Innovative approach for environmental pollution assessment using seabird eggs: mercury in black-tailed gull (Larus crassirostris) eggs from the Korean islands (2012-2021)

Since black-tailed gulls derive energy for egg production around their habitat, analyzing concentration of chemicals in the eggs reveals the local environmental pollution. This is, however, complex due to the diversity of seabird diets across multiple ecosystems. This study determined the influence of food source and trophic position (TP) on the mercury concentration ([Hg]) in eggs and subsequently mitigated these influences by adjusting through [Hg]-TP relationship, thereby enabling spatial and temporal comparisons among individuals. Following TP adjustment, the [Hg] that previously exhibited significant regional differences no longer displayed such a variation. Moreover, by normalizing to trophic level 4, as suggested by the European Union (EU), the total [Hg] was standardized from 1001 ± 415 ng g^-1 to 1347 ± 516 ng g^-1 in all the egg samples, far exceeding the EU criteria. These two approaches provide valuable insights for the effective monitoring of marine pollution and past environmental reconstruction by adjusting/normalizing [Hg] in seabird eggs.