Kinetics, dose-response, and excretion of methylmercury in free-living adult Cory's shearwaters

We evaluated methylmercury (MHg) kinetics, dose-responses, and excretion in free-living adult Cory's shearwaters using a nondestructive multi-tissue a pproach. Elimination of MHg in blood comprised an initial fast phase, with half-time of 1 d, and a slow terminal phase with half-time between 44 and 6 5 d. Molt was a crucial factor in determining the rate of MHg elimination. Half-times were independent of dose. A relationship between steady-state bl ood concentrations and dietary intake of MHS was derived. Ratios between Hg concentrations in eggs or hatchlings' plumage and parental blood were inde pendent of dose, with tissue-blood partition coefficients identical to thos e in controls. Dose-response relationships were linear. Females were subjec ted to Hg concentrations 18% higher than males but exhibited a 10% lower do se-response in blood. The difference is not fully accounted for by excretio n into the egg and may be due to unidentified sex-related differences in ph ysiology. Excretion rates into plumage showed no dose dependency but were h igher (33% of intake) in birds exposed during molt than in birds dosed 2 mo nths before the start of molt. Hg excretion through the skin in exfoliated epidermal cells that adsorb into plumage was estimated, to represent 8% of the intake. The results of this study may be used in advanced modeling of t he kinetics of MHg in adult birds to fill the current gap of a bioenergetic model for avian exposure to MHg.