Application of confocal laser Raman spectroscopy on marine sediment microplastics

Marine sediment is the primary sink of microplastics and is an indicator of pollution levels. However, although there are well-developed detection methods, detection is rarely focused on low-micrometer-sized particles, mainly due to technique limitations. In this study, a simplified process omitting digestion procedures was developed to pretreat microplastics obtained from marine sediment and was coupled with micro-Raman spectroscopy to identify microplastics. Based on the overall analysis of the characteristic peak assignments, a Raman spectral reference library was constructed for 18 types of plastic. In addition, the effects of the measurement parameters were systematically described. Field research was then conducted to validate the developed process and investigate microplastic contamination in Huiquan Bay, Qingdao, China. This simplified process could retain the original appearance of microparticles and accomplish the detection of <500 μm-sized microplastics in environmental samples. Microplastics in the size range of 10–150 μm accounted for 76% of all microplastics, and 56% of the total particles was particles smaller than 50 μm. Polypropylene (42%) and polyethylene (20%) were predominant components of the particles. In particular, polypropylene particles smaller than 10 μm were identified in marine sediment. This work demonstrates that Raman spectroscopy is not only an effective tool for detecting environmental particles but also highly applicable for identifying particles extracted from marine sediment.