An investigative biomonitoring study was carried out in a eutrophic coastal system with a moderate contamination by metals (Obidos lagoon, Portugal), combining the evaluation of exposure concentrations with metals accumulation and oxidative stress responses in gills of the golden grey mullet (Liza aurata). Two contrasting seasons (winter and summer) were considered at three sites: Barrosa (BB) and Bom-Sucesso (BS) branches; Middle lagoon (ML). Data on the water column pointed to a higher metals and nutrients availability at BB that was reflected in the higher metal concentrations in gills, particularly in winter. Similarly, oxidative stress responses demonstrated a pro-oxidant challenge at BB (winter and summer), which was corroborated by an integrated biomarker response index (IBR). Metal concentrations in gills were higher in summer than winter, reflecting the increased environmental concentrations in combination with elevated metabolic rates. Catalase (CAT), glutathione-S-transferase (GST), total glutathione (GSH(t)) and lipid peroxidation (LPO) increases observed in winter at BB were related with metal accumulation, while summer enhancement of glutathione peroxidase (GPx), glutathione reductase (GR), GST and GSH(t) was associated with other stressors. Inter-site differences on the basis of IBR were more accentuated in winter. Gills can be considered as an important route of entry for contaminants and were demonstrated to reflect water contamination and are therefore useful in the context of environmental assessment.
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