To categorize the marine environmental health status, the Oslo and Paris commissions have recently formulated Ecological Quality Objectives (EcoQOs) for many ecological features including the contamination of coastal bird eggs with mercury and organochlorines. In this study, we describe spatial and temporal patterns of egg contamination around the North Sea and compared them to the EcoQOs. Concentrations of mercury, polychlorinated biphenyl (SPCB) congeners, dichlorodiphenyltrichloroethane (SDDT) and derivatives, hexachlorobenzene (HCB) and hexachlorocyclohexane (SHCH) isomers were analysed in two tern species (Sterna hirundo and Sterna paradisaea) and Oystercatcher (Haematopus ostralegus) eggs collected between 2008 and 2010 in a total of 21 sites in seven countries surrounding the North Sea. Hg, SPCB and HCB were highest in the southern sites, while SDDT and SHCH concentrations were greatest in eggs from the western North Sea and the Elbe estuary. There were rarely any consistent decreases over time for any compounds. In the terns, Hg, HCB and SHCH increased at most sites, SPCB and SDDT in Sweden and Norway. In the Oystercatcher, HCB and SHCH increased at more than the half of the sites, SPCB, SDDT and Hg at several German sites. In the terns, Hg, SPCB and SDDT exceeded the EcoQO in all, HCB in most years and sites. At most sites, SHCH fulfilled the EcoQO in some study years. In the Oystercatcher, Hg, SPCB and SDDT exceeded the EcoQO in all or most years and sites. HCB and SHCH fulfilled the EcoQO in some or all years at most sites. The EcoQO was exceeded most frequently in estuaries. We conclude that EcoQOs are suitable for drawing contamination patterns of the coastal North Sea in an easily understandable manner, offering the opportunity to harmonize the EcoQOs with coordinated environmental monitoring programmes.
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