Organochlorine contaminant residues and shell thickness of eggs from known-age female ospreys (Pandion haliaetus) in Michigan during the 1980s

Eggs have been widely used as indicators of exposure to lipophilic contamin ants in wild birds, but very few studies have examined the relationship bet ween female age and egg contaminant concentrations. Organochlorine contamin ant (OC) levels and eggshell thickness were determined for 25 addled eggs l aid by female ospreys (Pandion haliaetus), 3-15 years old, in Michigan duri ng the 1980s. A wide range of OCs was detected, but there was no significan t variation in wet weight concentrations of any compound with female age or year. Similarly, eggshell thickness did not vary significantly with female age or year. Among PCB congeners, neither the degree nor the positioning o f chlorine substitution on the biphenyl ring, nor the degree of hydrophobic ity, had any significant influence on contaminant bioaccumulation as birds aged. Eggs from females sampled in more than one year indicated considerabl e annual variation in OC levels, presumably reflecting differences in recen t exposure and/or the extent to which endogenous lipid reserves were used t o form the egg. In general, OC concentrations in these female ospreys durin g the 1980s appeared to have reached a life-time equilibrium level by the a ge of first breeding (3-4 years usually). Therefore, eggs from any female o sprey can provide a consistent indication of OC uptake, independent of the bird's age. (C) 1999 Elsevier Science Ltd. All rights reserved.