Available online at http://link.springer.com Ocean Sci. J. (2018) 53(4):631639 http://dx.doi.org/10.1007/s12601-018-0051-x pISSN 1738-5261 eISSN 2005-7172 Article Desorption of Hydrophobic Organic Chemicals from Fragment-Type Microplastics Hwang Lee 1 , Da-Eun Byun 1 , Ju Min Kim 2,3 , and Jung-Hwan Kwon 1 * 1 Division of Environmental Science and Ecological Engineering, College of Life Sciences & Biotechnology, Korea University, Seoul 02841, Korea 2 Department of Energy Systems Research, Ajou University, Suwon 16499, Korea 3 Department of Chemical Engineering, College of Engineering, Ajou University, Suwon 16499, Korea Received 6 May 2018; Revised 10 July 2018; Accepted 30 July 2018  KSO, KIOST and Springer 2018 Abstract  Microplastics provide an important medium for hydrophobic organic chemicals (HOCs), and the desorption of HOCs from microplastics is an important process for the dynamics of HOCs associated with microplastics. Although desorption kinetics has been studied for microplastics with ideal geometries, most of the microplastics isolated from the environment are irregular fragment-type microplastics. This study investigated the desorption of six model HOCs from polyethylene (PE) and polypropylene (PP) fragments to artificial seawater and compared the results with those predicted assuming ideal geometries (e.g., sphere and infinitely flat sheet) of microplastics. The experimental desorption was explained well by the model predictions with the characteristic radius for a sphere and the thickness for a plate estimated from visual imaging. The mass fraction remaining at the later stage of desorption was higher than the model simulation assuming a single characteristic length, likely due to the heterogeneity of the particle size distribution. Although there are inevitable uncertainties, it would be useful to assign a single length dimension in desorption modeling for even fragment-type microplastics, especially for the estimation of desorption half-life. Keywords  plastic debris, partition coefficient, diffusion coefficient, desorption kinetics, Biot number 1. Introduction Accumulation of marine plastic debris has been one of the most important environmental pollution issues (Derraik 2002; Moore et al. 2001, 2008; Thompson et al. 2004). Microplastics are defined as plastic particles with size less than 5 mm (Andrady 2011; Engler 2012), and they may contain hazardous organic chemicals as additives or sorbed from the environment. Among the many other potential harmful consequences of microplastics, desorption or leaching of hydrophobic organic chemicals (HOCs) has received significant attention because of the high sorptive capacity of microplastics toward HOCs (Bakir et al. 2014; Endo et al. 2013; Jang et al. 2017; Koelmans et al. 2013; Kwon et al. 2017; Lee et al. 2018). A quantitative description, using mathematical models, of the desorption of HOCs from microplastics is very important for estimating the release of organic additives to the surrounding environment (Kwon et al. 2017) as well as for the evaluation of potential trophic transfer of HOCs associated with microplastics to marine organisms at higher trophic levels. Desorption of HOCs from plastic particles to a surrounding fluid medium such as seawater is often described by a two- step process: internal diffusion of HOCs in the plastic phase followed by convective mass transfer in the fluid medium (Endo et al. 2013; Lee et al. 2018; Seidensticker et al. 2017). For example, Endo et al. (2013) investigated desorption of polychlorinated biphenyls from polyethylene (PE) pellets and compared their experimental results with desorption models controlled by internal diffusion in plastic and by convective mass transfer in water, assuming an ideal sphere. Lee et al. (2018) measured diffusion coefficients of six persistent organic pollutants (isomers of hexachlorocyclohexanes and polychlorinated benzenes) and independently measured desorption of these pollutants from PE and polypropylene (PP) films. Experimental data, including both diffusion in *Corresponding author. E-mail: junghwankwon@korea.ac.kr