Forever Chemicals in the Farmland

PFAS contamination in agricultural soils — from decades of biosolid application, irrigation with contaminated water, and firefighting foam runoff — affects farmland across the US, but no field-validated remediation technologies exist, no federal soil contamination thresholds have been established, and the behavior of over 14,000 identified PFAS compounds in agricultural systems is largely unknown. Crops grown in PFAS-contaminated soil can take up PFAS through roots, but uptake rates vary dramatically by crop species, PFAS chain length, soil type, organic matter content, and pH, making risk assessment for any specific farm practically impossible with current knowledge.

An estimated 20 million acres of US farmland have received biosolids that may contain PFAS, and farms near military bases, airports, and industrial facilities face additional contamination from firefighting foam (AFFF). When PFAS contamination is discovered, farmers face devastating consequences — loss of organic certification, inability to sell produce or livestock, and no clear remediation path. In Maine, dozens of farms have been shut down after PFAS testing, with some families losing multi-generational operations. The absence of federal thresholds means states set their own limits, creating a patchwork of regulations that varies by orders of magnitude and makes farming across state lines unpredictable.

Activated carbon and biochar soil amendments can adsorb PFAS but the NASEM report found that "key uncertainties remain around long-term field performance, desorption potential, incorporation depths, and performance across soil types." Performance varies wildly — biochar from different feedstocks and pyrolysis temperatures shows different PFAS affinities, and soil properties (clay content, organic matter, pH) modulate effectiveness unpredictably. Phytoremediation (using hyperaccumulating plants to extract PFAS) is in early research stages with unclear disposal pathways for contaminated biomass. Denitrifying bioreactors show "slow and incomplete" PFAS degradation. Soil excavation and landfilling is prohibitively expensive at agricultural scale. No PFAS-specific design manuals exist for agricultural water management or conservation practices.

Field-validated amendment protocols (biochar, activated carbon, organoclay) with performance data across representative soil types, PFAS compound classes (short-chain vs. long-chain, carboxylic vs. sulfonic), and climatic conditions. Rapid, affordable PFAS soil screening methods for farmer decision-making — current analytical methods cost $300–500+ per sample and take weeks, making spatially informed management impossible. Crop-specific PFAS uptake models that predict which crops are safe to grow at different contamination levels. Federal soil contamination thresholds to give farmers, regulators, and remediation providers a common decision framework.

A student team could compare PFAS sorption capacity of different biochar types (varying feedstock, pyrolysis temperature, activation method) across representative agricultural soil types using standardized batch adsorption tests, focusing on the PFAS compounds most commonly detected in biosolid-amended soils. Alternatively, teams could develop a low-cost PFAS soil screening protocol using emerging portable detection technologies (fluorescence-based sensors, immunoassays) calibrated against laboratory LC-MS/MS reference methods. Relevant disciplines: environmental engineering, soil science, analytical chemistry, agricultural science.