Spatial and seasonal distribution of microplastic in surface water of Bueng Boraphet Wetland—a Ramsar wetland in Thailand

This study sought to assess microplastic contamination in the surface water of the inland freshwater wetland, Bueng Boraphet Wetland, Thailand, which is a lentic system with various land-use patterns, including community areas, agricultural areas, and natural resource conservation areas. In 2019, water samples were collected during the wet and dry periods from the three land-use zones at depths of 0-30 cm using a plankton net with 333 µm in mesh size. The water samples were digested via a wet peroxide oxidation process prior to the identification of microplastic morphology using a stereomicroscope. The polymer types of microplastic were analyzed using Fourier transform infrared spectrophotometry. Microplastic was found to range from 0.00 to 4.61 particles/m (0.34 ± 0.81 particles/m) or 0.0 to 19.57 particles/m (1.44 ± 3.4 particles/m). Furthermore, significantly high amounts of microplastics were found in samples from the community area. No microplastic was detected in the sample from the natural resource conservation area. The quantity of microplastic did not significantly differ between the sampling periods. Polymer types, including polyester, polypropylene, and polyethylene terephthalate, were identified in this study. The microplastics were predominantly small and were colored black or red. Microplastic with a fiber shape (93.8%) was observed. Besides the specific gravity of the microplastic and hydrological characteristics, the high concentration of microplastics found in samples from the community area (0.62 ± 0.79 particles/m or 2.63 ± 3.36 particles/m) is likely related to the high human pressure. As microplastic contamination can impact aquatic animals and wetland ecosystems, appropriate control measures for human activities and plastic waste management are required.