Long-term ecotoxicological assessment of a reintroduced osprey population: an integrated approach in coastal environments of Central Italy

Apex predators are particularly vulnerable to environmental stressors due to their high trophic position. Understanding both exposure and physiological impacts is essential to support the long-term success of conservation efforts. We investigated contaminant levels and health indicators in a recently reintroduced osprey Pandion haliaetus population in Central Italy, a top predator in aquatic food-webs. From 2015 to 2022, we applied a standardized, multidisciplinary monitoring framework to 55 wild-born osprey chicks, integrating non-destructive blood and feather sampling with trace element and POPs analyses, genotoxicity biomarkers, biological and behavioral metrics (e.g., sex, morphometrics, GPS-tracked adults' space use). Among trace elements, Se showed the highest blood concentrations (4.5 ± 2.1 mg/kg dw), while Cu predominated in feathers (11.5 ± 2.7 mg/kg dw); both Cd and Pb were consistently low. Hg and Se showed significant differences among breeding sites. Significant positive correlations were observed in blood for HgSe, HgPb, PbSe, and in feathers for CdCu. A low frequency of micronuclei (0.4 ± 1.1 ‰) was observed, with lobed nuclei accounting for 81 % of observed abnormalities (mean: 26.5 ± 24.1 ‰). Hematological profiles were dominated by heterophils, followed by lymphocytes, eosinophils, monocytes, and basophils, with a mean heterophil-to-lymphocyte ratio of 1.3 ± 0.6 and thrombocyte counts averaging 246.1 ± 132.9 ‰. The most abundant POPs were PCB153 > PCB138 > PCB180 > PCB149 + 118 > PCB187, which together accounted for almost 40 % of total PCBs on average, confirming multi-year exposure in nestlings. Among DDTs, pp'DDE alone constituted between 15 % to 63 % of the total DDTs. We highlight the importance of integrative biomonitoring for assessing environmental quality and health in this critically endangered population, offering new insights into contaminant dynamics in reintroduced top predators and emphasizing the need for long-term, ecotoxicologically informed conservation strategies.