Comparison of MPs Contamination between Downstream and Upstream Sites: A Case Study of Lower Chao Phraya River, Thailand

Abstract

Microplastics (MPs) were ubiquitously found and distributed globally in the environments especially marine environment. Majority of MPs were discharged from land to the sea. However, most of the studies focused on the marine environment and few reports were studied MPs in the freshwater environment especially from Asia continent which was reported to be main contributor for MPs pollution. Thailand as one of the top countries that was estimated to produce mismanaged plastic waste to the ocean is expected to discharge MPs to the river and the sea. This study investigated MPs pollution in Chao Phraya river, major river in Thailand, by focusing on the lower Chao Phraya river at two sites: upstream at Pathum Thani province and downstream at Bangkok Metropolis to identify concentration and characteristics of MPs in surface water and evaluate impact of urbanization by comparing MPs results from two different sites. MPs were sampled on surface water by manta trawl. Results of MPs concentration were 4.0 and 22.9 MPs particles/m³ at upstream and downstream sites, respectively. FT-IR results reveal that majority of MPs were polyethylene and polypropylene which are common materials for single use plastics. In addition, the compared results showed that the downstream site had higher MPs concentration and component types which indicate higher MPs inputs from several sources which clearly showed effects of urbanization at Bangkok. More investigation about MPs sources and seasonal variation are recommended for future study. In addition, results of MPs size distributions at both sites showed a similar trend toward smaller size and 8 percent of MPs found at the downstream site were below 335 µm which is mesh site of manta net used in this study. Thus, investigation of smaller MPs is also recommended in the future.