Mechanistic insights into PFHxS phytotoxicity and uptake dynamics in Lupinus polyphyllus

Perfluorohexane sulfonic acid (PFHxS), a recently classified persistent organic pollutant, is being increasingly detected in agricultural soils, yet its phytotoxicity, uptake and trophic transfer remain poorly understood. We investigated the effects of PFHxS on the growth, antioxidant regulation, uptake, and ultrastructure of the legume Lupinus polyphyllus grown in PFHxS-spiked soil (5, 25, and 125 mg/kg) after 90 days. High PFHxS concentrations (125 mg/kg) inhibited germination, whereas 5 mg/kg produced a hormetic stimulation of seedling viability and post-germinative biomass. Inhibitory effects emerged from 25 mg/kg onwards. Antioxidant enzyme activity was associated with reduced lipid peroxidation malondialdehyde (MDA), suppression of catalase (CAT) and ascorbate peroxidase (APX), and compensatory induction of peroxidase activity (POD). Photosynthetic pigments decreased at ≥25 mg/kg, indicating impaired light-harvesting capacity. Root uptake reduced PFHxS concentrations in the rhizosphere (1.78-32.96 mg/kg) relative to those in the bulk soil (2.82-105.95 mg/kg), corresponding to an elevated rhizosphere-referenced bioaccumulation factor (BAF). The root BAF increased from 0.63 to 0.92 (bulk) to 0.89-4.17 (rhizosphere), whereas the shoot BAF increased from 1.29 to 2.69 to 3.29-5.75. Increased PFHxS exposure induced a shift from efficient translocation of PFHxS to transport-limited accumulation, characterized by strong rhizosphere depletion. Transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) revealed enrichment of membrane and vascular-associated transport with phloem parenchyma. Overall, PFHxS accumulation in L. polyphyllus appears to be controlled by tissue partitioning and vascular transport, with uptake largely influenced by rhizosphere bioavailability rather than total PFHxS soil concentration.