Development of a rapid detection protocol for microplastics using reflectance-FTIR spectroscopic imaging and multivariate classification

Microplastics present a serious and worsening environmental threat to marine and aquatic ecosystems. Continued monitoring is crucial in assessing the hazards and provenance of plastics. Unfortunately, analytical methods that are currently available suffer limitations that prevent widespread uptake of microplastic monitoring across the environmental sector. Reflectance-FTIR spectroscopy may present an alternative to current microplastic analytical methods, as it provides spatially resolved chemical specificity (allowing determination of particle size, abundance and polymer identity); is a non-contact method (allowing high throughput of samples); eliminates the problems of complete infrared absorption by larger particles; and does not require expensive infrared-transparent substrates. This study has used reflectance-FTIR spectroscopic imaging to build a spectral library, which was then coupled with multivariate statistics (chemometrics) to develop a protocol for microplastic detection and a semi-automated data processing pipeline. The workflow was used to detect microplastics from marine salt samples that were concentrated via filtration onto cost-effective and routinely available Whatman cellulose filter papers. Specifically, polyethylene (PE) and polypropylene (PP) microplastics from marine salt samples could be identified with 100% specificity (PE and PP) and sensitivities of 78% (PE) and 82% (PP), highlighting the immense potential for future use of this method as a cost-effective option for high-throughput and semi-automatable microplastic analyses. Reflectance-FTIR spectroscopy provides opportunities for faster, more automated, and cheaper detection of microplastics in the environment.