An Overview of PFAS and Land-Applied Biosolids

PFAS is an abbreviation for a group of synthetic chemicals called per- and poly-fluoroalkyl substances. Thousands of chemicals are classified as PFAS, and many of them have been used globally since the 1940s. PFAS can resist heat, oil, stains, grease, and water. Because of their unique properties, PFAS are used in many products such as textiles, building and construction materials, electronics, automotives, aqueous film-forming firefighting foams, and many others. Some of the most common products that may contain PFAS include non-stick cookware, water and stain-repellent coatings, and food packaging. 

How can Biosolids Contain PFAS?

PFAS can enter the environment through wastewater discharges from manufacturing industries, normal wear and tear releases when PFAS-containing products are used by consumers, or when these products are disposed of. Since many consumer products contain PFAS, wastewater from our toilets, sinks, washing machines, dishwashers, and showers/bathtubs can contain different types and concentrations of PFAS that eventually end up at a wastewater treatment plant (WWTP). In urban areas, wastewater from homes is directly piped to central WWTPs. In rural areas, residents typically use on-lot septic systems to treat their domestic wastewater. Over time, septic tanks fill with solids and require pumping. Whenever tanks are pumped, these solids also end up at a WWTP for treatment. In addition to private residences, WWTPs may also receive wastewater containing PFAS from businesses and industries located within the communities they serve.

PFAS are just one of the many contaminants that can be in wastewater. At the WWTPs, wastewater is treated and cleaned using processes that separate the solids from the liquids, remove some dissolved chemicals, and kill pathogens. After treatment, this water (also known as effluent) is discharged into surface water sources (e.g., rivers and lakes) or is reused through irrigation on agricultural and forested sites. When discharged to lakes or rivers, effluent mixes with surface water and recharges groundwater aquifers when reused through irrigation. Eventually, treated wastewater effluent becomes part of the water cycle.

Solids separated from wastewater are called sludge. Sludge undergoes additional treatment, then it is stabilized and dried to further kill pathogens and reduce the smell. After this treatment, it is called biosolids. Sometimes, the terms sludge and biosolids are used interchangeably, but they're technically different materials. Sludge is the raw solids separated from wastewater during treatment that cannot be land-applied, while biosolids are treated sludge that meets safety standards for land application. You can learn more about methods for treating sewage sludge to produce biosolids from this Penn State Extension article What Is Sewage Sludge and What Can Be Done with It?.

WWTPs do not make or add PFAS as they treat wastewater or biosolids. However, PFAS have been detected in treated effluent and biosolids because they are not easily broken down during the treatment processes. The concentrations of PFAS in effluent and biosolids can vary from one WWTP to another, often reflecting PFAS use in industries, businesses, and domestic dwellings within the communities that each WWTP serves. In general, higher PFAS concentrations in effluent and biosolids have been found in WWTPs that service a high density of industries and businesses that either manufacture PFAS or use PFAS in their production processes.

How are Biosolids Disposed of?

The Pennsylvania Department of Environmental Protection (PA DEP) estimates that about 2.2 million tons of biosolids are generated annually (PA DEP Biosolids Program). This includes solid waste from septic systems and sludge from WWTPs. In the US, biosolids can be managed in three ways, these are:

1. land application, which is considered a beneficial reuse of nutrients including nitrogen (N), phosphorus (P), and organic matter in biosolids,
2. landfilling when reuse is not possible,
3. burning biosolids at high temperatures (also known as incineration), and the residual ash is landfilled.

As shown in the Table 1 below, each method of managing biosolids has its benefits, costs, and associated environmental implications.  You can learn more about general biosolids management options from this Penn State Extension article What Is Sewage Sludge and What Can Be Done with It?.

How Have Environmental Contaminants been Managed with Land Application of Biosolids?

National regulations for land application of biosolids were finalized by the US EPA  in 1993 (40 Code of Federal Regulations Part 503). State permitting bodies, such as PA DEP, adopted these rules. The regulation addresses pollutant limits, pathogen and vector attraction reduction requirements, land management practices, environmental monitoring, recordkeeping, and reporting. Maximum pollutant limits in land-applied biosolids were established for heavy metals, including arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc, as well as polychlorinated biphenyls (PCBs). Biosolids can be divided into Class A and B. Class A biosolids, also called exceptional quality (EQ), meet all pollutant limits for heavy metals and PCBs and are treated to a level where there are no detectable pathogens. They can therefore be used as fertilizer in agricultural fields, parks, or residential lawns and gardens. Class B biosolids must meet pollutant limits for all the heavy metals and PCBs, but may still contain some pathogens at low levels. They can only be applied in following the strict rules discussed below federal and state regulations. Biosolids that fail to meet Class A or B guidelines cannot be land applied and must be disposed of through either incineration or landfilling. Learn more from this Penn State Extension article: Use of Biosolids in Crop Production.

Permitted land applications of Class B biosolids are required to follow additional guidelines to protect water resources, animals, and humans, including specific setback distances enforced by. PA DEP. A setback distance is a minimum physical separation between a biosolids application site and an environmentally sensitive area such as a water source (PA Code Title 25 Chapter 275). These setback distances are summarized below in Table 2. Beyond this, biosolids applications are also prohibited on steep slopes and on land where the water table is less than 4 feet below the soil surface. All applications must also follow strict nutrient guidelines to avoid over-enriching the soil and waiting periods before harvesting crops, grazing animals, or allowing public access to the application site.

Although PFAS have been used since the 1940s, it was not until the early 2000s that scientists began studying their fate in the environment, wildlife, and humans, thanks to advancements in analytical tools and methods that allowed for accurate detection. PFAS are measured at very low concentrations in parts per billion or micrograms per liter (ppb or µg/L) and parts per trillion or nanograms per liter (ppt or ng/L). These levels are incredibly small. One ppb or µg/L equals just one drop of water in an Olympic-size swimming pool. One ppt or ng/L is a thousand times smaller and is comparable to one drop of water in one thousand Olympic-sized swimming pools.

Because PFAS were long assumed to be environmentally safe due to their incredible resistance to decay, and because tools to accurately detect them in wastewater and biosolids were not available until the early 2000s, they were not included in the EPA's 1993 biosolid regulations. As a result, people who generated PFAS-containing wastewater (i.e., households, businesses, industries, etc.), the facilities that treated this wastewater and biosolids (i.e., WWTPs), the farmers that accepted these biosolids, and the regulators that oversaw these entities were all operating with only the knowledge and rules available to them at the time. They were unaware of the environmental health risks that we have only recently started to understand surrounding PFAS in biosolids.

What Happens to PFAS on Farms?

PFAS may end up on farm fields by using biosolids with high concentrations of PFAS as fertilizer. Farmlands can also contain PFAS if fields are watered with PFAS-contaminated irrigation water, WWTP effluent, or if farms are located near potential PFAS sources such as industrial discharges, or sites such as airports, military bases, or firefighting training areas where PFAS-containing fire suppression foam was used.

Depending on the chemical properties of individual PFAS and soil characteristics, PFAS have different fates. Some PFAS are hydrophobic, meaning they do not dissolve easily in water and will tightly stick to soil particles and organic matter. Because hydrophobic PFAS don't move easily through the soil, they can build up in the soil over time. Eventually, it can contaminate groundwater and surface water sources through surface runoff or because of changes in soil and site conditions. Other PFAS are hydrophilic, meaning they mix easily with water and can move through the soil, increasing the risk of reaching groundwater and surface water sources. Planted crops may also take up different PFAS in soil or irrigation water. Farm animals can be exposed if they consume PFAS-contaminated water or feed, or if they graze on contaminated pastures. Human drinking water sources like wells or springs can also be polluted through leaching or surface runoff.

What Factors Influence the Occurrence of PFAS on the Farm?

Many farms with previous and current biosolids applications do not have a PFAS contamination issue. This is because the application of biosolids on a farm does not automatically mean that the farm resources are contaminated with PFAS. The impact on the farm is influenced by a wide variety of factors:

PFAS levels in the land-applied biosolids: While PFAS have been detected in many biosolids samples, not all biosolids have PFAS contamination levels that pose a threat to farms. Higher PFAS levels have been found in biosolids generated by WWTPs serving a high density of industries and businesses that either manufacture PFAS or use PFAS in their production processes. Because PFAS do not break down easily in the environment, when biosolids with high concentrations of PFAS are used to amend the soil, they persist for long periods of time, allowing them to be transported to soil, water resources, and be absorbed by planted crops.

Land application practices: Biosolids application rates refer to the quantity of biosolids applied to a field, measured in dry weight per acre. Biosolids application rates are typically based on the nutrient requirements of the crops being cultivated. Low-rate applications could pose a lesser risk in comparison to higher application rates of contaminated biosolids that can introduce more PFAS into the site.  

Soil properties: Soil properties can influence whether PFAS in land-applied biosolids leach to groundwater, accumulate in the soil column, or get absorbed by cultivated crops. Coarse-textured and well-drained sandy soils with low organic carbon contents provide minimal binding of PFAS. They can therefore allow PFAS to be transported easily through the soil column to groundwater or be washed off to surface water sources through surface runoff. On the other hand, soils with high organic carbon content and less water movement can trap PFAS in soil particles. This will reduce PFAS movement to groundwater and surface water resources but can also allow PFAS to accumulate in the soil and be absorbed by crops.

Site-specific conditions and farm practices: Other factors that can influence overall PFAS concern include groundwater flow directions, location of surface and groundwater supply sources relative to biosolids-amended sites, and how the amended sites are used, e.g., for animal grazing, and the types of crops cultivated.  

What Testing Options are Available?

Laboratory testing is the only way to know for sure if PFAS have contaminated water sources or soil. Testing is often needed to make informed on-farm management decisions, such as limiting biosolid applications, restricting animal grazing, or switching water sources. Table 3 below shows the current laboratories across Pennsylvania capable of testing for PFAS in water. Some can also test PFAS in soil, biosolids, and plant/animal products. PA DEP provides accreditation to all these laboratories for testing PFAS in water, but at the moment, there is no accreditation program for other biosolids, soils, or plant tissue.  

The US EPA has developed and validated different testing methods for PFAS in water, wastewater, soils, biosolids, and tissue samples. The two main methods for drinking water are US EPA Method 537.1, which measures 18 PFAS compounds, and Method 533, which measures 25. While Method 533 is more comprehensive, both methods have several PFAS compounds in common and include those that are the focus of state and federal drinking water regulations. Method 1633 measures 40 PFAS compounds in wastewater, surface water, groundwater, soil, biosolids, sediment, landfill leachate, and fish tissue. Laboratories use different testing methods depending on their accreditation, analytical capabilities, and the type of sample to be tested. Many laboratories provide sampling kits containing bottles and detailed method-specific instructions for collecting, handling, and shipping samples. Learn more about the different EPA PFAS testing methods at PFAS Analytical Methods Development and Sampling Research.

*For an up-to-date list of PA DEP-certified laboratories for PFAS testing in water, please visit the PA DEP Laboratory Certification Tool.

Testing for PFAS can cost around $250 to $500 per sample, depending on the type of sample (e.g., soil, water, tissue). Given how costly it can be to test, prioritizing sampling by starting with a 'screening evaluation' of areas with the most concern, for example, private wells or springs used for human drinking water supply, or soils in fields where biosolids were applied, makes sense as a starting point. Additional sampling needs can then be determined after screening results are reviewed.

Some state or federal programs offer financial assistance for farmers who need to test their soil or water. Current programs include:

• Conservation Evaluation and Monitoring Activity - PFAS Testing in Water or Soil - USDA’s Natural Resources Conservation Service (NRCS) offers financial assistance for sample collection and laboratory analysis to provide information to producers to determine if PFAS might be present in soil or water on their agricultural operation. This prescreening testing uses EPA-approved or state-approved field sampling and laboratory methods and is part of what NRCS calls a Conservation Evaluation and Monitoring Activity (CEMA). To learn more about PFAS testing options available through NRCS, contact your local USDA Service Center. Find Your Local USDA Service Center

What Do the Numbers Mean?

When test results for an individual PFAS compound show "non-detect" or "not detected" (ND), it indicates the chemical is either not present in the sample or present at a level too low for the laboratory to detect using current technology and methods.  Test results may also show "method reporting limit" (MRL) or "reporting limit" (RL). This indicates PFAS were detected but at levels that were too low to be accurately quantified with the methodology used. Because of their extensive use for a very long time,  PFAS are now commonly found at low levels in soil, groundwater, and surface water sources, often called background levels.

Although safe thresholds have not yet been established for some PFAS compounds in water, soil, or farm produce, testing for these PFAS can still provide useful information when the results are compared to the growing list of PFAS compounds that do have current regulations, guidelines, and advisories. For example, in 2024, the US EPA established Maximum Contaminant Levels (MCLs) or national drinking water standards for six PFAS chemicals in public drinking water (Table 4). While private water systems, including those on farms, are not covered by these regulations, these MCLs can be used as a reference for safe levels for PFAS in private drinking water supplies. And while there are no current US Food and Drug Administration (FDA) standards for PFAS in food products, the state of Maine recently created action levels for the PFAS compound Perfluorooctane sulfonic acid (PFOS) in milk and beef. The action levels are not legally enforceable but can be used as guidance to help farmers and the public determine if an animal product contains potentially unsafe levels of PFOS.

What Happens if Elevated Levels of PFAS are Detected?

Finding out that there are elevated levels of PFAS in water, soil, or farm produce can be challenging news, especially because management options on farms are not well established. Table 5 below summarizes some actions that farmers and others can take depending on the areas of concern.

The following state and federal programs may provide guidance and support for impacted sites:

• Dairy Indemnity Payment Program - Dairy producers are now eligible to receive a payment for the loss of dairy cows because of contamination, including PFAS contamination. USDA’s Farm Service Agency (FSA) has updated the Dairy Indemnity Payment Program (DIPP) to address permanent milk contaminations. To learn more or to participate in DIPP, contact your local USDA Service Center. Find Your Local USDA Service Center

What are Regulatory Bodies Doing Right Now?

State governments and the US EPA are taking various measures to address the concerns surrounding PFAS in land-applied biosolids. In January 2025, the US EPA released a draft sewage sludge risk assessment for perfluorooctanoic Acid (PFOA) and perfluorooctane Sulfonic Acid (PFOS). The risk assessment indicated that biosolids containing PFOA and PFOS can result in levels in water above US EPA thresholds under some scenarios. This draft risk assessment is not legally enforceable, but will inform potential future regulations and is currently available for public commentary until August 14^th, 2025.

Because of the lack of federal limits for PFAS in biosolids, several states have taken action to address contamination issues and public concerns (Table 6). These actions can take the form of non-enforceable guidelines or recommendations known as advisories. While advisories are not enforceable, they provide information to different stakeholders on how to handle biosolids with PFAS. In other states, enforceable regulatory limits for PFOA and PFOS in land-applied biosolids have been developed. Finally, some states have implemented a regulatory ban that prohibits or restricts land application of biosolids within their jurisdictions. There are currently no advisories or regulatory limits for PFAS in biosolids in Pennsylvania.

What Can WWTPs Do?

Through the National Pretreatment Program, WWTPs are encouraged to collect samples throughout their service areas and identify industrial users that are emitting high concentrations of PFAS to the plant. Identified users can then work with the WWTP to establish a monitoring and pretreatment plan for their wastewater in order to lower the levels that end up at the WWTP. Learn more about this at the US EPA National Pretreatment Program and this Memo.  

How Can You Tell if Your Farm Received Biosolids?

PA DEP permits and keeps records for all legal biosolids applications. To learn if biosolids were applied on your farm, look through existing farm records or contact your regional PA DEP biosolids coordinator