Temporal Trends of Great Lakes Legacy Contaminants: Ecological and Biological Considerations Applying the Age-Trend Model

The USEPA Great Lakes Fish Monitoring and Surveillance
Program
(GLFMSP) has been monitoring top predator lake trout and walleye contaminant
concentrations since the early 1970s. Our research revealed that select
legacy contaminant groups (∑PCBs, ∑DDTs, ∑chlordanes,
and ∑5PBDEs) have similar t1/2 and k2 values across the Great Lakes, with the exception
of both Lake Erie sites and the Lake SuperiorKeweenaw Point
site. The slower halving times determined at both Lake Erie sites
are consistent with legacy contaminant remobilization due to extreme
weather climate effects and past remedial actions on the Detroit River,
whereas the Lake SuperiorKeweenaw Point site demonstrates
contaminant halving times approaching the exponential minimum. Overall,
Great Lakes select contaminant groupings have decreased between 25.8
and 97.9% since 2004. An age-normalized Great Lakes Contaminant Index
(GLCI) was devised, indicating both Lake Michigan sites as the most
highly impacted. The mean absolute deviation statistic was applied,
documenting the need to age-correct contaminant trends due to highly
variable age profiles. With the noted exceptions, the uniformity of
age-corrected trend modeling suggests that a combination of the fundamental
biological and physicochemical mechanisms of natural contaminant sequestration,
declining dissolved water concentrations, accumulation/metabolism/depuration,
and the overall reduction of legacy contaminant loading are driving
the generally consistent rates of declines in the Great Lakes. Many
of the biological and ecological stressors currently associated with
climate change appear to be accounted for by the age-trend model.