Use of Periphyton As a Monitoring Tool to Evaluate PCB Uptake in a Large River System

The accumulation of polychlorinated biphenyls (PCBs) in freshwater food webs often results in concentrations in the top predator that are harmful to human health. The mountain whitefish of the Wenatchee River in eastern Washington have sufficient total PCB concentrations to trigger a health advisory. During a source assessment study for PCB contamination in the Wenatchee River we compared the PCB burdens in dissolved phase in the river water with those bound in periphyton. PCB congeners (209) were analyzed in each matrix. Estimated total PCB concentrations in the water (pg L^-1) and PCB burdens in the periphyton (pg g^-1 OC) were significantly correlated (r = 0.96; p<0.001). Furthermore, the congener profiles for both matrices were very similar at the sites with the highest concentrations suggesting direct absorption of PCBs and little adsorption which could discriminate against the heavier compounds. The spatial trend of stable nitrogen isotopes (δ¹⁵N) in periphyton shows a strong influence from anthropogenic nitrogen in the lower reach of the river. The range in δ¹⁵N of -0.88 to 6.19 ‰ in periphyton should be considered in any use of stable nitrogen isotopes to describe trophic position in the context of bioaccumulation.