Levels of polychlorinated biphenlyls, organochlorine pesticides, mercury and lead in relation to shell thickness in marsh harrier (Circus aeruginosus) eggs from Charente-Maritime, France

The resident breeding population of marsh harriers at l'ile d'Oleron, Chare nte-Maritime, France, has declined by more than 60% over the last decade. B reeding success in this population is lower than reported for other populat ions of marsh barriers. This paper presents the results of an analysis of c ontaminants and shell thickness from 13 unhatched eggs from the wild popula tion, and 1 egg from a captive bird. DDE (a principal metabolite of dichlor o-diphenyl-trichloro-ethane-DDT) and mercury (Hg) concentrations were below concentrations considered to influence breeding success, and egg lead conc entrations were very low. There was a high degree of inter-correlation betw een contaminants, and egg concentrations of mercury and several polychlorin ated biphenyl (PCB) congeners (but not DDE) were significantly negatively c orrelated with shell thickness. Total PCB concentrations in 3 of 13 eggs (2 3%), i.e. one or more eggs from 2 of 11 different clutches (18%), were with in the range (8-25 ppm wet weight) thought to influence breeding success in a range of bird species. We consider that further and more detailed invest igation of the extent to which this population is exposed to PCBs is requir ed. (C) 1999 Elsevier Science Ltd. All rights reserved.