Influence of persistent organic pollutants on the endocrine stress response in free-living and captive red kites (Milvus milvus)

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Persistent organic pollutants (POPs) have the potential to impair the endocrine regulation of organisms and alter their ability to respond to environmental changes. We studied whether polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) affected the endocrine regulation of free-living and captive red kites (Milvus milvus) through studying the dynamics of corticosterone (CORT) and dehydroepiandrosterone (DHEA). We sampled migratory free-living kites coming from northern Europe and captive kites born in a rehabilitation center in Spain. We used body feathers from the interscapular region as a minimally-invasive and integrative matrix. The most abundant compound detected in free-living kites was 4,4′-dichlorodiphenyldichloroethylene (4,4′-DDE; 6.10 ± 1.56 ng g−1 dw feather) followed by CB-153 (3.10 ± 0.63 ng g−1 dw feather) and CB-180 (2.43 ± 1.08 ng g−1 dw feather). In captive kites, the most abundant compounds were 4,4′-dichlorodyphenyltrichloroethane (4,4′-DDT; 2.38 ± 1.30 ng g−1 dw feather), CB-153 (2.15 ± 0.47 ng g−1 dw feather) and hexachlorobenzene (HCB; 2.03 ± 0.45 ng g−1 dw feather) at similar concentrations. Free-living kites showed higher levels of 4,4′-DDE and CB-180 in comparison to captive kites. Age influenced HCB and CB-101 levels, whereas body mass was inversely related to CB-180 and 4,4′-DDT. Interestingly, captive kites showed a ratio DDT/DDE higher than 1 suggesting a relatively recent exposure of DDT, in contrast to free-living kites. Regarding hormonal levels, free-living kites showed higher levels of CORT (3.30 ± 0.22 pg mm−1 feather) than captive (2.40 ± 0.16 pg mm−1 feather), reflecting higher allostatic load. In addition, a positive association between PCBs and DDTs and adrenal hormones was found in free-living kites, suggesting an increase of CORT as a response of the endocrine system to cope with stressors and a subsequent elevation of DHEA to ameliorate the potential negative effects that high CORT levels could cause to the organism.