Onboard measurement of polyethylene microplastics on a research vessel using Raman micro-spectroscopy: A preliminary study for testing feasibility

Microplastic pollution in marine environments poses significant environmental risks due to its widespread presence. Traditional micro-imaging measurement of microplastics often rely on post-cruise laboratory analyses. In this study, we explored the feasibility of onboard microplastic measurement using Raman spectroscopy, with a focus on polyethylene (PE). A measurement system was developed, and two concentration estimation approaches were proposed. To evaluate recovery and validate the methodology, artificial microplastic samples were prepared, yielding a recovery rate of 94.8 % +/- 10.4 %. Environmental samples were then analyzed using the developed system, with results validated against conventional Fourier-transform infrared (FTIR) spectroscopy. The estimated PE concentration was 583 pieces/m3 (95% confidence interval: [2, 1542] pieces/m3) using the direct approach and 1453 pieces/m3 (95% credible interval: [291, 92,837] pieces/m3) using the Bayesian approach. Both estimates were consistent with the 333 pieces/m3 obtained through validation with FTIR, indicating adequate accuracy. However, the wide confidence intervals highlight the need for improved precision. While challenges remain, this study provides a comprehensive experimental procedure and introduces a robust data analysis framework, which could offer a foundational methodology for future onboard microplastic measurement research.