Can amoxicillin be detected in the aquatic environment? A critical assessment

Amoxicillin is a broad-spectrum β-lactam antibiotic widely used in both human and veterinary medicine. Following administration, approximately 60-80% of the dose is excreted, largely unmetabolized, via urine within a few hours. Consequently, environmental contamination with amoxicillin, especially in aquatic systems, is a significant concern. Due to its potential ecological risks and the current scarcity of data required for a full assessment, it was included in two consecutive European Union Watch Lists (2018, 2020) of substances for comprehensive monitoring to inform water policy. However, data on amoxicillin levels in aquatic environments are contradictory, ranging from high concentrations in some studies to non-detection in others. The presence of intact amoxicillin in aquatic environments is inherently transient, and the risk of substantial analytical errors in its detection, identification, and quantification is considerable unless stringent methodological precautions are applied. Driven by the need for reliable environmental data, inconsistencies in the existing literature and our own extensive analytical experience, we comprehensively investigated amoxicillin degradation in surface water, influent and effluent wastewater under various conditions. Experiments were conducted under both dark and sunlight conditions using water samples spiked with amoxicillin at 5 μg/L and 50 μg/L. The parent compound was quantified by liquid chromatography-tandem mass spectrometry, whereas transformation products were identified by high-resolution mass spectrometry. By critically assessing the factors that influence the analysis and environmental occurrence of amoxicillin, this study resolves discrepancies in prior reports and clarifies the realistic prospects for its detection. We demonstrate that the parent antibiotic should be rarely found in water samples due to its rapid degradation. Therefore, future monitoring efforts should be focused on its primary degradation product, amoxicillin penicilloic acid, as more reliable indicator of contamination in aquatic environments.