Introduction Pharmaceutical compounds used in intensive animal husbandry represent an important type of emerging micropollutants (EMs) as their environmental occurrence has increased in the last decades. Aerobic degradation tests simulating environmental conditions were performed on a model EM, oxytetracycline (OTC), a broad-spectrum antibiotic used in livestock, in order to assess its environmental fate and toxicity evolution. Materials and methods Degradation of OTC in water/sediment systems was studied in biotic and abiotic conditions at pH 5.5 and 7.5 following OECD guidelines. Experiments were carried out in aerated glass bottles equipped with redox, pH, dissolved O2 and temperature sensors, under agitation. Aqueous samples were withdrawn and analyzed at different times using HPLC-MSn. Sediment was prepared in laboratory using sand, kaolinite clay and peat, and OTC and metabolites were desorbed and analyzed at the end of the experiments. Ecotoxicity monitoring experiments of the aqueous samples were designed using microalgae Pseudokirchneriella - which were proven to be sensitive to OTC with IC50 at 1 ppm - at different sample dilutions. Results OTC degradation was strongly dependent on the studied environmental conditions, reaching 1% of the initial concentration sooner in biotic and lower pH conditions. Prevalence of OTC in sediment showed a similar trend, mostly accumulating in abiotic and higher pH conditions, proving that presence of microorganisms plays an important role in OTC degradation. A total amount of 20 transformation products and intermediates were characterized, allowing the proposal of multiple degradation pathways. Although most of the products are present in all studied conditions, they differ in concentration and time of appearance, which may influence the system’s overall toxicity. Furthermore, roughly half of them appear to be more persistent than OTC, as they can still be found in water and sediment after two months of initiating the experiment, which is important to consider when developing new monitoring and remediation strategies.

Simulated environmental degradation tests of emerging micropollutants under biotic and abiotic conditions

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