Uptake of per- and polyfluoroalkyl substances by Conservation Reserve Program’s seed mix in biosolids-amended soil

Abstract

To test the effectiveness of phytoremediation of per- and polyfluoroalkyl substances (PFAS), we cultivated a mixture of nine grass-legume species native to Maine, US, in two types of soil amended with biosolids containing both pre-existing and spiked PFAS. To investigate how biochar amendment affects plant uptake of PFAS, two types of biochar at varying doses (i.e., 0%, 0.05%, 0.2%, 1%) were added to the biosolids before mixing with soil and cultivating plants. Our findings indicate that six representative PFAS, including short- and long-chain perfluoroalkyl carboxylic acids (PFCAs) (C6-C8) and perfluoroalkylsulfonic acids (PFSAs) (C4, C6, and C8), were effectively transferred from the biosolids amended soil (BAS) system to the harvestable grass-legume shoots. During the initial growth stage (Day 33), PFOA, PFHxS and PFOS were primarily detected in the grass shoots, showing a removal efficiency of 2-3%. As the growth period extended to Day 92, the uptake of short-chain PFBS, PFHxA, and PFHpA became increasingly dominant with an average removal efficiency of 5-20%. Notably, more than 10% of PFOA was uptaken by the shoots harvested from the Scantic soil amended with Biochar 2. These results were observed in grass-legume shoots when the soil was amended with a low dose of biochar (0.05%). However, when 1% biochar was added, PFAS were effectively stabilized, preventing their transfer to the above-ground plant compartments. Aside from different effect of different dose of the biochar, this study also revealed that plant’s uptake of PFAS is highly dependent on soil properties. Overall, this study demonstrated the feasibility of using a grass-legume mix for removing PFAS from contaminated soil and raised the need of developing site-specific treatment strategies to maximize the performance of phytoremediation.