Potential Effects of Contaminants on Fraser River Sockeye Salmon

3. For hardness-dependent water quality guidelines, substitute the interceptvalue for sockeye salmon or the most sensitive salmonid species for theintercept value for the non-salmonid species used to derive the toxicityscreening value (the slope was not adjusted, however);4. Calculate the ratio <strong>of</strong> the final acute value for sockeye salmon or the mostsensitive salmonid species to the final acute value for the species that wasused to derive the water quality guidelines. Multiply the toxicity screeningvalue by the ratio <strong>of</strong> final acute values derived in this manner to estimatethe toxicity threshold for sockeye salmon; or,5. Identify the toxicity threshold directly from the maximum acceptabletoxicant concentration reported for a sub-lethal endpoint obtained based onthe results <strong>of</strong> an acceptable long-term study on sockeye salmon or anothersalmonid species.• For substances for which the selected toxicity screening value was based ontoxicity data for salmonid species, toxicity thresholds for sockeye salmon wereestablished using the following procedures:1. Calculate the ratio <strong>of</strong> the final acute value for sockeye salmon to the finalacute value for the salmonid species that was used to derive the waterquality guideline. Multiply the toxicity screening value by the ratio <strong>of</strong> finalacute values derived in this manner to estimate the toxicity threshold forsockeye salmon.In some cases, the toxicity screening values used in the preliminary evaluation wereadopted directly as the toxicity thresholds for sockeye salmon. In these cases, thetoxicity screening value was already based on salmonid toxicity data and/or nosockeye-salmon specific toxicity data were available. The toxicity thresholds that wereselected for evaluating surface-water chemistry data from the Fraser River Basin arepresented in Table 5.1.For each surface water sample, a water quality index score was also calculated usingthe methods described in CCME (1999). The water quality index provides aconsistent basis for evaluating the proportion <strong>of</strong> toxicity screening values exceeded,the frequency <strong>of</strong> exceedance <strong>of</strong> the toxicity screening values, and the magnitude <strong>of</strong>exceedance <strong>of</strong> the toxicity screening values. Accordingly, the water quality indexprovides a convenient tool for comparing water quality conditions across geographicareas and across time periods (see Appendix 5 and CCME 1999 on detailedinformation for calculating the water quality index).60