H2o2 p a

30% (v/v) H₂O₂ (p.a.) supplied by Merck (Darmstadt, Germany) was used for aging experiments of polystyrene samples. Artificial seawater (prepared as described by Kester et al.⁴³ ) spiked with 10 ppb of Cd (ICP-multi elemental solution VIII in diluted HNO₃ obtained from Sigma–Aldrich, Buchs, Switzerland) was used for exposure of polystyrene samples. Metal-free water (resistivity 18.2 MΩ cm⁻¹) dispensed from a Barnstead EASYPURE II water system (ThermoFisher Scientific, Marietta) was used for sample rinsing and dilutions. H₂S (100 ppm), SO₂ (100 ppm) and synthetic air (5.0) used for weathering experiments was supplied by Messer, Austria. O₃ was produced using an ozonisator (Airmaster OMX 500, Topchem GmbH, Germany) with O₂ (5.0) supplied by Messer, Austria.

Systemic distribution of NPs in blood and to various organs, such as spleen, kidney, liver, brain, and lymph nodes (LNs), was quantified by elemental analysis of Ce using inductively coupled plasma mass spectrometry (ICP-MS) (Matter et al., 2020 (link)). To this end, whole blood (100 μL) or organ samples (50–300 mg) were transferred to a polytetrafluoroethylene container and mixed with 3 mL of 65% HNO₃ p. a. (Merck) and 1 mL of 30% H₂O₂ p. a. (Merck). These samples were then digested using a microwave (TurboWAVE, MLS GmbH, Germany) at 250°C and 120 bar for 18 min. Cerium was then quantified using ICP-MS (Model 7900, Agilent, Santa Clara, CA) (Oertli et al., 1994 (link); Kulber et al., 1997 (link)) by measuring isotope Ce140. Lu175 was used as an internal standard to correct for non-spectral interferences (Matter et al., 2017 (link); Lese et al., 2021 (link)).