The overlooked toxicity of environmentally persistent free radicals (EPFRs) induced by anthracene transformation to earthworms (Eisenia fetida)

Environmentally persistent free radicals (EPFRs) as intermediate products exist widely in the PAHs-contaminated soils, but toxicity assessment associated with EPFRs for terrestrial invertebrates remains unclear. Using the model organism Eiseniafetida, we compared the adverse effects among anthracene (ANT), anthraquinone (ANQ), and EPFRs induced by ANT transformation on clay surfaces. Our results showed that EPFRs-exposed earthworms experienced histopatholo-gical damage, which was more severe than ANT and ANQ-exposed earthworms. The source of EPFRs damage was as-sociated with the obvious dysbiosis of reactive oxygen species in earthworms. Specifically, EPFRs trigged more severe antioxidant responses and oxidative damages (e.g., membrane lipid and DNA injury) in comparison with ANT and ANQ exposure, as evidenced by the values of integrated biomarker response (IBR) following the order of EPFRs (14.5) > ANT (12.8) > ANQ (10.9). Moreover, high-throughput sequencing found that EPFRs induced dramatic changes in the composition and structure of earthworm gut microbiota, which may involve immune and metabolism dysfunction, in turn aggravated EPFRs toxicity. Overall, the obtained information highlights the more severe injury of EPFRs to terrestrial organisms, deserving more attentions for the assessment of potential risks associated with radical intermediates in PAHs-contaminated soils.

Automated summary

This study compared the adverse effects among anthracene (ANT), anthraquinone (ANQ), and environmentally persistent free radicals (EPFRs) induced by ANT transformation on clay surfaces in earthworms. The results showed that EPFRs-exposed earthworms experienced more severe histopathological damage, dysbiosis of reactive oxygen species, and oxidative damages compared to ANT and ANQ exposure. High-throughput sequencing analysis further revealed that EPFRs induced significant changes in the composition and structure of earthworm gut microbiota, potentially aggravating EPFRs toxicity. These findings highlight the importance of assessing the potential risks associated with EPFRs in PAHs-contaminated soils.