Worldwide plastics production is 360 million tons (Plastic Europe, 2015; Zainuddin ea al., 2022), and it has been reported that worldwide wastes reached 60 million to 90 million tons in 2015 and are expected to increase to 155 million to 260 million tons by 2060 (Lebreton and Andrady, 2019; Zainuddin ea al., 2022). It is known that about 8 million tons of plastics used as such flow into the ocean annually due to wastes or dumping (Jambeck et al., 2015). The plastics introduced into the ocean are granulated (Andrady, 2011) through mainly photochemical processes and are divided into the forms of megaplastics (over 1 m in size), macroplastics (greater than 2.5 cm and smaller than 1 m in size), mesoplastics (larger than 5 mm and smaller than 2.5 cm in size) and microplastics (smaller than 5 mm in size) (GESAMP, 2016).
The microplastics as such can be divided into primary microplastics and secondary microplastics according to their origins (Li et al., 2018; Piñon-Colin et al., 2018). Primary microplastics refer to those microplastics that have been intentionally manufactured as microplastics (microbead, resin pellets, microcapsules, etc.), and secondary microplastics refers to those microplastics that have been granulated over time due to the effects of physicochemical actions, photochemical actions, mechanical wear, temperature fluctuations, winds, and waves (Auta et al., 2017; Barnes et al., 2009; Bergmann et al., 2017; Ling et al., 2017).
Microplastics decomposed through the processes as such are not well distinguished in size from phytoplankton and organic detritus, some are used as an attachment base for attached algae (Boerger et al., 2010), or wrongly ingested by zooplankton and fry (Cole et al., 2015). Ingested microplastics are not digested and remain in the body, affecting the physiology of zooplankton and may affect their survival (Cole et al., 2015).
In addition, microplastics may be ultimately delivered to humans in addition to fish and mammals, which are upper predators, through the food chain of the marine ecosystem to act as factors affecting human health (Lattin et al., 2004; Farrell and Nelson, 2013). Although ingested microplastics not larger than 130 µm are mostly excreted, there are findings indicating that some can move into cells through binding to intestinal cells to cause local immune responses or to be distributed throughout the body so that harmful additives, heavy metals, and adsorbed PCBs, etc. included in plastics are released to show harmfulness (Cox et al., 2019), and although microplastics introduced into the human body and respiratory organs through respiration can be removed by the mucociliary clearance mechanism of the lungs, it has been reported that very negative effects are expected in the event of poor health conditions of individuals and long-term exposure (Lehner et al., 2019). Furthermore, Yang et al. (2004) reported that small-sized nanoparticles (polystyrene of ≤ 20 nm sizes) of plastics can pass through the blood-brain barrier to cause cerebral ischemia and reperfusion.
Although a mention about microplastic contamination as such first appeared in the literature in 1972 (Carpenter et al., 1972), full-scale studies have been conducted from 10 years ago (Avio et al., 2017; Lvar do Sul and Costa, 2014; Zarfl et al., 2011). Internationally, pretreatment methods (Lvar do Sul et al., 2014; Lusher et al., 2014: Hall et al., 2015; Claessens et al., 2013; Desforges et al., 2014; Tanaka and Takada, 2016; Zhao et al., 2016; Cole et al., 2014; Courtene-Jones et al., 2017), microplastic detection methods (Löder et al., 2015; Dümichen et al., 2015; Fischer et al., 2017), internal residues ((Claessens et al., 2013; Cole and Galloway, 2015; Avio et al., 2017; Wright et al., 2013), etc. are being studied. In South Korea, pretreatment methods for microplastics (Chae et al., 2014; Song et al., 2019; Cho et al., 2019), adsorption characteristics (Eom et al., 2019; Jang et al., 2020), internal residue investigation (Kim et al., 2020; Kim et al., 2020; Lee et al., 2020; Chae et al., 2020), and presentation of policy directions (Kim and Chung. 2020) have been studied.
Meanwhile, as plastics are eventually introduced into the ocean through many processes, in many countries, many studies on the distribution characteristics of microplastics in their territorial waters are conducted to find institutional methods (Zheng et al., 2021; Amelia). et al., 2021; Lee. et al., 2013; Chae et al., 2015; Song et al., 2018; Kang et al., 2018; Kwon et al., 2020; Jung et al., 2021). Whereas many studies have been conducted on coasts and estuaries as such, studies on open waters are insufficient. In particular, studies on the behavior and distribution characteristics of microplastics in the East China Sea in the southwest of Jeju Island in South Korea, which is waters where quite diverse inflow sources such as the influent from the Yangtze River in China, the Chinese coastal current, the Sushima warm current as a tributary of the Kuroshio Current, and the Taiwan current act, are lacking (Jiang et al., 2020). As the seawater introduced into this waters is not a problem of one country but affects the territorial waters of many countries as it passes the Korea Strait and moves to the East Sea, studies of it is considered to be urgently necessary (Isobe et al., 2015). Therefore, this study is intended to collect surface seawater from the Yangtze River in China and the East China Sea, a waters southwest of Jeju Island in South Korea, and investigate the abundance, materials, sizes, shapes, etc. of microplastics through qualitative and quantitative analyses using FT-IR equipped with a particle tracking mode (MCT detectors) to find out the distribution characteristics.