Carbon-centered environmentally persistent free radicals induce stronger toxicity than oxygen-centered ones in earthworms (Eisenia fetida)

Environmentally persistent free radicals (EPFRs) have attracted significant research interest regarding their generation and potential toxicities. However, conventional toxicity assessments of EPFRs have primarily relied on apparent concentrations, failing to account for the differential toxicity of multiple radical types, particularly oxygen-centered (O-EPFRs) and carbon-centered (C-EPFRs) radicals. We established two systems by loading catechol (CT) and anthracene (ANT) onto molecular sieves, generating particles dominated by O-EPFRs and C-EPFRs, respectively, with comparable apparent radical concentrations. EPFR quenching experiments confirmed that the observed toxicity to earthworms ( Eisenia fetida ) was solely attributed to EPFRs. Our results demonstrated that C-EPFRs exhibited stronger biotoxicity than O-EPFRs at comparable concentrations. C-EPFRs induced significantly more severe tissue damage and provoked more intense oxidative stress, evidenced by the marked upregulation of antioxidant enzyme activities and elevated levels of malondialdehyde and 8-hydroxy-2′-deoxyguanosine (a biomarker of DNA damage). Reactive oxygen species trapping experiments demonstrated that C-EPFRs generated higher amounts of ∙OH and O₂∙ − than O-EPFRs. This may be due to their higher singly occupied molecular orbital (SOMO) energy levels, indicating a stronger electron-donating capacity. Transcriptomic analysis further revealed that O-EPFRs primarily triggered adaptive responses. In contrast, C-EPFRs caused metabolic disruption, compromised antioxidant defenses, DNA damage, impaired protein synthesis, and significant histopathological damage. This study established a useful model for investigating the reactivity and toxicity of different types of EPFRs, providing the first mechanistic insight into their differential toxicities and highlighting the importance of distinguishing EPFR types in toxicity assessment. • A novel model for toxicity comparison of O- and C-centered EPFRs was established. • C-EPFRs exhibited stronger biotoxicity than O-EPFRs at equal concentrations. • Higher SOMO energy of C-EPFRs leads to greater ROS and distinct toxicity mechanisms. • Transcriptomic analysis reveals C-EPFRs caused metabolic disruption and DNA damage.