According to a recently published draft risk assessment from the Environmental Protection Agency (EPA), there may be an elevated risk of exposure to per- and polyfluoroalkyl substances (PFAS) through food grown on land where contaminated biosolids are heavily used as fertilizers. Although EPA’s analysis does not suggest that the general food supply is impacted by the use of biosolids, the agency recognizes that certain “hot spots” and specific farming operations may have higher PFAS levels if contaminated biosolids were applied, and that it is important to do further research to better understand the associated risks.

Biosolids, also known as “sewage sludge,” are a semi-solid, nutrient-rich product resulting from wastewater treatment processing. EPA typically uses the term “biosolids” to refer to sewage sludge that has been treated to meet regulatory standards and is suitable to be applied to land as a soil conditioner or fertilizer. Biosolids are sometimes applied to agricultural fields or on nonagricultural lands to promote plant health and productivity.

EPA’s latest draft risk assessment focuses on a specific, narrow population of people that are most likely to be exposed to two PFAS of concern—perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)—from the land application of biosolids or through consumption of products from land where biosolids were used as fertilizer. The risk assessment modeled hypothetical health risks for those living on or near sites impacted by PFOA or PFOS, or for people relying primarily on those sites’ products (e.g., food crops, animal products, or drinking water).

The preliminary findings of the draft risk assessment indicate that there can be human health risks exceeding EPA’s acceptable thresholds, sometimes by several orders of magnitude, for some scenarios in which a farmer applied biosolids containing 1 part per billion (ppb) of PFOA or PFOS (which is near the current detection limit for these PFAS in biosolids). These modeled scenarios include farms with one application of biosolids at a rate of 10 dry-metric-tons per hectare and 40 consecutive years of biosolids land application at this same rate. The modeling in this assessment also finds human health risks exceeding the EPA’s acceptable thresholds in some scenarios where biosolids containing 1 ppb of the chemicals are placed in an unlined or clay-lined surface disposal unit.

However, biosolids only account for less than one percent of the fertilized acreage of productive agricultural land in the U.S. per year, meaning the draft risk assessment does not apply to the general food supply or population.

Once finalized, EPA will use the risk assessment to help inform future risk management actions for PFOA and PFOS in sewage sludge. The draft risk assessment will be available for public comment until March 17, 2025.