Reactivity Evaluation between Microplastic Pretreatment Reagents and Ship Paint-Derived Microplastics

Abstract

As the concerns about microplastic pollution in the marine environment are increasing, ship paint-derived microplastics are also gaining more attention. While microplastic pretreatment techniques for removing various organic matters contained in environmental samples are well established, the effects of existing pretreatment reagents on ship paint-derived microplastics, which are likely weaker and more brittle than common microplastics, have not been studied. Since ship paint-derived microplastics exist together with various hull-fouling organisms (e.g. bacteria, microorganisms, small invertebrates, algae, fish eggs, etc.), it is more important to remove interfering organic matter through appropriate pretreatment technique before qualitative and quantitative evaluations. Reactivity tests were conducted with three kinds of pretreatment reagents (10% KOH, 30% H2O2, Fenton’s reagent) on nine types of ship paints (two types of primer as anticorrosive paint, two types of tie-coat as adhering agent between the primer and top-coat, and five types of top-coat as antifouling paint and deck paint). Each paint was pulverized into secondary microplastics using a mortar, under liquid nitrogen, and sieved through a 2 mm-sized mesh. After that, they were exposed to the pretreatment reagents for up to 7 days at 40 ℃ and 60 rpm using a thermo shaker. After the exposure to pretreatment reagents, they were vacuum-filtered onto pre-weighed GF/F filter paper and washed with distilled water to stop further reaction. The microplastics on filter papers were dried at 40 ℃ for 24 hours. The pretreated microplastics were compared to untreated control groups in weight and size variations on a microscope, and the changes in physicochemical characteristics were analyzed using Scanning Electron Microscope - Energy Dispersive X-ray Spectroscopy (SEM-EDS) and Fourier Transform Infrared Spectroscopy (FTIR). For accurate qualitative and quantitative evaluation of ship paint-derived microplastics, the pretreatment reagent should not degrade the microplastic polymer. This study will contribute to more clearly identifying ship paint-derived microplastics by establishing an appropriate treatment method and thus to properly assessing the risk posed by ship-paint derived microplastic sources in the marine environment.