. Dietary exposure is likely important for many hydrophobicorganic contaminants that accumulate in fish tissues, however.5.4.3 <strong>Potential</strong> <strong>Effects</strong> on Sockeye Salmon Associated with Accumulation<strong>of</strong> <strong>Contaminants</strong> <strong>of</strong> Concern in Fish TissuesData from several studies indicate that sockeye salmon accumulate a variety <strong>of</strong> persistentcontaminants in their tissues (DeBruyn et al. 2004; Kelly et al. 2007; Siska TraditionsSociety 2009). In this study, risks to sockeye salmon associated with exposure tobioaccumulative contaminants <strong>of</strong> concern were evaluated by comparing the measuredconcentrations <strong>of</strong> bioaccumulative substances in fish tissues to critical body burdens forfish or tissue-specific toxicity thresholds (i.e., toxicity reference values). For eachgeographic area, exposure point concentrations were estimated for each tissue type (i.e.,theggs and muscle) by calculating the 95 percentile concentration <strong>of</strong> each <strong>of</strong> thecontaminants <strong>of</strong> concern that were retained for detailed evaluation (i.e., mercury,selenium, PCBs, PCDDs, and PCDFs; Table 5.8). Sockeye salmon exposure to PCBs,PCDDs, and PCDFs was evaluated by calculating 2,3,7,8-TCDD toxic equivalents foreach tissue sample. These exposure point concentrations were used to calculate hazardquotients for each contaminant <strong>of</strong> concern in each geographic area (i.e., by dividing theexposure point concentration by the selected toxicity reference values for fish tissues;Table 5.20).69