Exposure to and Biomarker Responses From Legacy and Emerging Contaminants Along Three Drainages in the Milwaukee Estuary, Wisconsin, USA.

This article focuses on assessing legacy contaminants and contaminants of emerging concern (CECs) in tree swallow (Tachycineta bicolor) tissues and diet from three drainages within the Milwaukee estuary, Wisconsin, USA, compared to two remote reference lakes. Elevated concentrations of bioaccumulative contaminants—polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and per- and polyfluoroalkyl substances (PFAS)—were found in the estuary sites relative to reference lakes, with PCBs notably higher near a Superfund site at Cedarburg. Nonpersistent pesticides were generally low, except for desethylatrazine, a metabolite of atrazine, which was consistently detected and showed correlations with thyroid hormones and oxidative stress biomarkers. Polycyclic aromatic hydrocarbons (PAHs) in diet and sediment indicated primarily pyrogenic sources, and biomarker responses in swallows showed limited associations with contaminant levels, suggesting exposures were below thresholds for sublethal effects. The study highlights the complexity of contaminant exposure in urban-industrial landscapes and the importance of careful sampling strategies for detecting low-level contaminants.