Research ArticleENVIRONMENTAL STUDIES

Environmental exposure enhances the internalization of microplastic particles into cells

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Science Advances  09 Dec 2020:
Vol. 6, no. 50, eabd1211
DOI: 10.1126/sciadv.abd1211
  • Fig. 1 Images of particle-cell interactions of microplastic particles exposed to fresh water for 2 weeks.

    DIC: Differential interference contrast microscopy images of particle-cell interactions. Fluorescence: Spinning disc confocal images of the cells with fluorescently labeled filamentous actin (false color image, maximum intensity projection showing arbitrary units). XY, YZ, and XZ projections of three-dimensional confocal images allow the differentiation of microplastic particles (A) attached to cell membranes or (B) internalized microplastic particles. Arrows indicate microplastic particle position. Scale bars, 10 μm.

  • Fig. 2 Combined results of particle-cell interactions and internalized microplastic particles.

    (A) Numbers of particle-cell interactions and (B) numbers of internalized microplastic particles following 2 (light color) or 4 (dark color) weeks of incubation (all numbers indicate the means ± SE, table S1; IgG, positive control; FW, particles exposed to fresh water; SW, particles exposed to salt water; UW, negative control, pristine particles from ultrapure water). The numbers of particle-cell interactions and internalized microplastic particles were standardized to coverslips with 23,000 cells to which 29,000 particles were added. Because the data span almost three orders of magnitude, the ordinate is scaled logarithmically. The IgG treatment differs highly significant from all other treatments for either incubation time. Fresh water and salt water differ significantly from ultrapure water (except where specified otherwise, a Kruskal-Wallis test followed by a Games-Howell post hoc test was conducted to investigate significant differences between treatments, ***P ≤ 0.001, **P ≤ 0.01, *P = 0.05). The salt water treatment shows a significant increase in the numbers of particle-cell interactions and internalized microplastic particles over the incubation time, and fresh water shows a significant increase in the number of internalized microplastic particles during the incubation time (Mann-Whitney U test: **P ≤ 0.01, *P = 0.05).

  • Fig. 3 Representative SEM images of microplastic particles after 4 weeks of incubation, with enlarged views of the surface.

    (A) FW: Microplastic particles incubated in fresh water, with an enlarged view of the irregular surface modifications (arrows). (B) SW: Microplastic particles incubated in salt water, with an enlarged view of the irregular surface modifications with small salt crystals (arrows). (C) UW: Microplastic particles incubated in ultrapure water showing a plain surface. (D) IgG: Microplastic particles opsonized with IgG with an enlarged view of its homogeneously rough surface. Scale bars, 1 μm; SEM settings: 2 to 3 kV, InLens/SE2 detector.

  • Fig. 4 Raman spectroscopic analysis of the coating of microplastic particles incubated with fresh water.

    (A) False color Raman image of the microplastic particles (red) and the biomolecules forming a putative eco-corona (blue) on their surfaces, generated from the spectral mapping data. Scale bar, 2 μm. (B) The spectrum in red represents Raman signatures corresponding to the microplastic particles, and the spectrum in blue corresponds to signatures representative of the eco-corona. The Raman vibrational modes associated with biomolecules are mainly the C-S stretching mode (701 cm−1), the PO4 stretching mode (950 cm−1), the C─H bending mode (1410 cm−1), the C═O stretching mode (1664 cm−1), the C─H and C─H2 stretching mode (2851 cm−1), and the Raman band at 2126 cm−1 (C─N─S), together with the stretching mode at 701 cm−1, which could be indicative of the presence of thiocyanate molecules. Spectral signatures such as the ═C─H stretching mode (3053 cm−1), the C─H bending mode (2906 cm−1), the C─C bending mode (1604 cm−1), the C─H bending mode (1032 cm−1), and the C─C ring stretching mode (1001 cm−1) correspond to the PS microplastic particles.

  • Fig. 5 Core-level spectra of microplastic particles incubated in ultrapure water (gray), fresh water (green), and salt water (blue).

    (A) C 1s region showing the characteristic PS signals at 284.8 and 291.5 eV corresponding to carbon from (─C─C─ aliphatic and aromatic) and π-π* shake-up processes, respectively (44). In addition, all the samples display a signal at 286.5 eV, attributable to the carbon bound to oxygen as in alcohol or ether functional groups. Microplastic particles from salt water additionally show a signal at 289 eV, possibly from the carbon in ─O═C─N or ─O═C─O functional groups. (B) N 1s region from all the samples, confirming the presence of nitrogen on the surface of microplastic particles incubated in fresh water and salt water with the maximum at 400.1 eV. (C) S 2p region showing prominent signals at 168.5 and 169.8 eV on the surface of microplastic particles from ultrapure water and fresh water, and salt water, respectively, corresponding to sulfate functional group.

Supplementary Materials

  • Supplementary Materials

    Environmental exposure enhances the internalization of microplastic particles into cells

    A. F. R. M. Ramsperger, V. K. B. Narayana, W. Gross, J. Mohanraj, M. Thelakkat, A. Greiner, H. Schmalz, H. Kress, C. Laforsch

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