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Sally Brown

Marriage and PFAS have a lot in common. The most obvious is that “forever” aspect.  Your wedding vows traditionally include phrases like “until death do us part.” While PFAS technically stands for per- and polyfluoroalkyl substances, they are much more commonly known as “forever chemicals.” Because of a combination of historic cases of contamination and the media, it has seemed as though biosolids and PFAS are pledged in matrimony. Read much of the coverage on these chemicals and you will start to believe that exposure via biosolids is a primary exposure pathway for people everywhere. While composts haven’t been hit quite as hard, it is the rare pile that is completely PFAS free.

If you want an example, take that write up from a few years back in the New York Times or rather the column that I wrote about it. If that doesn’t convince you, take a look at the first draft of the EPA risk assessment, or rather the column that I wrote about it.

But the thing is that a very high percentage of marriages are not till death do us part.  What can seem like a perfect union on the surface often has tons of cracks.  These unions are perfect only until these cracks start to surface and can fracture when the divorce is finalized.

The same may be the case with PFAS and organics. I realize that it may not seem like it right now but let me explain.  Remember as you read that it is always darkest just before dawn. Let’s start with the New York Times.  Not the science writer who has been crying wolf but the sustainability editor from the Wirecutter section. This is the  section that was recommending PFAS-laden cookware, cosmetics and rain gear at the same time that the science editor was forecasting doom and destruction as a result of PFAS in wastewater.  Here in my inbox is an article saying that the editor is now feeling ‘“optimistic” about PFAS. It includes recommendations for PFAS-free items for cookware, cosmetics and rain gear.

Decline in PFAS Exposure

These recommendations are possible because of a decline in the number of products that contain PFAS, partly due to consumer demand and partly due to regulatory requirements. In fact, likely due to phasing out of both PFOA and PFOS, enacted about 20 years ago, our body burden of these chemicals is on the decline (Kudzin et al., 2026).  This study found that blood PFOA declined by 89.6%, PFOS by 85% and PFHxs by 87.7% over a 20 year period.  The authors also found that blood concentrations of next generation compounds, including things like PFDA and PFNA, increased relative to their brethren, but on the whole are reasons for optimism. Perhaps, like many old flames, the relationship between people and PFAS (why it is in biosolids and organics in the first place) is fading into the sunset.

The peer review literature is also suggesting that biosolids and composts are not typically industrial sources of the stuff but generally have only as much PFAS as we do.  We can start with a paper from Chris Higgins.  Dr. Higgins was one of the first to send the wedding announcements about biosolids and PFAS (Blaine et al., 2013).  In a recent publication he estimates the quantity of PFAS from different sources and in different atmospheric pools (Adamson et al., 2026).  For this he uses relatively high average biosolids concentrations (2.5-110 ppb PFOS and 3-66.7 ppb PFOA).  Even with those high concentrations, the biosolids are estimated to contribute about 10x less PFOS (71 kg) annually than rainwater (740 kg).

You can read another column about that research. The paper notes that the reservoir of PFAS in surface waters and soils are almost 10,000 and 100,000 greater than what comes through all water reclamation facilities. Another thing to consider with the estimates used here is that PFOS in Michigan biosolids — before they started industrial pretreatment — was 40 ± 15 ppb with a median value of 10 ppb.  That low median value means that a few industrially contaminated materials were driving up the mean concentration. Just look at the column about the effectiveness of pretreatment to see what I mean. With the pretreatment, it is significantly lower. Apply that lower value to the estimates used in Adamson et al and you see an even smaller impact of biosolids in the PFAS picture.

Image courtesy of Sally Brown.

A recent national survey proves the point. The survey looked at long and short term biosolids sites across 16 states (Pepper et al., 2026).  The median PFOS concentration was 0.52 ppb in the soils that had received high rates of biosolids. The median PFOS in the control soils measured 0.1 ppb.  In contrast, the soil at the Stoneridge Farm in Maine measured up to 878 ppb. (The Stoneridge Farm contamination brought to light PFAS contamination on farms in Maine.) Also, thankfully, the historic case in Maine is seemingly more and more like the exception rather than the rule.

The recent survey also found that the longer chain PFAS tend to stay put.  Movement through the soil was limited with 92% of the PFOS (and 69% of all measured PFAS) staying above 6 feet (180 cm). This data suggests that the pairing of PFAS and biosolids in Maine was a very special relationship (a perfect marriage) — far from what is generally seen.

Are Biosolids and PFAS United?

Even if you go to Maine, where many of the marriage rumors originated, it is far from clear that biosolids and PFAS are united and the source of exposure for the vast majority of people. Recall here that much of the panic about PFAS stemmed from multiple farms in Maine where contaminated biosolids and pulp sludge had been added to soils resulting in concentrations in soil and groundwater high enough to truly qualify as terrifying. A new study out of Maine looked at what factors in a biosolids-impacted community were responsible for increases in blood lead (Pb). The researchers went to an area where contaminated biosolids had been applied and did some couples counseling (aka taking blood samples and asking questions (Rokoff et al., 2026).  They found that contaminated drinking water was a big factor in blood PFAS concentration, explaining as much as 24.5% of the PFOS concentrations and 40% of the PFOA concentrations in residents’ blood samples.

After water though, things get muddy.  Working with biosolids explained 0.6% of the PFOA concentrations and 3.1% of the PFOS concentrations.  In comparison, sex post-menopause explained 2.4% and 3.7% of PFOA and PFOS.  If groundwater is not an issue (as suggested by the Pepper et al. study), then it appears that the relationship between PFAS, biosolids and human exposure is distant at best.

EPA has also had second thoughts about the marriage between biosolids and PFOS.  In new draft guidance, it suggests that the first go around was quite possibly way off.  It notes that biosolids are only applied to a very small portion of total farmland (a figure of <1% is used). EPA also notes that the exposed individuals modeled in the first draft of the risk assessment are unlikely to exist. It says that regulating industrial input may be a good way to go.Granted, this new assessment does not include a lot of science.  In fact, the science on how low-PFAS biosolids behaves is lacking but as wastewater from homes is the primary source, logic suggests that home exposure is the big thing to worry about. It would seem that the marriage between biosolids and PFAS may be heading towards an amicable separation.

Speaking of amicable separations, this is my last column for BioCycle. It has been a great run and a wonderful privilege. A new editor and a new direction suggest that it is time for us to go along different paths.  But the combination of bad jokes and science is not over — you’ll be able to find the column at the US Compost Council website and through regional biosolids associations.

Sally Brown, BioCycle Senior Adviser, is a Research Professor at the University of Washington in the College of the Environment.