Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Plant, Soil, and Environmental Sciences

Advisor

Rachel Schattman

Second Committee Member

Jean MacRae

Third Committee Member

YongJiang Zhang

Additional Committee Members

Caleb Goossen

Abstract

The presence of per- and polyfluoroalkyl substances in agroecosystems is a threat to the viability of farms and the health of humans, posing nuanced challenges to local and global food systems. As of 2021, elevated PFAS levels were detected on at least 60 Maine farms, but Maine only represents a microcosm of the global state of PFAS contamination (Maine Department of Environmental Protection, 2021). As a result of widespread contamination, there is uncertainty surrounding what crops, if any, can be grown viably and safely to protect farmer livelihoods and consumers. In the work presented here, we investigate the PFAS soil-to-plant uptake dynamics of three distinct crops: lettuce, tall fescue and tomato.

The field of research investigating PFAS uptake in agroecosystems is relatively young but is moving extremely quickly due to the vast impacts of these contaminants on the livelihoods of farmers and consumer safety. In this thesis, a thorough review of the literature was conducted to aggregate mechanisms known to drive PFAS uptake into plants (Chapter 1). This was expounded upon through linking these drivers of uptake to agricultural management strategies. The key insight from this synthesis of uptake literature is that chemical and soil conditions with high bioavailability are ideal for strategies like phytoextraction or PFAS immobilization. In contrast, agroecosystems where PFAS is less mobile and contamination levels are lower should focus on alternative agricultural practices, such as strategic plant pairings or cultivating species with low accumulation potential.

To expand upon this, a paired greenhouse and field study was conducted. The greenhouse study evaluated the uptake of lettuce, tall fescue, and tomato in spiked potting media (Chapter 2). The objectives of this study were to (1) quantify bioconcentration factors (BCFs) among these three crops; (2) evaluate the role of chain length, functional end groups and soil concentration on BCFs, and (3) test the influence of plant neighbor on BCFs. The key findings from this study were that BCFs were influenced by time between seeding and harvest, with greater BCFs associated with plants being in the ground longer. Additionally, chain length was a greater explanatory variable of BCFs than functional end group. The degree of soil concentration was also shown to influence BCFs, more so in short-chain than long- chain compounds. Plant pairings in the greenhouse were found to be effective in altering the movement of short-chain uptake, particularly in tomato/lettuce combinations in which this pairing reduced BCFs of PFBA into tomato fruits.

The greenhouse experiment was conducted alongside a field experiment. In the field, high levels of in-field variation in soil concentrations were identified, but no spatial autocorrelation was detected (Chapter 3). Moreover, BCFs in the field were often statistically different from the greenhouse, with the greenhouse BCFs being greater than those in the field. Similarly to the greenhouse, field BCFs were inversely related to chain length and carboxylates were the dominant functional end group. Plant pairings did not effectively lower BCFs in edible plant portions (EPCFs), but often increased them, illustrating that biotic relationships between plants may facilitate PFAS uptake.

This study adds to the growing body of BCFs reported in the literature, which will be of ultimate use for improving plant uptake models and informing decision-making among policymakers and agricultural producers. It additionally offers methodological dos and don’ts for PFAS studies aiming to understanding uptake mechanisms and applications for field environments. Together, these findings are important for future PFAS research with implications in agroecosystem management, public health and policymaking.

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