This study presents methodological advancements for characterizing atmospheric nanoparticles (NPs) accumulated in tree bark, a passive bioindicator of urban nanoparticle pollution. Accurate assessment requires efficient degradation methods that remove organic matter while preserving inorganic NP properties. Preliminary imaging (SEM, X-ray microtomography) and chemical mapping revealed heterogeneous NP distributions, with preferential accumulation at the bark surface and partial penetration into internal porous structures. Two degradation strategies – tetramethylammonium hydroxide (TMAH) digestion and cold O 2 plasma treatment – were evaluated using bark doped with enginereed NPs (Au, Fe 2 O 3 , MnO 2 , TiO 2 , Al 2 O 3 , CuO) at environmentally relevant concentrations. TMAH removed 27% of bark dry weight, while O₂ plasma achieved 89%, confirmed by FTIR analysis showing disappearance of lignin and cellulose peaks. spICP-MS quantification demonstrated that O 2 plasma preserved TiO 2 and Al 2 O 3 (~100% recovery), partially degraded Fe 2 O 3 (-43% mass loss), and fully degraded CuO and MnO 2 , likely due to ionization energy thresholds and oxidation state transitions. TMAH induced partial Fe 2 O 3 dissolution and CuO aggregation via complexation and electrostatic interactions. These results highlight the critical influence of degradation protocols on NP stability and underscore the need for optimized methods that efficiently remove organic matter while maintaining NP integrity. This work provides a robust analytical framework for environmentally relevant studies of nanoparticle behavior, persistence, and potential hazard in complex biological matrices. • Metallic NPs are localized at bark surface and in porous inner structures • First application of cold O₂ plasma and TMAH digestion to tree bark • O₂ plasma achieves 89% degradation and preserve selectively oxide NPs • Impact of degradation strategy on nanoparticle preservation is evaluated
Sophie et al. (2026) studied this question.