The U.S. EPA has released a draft risk assessment, or scientific evaluation of the potential human health risks associated with the presence of toxic per- and polyfluoroalkyl substances (PFAS) chemicals in biosolids, also known as sewage sludge. The findings for the draft risk assessment show that there may be human health risks associated with exposure to the 鈥渇orever chemicals鈥� PFOA or PFOS with all three methods of using or disposing of sewage sludge 鈥� land application of biosolids, surface disposal in landfills, or incineration. Once finalized, the assessment will help EPA and its partners understand the public health impact of forever chemicals in biosolids and inform any potential future actions to help reduce the risk of exposure.
Defining Biosolids
Wastewater produced by households and businesses, and sometimes industrial dischargers, is conveyed to a wastewater treatment plant, and ultimately treated. These treatment processes also produce a semi-solid, nutrient-rich product known as 鈥渟ewage sludge鈥� or 鈥渂iosolids.鈥� EPA typically uses the term 鈥渂iosolids鈥� to mean sewage sludge that has been treated to meet regulatory standards and is thereby suitable to be land applied as a soil conditioner or fertilizer. In turn, biosolids can be beneficially reused as land applied fertilizer on agricultural fields or on nonagricultural lands to promote plant health and productivity.
Draft Risk Assessment
This draft risk assessment focuses on a specific and narrow population of people that EPA considers most likely to be exposed to PFOA or PFOS from the land application of biosolids or through consumption of products from land where biosolids were used as fertilizer. The draft risk assessment scientifically models hypothetical human health risks for people living on or near sites impacted by PFOA or PFOS or for people relying primarily on those sites鈥� 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鈥檚 acceptable thresholds, sometimes by several orders of magnitude, for some scenarios where the 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鈥檚 acceptable thresholds in some scenarios where biosolids containing 1 ppb of PFOA or PFOS are placed in an unlined or clay-lined surface disposal unit. Once finalized, EPA will use the risk assessment to help inform future risk management actions for PFOA and PFOS in sewage sludge. For the incineration scenario, risk is not quantified due to significant data gaps.
EPA鈥檚 analysis does not suggest that the general food supply is impacted by the use of biosolids that contain PFOA or PFOS. The U.S. Department of Agriculture and Food and Drug Administration are monitoring for PFAS in the food supply broadly and have taken protective actions to address impacted products from domestic and imported sources. Based on the best available data, biosolids account for less than one percent of the fertilized acreage of productive agricultural land in the United States per year. EPA recognizes that certain 鈥渉ot spots鈥� and specific farming operations may have higher levels of PFOA or PFOS if contaminated sludge was applied, and that further collaboration with impacted operations and other federal agencies will be important to fully understand risks and support impacted farmers.
EPA鈥檚 analysis finds that the risks of exposure to PFOA and PFOS through biosolids increases proportionally with the amount of those chemicals in the biosolids. This means that if you lower the concentration of PFOA or PFOS in biosolids or the amount of biosolids applied to agricultural land, you lower the risk. The actual risks from exposure to PFOA or PFOS will vary at farms that land-apply biosolids or at biosolids disposal sites based on the amount of PFOA or PFOS applied, as well as geography, climate, soil conditions, the types of crops grown and their nutrient needs and other factors. Where smaller amounts of PFAS-contaminated biosolids have been spread, or fewer applications have been made over time, or lower concentrations of PFOA and PFOS were in the biosolids, the risk will be reduced.
The findings of the draft risk assessment underscore the importance of proactive federal and state policies to control and remove PFAS at their source. Under EPA鈥檚 PFAS Strategic Roadmap, the agency has provided tools to restrict PFAS from entering the environment and to hold polluters accountable, including increasing reviews of new PFAS before they enter commerce and encouraging states to use their Clean Water Act permitting authorities and industrial pretreatment programs to require industrial dischargers of PFAS to remove them before sending their effluent to the environment or to wastewater treatment plants. Moving forward, EPA is working to set technology-based limits on discharges from several industrial categories鈥攊ncluding PFAS manufacturers, electro- and chrome-platers and landfills鈥攗nder the agency鈥檚 Effluent Limitations Guidelines program.
Forever Chemicals in Wastewater
PFOA and PFOS get into sewage sludge via the wastewater that enters municipal wastewater treatment plants (WWTPs), which do not intentionally use or add these substances in their treatment processes. WWTPs may receive PFOA or PFOS from manufacturers and other facilities that currently use, or historically have used, these PFAS and release contaminated wastewater to WWTPs. Households and businesses can also be sources, as PFAS from consumer products (e.g., cookware, clothing or cosmetics that may contain certain PFAS) are washed down drains and make their way to a WWTP.
EPA and State Actions on Forever Chemicals
Under EPA鈥檚 PFAS Strategic Roadmap, the agency has made historic progress in advancing the science and establishing standards to protect communities from PFAS pollution. These actions include finalizing the nation鈥檚 first drinking water standards for PFAS, holding polluters accountable to clean up PFAS across the country and declaring PFOA and PFOS hazardous substances under the Superfund law. By releasing this draft risk assessment, EPA is providing stakeholders with a rigorous, data and science-driven report that, once finalized it may help the agency determine whether regulating PFOA and PFOS in sewage sludge under the Clean Water Act is appropriate.
Several states have begun monitoring for PFAS in sewage sludge and published reports and data that are publicly available. EPA鈥檚 draft risk assessment document provides an overview of PFOA and PFOS occurrence data from peer-reviewed literature and state reports in Section 2.4 and Appendix A. Some states continue to collect additional sewage sludge PFAS monitoring data.