Aquatic ecotoxicology in a climate change scenario to support ecopharmacovigilance of veterinary antibiotics

Aquatic ecosystems are increasingly impacted by the dual pressures of climate change and pharmaceutical pollution, particularly from veterinary antibiotics discharged through aquaculture and livestock effluents. Among these, fluoroquinolones (FQs) are of special concern due to their environmental persistence, biological activity, and potential to harm non-target species. While antimicrobial resistance has dominated the environmental discourse, antibiotics can also act as direct contaminants, disrupting cellular homeostasis, reproduction, and stress responses in marine organisms. This doctoral thesis investigates these overlooked ecotoxicological effects, contributing new evidence to support eco-pharmacovigilance under climate-relevant scenarios. A multi-scale experimental approach was adopted using marine bivalves. In vitro assays on Mytilus galloprovincialis explored the effects of six FQs on subcellular fractions from gills and digestive gland, and examined spermatozoa responses to enrofloxacin (ENR) and ciprofloxacin (CIP). These tests revealed that both essential tissues and reproductive cells are vulnerable to FQ-induced oxidative and genotoxic stress, providing early indicators of toxicity. In vivo exposures of M. galloprovincialis to environmentally relevant ENR concentrations showed systemic and tissue-specific alterations, including oxidative imbalance and gene expression changes related to detoxification, energy metabolism, and cellular defense. To evaluate environmental modulation of toxicity, complementary experiments on Ruditapes philippinarum tested the combined effects of ENR with temperature and salinity shifts. These studies revealed that climate-related stressors can amplify or mitigate antibiotic toxicity, emphasizing the importance of multifactorial assessments in ecotoxicology. Overall, this research demonstrates that FQs induce measurable biological disruptions across molecular, cellular, and organismal levels in marine bivalves, and that environmental factors strongly influence these responses. By integrating in vitro and in vivo data across species and stressors, this thesis advances our understanding of pharmaceutical pollution in marine systems and highlights the need for climate-aware eco-pharmacovigilance to protect biodiversity and ecosystem functioning in coastal environments.