Thirty-Year Time Series of PCB Concentrations in a Small Invertivorous Fish (Notropis Hudsonius): An Examination of Post-1990 Trajectory Shifts in the Lower Great Lakes

Abstract

The production and use of polychlorinated biphenyls (PCBs) have been restricted in North America since the 1970s; yet, PCBs are still detected in all components of the Great Lakes ecosystems. Our objective was to determine how total PCB (PCBT) concentrations in spottail shiner (Notropishudsonius) changed over the period 1975–2007 in the lower Great Lakes. Trends were best described by three basic models: (1) piecewise models where concentrations followed a decreasing trend before the break point (T) and an increasing trend post-T (Lake St. Clair, eastern Lake Erie, and upper Niagara River); (2) piecewise models where concentrations decreased both pre- and post-T but where the rate of decline post-T was less than that pre-T (western Lake Erie and Niagara River’s Tonawanda Channel); and (3) linear models where concentrations declined at a constant rate across the entire temporal range (lower Niagara River and western Lake Ontario). Piecewise models best described the trends in shallow areas that are susceptible to full water-column mixing whereas constant-slope models best described trends in deeper areas. For piecewise models, T typically occurred during the years 1988–1992. Two events coincided with this timing: (1) a sustained shift towards warming summer temperatures and (2) the proliferation of dreissenid mussels (Dreissena spp.). The weight-of-evidence suggests that the dreissenid invasions were a more likely driving factor behind the observed trends.