A multi-approach to the removal and analysis of micro-/nano- plastics (MNPs)

Abstract

The wide occurrence of micro- and nano plastics (MNPs) in food, water, soil and air has caused increasing concerns on potential human health impacts and environmental pollution. Accurate identification and efficient elimination of these particles continue to pose difficulties owing to their diminutive size, chemical heterogeneity, and interactions within intricate matrices. This work explored a multi-modal methodology for the detection and removal of MNPs in liquids. A plastic-free, chemically densified carbon nanotube (DCN) membrane was assessed for its effectiveness in filtering MNPs and foodborne pathogens, using the fluorescent polystyrene (PS) particles and Escherichia coli and Listeria innocua as model targets in the studies. Additionally, our collaboration with Dr. Ruogu Tang and Dr. Juzhong Tan explored the use of biochar for removing MNPs. Both DCN and biochar filters exhibited excellent removal of MNPs, with biochar displaying a higher efficacy on removing bigger aggregated particles in HPLC water. DCN membranes consistently demonstrated superior removal of MNPs, with 0.95 and 2.1 µm particles typically decreased by over 90%. Biochar filters exhibited comparable performance for submicron particles (0.1 and 0.5 µm) and demonstrated a pronounced effectiveness for bigger MNPs, with removal rates for aggregated MNPs (2 µm) often surpassing 85–90%. Test solutions, comprising HPLC water, bottled water, and apple juice, were added with model MNPs and treated in vitro digestion, simulating stomach and intestinal conditions. MNPs in the solutions before and after digestion were evaluated by different methods. ☐ The quantitative and qualitative evaluation of MNPs was performed utilizing Nile Red fluorescence staining with fluorescence imaging or reading, Dynamic Light Scattering (DLS), Nanoparticle Tracking Analysis (NTA), and Scanning Electron Microscopy (SEM). In this phase of the study, commercial 0.5 and 2 µm MNPs (fluorescently labeled and non-labeled), alongside with various pretreatment methodologies (in vitro or chemical digestion, matrix-specific background correction rinsing, and centrifugation were added into HPLC water, bottled water and apple juice, and then quantified by the various methods. Nile Red staining of non-labeled PS particles generated fluorescence signals that were dependent on MNPs concentration and size, facilitating the creation of calibration curves for both 0.5 and 2 µm MNPs. The bigger MNPs often exhibited higher apparent recoveries owing to enhanced dye adsorption and aggregation. The fluorescence responses of labeled MNPs aligned with these trends and served as an internal validation of staining efficacy, especially in intricate matrices where apple juice displayed significant autofluorescence, necessitating pretreatment (e.g., dilution and/or centrifugation) to enhance the signal-to-background ratio. In all matrices, chemical digestion and filtration resulted in significant reductions in fluorescence intensity for both size categories, consistent with DLS, NTA, and SEM findings on particle removal or aggregation. The integrated Nile Red-based method is effective for monitoring both non-labeled MNPs in the test solutions although more research is still needed for improvement of recovery rate and detection sensitivity. These findings will be useful for creating a cohesive analytical and filtering platform to determine MNP in diverse food systems. Furthermore, the integration of improved characterization techniques with novel filtration materials such as DCN and biochar presents interesting approaches for future detection and mitigation tactics in evaluation of dietary MNPs and assistance in advancement of advance the regulatory policies on health impacts of MNPs. Embargoed until 07-31-2027.