Fig. 1. Spontaneous radical generation and surface electrostatics at PS microplastic–water interfaces.
a–i, Spontaneous radical generation at PS microplastic–water interfaces. a, Left: photos showing methyl orange degradation in water after incubating with PS microplastics for 10 days. Right: supernatants collected from methyl orange solutions prepared in different solvents with (PS(+)) or without (PS(−)) PS microplastics after 10 days. b, Time trace of absorbance changes of methyl orange in water incubated with or without PS microplastics. Data are the mean ± s.d.; n = 3 aliquot measurements. Two-way repeated-measures analysis of variance; curves differed significantly (P < 0.0001). c, Methyl orange absorbance in solvents with or without PS microplastics after 10 days. Data are the mean ± s.d.; n = 3 aliquot measurements. d, ESR spectra of radicals generated by PS microplastics suspended in water using DMPO as a radical trapper; simulated and experimental spectra agree. Data are representative of three independent experiments. e, Reaction scheme of APF for •OH detection. f, Confocal fluorescence images of PS microplastics incubated with 5 μM APF in PBS (left) or PBS containing 0.1% Triton X-100 (right). g, Time trace of APF fluorescence at a representative PS microparticle surface in PBS with or without Triton X-100. Data are representative of duplicate experiments. h, High-performance liquid chromatography analysis monitored at 488 nm confirms continuous APF conversion to fluorescein by PS microplastics in water, whereas APF is fully retained when 0.1% Triton X-100 is present in the PS–water mixture. Data are representative of duplicate experiments. i, APF fluorescence quantification of PS microparticle surfaces in PBS containing varying Triton X-100 concentrations. Values are presented as area-weighted mean fluorescence intensities ± s.d. from particle regions at 0% (n = 17), 0.001% (n = 6), 0.01% (n = 7), and 0.1% (n = 7) Triton X-100, respectively. One-way analysis of variance with Tukey’s test; PS in PBS differed from all Triton X-100 conditions (P < 0.005). j–m, Surface electrostatics at microplastics–water interfaces. j, Zeta potential of PS microplastics in 1 mM NaCl containing varying Triton X-100 concentrations (left axis) and their corresponding APF fluorescence at particle surfaces in PBS (right axis). Data are presented as mean ± s.d. Zeta potential data represent n = 4, 7, 5 and 4 independent measurements at 0%, 0.001%, 0.01%, and 0.1% Triton X-100, respectively. For the fluorescence measurement, the same data from panel i are shown here. k, Zeta potential of PS microplastics in water or ethanol (left axis) and corresponding methyl orange conversion (right axis). Data are mean ± s.d. Zeta potential data represent n = 10 and 3 independent measurements in water and ethanol, respectively. Methyl orange conversion is determined from n = 3 aliquot measurements. l, Surface electrostatics visualized using positively charged Rh800 (1 μM) in water, 0.1% Triton X-100, or ethanol. m, Corresponding intensity profiles along the white dashed lines in panel l. Scale bars, 50 μm (f), 20 μm (l).