# Modeling and Parametric Simulation of Microplastic Transport in Groundwater Environments
## 1 Introduction  
Microplastics (MPs) include primary MPs that are intentionally made with sizes of 5 mm or smaller, as well as secondary MPs that have been weathered by ultraviolet radiation, biodegradation, physical wear, or chemical oxidation [1]. It is estimated that 1.15 to 2.41 million tons of plastics flow into the ocean worldwide through streams and rivers because of low recycling rates and poor waste management [2, 3]. Among these plastics, MPs can absorb toxic pollutants because of their high specific surface area and reactivity while releasing phthalate, bisphenol A, and brominated flame retardants, causing adverse effects on organisms that accidentally feed on these plastics [4]. Although the interest of the international community is increasing concerning this problem as MPs have emerged as a serious global environmental threat [5, 6], public anxiety and concerns about MP pollution in terrestrial ecosystems are on the rise in Korea, as most pollution surveys have focused on marine and coastal environments [7, 8, 9]. In particular, the current conditions of MP pollution in groundwater have not been actively investigated in Korea. The transport of MPs in subsurface environments needs to be evaluated to address public concerns and anxiety over MP pollution, as well as to ensure consistency considering the quality of groundwater resources [10]. The European Union (EU) is preparing institutional strategies to monitor MPs in drinking water, including spring water, and they are devising preventive measures in circular economy packages, such as developing plastic recycling technologies and biodegradable plastics, classifying toxic substances in plastics, and preventing marine waste. The Swedish Environmental Protection Agency (SEPA) has aimed to reduce plastic usage, achieve efficient plastic recycling, and prevent plastic contamination from land-based sources by supporting projects concerning the sustainable use of plastics and adequate managementof plastic waste by non-profit organizations, public organizations, universities, and research institutes from 2020 to 2021 [11]. In the Netherlands' TRAMP research project, which extended from 2015 to 2019, relevant ministries, research institutes, and universities participated in the development of nanoplastic and MP detection technologies for freshwater environments; developed plastic transport, risk, and impact evaluation technologies; and predicted the current and future risks of plastics in freshwater environments [12]. In Germany, various studies on the transport of MPs in ecosystems, the biological impact of MPs, and natural attenuation of MPs have been underway for several years, and associated research findings have been published in academia [13; 14; 15; 16]. A recent study has also focused on the existing water quality index and its modification using a multi-criteria decision-making method [11; 17; 18; 19]. The U.S. National Oceanic and Atmospheric Administration (NOAA) supports a variety of studies through collaborations with schools and research institutes related to MPs, and a recent study on MP discovery in a karst aquifer by a team at the University of Illinois was also supported by the U.S. National Science Foundation (NSF). The 5 Gyres Institute and the San Francisco Estuary Institute, supported by the Gordon and Betty Moore Foundation, investigated the current status, influx routes, and transport of MPs in the San Francisco Bay area for three years through the San Francisco Bay Microplastics Project (www.sfei.org; accessed on 12 July 2021). Adventure Scientists, a non-profit organization in the United States, surveyed the level of MP pollution in marine and freshwater systems worldwide from 2013 to 2017, and they established a database for the current status of pollution [20; 21; 22].