Extended Data Fig. 1. Solvent dependence, generality, and apparent rates of hydroxyl radical generation at water-PS microplastic interfaces.

a, Time tracking of methyl orange (MO) absorbance (OD_465nm − OD_700nm) with/without PS microplastics in MeOH, EtOH, MeCN, and DMF. While MO spectra vary slightly among solvents, this measurement can follow MO degradation and correct for scattering contributions at 700 nm. No MO degradation occurred in organic solvents, unlike its complete degradation in water.  Data are the mean ± s.d.; n = 3 aliquot measurements. b, Universal surface reactivity at PS-water interface in •OH generation. Surface reactivity and functionality are evaluated for PS from different vendors. Surface reactivity: APF fluorescence (left) shows spontaneous •OH generation at hydrophobic PS–water interfaces; stimulated Raman scattering images (middle) show PS C–H vibrations at 3050 cm⁻¹. Scale bar, 50 μm. Surface functionality: PS microplastics may experience oxidative aging, which introduces oxygen-containing groups (e.g., C = O, O-H). This can be evaluated using XPS spectroscopy (right). PS from vendor 1, characterized by a pristine surface, served as the model sample in this work. Although all samples exhibited surface reactivity, it decreased with increasing oxidation; PS from vendor 2 and 3, enriched in oxygen-containing groups, were less hydrophobic and showed reduced activity. c, HPLC analysis of APF reacting with •OH with/without Triton X-100. APF showed no conversion in water (top; negative control), whereas the Fenton-generated •OH converted APF to fluorescein (middle; positive control). Adding Triton X-100 into Fenton reagent did not inhibit APF reaction with •OH, indicating the observed APF signal in Fig. 1i results from Triton’s interactions with PS-water interfaces to modulate the surface reactivity (bottom). The top panel shows data representative of 5 independent experiments; the middle and bottom panel each show data from one independent experiment. d-e, Semi-quantitative estimation of apparent •OH production rate at PS-water interfaces under different environments. d, Representative time-dependent APF fluorescence measured at individual PS particle surfaces under different solution environments from measurements of n = 6 and n = 8 particle regions, respectively. The surface-associated fluorescence increase is largely linear over the measurement window, supporting the use of linear fitting to extract the rate of fluorescence increase for each particle. e, Apparent interfacial fluorescein generation rates at PS surfaces in PBS, cell culture medium, and serum, calculated by converting fluorescence increase rates into apparent generation rates using solution-specific calibrations. Each point represents one measured particle region; n = 8, 6 and 8 for PBS, cell culture medium, and serum, respectively.