Five takeaways from the EPA's draft sewage sludge risk assessment for PFOA and PFOS

The U.S. Environmental Protection Agency (EPA) released its Draft Sewage Sludge Risk Assessment on January 14, 2025, for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS).

The draft risk assessment indicates that in some scenarios, the EPA’s acceptable risk threshold may be exceeded when sewage sludge containing PFOA and PFOS is land applied for beneficial reuse or surface disposed.

The draft risk assessment focuses on people living on or near impacted farms or those that rely primarily on their products.

The EPA also released a fact sheet, which includes some of the questions and answers listed below.

What are sewage sludge and biosolids?

The EPA defines sewage sludge as the liquids that are separated from the solids in the wastewater treatment process.

Biosolids are sewage sludge that is intended to be applied to land as a soil conditioner or fertilizer.

What are PFOA and PFOS?

According to the EPA, PFOA and PFOS are two chemicals in a larger class of synthetic chemicals called per- and polyfluoroalkyl substances (PFAS).

PFOA and PFOS can persist in the environment for long periods of time. The chemicals have been linked to a variety of adverse human health effects.

PFAS manufactures voluntarily phased out domestic manufacturing of PFOA and PFOS and the EPA restricted their use by Significant New Use Rules (SNURs) issued under the Toxic Substances Control Act (TSCA).

1. Why is the EPA concerned about the presence of the chemicals in sewage sludge?

According to an EPA fact sheet, multiple activities still result in PFOA, PFOS and their precursors being released to WWTPs.

Traditional treatment technology does not remove or destroy the two compounds, and the chemicals typically accumulate in sewage sludge.

The chemicals can move from soils to groundwater or nearby waterbodies and be taken up into fish, plants and livestock.

The EPA is concerned about these chemicals in sewage sludge because these factors raise questions about the potential risks associated with the presence of PFOA and PFOS in sewage sludge that is being land applied, surface disposed or incinerated.

2. What are the potential sources of PFOA and PFOS in sewage sludge?

According to the EPA, potential sources of the chemicals include:

• Industrial releases (firefighting foams, pulp and paper plants)
• Commercial releases (car washes, industrial launderers)
Down-the -drain releases from homes (consumer products containing PFOA or PFOS)

3. What is the risk assessment?

The EPA describes the risk assessment as a “scientific process that is used to understand health risks to people, livestock, or wildlife across the country.”

The risk assessment allows the agency to determine if further regulatory action is required to protect those who may experience risks from sewage sludge or disposal.

However, this risk assessment doesn’t assess risks to the general population.

4. What does this risk assessment suggest?

This draft sewage sludge risk assessment focuses on those living on or near impacted sites, or those that rely primarily on their products.

The EPA states that “there may be human health risks exceeding the EPA’s acceptable thresholds for some modeled scenarios when land applying sewage sludge that contains 1 part per billion (ppb) of PFOA or PFOS. The EPA also finds that there may be human health risks associated with drinking contaminated groundwater sourced near a surface disposal site when sewage sludge containing 1 ppb of PFOA or sewage sludge containing 4 to 5 ppb of PFOS is disposed in an unlined or clay-lined surface disposal unit.”

5. What is the EPA doing to reduce exposure?

According to the EPA, “the potential risks posed by PFOA, PFOS and other PFAS demand that the EPA address the problem on many fronts using all applicable statutory authorities.”

The EPA has yet to take any direct regulatory actions on PFOA and PFOS in sewage sludge but continues to fund research and take actions to reduce the chemicals discharged to WWTPs.

Some actions the EPA is taking include:

• Restricting PFAS discharges to WWTPs using effluent limitation guidelines
• Track releases through Toxics Release Inventory (TRI) reporting
• Updating the interim guidance on the destruction and disposal of PFAS and materials containing PFAS