A recent Bloom presentation featuring Zachary Borrenpohl, P.E., program manager and civil engineer at DC Water, examined the evolving regulation and science surrounding PFAS in biosolids. One central theme was that biosolids should not be treated as a single category when evaluating PFAS risk: concentration, source characteristics, individual PFAS compounds, and environmental fate all matter.
Below is a summary of the webinar. You can also watch the full presentation.
PFAS are a broader source-control problem
PFAS are a large family of persistent, fluorinated chemicals historically used in products ranging from food packaging and stain-resistant materials to cosmetics and firefighting foams. Because of their widespread use and persistence, PFAS can now be detected in soil, water, air and rainfall, including locations without an obvious point source.
That distinction is important for end users. Wastewater treatment plants receive PFAS rather than manufacture or intentionally add it. At DC Water’s Blue Plains facility, a 2022 industrial-user study conducted with Purdue University found that approximately 97% of sewage originated from residential and commercial sources. Industrial discharges accounted for only about 0.5% of the PFOA/PFOS loading examined, suggesting that PFAS entering this particular system is overwhelmingly diffuse and come from residential sources rather than attributable to a major industrial point source.
This leads to one of the presentation’s most consequential policy conclusions: upstream source reduction is ultimately the most important action to solve PFAS exposure to humans and stop these highly persistent compounds from entering the sewer system. DC Water cited product-focused restrictions, including Minnesota’s approach, as a model for addressing PFAS closer to its original source.
Municipal and industrially impacted biosolids can have very different PFAS profiles
Zach contrasted predominantly residential/commercial wastewater systems with facilities receiving significant PFAS-bearing industrial waste. Some highly publicized agricultural contamination cases have involved extensive industrial residuals being land applied that resulted in much higher PFAS concentrations in soils. Circumstances like these cases and their effects on soils should not be extrapolated to land-applied municipal biosolids with substantially lower concentrations.
One comparison presented illustrates the potential magnitude of that difference. A heavily affected Maine farm was reported as having soil PFOS concentrations of approximately 390 ppb. By contrast, a University of Arizona study involving Bloom reportedly measured 0.44 ppb PFOS in soil following biosolids application. These figures represent different sites and circumstances and therefore should not be interpreted as a controlled head-to-head comparison, but they illustrate why source history and measured concentration are critical variables in evaluating agricultural risk.
States like Maryland and Virginia are moving toward concentration-based regulation
Recent Maryland and Virginia legislation establishes concentration-based requirements for PFOA and PFOS in biosolids. Rather than prohibiting agricultural biosolids as a category, the frameworks distinguish among materials according to measured concentrations and impose increasingly restrictive requirements as concentrations rise. Compliance is based on recurring testing and rolling 12-month averages.
Bloom’s measured PFOA/PFOS concentrations
DC Water reported a rolling 12-month average of 13.4 ppb for PFOA and PFOS in Fresh Bloom, covering September 2025 through August 2026. Samples are analyzed monthly by a third-party laboratory. That places DC Water’s Bloom biosolids below the applicable Tier 1 benchmark concentration discussed for unrestricted land application.
In the Q&A, Zach stated again that the 13.4-ppb figure applies to the biosolids themselves rather than Bloom’s blended products. Woody Blend and Sandy Blend generally contain less than half that concentration, in part because the biosolids are blended with materials such as wood fines and sand.
Research is increasingly focused on what happens after land application
Researchers are also seeking to better understand soil accumulation, vertical transport, crop uptake, loading rates, soil characteristics, irrigation and repeated applications.
Zach highlighted ongoing University of Arizona work examining municipal biosolids across different soils, climates, irrigation regimes and application histories. According to the webinar, research to date has found very low PFAS concentrations in surface soils with historical municipal-biosolids applications, with median concentrations often below 1 ppb, as well as decreasing concentrations with soil depth. A subsequent phase is examining crop uptake.
DC Water is also participating in research with WSSC, Virginia Tech and the Water Research Foundation examining PFAS fate and transport following application of locally produced biosolids to fields with no previous biosolids history. Additional work is investigating whether relatively concentrated internal wastewater recycle streams could provide practical intervention points for PFAS treatment or destruction.
Analytical scope remains an important issue
Although regulation currently focuses heavily on PFOA and PFOS because of their extensive use as well as toxicological and environmental datasets, PFAS encompasses thousands of compounds. However, PFOA and PFOS are by far the most common PFAS found in the environment due to widespread use in numerous products over many decades.
DC Water reported using EPA Method 1633A to analyze a broader suite of PFAS compounds and said many other analytes in its biosolids are present at very low concentrations or are nondetects. The utility also reported conducting broader PFAS testing since 2019 and using additional approaches—including total oxidizable precursor (TOP) analysis and total organic fluorine—in source-characterization work.
