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Higher levels of persistent pollutants (Σ 16PCB, Σ 6PBDE, Σ HCH, Σ DDT, Σ CHL) were detected in fresh eggs of Common Terns Sterna hirundo from Rockabill Island near Dublin (Ireland's industrialised capital city) compared to Common and Arctic Terns S. paradisaea from Ireland's west coast. Intra-clutch variation of pollutant levels in Common Terns was shown to be low, providing further evidence that random sampling of one egg may be an appropriate sampling strategy. Significant differences in pollutant concentrations were detected between fresh and abandoned eggs on Rockabill. However, abandoned eggs can still provide a useful approximation of pollutants in bird eggs if non-destructive sampling is preferred. Levels of p,p' –DDE in tern eggs have decreased over time according to this study, in concurrence with worldwide trends. Results in this study fall below toxicological thresholds for birds and OSPARs EcoQO thresholds set for Common Tern eggs, except for mercury and HCH in the west coast. • Higher levels of pollutants in eggs from Dublin colony (near capital city) • Intra-clutch variation of pollutant levels low in Common Terns • Abandoned eggs may be used as non-destructive alternative to fresh eggs • Levels of pollutants below toxic thresholds and lower than OSPAR EcoQO, except mercury and HCH in the west coast • Levels of pollutants in terns are within internationally reported values [ABSTRACT FROM AUTHOR]

Seabird eggs are considered a favourable matrix for monitoring marine pollutants and are widely used as higher trophic level indicators. Persistent organic pollutants such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and other organochlorine compounds (OCs) as well as metals have been shown to have deleterious impacts on seabirds. The Northern Gannet Morus bassanus is an avian sentinel; the largest breeding seabird in Ireland and an obligate piscivore. Gannet eggs were collected from two island colonies off the east coast of Ireland in locations with divergent history of industrialisation. Contaminant levels were measured and differences in concentrations between colonies compared. Stable isotope ratios of carbon (δ 13 C) and nitrogen (δ 15 N) were measured in each egg to understand the influence of diet and trophic position on contaminant levels detected. Significantly higher levels of Σ 14PCBs, Σ 7PBDEs and total mercury were detected in Gannet eggs from Lambay Island near Dublin (Ireland's industrialised capital city) compared to Great Saltee Island. No differences were observed in levels of other OCs (HCB, Σ HCH, Σ CHL, Σ DDT) between the two colonies. Though Gannets travel significant distances when foraging for food, tracking studies have demonstrated that birds from proximal breeding colonies maintain exclusive feeding areas. Stable isotope ratio analysis in this study demonstrated that Gannets at both locations occupy similar dietary niches, indicating that dietary differences may not be the driver of differing contaminant levels between colonies. Levels of persistent pollutants in the Gannet eggs fall below most existing thresholds for adverse effects and are within internationally reported values. Recent population growth and range expansion of Gannets in Ireland suggest that persistent pollutants are not having an immediate impact on the Gannet population. This study will inform potential monitoring programmes that can help Ireland achieve good environmental status under the European Union's Marine Strategy Framework Directive. Image 1 • Higher levels of pollutants in eggs from Dublin colony (near capital city). • Gannets from both sites have a similar dietary niche. • Levels of pollutants below thresholds for adverse effects with exception of mercury. • Levels of pollutants in the Gannet are within internationally reported values. • Pollutants are not having an immediate impact on Gannet population in Ireland. Differences in contaminant burden between two colonies is most likely a result of Gannets from different sites having mutually exclusive feeding areas. Levels fall below most existing thresholds for adverse effects in other species, with the exception of mercury. [ABSTRACT FROM AUTHOR]