Mercury exposure and neurochemical impacts in bald eagles across several Great Lakes states

In this study, we assessed mercury (Hg) exposure in several tissues (brain, liver, and breast and primary feathers) in bald eagles (Haliaeetus leucocephalus) collected from across five Great Lakes states (Iowa, Michigan, Minnesota, Ohio, and Wisconsin) between 2002–2010, and assessed relationships between brain Hg and neurochemical receptors (NMDA and GABAA) and enzymes (glutamine synthetase (GS) and glutamic acid decarboxylase (GAD)). Brain total Hg (THg) levels (dry weight basis) averaged 2.80 μg/g (range: 0.2–34.01), and levels were highest in Michigan birds. THg levels in liver (r p = 0.805) and breast feathers (r p = 0.611) significantly correlated with those in brain. Brain Hg was not associated with binding to the GABAA receptor. Brain THg and inorganic Hg (IHg) were significantly positively correlated with GS activity (THg r p = 0.190; IHg r p = 0.188) and negatively correlated with NMDA receptor levels (THg r p = −0245; IHg r p = −0.282), and IHg was negatively correlated with GAD activity (r s = −0.196). We also report upon Hg demethylation and relationships between Hg and Se in brain and liver. These results suggest that bald eagles in the Great Lakes region are exposed to Hg at levels capable of causing subclinical neurological damage, and that when tissue burdens are related to proposed avian thresholds approximately 14–27% of eagles studied here may be at risk.