Immunotoxicity screening to understand the impacts of microplastics on human health

, Beijer Nick, Carlier Maxim, Wolter Helen, Mengelers Marcel, Dehaut Alexandre, Duflos Guillaume, Niemann Helge, Amaral-Zettler Linda, Staal Yvonne.

There is growing awareness of the quantity of minute plastic particles found in the food we consume, raising concerns on potential adverse effects. Macrophages play an important role in scavenging of particles, which may lead to induction of an immune response. To investigate the role of macrophages, we assessed the effects on macrophages of microplastics of different size and origin. Environmentally-weathered macroplastic samples were collected from the open-ocean South Atlantic Subtropical Gyre (G̈arbage Patcḧ) and from the French coastal environment. Plastics were cryo-milled to obtain sizes below 300 µm. Coastal plastic samples were identified as Poly-ethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) and subsequently size-fractionated to: 20-50 µm, 50-100 µm, and 100-200 µm size classes. We used (micro)Raman-spectrometry, FT-IR and Py-GC/MS, and phase-contrast microscopy to further characterize their physico-chemical properties. Differentiated macrophages (THP-1 cells) were grown in 96-well plates, and exposed to sinking particles directly or were placed on the basolateral side of inserts, to expose them to floating particles. After 48 hours of exposure, we assessed cell viability and cytokine response. Immunotoxicity response showed distinct patterns for each size class, but smaller particles were also detected in larger size fractions, making it difficult to interpret results. Macrophages also responded differentially to different plastic resin compositions. PET exposure produced the largest changes, including a dose-related response in cytokine production (IL-1β, IL-6, and TNF-α). Smaller particles (indicated size range) induced cytokine production at lower concentrations. We intend to use a combination of physiochemical and biological data for in-depth multi-dimensional data analysis to further explore the potency of particles properties in relation to their potential immunotoxicological effects. This research contributes to our understanding of the potential hazards of environmentally-sourced plastics on human health.

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