Summary¹

Per- and polyfluoroalkyl substances (PFAS) are a diverse family of synthetic compounds with valuable properties, such as high thermal and chemical stability; oil, water, and stain repellency; and lubricity. The exact number of PFAS is unknown in part because there is no single accepted definition of PFAS, but by some estimates there are more than 14,000. They are present in numerous consumer and industrial products, including nonstick cookware, textiles, packaging, and firefighting foams. The strength of the carbon–fluorine bond and the presence of multiple fluorine atoms per carbon contribute to their valuable properties but also allow them to persist in the environment. The resistance of the carbon–fluorine bond to breaking has earned PFAS the nickname “forever chemicals.”

Their widespread use facilitates a myriad of mechanisms via which they can enter and cycle in the environment. The compounds are dispersed via aqueous and atmospheric processes resulting in occurrence in soil, surface water, groundwater, sediment, and air. Even at low concentrations, PFAS may create potential hazards not only to human health but also to the nation’s natural resources and the economic enterprises and ecosystem services that these resources support, such as agriculture, forestry, and wildlife habitat. In agricultural settings, PFAS contamination of soil and water can render farmland unusable for crops or grazing if there are no viable mitigation options. There are cases in the United States of farms that have suffered tremendous economic losses because PFAS have moved from groundwater and soil into drinking water, forage, and feed of livestock and caused levels of PFAS in animals to be so excessive that subsequent milk and meat products were declared unsafe for human consumption. In some states, health advisories have been issued warning people not to consume fish, waterfowl, turkey, or deer caught or hunted from locations with high levels of PFAS in

PFAS IN AGRICULTURAL SYSTEMS

PFAS occur in two broad classes, polymers and non-polymers, with the latter including well-known compounds such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). PFOA and PFOS are legacy substances that have been phased out of production in the United States, yet they remain widely detected in the environment and in human blood because of their persistence and because they are terminal transformation products of precursor PFAS degradation. Precursor PFAS, such as perfluorooctane sulfonamide and 8:2 fluorotelomer alcohol, are polyfluoroalkyl substances that break down into terminal PFAS, such as PFOS and PFOA, respectively. Because PFAS are transported through air, water, soil, and biota, their presence is now widespread, even in areas with no obvious sources. Studies suggest that background levels exist globally because of atmospheric deposition.

PFAS behavior is strongly shaped by their chemical structure. Long-chain compounds tend to bind tightly to soil and accumulate in living tissue, while short-chain compounds are more mobile and likely to leach into water or be absorbed by plants. Some PFAS present in fire-fighting foams are cationic or zwitterionic, which highly sorb to soils regardless of chain length. The fate and transport of PFAS also depend on soil type, organic content, pH, climate, land management, and other factors.

PFAS enter the environment through point sources—such as industrial manufacturing facilities and military facilities using firefighting foam—and nonpoint sources. Nonpoint sources on farms may include contaminated biosolids, manures, pesticides, fertilizers, and water supplies, as well as atmospheric deposition. Once introduced, PFAS cycle within farms: they move into soils, are taken up by plants, pass into livestock feed and water, and reappear in manure that is reapplied to fields (Figure S-1). They also migrate off farm through runoff, leaching, atmospheric deposition, and sale of contaminated products. Some PFAS are persistent and bioaccumulative, so even low-level contamination can create risks to human and ecological health.

FEDERAL CONSERVATION SUPPORT AND PFAS IN AGRICULTURAL SYSTEMS

Since the 1930s, USDA has provided technical and financial support for conservation on privately owned working lands to customers who seek out these services. Today, NRCS focuses on delivering technical and financial assistance to customers to voluntarily plan and implement conservation practices, while FSA primarily provides financial incentives for the retirement of highly erodible and sensitive lands from agricultural production for the duration of the contract between the agency and the customer. The customer base for conservation support is broad, including farmers, ranchers, forest stewards, nonprofits, businesses, and governments.

Conservation planning is central to NRCS’s work. The planning process typically begins with discussions between the planner and the customer, leading to identification of site-specific concerns. NRCS defines a resource concern as degradation of soil, water, air, plant, or animal systems that impairs their sustainability or intended use; more than 40 such concerns are recognized and grouped under these five categories.

Once a resource concern is identified and inventoried, planners and landowners collaborate to select conservation practices that address it and create a plan that belongs to the customer. More than 160 national conservation practice standards exist, ranging from nutrient management to water and sediment control basins, all intended to improve environmental performance with some also maintaining or enhancing productivity.

Capabilities and Limitations for Conservation Programs and Practices to Address PFAS Concerns

Producers who pursue conservation technical and financial assistance do so through a number of FPAC conservation programs and subprograms. The committee was asked to characterize the capability of four programs—the Environmental Quality Incentives Program (EQIP), the Conservation Stewardship Program (CSP), the Agricultural Conservation Easement Program (ACEP), and the Conservation Reserve Program (CRP)—to address on-farm PFAS contamination and mitigation. NRCS administers EQIP and CSP, which are working lands programs, as well as ACEP, which protects farmland and wetlands through easements. FSA administers CRP, which takes environmentally sensitive cropland out of production, while NRCS provides conservation technical assistance to the program.

Among these, EQIP offers the broadest opportunities for addressing PFAS because it is widely used, covers most practice standards, and provides significant cost-share. It also supports Conservation Innovation Grants that could be leveraged to develop PFAS-specific mitigation practices. CSP can build upon EQIP by funding enhancements of conservation practices and bundles of enhancements, potentially including those targeting PFAS. CRP may provide another pathway by retiring contaminated land and mitigating PFAS impacts through vegetative covers, pilot projects, or partnerships under the Conservation Reserve Enhancement Program. ACEP, however, cannot be used for PFAS-contaminated land due to statutory restrictions tied to the risk of hazardous substances, namely PFOS and PFOA.

Though EQIP, CSP, and CRP have potential, they face practical limitations, including oversubscription and eligibility rules. Even when funds are available, producers may lack the initial capital to implement practices before financial assistance reimbursement, or they may fear added visibility by identifying a resource concern that could draw the attention of regulatory entities despite the purely voluntary nature of USDA conservation programs.

The committee was also asked to characterize the capability of conservation practices to address on-farm PFAS contamination and mitigation. Its assessment is that conservation practices may both help and harm in the PFAS context. For example, measures that reduce erosion can limit PFAS transport but may simultaneously increase leaching of PFAS to groundwater. Practices that involve importing organic soil amendments to the farm risk introducing new PFAS contamination. Careful selection and adaptation of practices to specific site conditions through conservation planning are essential.

Opportunities to Address PFAS Concerns through Conservation Support

There are opportunities for NRCS to explicitly integrate PFAS into its conservation framework. In the conservation planning stage, PFAS concerns could be incorporated explicitly or implicitly into existing categories of resource concerns, such as those that address pathogens and chemicals from manure, biosolids, or compost applications transported to groundwater and surface water. Another option would be to recognize PFAS as a distinct resource concern, similar to the way in which nutrient transport to water bodies is recognized, which would allow NRCS to directly evaluate the effects of practices on PFAS. The principal rationale for this approach is that PFAS contamination could be directly evaluated by NRCS for the effect of each conservation practice on this concern and would not be dependent on surrogate evaluations through the results for related resource concerns. Designating PFAS as a resource concern would help to ensure it receives proper consideration in the conservation planning process and that the most effective conservation practice solutions are planned for a specific site to mitigate PFAS contamination. However, calling out PFAS as a standalone resource concern could bring unwanted attention to customers affected by the issue or make customers less inclined to work with NRCS because of concerns of being singled out. As the fate and transport of different PFAS in the environment is not uniform, addressing PFAS as a specific resource concern in the conservation planning process is challenged by the variety of behaviors that could occur in response to conservation practices.

In terms of conservation practices, NRCS could explore both new and adapted approaches. Subprograms that support innovation could be used to test new practice standards, such as crop choices that minimize PFAS uptake, or to improve existing standards, such as filter strips designed to intercept contaminants before they reach water bodies. Currently, only one practice standard, Soil Carbon Amendment, explicitly references PFAS. Expanding references to PFAS across other standards, as is already done with nutrients and pesticides, could highlight risks and ensure planners are alert to the issue.

Addressing PFAS across diverse agricultural landscapes will be complex. Still, by creating new practices, revising practice standards, modifying existing resource concerns, supporting innovation, and strategically applying conservation programs, NRCS can begin providing its field staff with the tools needed to guide its customers in mitigating PFAS risks. Success will depend on integrating PFAS into conservation planning, balancing tradeoffs among conservation practices, and using innovative programmatic approaches, field trials, and research mechanisms to test and refine solutions.

DECISION-MAKING UNDER UNCERTAINTY

The lack of data regarding the extent and magnitude of PFAS contamination on agricultural land, combined with uncertainties about what different potential PFAS sources may contribute to farm contamination and the fate and transport of different PFAS, poses a challenge to advising farmers on how to manage PFAS risks. This challenge is further complicated by the absence of a working definition for PFAS in agricultural contexts. Such a definition may need to consider PFAS structural features, the ability to detect a specific PFAS, and thresholds for deciding when detected concentrations merit further investigation. Currently, one of the most pressing challenges is the lack of consistent regulatory criteria for PFAS in agricultural soils, including considerations for occurrence of PFAS mixtures. Due to the variation in regulations at the state level, federal guidance on thresholds in agricultural lands would be beneficial to assist conservation planners and others in contextualizing PFAS occurrence at agricultural facilities. Notably, all considerations that would inform a definition—structure, analytical methods, regulatory criteria, or the exceedance of a set threshold for some combination of PFAS persistence, bioaccumulation, toxicity, and mobility—are evolving areas of study and will require review and revision as the science advances.

Regarding the unknown magnitude of PFAS contamination, predictive models based on known PFAS sources and soil and hydrogeologic data could help identify at-risk agricultural lands. Machine-learning approaches have already been used to map groundwater contamination probabilities in several states and at the national scale. Extending these models to soils and agricultural contexts could assist NRCS planners and producers in assessing risks where site-specific data are unavailable.

The committee took this potential for predictive modeling and what is known about the occurrence, fate, and transport of PFAS and integrated these with the conservation planning process and how conservation practices, programs, and initiatives could

available to affected customers. NRCS could work with other agencies and entities to establish nationwide screening levels for different types of agricultural production facilities, soil types, and climatic systems. Machine-learning models could be trained, similar to those underlying current PFAS groundwater maps, using nationwide data on PFAS in agricultural soils and information in the Web Soil Survey, combined with data on proximity to PFAS sources, agricultural land uses, climate, and other features. Applied research could expand the capability of existing practices and the development of new practices to address PFAS concerns. In cases where decision-makers determine that PFAS risks are unacceptably high, FPAC programs that support farmers in taking land out of production may be necessary.

APPLIED RESEARCH GAPS

In the context of conservation on the land, applied research needs to focus on minimizing PFAS uptake into plants and animals, in situ sequestration, and removal of PFAS to the greatest extent possible. The committee identified four areas of research that could advance the ability of conservation practices to address PFAS contamination on agricultural land.

Discerning PFAS Fate and Transport in Varying Soil Types

Understanding how PFAS move through soils across the United States is complex because a combination of soil characteristics—including clay and oxide content, organic matter, pH, soil texture, cations, and water relationships—interacts with climate conditions such as precipitation, wind, and temperature to influence PFAS behavior. Climate in particular plays a critical role. Laboratory studies have shown that higher temperatures increase plant metabolism and transpiration, which in turn raises PFAS concentrations in plant tissues, especially leaves. Precipitation is also a major driver of PFAS leaching and mobility, though long-term field data linking rainfall patterns to PFAS behavior are lacking. Many greenhouse studies do not allow leaching from the pots, thereby leaving short-chain PFAS in close contact with roots longer than would occur under natural conditions, which limits the accuracy of those findings.

The type of PFAS present also matters. Short-chain PFAS tend to move more freely in soils, while long-chain compounds sorb more strongly. Less is known about zwitterionic PFAS, but evidence suggests that soil pH alters their charge and sorption magnitude. Differences between clay types also affect sorption, with kaolinite and montmorillonite behaving differently. Although significant research has examined sorption, less attention has been given to desorption. Studies of historically contaminated soils show that compounds such as PFOS can resist release even after multiple desorption steps, while lab-spiked soils show less persistence. These discrepancies highlight the need for further investigation into desorption hysteresis and its implications for PFAS persistence.

To advance understanding, a coordinated, national network of researchers could be created to study PFAS fate in diverse soils and climates. Using tools such as predictive modeling and the NRCS Web Soil Survey, scientists could identify vulnerable soils, expand data fields in the Web Soil Survey with respect to PFAS sorption and movement, and refine conservation practice standards based on these insights. Such a coordinated effort would help fill research gaps and provide practical knowledge for managing PFAS contamination in U.S. agricultural systems.

Opportunities to Trap or Sequester PFAS

Research on PFAS sequestration in agricultural settings points to several promising sorbents and complementary field strategies, though there are large evidence gaps. The benefits to sequestering PFAS include the potential to reduce plant uptake as well as leaching. Potential disadvantages are that PFAS are held in place, which may hinder success of future removal or destruction strategies. There is also the potential for changes in the PFAS sequestering sorbents over time that may lead to unforeseen release of PFAS.

Several designer sorbents have been tested at the bench-scale to target high PFAS sorption capacity; however, scalability in terms of provision and cost at the landscape scale are unlikely. Therefore, much attention has turned toward biochar that can be produced in large volumes. The intrinsic performance of biochar as a sorbent depends on feedstock, pyrolysis temperature and hold time, surface area, and the carbon–oxygen ratio. Higher temperatures generally increase specific surface area, resulting in biochars

Understanding Plant Characteristics That Affect PFAS Uptake and Accumulation

In the context of conservation practices, the selected planting of specific crops or other vegetative cover could address PFAS contamination on agricultural land via plant uptake in one of two ways: (1) by trying to minimize PFAS accumulation in harvested and grazed crops or (2) by trying to maximize plant uptake for phytoremediation. For either approach to be successful, there is an urgent need to better understand the variation in PFAS uptake among agricultural and conservation plants and of the various plant characteristics that influence that uptake. Studies could address quantification of soil-to-plant transfer of PFAS across a broader range of crops and growing conditions than currently exist in the literature. To be most useful for crop selection decisions, these studies should be conducted in the field under real-world conditions and preferably over multiple years to capture year-to-year variability.

Transpirational flow is seen as the primary driver of PFAS uptake and accumulation into the plant. Although sorption to soil serves as a control for what is available in the porewater for transpiration, plant features such as protein and lipid contents, root macrostructure, and root exudates have all been proposed as plant-based mechanisms that lead to PFAS uptake differences among plant species and cultivars. Further research is needed to investigate the relative importance of these factors, as well as the influence of selective membranes and other transfer barriers in roots and shoots. Research into transpiration rates could also explain differences observed in the amount of PFAS plant uptake among crop species and across seasons.

How crop management affects plant PFAS uptake is a topic that has barely been addressed but is of great importance in the context of conservation practices. Researchers have investigated fertilization and intercropping on crop PFAS uptake with mixed effects. No known studies exist on how PFAS uptake is influenced by conservation tillage/no-till, which is known to affect root distribution under certain conditions, crop rotation, crop density, or irrigation.

Research is also needed to determine and use appropriate vegetative covers that are not detrimental to the health of wildlife by their consumption. Harmful exposure of wildlife (or grazing livestock) to PFAS because of plant uptake would be at odds with conservation practices developed to provide habitat.

PFAS Mitigation in Livestock

Mitigating PFAS contamination in livestock remains a significant challenge, as animals exposed through water or feed can accumulate these chemicals in meat and milk. Dairy consumption is a primary agricultural exposure pathway of concern because forages (leafy crops) are important feed sources for dairy animals, and PFAS bioaccumulate and biomagnify in animals and their milk. Guidance developed in Maine offers some practical steps. PFAS levels in animals can decline once exposure ends, with PFOS in milk and beef tissues showing half-lives of 8–12 weeks. Switching cattle to uncontaminated feed or pastures during finishing can reduce risk. Diluting contaminated feed with clean feed can also help, though it requires careful tracking of hay and silage