PFAS-induced morpho-physiological, photosynthetic and tissue accumulation responses of pot-grown hemp, sunflower and maize under soil amendment with humic acids

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are persistent per- and polyfluoroalkyl substances (PFAS) of environmental concern that can interfere with plant growth and hysiological processes. This study evaluated the morpho-physiological response and PFAS accumulation in hemp (Cannabis sativa L.), maize (Zea mays L.), and sunflower (Helianthus annuus L.) grown in soil-filled pots for 32 days under greenhouse conditions. Silty loam soil was spiked with PFOA+PFOS (500 μg kg-1 each), with or without a single exploratory soil application of humic acids (HAs; 1 g kg-1). Across species, PFAS exposure caused no significant reduction in total biomass or visible phytotoxicity, and leaf SPAD values were largely maintained. Photosynthetic measurements were conducted exclusively on hemp, which revealed increased PSII operating efficiency (Fv′/Fm′) while significantly reducing stomatal conductance (−46%), transpiration (−40%), and net CO2 assimilation, alongside an 83% reduction in electron transport rate at near-saturating irradiance, under PFAS. This response is consistent with a decoupling between photochemistry and carbon assimilation, likely indicative of physiological stress. Hemp showed the highest foliar PFAS accumulation (PFOA: 5.39 μg g-1 d.w.; PFOS: 2.59 μg g-1 d.w.) and strong root−to−shoot translocation. Maize and sunflower achieved comparable or greater total plant PFAS burden per plant owing to their higher biomass. HAs significantly increased total dry weight in maize (+17%) and sunflower (+20%), and increased sunflower root dry weight (+49%). While the effects of HAs on PFAS accumulation were largely non-significant, in hemp PFAS+HAs significantly reduced the translocation factor (TF) of both PFOA and PFOS compared with PFAS alone. Future studies should evaluate PFAS removal over full growth cycles under field conditions, compare multiple HA rates and application methods including foliar spraying, and extend detailed photosynthetic characterization to all three species.