Enhancement of Per- and Polyfluoroalkyl Substance Uptake from Contaminated Soil by Applying Plant Growth Regulators:...

Innovative approaches are urgently needed to improve the phytoremediation of complex mixtures of per- and polyfluoroalkyl substances (PFAS) in contaminated soils. This study investigated the effectiveness of plant growth regulators (PGRs) in enhancing the uptake of a mixture of eight PFAS (100 μg/kg each) by Timothy grass (TG) from soil. A suite of PGRs including auxins (indole-3-acetic acid [IAA], indole-3-butyric acid [IBA]), gibberellic acid (GA), jasmonic acid, α-naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid) was applied individually via foliar spray at concentrations ranging from 0.1 to 200 μM. Among all treatments, IBA at 10 μM (IBA-10), IAA-1, and GA at 0.1-1 μM significantly enhanced shoot accumulation of PFHxA and PFHpA, with maximum uptake reaching ∼23% in TG during the second harvest (days 55-108). Compared to the controls without exposure to PGRs, this enhancement was ∼63%. In addition, PGRs enhanced the translocation of long-chain PFOS and PFNA, with increases of 45-82% over the controls. Uptake of ΣPFAS peaked around 7-9% of the total spiked mass for those with IBA-10, IAA-1, or GA-1/GB-0.1, underscoring the importance of type and concentration of PGRs in enhancing phytoextraction. Similar results were also observed for alfalfa undergoing similar treatment with PGRs. Insight from both TG and alfalfa indicates that not all PGR applications led to enhanced biomass weight and PFAS uptake percentage. Some treatments increased tissue PFAS concentrations without improving biomass dry weight, while others enhanced biomass but resulted in only modest increases in PFAS translocation. These results demonstrate that some foliar-applied phytohormones can regulate PFAS accumulation in plants, offering a potential strategy to improve phytoextraction efficiency. The underlying mechanisms, however, will need to be further elucidated.