Synthesis, spectroscopic characterization, and ecotoxicity evaluation of ciprofloxacin-metal (Fe, Co, Ni, Cu) complexes on freshwater algae

The co-occurrence of heavy metals and antibiotics in aquatic environments raises concerns regarding the complex interactions that alter their bioavailability and ecotoxicological effects on primary producers, such as algae. Four ciprofloxacin-metal complexes (CIP-Ms): CIP-Fe(III), CIP-Co(II), CIP-Ni(II), and CIP-Cu(II), were synthesized, and characterized using FT-IR, UV-visible spectroscopy, MALDI-TOF, and ICP-MS. The comparative toxicities of CIP, free metal ions, and CIP-Ms were evaluated with freshwater algae (Spirogyra columbiana) under controlled laboratory conditions. Algal growth inhibition and chlorophyll content were measured using UV-visible spectroscopy after 72 h of exposure. The CIP-Ms exhibited higher toxicity than CIP and free metal ions. Among them, CIP-Cu(II) exhibited the strongest inhibitory effect. The enhanced toxicity of CIP-Ms is attributed to increased lipophilicity, improved bioavailability, and oxidative stress induced by high levels of reactive oxygen species (ROS). These findings suggest that assessing individual contaminants may underestimate environmental risks, and emphasize the need to consider pollutant interactions for more realistic ecological risk assessment.