RESUMEN
Microplastics have become a global concern due to their persistent properties and impacts on the marine environment. This research investigates pollution sources and behaviors of microplastics at UNESCO Can Gio Mangrove Biosphere Reserve. Density flotation with sodium chloride is employed to extract microplastics from sand at Can Gio Beach, and a double-filtration procedure is developed to recover microplastics from seawater at the beach and Dong Tranh Cape. The microplastics' morphology and type are analyzed by micro-Raman spectroscopy. The results show that microplastics are accumulated at concentrations from 31.99 to 92.56 MPs g-1 at various sand layers. The seawater at Can Gio Beach and Dong Tranh Cape contains 6.44 and 3.75 MPs L-1 of microplastics, respectively. White polyethylene fragments predominate, and all the microplastics comprise small secondary microplastics with a minimum size of 25 µm and a maximum size of 260 µm for fragments and a length of 640 µm for fibers. The proportions of polyethylene, polypropylene, polystyrene, and polymethylmethacrylate are similar. The differing percentages of other compositions in sand and seawater are attributed to the morphology and density of the microplastics. The results indicate the extent of microplastic pollution and suggest appropriate strategies for tourism development at the Biosphere Reserve.
RESUMEN
Trimethylbenzene (TMB) isomers (1,2,3-TMB, 1,2,4-TMB, and 1,3,5-TMB) are often used as conservative tracers in anaerobic, contaminated aquifers for assessing BTEX (benzene, toluene, ethylbenzene, xylenes) biodegradation at field sites. However, uncertainties exist about the behavior of these compounds under anaerobic conditions. For this reason, the influence of various parameters (temperature, residence time) on the biodegradability of TMB isomers was investigated under denitrifying and sulfate-reducing conditions in microcosms and 1D-column experiments. Soil and groundwater contaminated with a cocktail of aromatic hydrocarbons including the TMB isomers, both collected from an industrial site in Berlin, Germany, were used for the laboratory investigations. A continuous and complete biodegradation of 1,3,5-TMB and 1,2,4-TMB under denitrifying conditions was observed independent of realized temperature (10â»20 °C) and residence time. Biodegradation of 1,2,3-TMB started after longer lag-phases and was not continuous over the whole experimental period; a strong dependence on temperature and residence time was identified. The biodegradability of all TMB isomers under sulfate-reducing conditions was continuous and complete at higher temperatures (20 °C), whereas no degradation was observed for lower temperatures (10 °C). First-order biodegradation rate constants ranged from 0.05 to 0.21 d-1 for 1,3,5-TMB and 1,2,4-TMB and from 0.01 to 0.11 d-1 for 1,2,3-TMB.