Date of Award

Summer 7-30-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Forest Resources (MFR)

First Committee Advisor

Ling Li

Second Committee Member

Yong-jiang Zhang

Third Committee Member

Onur G. Apul

Additional Committee Members

Ivan J. Fernandez

Abstract

PFAS are a group of persistent organic compounds found to be widely dispersed throughout the environment via anthropogenic activities; the application of biosolids in the farmland of Maine being a major problem. We investigated the effects of biochar amendment on the immobilization of PFAS in soil and uptake by two commonly grown and consumed vegetables, lettuce and tomato, in order to determine management approaches to reduce PFAS uptake from soil to edible parts. Plants grown in PFAS contaminated soils can uptake PFAS, which poses risks to the ecosystem and is harmful to human health. To characterize the bioavailability of PFAS in soils, PFAS uptake of two major vegetable crops, and the effect of biochar amendments on crop PFAS uptake, a greenhouse experiment was conducted. We used three treatments: (1) a control consisting of a PFAS-spiked soil (i.e., a potting mix), (2) a biochar treatment in which biochar was blended into the PFAS-spiked soil (30% of the mix by volume), and (3) a soil treatment, where PFAS-free potting mix was added to the spiked soil at the same application rate to assess the PFAS dilution effect. Four PFAS species (i.e., perfluorobutanoic acid (PFBA); perfluorobutane sulfonate (PFBS); perfluorooctanoic acid (PFOA); perfluorooctane sulfonate (PFOS)) were spiked in potting mix at 220 µg/kg each across all three treatments. The results showed that biochar amendment can reduce bioavailable PFAS in leachate

dramatically in both crops. In biochar amendment, long chain PFAS (PFOA and PFOS) were not detected in tissue samples in both crops and short chain PFAS (PFBA and PFBS) were reported in lower concentration (reduced 40-60%) as compared to control and dilution treatment. Thus, biochar amendment could be an effective material for immobilizing PFAS in soil and reduce their uptake by crops. Alongside, a field experiment was also conducted to study the effect of biochar amendment under field conditions with diverse PFAS species and its precursors at varying concentrations. Thus, this study aimed to assess the role of woody biochar in PFAS sorption from soils and the reduction of PFAS uptake by two vegetable crops, lettuce and tomato. Like the greenhouse study, there were three treatments (control, compost amendment, and biochar amendment), but for the dilution treatment, compost amendment was done at the same application rate, i.e., 30% v/v. Our results revealed that biochar amendment could significantly immobilize the various PFAS species in soil and reduce their uptake in lettuce leaves and tomato fruits. In tomato fruits, no long-chain PFAS were detected across all treatments and significantly reduced the uptake of short chain PFAS (PFBA). In lettuce, PFOA was below limit of detection (LOD) in biochar treatment but PFOS was detected and was significantly lower than that of control, and compost amendment. PFAS precursor, N-Ethyl perfluoro sulfonamide acetic acid has also been reported in biochar and control plots which can degrade to PFOS in soil/plants. Overall, no negative effect on yield of crop was reported in biochar treatment and no phytotoxicity symptoms were reported in both greenhouse and field experiment. Above all, these results show that adding biochar to soil can lower the amount of PFAS uptaken by lettuce and tomatoes by immobilizing the chemicals in the soil. This is a promising way to lower the amount of PFAS uptaken by crops.

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