title: Use of sunlight to degrade oxytetracycline in marine aquaculture's waters.
abstract: Oxytracycline (OTC) is a broad spectrum antibiotic authorized for use in European aquaculture. Its photo-degradation has been widely studied in synthetic aqueous solutions, sometimes resorting to expensive methods and without proven effectiveness in natural waters. Thus, this work studied the possibility to apply the solar photo-degradation for removal of OTC from marine aquaculture's waters. For that, water samples were collected at different locals of the water treatment circuit, from two different aquaculture companies. Water samples were firstly characterized regarding to pH, salinity, total suspended solids (TSS), organic carbon and UV-Vis spectroscopic characteristics. Then, the samples were spiked with OTC and irradiated using simulated sunlight in order to evaluate the matrix effects on OTC photo-degradation. From kinetic results, the apparent quantum yields and the outdoor half-life times, at 40°N for midsummer and midwinter days were estimated by the first time for these conditions. For a midsummer day, at sea level, the outdoor half-life time predicted for OTC in these aquaculture's waters ranged between 21 and 25 min. Additionally, the pH and salinity effects on the OTC photo-degradation were evaluated and it has been shown that high pH values and the presence of sea salt increase the OTC photo-degradation rate in aquaculture's waters, compared to results in deionised water. The results are very promising to apply this low-cost methodology using the natural sunlight in aquaculture's waters to remove OTC.
authors.affiliation: Department of Chemistry and CESAM, Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: joanaleal@ua.pt.
authors.forename: J F
authors.initials: JF
authors.lastname: Leal
authors.affiliation: Department of Chemistry and CESAM, Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: valdemar@ua.pt.
authors.forename: V I
authors.initials: VI
authors.lastname: Esteves
authors.affiliation: Department of Chemistry and CESAM, Centre for Environmental and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: edsantos@ua.pt.
authors.forename: E B H
authors.initials: EBH
authors.lastname: Santos
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D017756:Aquaculture; D005060:Europe; D006207:Half-Life; D010118:Oxytetracycline / Q000737:chemistry*; D010782:Photolysis; D054712:Salinity; D013472:Sunlight; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D000900:Anti-Bacterial Agents; D014874:Water Pollutants, Chemical; D014867:Water; D010118:Oxytetracycline
keywords: Antibiotics; Aquatic systems; Photo-degradation; Quantum yield; Sunlight