Thailand is one of the largest contributors to plastic waste in the oceans. Since mismanaged plastic waste can enter the ocean via inland waterways, microplastic contamination in freshwater used for tap water production has been raised as a potential issue. This study was conducted to determine the abundance and characteristics of microplastics in freshwater and treated tap water in Bangkok. Freshwater and treated water were collected from the eastern and western water supply systems in the dry and wet seasons. The source waters of the eastern and western water supply systems are the Chao Phraya River and Maeklong River, respectively. Approximately 0.40-2.40 particles/L microplastics was determined in the freshwater samples. No significant differences in microplastic abundance with respect to water supply system or season were found. Approximately 82.1% of the total microplastics found in the freshwater were smaller than 300 µm in size. The percentage contribution of various microplastic size ranges decreased with increasing size. The majority of microplastics found in freshwater were fragments (90.2%), colorless (64.3%), and made of polyethylene polymer (45.1%). Only the eastern water supply system was capable of removing microplastic particles (27.7%) from freshwater. The identification of microplastics larger than 100 µm in size in the treated tap water indicated potential contamination from microplastics in the treatment system, particularly after the sand filtration unit. The major characteristics of the microplastics found in treated tap water were similar to those found in freshwater, with 85.6% fragments, 85.1% colorless, and 47.9% made of polyethylene polymer.
Keywords: Chao Phraya River; Drinking water treatment system; Maeklong River; Microplastic; Plastic polymer; Water supply.