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Raman spectra characterization of size-dependent aggregation and dispersion of polystyrene particles in aquatic environments.
Summary
This study used Raman spectroscopy to examine how the presence of salt, proteins, and organic matter influences the aggregation and dispersion of polystyrene nanoplastics in water. The findings show that environmental conditions significantly alter nanoplastic behavior and can complicate their detection, which has implications for understanding how nanoplastics move through aquatic environments.
Aqueous environments are generally thought to be a source of pooling and re-distribution for both micro-plastics (MPs) and nano-plastics (NPs); however, significantly less data on NPs than MPs have been reported. The occurrence of salts, proteins, and other organic matter may promote or inhibit the aggregation of NPs to form agglomeration particles, making their detection more difficult. In this study, 80 and 500 nm polystyrene nano-plastics (PS-NPs) modified by four different functional groups (PS-Bare, PS-COOH, PS-NH, and PS-CHO-500 nm) were selected to mimic the flocculation and/or sedimentation of NPs in salts (NaCl, CaCl, and NaSO) and protein solutions. The results showed that the 80 nm PS-NPs are only colloidal in pure water. All four strong electrolyte solutions that were tested significantly promoted the aggregation of PS-NPs, including those that were protein-coated. In addition, 500 nm PS-CHO did not flocculate but gradually settled into sedimentation. Therefore, Raman spectrometry can be used to analyze assembled PS-NPs, but is not suitable for analyzing normal PS-NPs. By combining fractal morphology, this study provides insight into the comprehensive analysis of PS-NPs in water solutions, including the digestion of biological samples.