Investigation of input pathway for microplastics to marine environment in Masan Bay, South Korea

Abstract

In order to understand the behavior of microplastic (MP) entering the marine environment from terrestrial sources, studies on input pathways of MP has been actively carried out. The major transport pathway of MPs from land to sea can be riverine discharge, direct discharge from wastewater treatment plants (WWTPs), and atmosphere transportation. However, most studies have been focused on individual input pathway (e.g. river, WWTPs, or atmosphere). There is no case of comprehensively evaluating multiple land-based sources. Therefore, it is necessary to evaluate the relative contributions and input characteristics of various land-based MP sources. This study investigated the MP contamination in five creek waters, effluent of two WWTPs, and atmospheric deposition samples around Masan Bay, and estimate the annual input load of MP through three input sources to Masan Bay using in situ data. The mean abundance of MPs in five creek waters and effluent of two WWTPs was 1681±480 n/m3 and 4345±2247 n/m3, respectively. The mean atmospheric deposition rate of MPs was 39±27 n/m2/day. In all samples, fragment (>70%) was the dominant type of MP, and the most common size class was 100–150 µm (>30%). Polypropylene, polyethylene, and polyester were found as major polymers accounting for >60%. It was estimated that about 1.7 trillion particles, and 2.31–6.85 tons of MPs enter Masan Bay annually through three types of input sources. The annual MP load in Masan bay through creek water, WWTP effluent and atmospheric deposition were accounting for 19%, 28%, and 53%, respectively. By weight basis, it accounted for 10–13%, 59–63%, and 27–28%, respectively. We identified that a significant amount of MP can enter into marine environment via various land-based input and that atmospheric deposition as well as aquatic transport make a great contribution. Therefore, it is necessary to investigate the land-based input of MPs including atmosphere transportation, along with aquatic input pathways.