Nitrogen-Centered Persistent Free Radicals from Roxarsone Phototransformation on Soil Minerals: Magnetic Coupling Mechanism and PFR-Driven Ecological Risks

Here, we report the generation of unique nitrogen-centered PFRs during ROX phototransformation on soil mineral surfaces. Unlike typical environmental PFRs, these species exhibit a distinct triple-peak EPR signature, which is proposed to arise from the magnetic coupling between •NO and •NHR radicals following C–As bond cleavage.

Mineral composition strongly governs radical evolution, with MnO₂ enhancing and Fe₂O₃ suppressing PFR stability. These nitrogen-centered radicals act as efficient electron shuttles, sustaining the production of reactive oxygen species (•OH, •O₂^–, H₂O₂). Multitrophic toxicity tests (bacteria-plant-earthworm) combined with rigorous arsenic-controlled conditions (As(V)≤150 ppb, As(III)≤20 ppb) reveal that the observed growth inhibition, oxidative damage, and histopathological effects are predominantly driven by PFR-mediated processes rather than by released inorganic arsenic.