Establishing Spectral Library of Ship Paint-Derived Microplastics by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope - Energy Dispersive X-ray Spectroscopy (SEM-EDS)

Abstract

Although the International Union for Conservation of Nature (IUCN) and the International Maritime Organization (IMO) identified marine coatings as potential sources of microplastics, there are not enough studies reporting the status of microplastic pollution derived from ship paints. Qualitative and quantitative evaluations are possible only after the chemical and material property data of ship paint-derived microplastics are well accumulated, such as polymer types and elemental compositions. To establish a spectral library of ship paint-derived microplastics, a total of nine types of representative 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) were selected according to their functions and working mechanisms. Each dried paint was pulverized into secondary microplastics using a mortar under liquid nitrogen and sieved through a 2 mm-sized mesh to simulate environmental samples. The FTIR spectrum of the secondary microplastics was measured and the spectral information on the absorption peaks, their appearance, corresponding functional groups with mode of vibrations, as well as the fingerprint of specific constituents, was reported in this presentation. When blind samples were analyzed after library construction, they showed an average matching rate of 96.0% or more with the established library spectrum. In addition, the external characteristics and constituent element information of secondary microplastics were analyzed by using SEM and EDS. As a result of observing the external image through SEM, it was found that copper chunks were embedded in some antifouling top-coats. In addition to C and O, which are the most dominant elements in all types of ship paint-derived microplastics, Mg and Si were clearly detected in primers; Si, Ti, and Ba in tie-coat; Cu, Zn, Fe, and Ca in antifouling top-coat; Mg, Si, Ca, Fe, and Ba in epoxy based top-coat; and Ca and Ti in urethane based top-coat. Their relative compositions were unique among different types of paint-derived microplastics. Establishing a library on the polymer type by FTIR, external features by SEM, and elemental compositions by EDS will contribute to clearly identifying ship paint-derived microplastics in environmental samples, and thus to better quantitative analysis required for risk assessment.