On January 23, Bloom hosted a webinar, “Emerging Research on the Fate, Transport, and Plant Uptake of PFAS in Biosolids,” bringing together leading experts and researchers in water resource recovery, environmental microbiology, and soil chemistry. With more than 500 registrants, the event reflected growing interest and concern around PFAS (per- and polyfluoroalkyl substances) in the environment, particularly in biosolids land application. The webinar featured presentations from Chris Peot, Director of Resource Recovery at DC Water; Dr. Ian Pepper, Regents Professor at the University of Arizona; and Dr. Linda Lee, Distinguished Professor at Purdue University. If you missed it, you can watch it on our YouTube page.

Biosolids, Bloom, and Background PFAS Levels

Chris Peot opened the webinar with an overview of Bloom, DC Water’s Class A Exceptional Quality biosolids product produced at the Blue Plains Advanced Wastewater Treatment Plant. Using thermal hydrolysis followed by anaerobic digestion, the process eliminates pathogens, generates renewable energy, and produces a stable, low-odor soil amendment rich in organic matter and nutrients.

Peot emphasized a key distinction that framed the discussion: municipal biosolids versus industrially impacted biosolids. At Blue Plains, approximately 97% of wastewater inputs are residential or commercial, resulting in PFAS concentrations that reflect societal background levels, similar to those found in rainfall and even human blood serum.

Using Maryland precipitation data, Peot showed that PFAS concentrations in Bloom biosolids translate to annual agronomic rates per acre that are comparable to what farms receive from rainfall alone. Studies from New York and elsewhere also show that “undisturbed” soils not  treated with biosolids often contain PFAS in the same low parts per billion (ppb) range, likely from atmospheric deposition. 

The National Collaborative PFAS Study

Dr. Ian Pepper presented findings from the National Collaborative PFAS Study, one of the most comprehensive field investigations of PFAS in land-applied biosolids to date. The study includes 23 long-term land application sites across 17 states, spanning diverse climates, soil types, and histories of biosolids use dating back to the 1980s.

The study focused on indirect exposure pathways, primarily leaching from soil to groundwater, and uptake into crops grown on biosolids-amended soils.

At each site, researchers collected 27 soil samples—including control plots and low- and high-application plots—at depths of 0–1 ft, ~3 ft, and ~6 ft. All samples were analyzed at the University of Arizona using EPA Method 1633, ensuring consistent methodology nationwide.

Key findings from Phase 1 include:

  • Median PFAS concentrations in surface soils were below 1 ppb for all analytes measured.
  • Significant attenuation with depth: on average, 50% attenuation by 3 feet and 72% attenuation by 6 feet, demonstrating soil’s protective role for groundwater.
  • PFOS was the dominant PFAS by mass, while PFOA was the most frequently detected, patterns consistent with historical use.
  • Control soils often contained measurable PFAS, underscoring the role of non-biosolids sources such as atmospheric deposition.

Importantly, about 80% of samples met Michigan’s PFAS screening criteria. The few exceptions were linked to landfill leachate inputs, highlighting the importance of source control and industrial pretreatment.

Dr. Pepper emphasized that the study focuses on municipal biosolids, not paper mill sludges or other industrial residuals associated with documented PFAS contamination events.

PFAS Chemistry, Legacy Contamination, and Crop Uptake

Dr. Linda Lee provided a deeper look at PFAS chemistry and behavior in soils, water, and plants. She explained the differences between short-chain PFAS, which are more mobile but less bioaccumulative, and long-chain PFAS such as PFOS and PFOA, which persist in soils and biomagnify in food webs.

Across multiple long-term field sites, Dr. Lee showed that:

  • Legacy PFAS dominate soil profiles, even years after biosolids application has ceased.
  • Newer biosolids contain far fewer long-chain PFAS, with signatures increasingly dominated by short-chain compounds and precursors.
  • Groundwater monitoring wells at most sites showed PFAS concentrations below EPA drinking water limits, with occasional exceedances typically linked to off-site sources such as contaminated surface waters or historic industrial activity.

Dr. Lee also presented emerging findings on plant uptake. In both field and greenhouse studies:

  • PFOS and PFOA showed very limited transfer into edible crop portions, including corn grain and soybean beans—even in highly contaminated soils.
  • Uptake was largely confined to short-chain PFAS, which are less bioaccumulative.
  • Crop selection matters: certain crops can be grown without major bioaccumulation even on legacy-impacted soils.
  • Soil amendments such as biochar or wood ash showed potential, albeit variable, reductions in PFAS uptake, with effectiveness influenced by weather and soil moisture.

Dr. Lee concluded that management strategies should focus on legacy contamination, runoff control, and informed crop choices.

In conclusion, speakers emphasized that current evidence does not support municipal biosolids as a major PFAS exposure pathway when properly managed. Instead, the science points to:

  • The importance of source control, especially landfill leachate and industrial inputs
  • The protective role of soils in limiting PFAS mobility
  • The need for risk-based regulation, not one-size-fits-all bans
  • Continued research, particularly on crop uptake and long-term fate