Comparative phytotoxicity of PFOS and its substitute OBS in mulberry and implications for a mulberry-silkworm exposure system.

Perfluorooctane sulfonic acid (PFOS) is a persistent perfluoroalkyl substance known to exert adverse effects on soil and terrestrial ecosystems. However, the toxicological risks of its substitutes, particularly sodium p-perfluorinated nonenoxybenzene sulfonate (OBS), and their impacts on perennial plants and food-chain transfer remain insufficiently understood. Here, mulberry (Morus alba) seedlings were used as a model perennial species to compare the phytotoxic effects of PFOS and OBS. PFOS exerted markedly stronger inhibitory effects than OBS, as evidenced by significant reductions in plant height, biomass, and photosynthetic performance. Transcriptomic analyses revealed that both compounds primarily modulated general stress-responsive pathways, whereas OBS induced substantially fewer differentially expressed genes than PFOS, indicating a lower level of molecular disturbance. PFOS accumulation in mulberry was dominated by root retention, with approximately 85.2% retained in roots, followed by leaves (around 14.3%) and stems (around 0.5%). To assess PFOS toxicity along the mulberry-silkworm PFOS exposure, silkworms (Bombyx mori) were fed PFOS-contaminated mulberry leaves. Low PFOS exposure did not affect silkworm growth or silk production, whereas high exposure levels caused growth retardation and impaired cocoon formation. Approximately 58.6% of ingested PFOS was eliminated via excretion. Transcriptomic analysis further revealed that reduced silk production under high PFOS exposure was associated with the downregulation of genes involved in silk protein biosynthesis and processing, including polypeptide N-acetylgalactosaminyltransferase (GALNT). Collectively, these findings improve our understanding of PFOS- and OBS-induced stress responses in mulberry and highlight the potential of mulberry as a candidate species for PFOS uptake and provide preliminary information relevant to future phytoremediation research.