Occurrence of Imipenem in natural water: Effect of dissolved organic matter and metals

The occurrence of trace antibiotic residues in the environment poses a threat by promoting antibiotic resistance and spreading resistant genes. Recent studies show that these residues interact with metals, forming toxic and persistent antibiotic-metal complexes (AMCs). Investigating the photodegradation of these contaminants in environmental waters is essential to understand their fate and ecotoxicological risk assessment in environmental waters. In this sense, the present work delineates the fate of IMP, a carbapenem antibiotic, in the environmental matrix and studies its interactions with humic acid and metals. The study established that the drug was labile and underwent degradation under light and ambient temperatures. Further, analytical studies with dissolved organic matter (DOM), such as humic acids, established an accelerating effect on antibiotic degradation via indirect photochemical pathways. For instance, for a concentration of 100 mg/L IMP mixed with 20 mg/L HA in volumetric ratios of IMP: HA 1:2, 1:1, and 2:1, the final concentrations of IMP after 24 h were 26.11 mg/L (-73.89 %), 34.44 mg/L (-65.56 %), and 44.22 mg/L (55.78 %), respectively. The higher the humic acid, the faster the degradation of IMP, thereby supporting the photochemical generation of reactive oxygen species (OH•) and subsequent oxidative degeneration of the drug. The interactions with metals, specifically copper, accelerated the degradation kinetics of the drug. The promotion effect was owed to the action of the OH• as the oxidizing agent. Based on the degradation products identified by LC-MS/MS, a scheme of the synergistic action of copper-redox coupling and imipenem, resulting in the oxidative degradation of the drug, was proposed. Understanding the photochemical behavior of antibiotics, and their behavior in the presence of DOM and metal is vital for unravelling their fate and complexity in wastewater.