Microplastic fouling: A gap in knowledge and a research imperative to improve their study by infrared characterization spectroscopy

The marine weathering of microplastics is spectrally characterized by the appearance of new bands that disturb our understanding of the information carried by the spectra. Yet, no explanation has been provided on the chemical origin of these new bands. Thus, the main objective of this work was to identify the origins of these additional bands. To this end, 4042 spectra of poly (styrene), poly(ethylene) and poly(propylene) microplastics collected in the Mediterranean Sea, were analysed using principal component analysis. The results showed that the spectral variability was mainly related to only three processes: chemical ageing, organic and inorganic fouling. These processes probably differ from one polymer family to another due to surface affinities. This work has also led to the proposal of two new polymer indices that could be used to monitor the intensity of (bio)fouling. Finally, the development of advanced analyses could also provide information on the nature of the plastisphere. [Display omitted] •Spectra of weathered microplastics have shown new bands.•This spectral variability was mainly related to only three processes: chemical ageing, organic and inorganic fouling.•Two new polymer indices able to monitor the intensity of (bio)fouling were proposed.