The manufacture and use of polychlorinated biphenyls (PCBs) was banned in the United States in 1977 after it was determined that these compounds adversely affect animals and humans. The Wisconsin Department of Natural Resources has quantified total PCB concentrations in Lake Michigan chinook (n. =. 765) and coho (n. =. 393) salmon (. Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) filets since 1975. We analyzed these data to estimate trends in PCB concentrations in these fish (1975-2010). We used generalized linear models with a gamma error distribution and log link fit to the untransformed concentrations. Trend patterns were examined using graphical smoothing and generalized additive models. We identified a candidate set of models that included time trend and other predictor variables. Using the Akaike Information Criterion to select among models we found the best models for both species included piecewise linear time trends, total body length, % lipid, and collection season as predictor variables. The intersection of the two trends was 1985 for chinook salmon and 1984 for coho salmon. PCB concentrations in both species increased with body length and % lipid, and were higher for individuals caught in the fall. Our data reveals a dramatic decline in PCB concentrations of -. 16.7% and -. 23.9% per year for chinook and coho, respectively, up until the intersection year likely reflecting implementation of restrictions on Aroclor-based PCBs. After the intersection year to 2010, PCB concentrations declined at an annual rate of -. 4.0% (95% CI: -. 4.4% to -. 3.6%) and -. 2.6% (95% CI: -. 3.3% to -. 1.9%) for chinook and coho, respectively.
Rasmussen, P. W., Schrank, C., & Williams, M. C. W. (2014). Trends of PCB concentrations in Lake Michigan coho and chinook salmon, 1975-2010. Journal of Great Lakes Research, 40(3), 748–754. https://doi.org/10.1016/j.jglr.2014.05.011