Publication Summary

Rainbow trout, mountain whitefish, and largescale suckers from the upper Spokane River were collected for PCB analysis in August 1996 to determine if concentrations had decreased from the levels seen in 1993-94. Samples were collected above Upriver Dam, above Monroe Street Dam, above Nine-Mile Dam, and in the Little Spokane River. In eight of the ten sample sets evaluated, mean PCB concentrations showed a consistent decrease from when first analyzed in 1993 or 1994. The decline in PCB concentrations was statistically significant in the four instances where there were sufficient data for testing.

Rainbow trout, mountain whitefish, and largescale suckers from the upper Spokane River were collected for PCB analysis in August 1996 to determine if concentrations had decreased from the levels seen in 1993-94. Samples were collected above Upriver Dam, above Monroe Street Dam, above Nine-Mile Dam, and in the Little Spokane River. In eight of the ten sample sets evaluated, mean PCB concentrations showed a consistent decrease from when first analyzed in 1993 or 1994. The decline in PCB concentrations was statistically significant in the four instances where there were sufficient data for testing.

Mean PCB concentrations in rainbow trout above Upriver Dam and in whitefish above Nine-Mile Dam were higher in 1996 than in 1994. The 1996 results for Upriver trout were strongly influenced by one outlier sample very high in PCBs. The increased concentrations found in Nine-Mile whitefish may be related to much larger individuals being analyzed than in past years. Both species from these two sites had lower mean concentrations compared to initial results from 1993.

Factors that may have broadly influenced the findings for 1996 include the unusually high river flows that preceded sample collection and the existence of continuing sources of PCBs. Source sampling conducted by EILS in November-December 1995 detected PCBs in effluents from the Kaiser Trentwood aluminum mill and wastewater from the Spokane Industrial Park, which goes to the City of Spokane treatment plant above Nine-Mile Dam. The final phases of cleanup at these facilities are to occur during the next permit cycle.

Although the 1996 results suggest PCB levels have decreased in both the upper Spokane and Little Spokane River, more than two to three years of data are needed before strong conclusions can be made. Fish from these areas continue to have elevated concentrations compared to other parts of the state. PCB concentrations still exceed levels considered protective of wildlife and human health, the existence of significant human health concerns depending on the amount of fish in the diet.

Link to EIM data for User Study ID AJOH0008