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 contaminants in wild birds, but very few studies have examined the relationship between female age and egg contaminant concentrations. Organochlorine contaminant (OC) levels and eggshell thickness were determined for 25 addled eggs laid by female ospreys (Pandion haliaetus), 3–15 years old, in Michigan during the 1980s. A wide range of OCs was detected, but there was no significant 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 of chlorine substitution on the biphenyl ring, nor the degree of hydrophobicity, had any significant influence on contaminant bioaccumulation as birds aged. Eggs from females sampled in more than one year indicated considerable annual variation in OC levels, presumably reflecting differences in recent exposure and/or the extent to which endogenous lipid reserves were used to form the egg. In general, OC concentrations in these female ospreys during the 1980s appeared to have reached a life-time equilibrium level by the age of first breeding (3–4 years usually). Therefore, eggs from any female osprey can provide a consistent indication of OC uptake, independent of the birdʹs age.