Читать книгу Sustainable Solutions for Environmental Pollution, Volume 2 - Группа авторов - Страница 17

Photo-degradation is an oxidation of organic compounds induced by solar radiation, mainly by the energetic part of the solar spectrum, i.e., the ultraviolet (UV) radiation. Aquatic OM is photo-chemically unstable under ambient sunlight. In a wetland, according to its chemical structure, OM can be subjected to solar radiation, leading to its photolysis (fragmentation into lower molecular weight molecules, more easily assimilated by microorganisms), photo-bleaching (decrease in UV-visible absorbance due to loss of aromaticity), and photo-mineralization (complete degradation into mineral elements). Organic micropollutants are susceptible to be degraded by photolysis, with a large range of half times, from a few days to several months (Avetta et al., 2016). This degradation is only partial, therefore, the by-products are likely to be other organic molecules, of smaller size and not fully oxidized end-products such as H₂O, CO₂, and NO₃^-. In the case of sulfamethoxazole (SMX), a widely used antibiotic in human healthcare and its human metabolites (86% of the ingested SMX dose), most metabolites were found to be photostable under environmentally relevant conditions. The degradation yields, based on carbon balance, reached 90% for SMX after 4 hours, but only 50% for N-acetyl SMX, the main human metabolite (50% of the ingested SMX dose) (Bonvin et al., 2013). The effect of solar irradiation is both direct and indirect: indirect photolysis refers to the action of hydroxyl and carbonate radicals and excited triplet states of dissolved OM formed in the water phase by solar irradiation.