Raquel Fernandes Pupo Nogueira

This review presents data regarding the occurrence of antibiotics in several aqueous matrices in Brazil reported in the last twelve years (from 2010 to 2022). Despite limited research on the topic, Brazil has the highest number of published data on antibiotics in surface water (SW) among Latin American countries. However, these studies primarily focused on the southern and southeastern regions, providing an incomplete picture of antibiotic occurrence in the aquatic environment of the country. Data from 24 papers show the detection of 23 antibiotics in 5 aquatic matrices, including drinking water, ranging from 0.13 ng L-1 to 37.30 μg L−1. Occurrence in SW was the most reported, and sulfamethoxazole was the antibiotic most prevalent and concentrated in this matrix (7112.4 ng L-1). Besides the fact that antibiotics are only partially removed in sewage treatment plants, in Brazil, only 55.8% of the sewage generated is collected, and 80.8% of the collected sewage is treated, which aggravates the release of antibiotics to the aquatic environment. This poses a significant concern due to potential harm to non-target organisms and antibioticresistant bacteria proliferation, worsening global antimicrobial resistance. Given this scenario, regular monitoring to assess the presence of antibiotics and resistant bacteria is crucial, enabling timely interventions and appropriate mitigation measures.

This study aimed to investigate the occurrence of photolysis of two relevant antibiotics, sulfamethoxazole and trimethoprim, when present in a Waste Stabilization Pond and its disinfection under tropical irradiance. The influence of pH and matrix components, and the generation of photoproducts during solar exposure were evaluated. The pH-dependent speciation of antibiotics had a greater influence on the photolysis of antibiotics than the water matrix, with higher photodegradation at pH 4.1 than at pH 7.2. Trimethoprim was more susceptible to indirect photolysis, indicated by the steeper influence of the photosensitizers nitrate and humic acid compared to sulfamethoxazole. The photoproducts generated were persistent to photolysis and remained present in the samples up to 70 h irradiation. Wastewater disinfection was achieved after 70 h of solar exposure. Nonetheless, the exposure time required to remove at least 50% of sulfamethoxazole was on average 29 h and of trimethoprim 83 h, at the natural pH of the matrix (pH 7.2). Given that the residence time in Waste Stabilization Pond is 41 h, which corresponds to a maximum of 26 h solar irradiation, the exposure time in Waste Stabilization Pond is not sufficient to completely photodegrade antibiotics or disinfect the effluent, demanding further treatment.

Two compositions of graphene oxide-magnetite nanocomposites were studied as catalysts in the heterogeneous Fenton process. Transmission electron microscopy and X-ray diffraction revealed that the graphene oxide sheets were covered with nanoparticles of magnetite, with an average crystallite size of 7 nm. Infrared spectroscopy analysis indicated that the phases interacted through covalent Fe-O-C bonds. The composites presented significantly improved catalytic activity, compared to pure magnetite, with a synergistic effect of up to a factor of 17.1 for the Fenton degradation of caffeine, achieving total removal after 90 min. This synergistic effect was a consequence of the interaction between the phases, resulting in improved mass transfer of caffeine to the catalyst surface, adsorption and efficient degradation, with enhanced HO^• generation. The surface reaction constant increased by up to three orders of magnitude, demonstrating the important role of graphene oxide in the degradation kinetics of the heterogeneous Fenton process. The surface-bonded hydroxyl radicals were responsible for caffeine degradation, achieving 9.4 μmol L^-1. After five degradation cycles, a loss of Fe-O-C bonds and increase in oxygenated groups were associated with a small decrease of caffeine removal efficiency, from 98 to 82%, without significant iron leaching, in the dark, and with low consumption of hydrogen peroxide.