A comprehensive assessment of contaminant exposure in an endangered tern population

Understanding contaminant levels in endangered species is critical for assessing whether and how environmental pollution is contributing to population declines. Here, we provide the first comprehensive assessment of contaminant presence in the last, and endangered, population of gull-billed terns ( Gelochelidon nilotica ) in Central Europe. Specifically, we analysed 118 compounds belonging to eight contaminant groups in the shells and contents of 26 unhatched eggs, as well as in eight livers and seven brains from chicks that died. We detected 57 out of the 118 compounds, with detection rates being highest in the egg content (84 %) and lowest in the chick brain and liver (53 %). Eggshells, however, exhibited the highest contaminant diversity, which we suggest to indicate direct environmental exposure in the nest supplementing the effects of maternal transfer important for all four tissues. In terms of importance of contaminant groups, persistent organic pollutants (POPs) were prevalent in brain, liver, and the egg content, while plasticizers and caffeine were abundant in both the eggshell and egg content. The detection of a large range of contaminants, including newly emerging ones, raises the question of their effects, and further research therefore is needed to assess the ecological impacts of these contaminants on gull-billed terns, and other wildlife. • We assessed levels of 118 contaminants in an endangered gull-billed tern population. • We detected 57 compounds, the highest diversity of which were found in eggshells. • Persistent organic pollutants were prevalent in chick brains/livers, and egg contents. • Plasticizers and caffeine were most abundant in egg shells and content.