Geographic trend in mercury measured in common loon feathers and blood

The common loon (Gavia immer) is a high-trophic-level, long-lived, obligate piscivore at risk from elevated levels of Hg through biomagnification and bioaccumulation. From 1991 to 1996 feather (n = 455) andblood (n = 381) samples from adult loons were collected between Juneand September in five regions of North America: Alaska, northwesternUnited States, Upper Great Lakes, New England, and the Canadian Maritimes. Concentrations of Mg in adults ranged from 2.8 to 36.7 mu g/g (fresh weight) in feathers and from 0.12 to 7.80 mu g/g (wet weight) in whole blood. Blood Hg concentrations in 3 to 6-week-old juveniles ranged from 0.03 to 0.78 mu g/g (wet weight) (n = 183). To better interpret exposure data, relationships between blood and feather Hg concentrations were examined among age and sex classes. Blood and featherHg concentrations from the same individuals were significantly correlated and varied geographically (r2 ranged from 0.03 to 0.48). Blood and feather Hg correlated strongest in areas with the highest blood Hg levels, indicating a possible carryover of breeding season Hg that is depurated during winter remigial molt. Mean blood and feather Hg concentrations in males were significantly higher than concentrations in females for each region. The mean blood Hg concentration in adults was 10 times higher than that in juveniles, and feather Hg concentrations significantly increased over 1 to 4-year periods in recaptured individuals. Geographic stratification indicates a significant increasing regional trend in adult and juvenile blood Hg concentrations from west to east. This gradient resembles U.S. EnvironmentalProtection Agency-modeled predictions of total anthropogenic Hg deposition across the United States. This gradient is clearest across regions. Within-region blood Hg concentrations in adults and juveniles across nine sites of one region, the Upper Great Lakes, were less influenced by variations in geographic Hg deposition than by hydrology and lak [ABSTRACT FROM AUTHOR]