January 21, 2025
On January 15, the U.S. Environmental Protection Agency (EPA) published a risk assessment for sewage sludge contaminated with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), two in a class of thousands of chemicals called per- and polyfluoroalkyl substances (PFAS). The risk assessment is the result of EPA’s application of the latest science to understand potential human health and environmental risks from PFOA and PFOS in sewage sludge that is land applied for use as a soil conditioner or fertilizer, surface disposed, or incinerated. The assessment looks at risk to those living on or near, or relying primarily on (e.g., consuming agricultural products from) sewage sludge sites.
EPA completed this assessment pursuant to its authority under Clean Water Act section 405 (33 U.S.C. 1345), which provides for EPA’s periodic review of its regulations regarding toxic pollutants in sewage sludge, the performance of scientific studies, and provision of information to the public on how to safely use or manage sewage sludge. The Agency developed the present risk assessment to evaluate risk of harm to human health or the environment and consider whether future regulation would serve to protect against such harms from exposure through sewage sludge use or disposal.
Sewage sludge is the product of separating liquids from solids in domestic sewage, which is also sometimes combined with industrial wastewater. Biosolids, a term often used synonymously with sewage sludge, is sewage sludge treated to meet the standards EPA has established in the regulation “Standards for the Use or Disposal of Sewage Sludge” (40 CFR part 503). Sewage sludge is generally addressed in one of three ways: 1) about 56% is land applied as a soil conditioner or fertilizer, 2) about 27% is disposed of in a monofill or municipal solid waste landfill, and 3) about 16% is incinerated. The draft risk assessment evaluates the potential for risk to human health from exposure to PFOA and PFOS from sewage sludge falling under the first and third categories of use/disposal.
Under the exposure scenarios applied (e.g., assumptions regarding the quantity of product a person consumes from a land-applied farm) in the risk assessment, EPA found that risk estimates are above the Agency’s acceptable human health risk thresholds for land-applied sewage sludge containing 1 part per billion of PFOA or PFOS. EPA also identified human health risks associated with drinking from groundwater wells contaminated from nearby sewage sludge that has been disposed of in an unlined or clay-lined surface disposal site. The risk assessment also includes a qualitative assessment of risk for those living near sewage sludge incinerators.
Public comments on the assessment are due March 17, 2025. EPA will consider comments and prepare a final risk assessment, which will be announced in the Federal Register.