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Spectroscopic evidence for adsorption of natural organic matter on microplastics
Summary
This study used Raman spectroscopy to directly detect natural organic matter (NOM) binding to low-density polyethylene microplastics, providing clearer evidence of this interaction than previous solution-based measurements. This matters because when microplastics become coated with organic matter in rivers and lakes, their surface properties change — affecting how they transport pollutants, interact with organisms, and move through aquatic ecosystems.
Abstract The interaction of microcroplastics (MP) with dissolved organic matter, especially humic substances, is of great importance in understanding the behavior of microplastics in aquatic ecosystems. Surface modification by humic substances plays an essential role in transport and interaction of MP with abiotic and biotic components. Previous studies on the interaction between MP and humic substances were largely based on a model compound, humic acid (Sigma‐Aldrich). In our work, we therefore investigated the interaction of natural organic matter (NOM) sampled from a German surface water with low‐density polyethylene particles (LDPE). High‐pressure size exclusion chromatography (HPSEC) and UV/vis absorption and fluorescence spectroscopy were used to characterize the incubation solutions after modifications due to the presence of LDPE, and Raman spectroscopy was used to characterize the incubated microplastics. While the studies of the solutions generally showed only very small effects, Raman spectroscopic studies allowed clear evidence of the binding of humic fractions to MP. The comparison of the incubation of NOM and a lignite fulvic acid which also was tested further showed that specific signatures of the humic substances used could be detected by Raman spectroscopy. This provides an elegant opportunity to conduct broader studies on this issue in the future.