Per- and polyfluoroalkyl substances, widely known as PFAS, represent a group of synthetic chemicals manufactured and used across various industries and consumer products since the 1940s. These substances are notable for their strong carbon-fluorine bonds, which contribute to their resistance to heat, water, and oil, earning them the moniker “forever chemicals” due to their environmental persistence. Biosolids are a nutrient-rich organic material derived from treated sewage sludge, a byproduct of wastewater treatment processes. The increasing detection of PFAS within these biosolids has become a growing concern, raising questions about potential environmental and public health ramifications.
How PFAS Enter Biosolids
PFAS chemicals primarily enter wastewater treatment plants through various pathways associated with their widespread use. Industrial discharges from manufacturing facilities, particularly those producing or utilizing PFAS, contribute significantly to this influx. Consumer products also play a large role; items such as non-stick cookware, stain-resistant fabrics, certain fire-fighting foams, and personal care products release PFAS when washed down drains. Stormwater runoff also carries PFAS from a multitude of sources, including contaminated sites and consumer product residues, eventually making its way into wastewater systems.
Once in wastewater treatment plants, their unique chemical structure challenges conventional treatment processes. PFAS are highly stable and do not readily break down, making them difficult to remove with typical wastewater treatment methods. Instead, these compounds accumulate and concentrate within the solid residual material separated during treatment. This solid material, once treated to meet regulatory standards, becomes biosolids, carrying concentrated PFAS.
Potential Harms from PFAS in Biosolids
Land application of PFAS-contaminated biosolids introduces environmental and health risks. PFAS can leach from the soil into groundwater and surface water, potentially contaminating drinking water sources. Their persistence and mobility allow them to move through the environment.
Plants can absorb PFAS from the soil where biosolids have been applied, leading to accumulation in crops. This uptake facilitates PFAS entry into the food chain, affecting both livestock that graze on contaminated land and humans who consume contaminated produce or animal products. Studies document PFAS levels in foods like milk and vegetables linked to sewage and paper mill sludge application.
Human exposure to PFAS from biosolids can occur through consuming contaminated food or water, or direct contact with treated soil. Exposure to PFAS has been associated with health concerns, as indicated by the EPA’s draft risk assessment for common PFAS compounds like PFOA and PFOS. Concerns include effects on the immune system, liver function, reproductive health, and potential links to cancers like kidney, prostate, and testicular cancer.
Addressing PFAS in Biosolids
Managing PFAS in biosolids involves regulatory actions, technological advancements, and alternative strategies. Federal and state regulatory bodies are developing responses to monitor and address PFAS contamination. The U.S. Environmental Protection Agency (EPA) has initiated a PFAS Strategic Roadmap to research, restrict, and remediate PFAS in the environment, including biosolids. Some states, like Maine, have limited or banned land application of PFAS-contaminated biosolids, while others, such as Michigan and Massachusetts, require monitoring of PFAS in biosolids.
Research is ongoing for technologies to remove or destroy PFAS from wastewater before it becomes biosolids, or from the biosolids themselves. Advanced oxidation processes and thermal destruction methods, such as incineration and gasification, are being investigated to break down PFAS’s stable carbon-fluorine bonds. Thermal destruction requires high temperatures and further research to understand potential volatile fluorine releases and incomplete destruction. Adsorption techniques are also being explored to capture PFAS compounds.
Alternative management strategies for biosolids are being considered to minimize PFAS release. Secure landfilling is an option for biosolids too contaminated for reuse, though leachate contamination may require further treatment. Broader efforts also focus on reducing PFAS at their source through product reformulation and stricter industrial discharge limits, considered the most cost-effective solution. These upstream controls aim to prevent PFAS from entering the wastewater stream, reducing their presence in biosolids.