The U.S. Environmental Protection Agency just released a well-written and well-researched document about the presence of perfluorinated compounds (and select pesticides and other organics) in food waste (US EPA, 2021). It includes consideration of the fate of these compounds in compost and digestates. It summarizes much of the current knowledge and provides recommendations. These include placing limits on these compounds in composts and digestates and/or limiting the use of these materials because of their PFAS (perfluoroalkyl substances) content. “A valuable resource” may be your first reaction. For me it was resisting the temptation to rant and rave at the authors from the comfort of my PFAS treated sofa.
Best to start with a brief review for those of you who haven’t been immersed in PFAS for the last few years. It turns out that if you add fluorine to carbon you can make a slew of compounds that can be very useful. These compounds make things resistant to grease, oil, heat and water. That means that you’ll find them in a wide range of products including food packaging (pizza boxes, take-out containers, nonstick cookware, popcorn bags, etc.) and consumer products. Examples of consumer products include stain resistant furniture and carpeting, clothing, rain gear, dental floss, and cosmetics. These compounds have been around for many, many decades. They have only recently (last two decades) made the transition from “useful” to highly hazardous.
So many uses for these compounds means that everyone has been exposed to them. They are in our homes. Quite often, they are in our drinking water. They are also in us. PFAS compounds have been detected in blood (100% of individuals sampled) and in breast milk (Olsen et al., 2017; Zheng et al., 2021). You can even find the stuff in beluga whales swimming in the northern reaches of the Canadian Arctic (Kelly et al., 2009).
While this stuff may be handy in your carpet, I for one don’t relish the thought of it being in my blood. I’m sure the whales aren’t too happy about it either. The question then becomes “What is the best way to get PFAS out of the environment?” A follow up to that — with our industry first and foremost in my brain — is whether paying attention to concentrations in composts and biosolids has a significant part to play in this saga.
A wide range of bad outcomes has been reported for people who either work in or live close to factories where these compounds are produced. Check out an article from 2016 in the New York Times for an example. The understanding of potential hazards resulted in a ban in U.S. use and manufacture of two of the longest chain (most complex) of these compounds — PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate) — prior to 2010. The bans are working. A survey of blood concentrations over time (Table 1) shows that both PFOS and PFOA have declined (Olsen et al., 2017). Bans and patience appear to be virtues in this case.
With the bans however, has come the proliferation of shorter chain versions of these chemicals (Pan et al., 2018). These newer versions are still being made and still being used. Something tells me that the shorter length does not mean a clean bill of health but the jury is still out on that. You have a long list of these compounds that have a multitude of uses and that have been used for decades. New versions are being made and used every day. That means that they are everywhere and will be for a long time. What exactly do I mean by everywhere? They are almost certainly in your blood whether or not you indulge in microwave popcorn or have carpet in your home. The newer versions of these compounds have been detected in surface waters across the world (Pan et al., 2018). It would seem that very little can escape the utility of compounds that make everything nonstick and moisture resistant.
While these compounds are very useful, they are also very persistent. You read now about “forever” chemicals. Used to be that they were talking about dioxins. Since those were banned 20+ years back, they are now a distant memory. Today, forever chemicals refer to compounds in the overall PFAS class. In general, the PFAS compounds are nearly impossible to degrade. You can change shorter ones into longer ones but they just don’t decompose. They are also expensive and tricky to analyze for. As the new EPA document points out, no standard protocol exists for analysis of these compounds in solids or soils. There are methods that people seem to use a lot and likely are good but there is no certified EPA method for analysis.
This gets a little more complicated because the concentrations that people are worried about here are so low that you need to really have a good understanding of units and zeros to quantify them. The normal units that people use are parts per billion (ppb) or 1 in 1,000,000,000. Although often, particularly in reference to water quality standards, those drop to parts per trillion (ppt) or 1 in 1,000,000,000,000. For example, the EPA health advisory standards for PFAS in water is 70 parts per trillion or 70 in 1,000,000,000,000. Several states have gone one step further and lowered that to 10 parts per trillion or 10 in 1,000,000,000,000.
PFAS In The Organics World
In the organics world, these compounds first made the headlines when biosolids produced by a treatment plant that accepted influent from a PFAS factory in Decatur, Alabama was land applied (Washington et al., 2010). The soils at the farm that received the biosolids had screamingly high concentrations of these compounds. Remember that “screamingly high” concentrations of these compounds are very, very low in comparison to contaminants of the past. Studies generally report the concentrations of the individual types of PFAS compounds in addition to the sums. The soils at the site did have high concentrations of these compounds: up to 320 ug g (ppb) for PFOA and 410 ug g for PFOS. Summing across all of the different compounds tested, soils in 6 of the 7 sites tested had total concentrations ranging from 1,000 to 6,000 ppb of PFASs (1-6 ppm).
From Decatur the fear traveled quickly to New England. A farm there had used pulp and paper residuals as soil amendments in the 1980s (Brown and Beecher, 2018). Remember how useful PFAS is to stop pizza from sticking to the top of the box? Well, those pulp and paper residuals came from mills making paper products for the food service industry. The soils at this farm — decades after the sludges had been applied — had concentrations of total PFAS of up to 880 ppb. The well water at the farm had concentrations of about 50 ppt but the milk from the cows had 690 ppt. To me these cases sound like exceptions rather than rules, but in many parts of the country they have been treated like they are status quo.
In the meantime, only a limited number of studies have measured concentrations of PFAS in biosolids and composts. Here the handful of studies have analyzed under 20 or so different materials. With that said, they suggest that while present, concentrations are more like muted tones rather than loud screams. A reported range for municipal biosolids and biosolids products is 9 ppb to 199 ppb (Lazcano et al., 2020). The range for composts containing food scraps is 2 ppb to 75 ppb. These concentrations are the sums of the different PFAS compounds tested.
Over time, with the bans on PFOA and PFOS, one would expect the concentrations of these two big guys to decrease. To test this in a not scientifically rigorous way, I averaged the concentrations in biosolids seen in one study published in 2005 with another published in 2020 (Higgins et al., 2005). While both studies sampled material from about the same number of wastewater plants, I have no idea if any of those plants were in the same part of the country, let alone the same plants over time. Turns out that PFOA has stayed the same and pretty low over time and PFOS seems to have come down quite a bit from much higher numbers (Table 2). Bans and patience likely work for biosolids as well as blood. Also note that the concentrations of both compounds in biosolids are not overly different than what is coursing through your veins.
When you look at the concentrations of these two compounds and then the concentrations of the sum of the range of compounds, you can see that these days, the two bad boys are only a small fraction of the PFAS compounds currently seen in biosolids. The key takeaway is that the majority of the compounds we are seeing in biosolids and food scraps composts are still legal, still being manufactured and still being used in everything from dental floss to rain gear (Boronow et al., 2019).
Will Bans, Rules And Limits Make A Difference?
Despite that, some states are banning biosolids applications and/or setting limits for PFAS in solids and waters that are in the “near impossible to see even with the finest equipment” range of detection. The Sierra Club just came out with a new document touting the hazards of biosolids because of these compounds (Sierra Club, 2021). These regulatory actions have certain communities looking at pyrolysis (a high capital-intensive option that may reduce/destroy PFAS) as an alternative to standard stabilization and land application. They also have the EPA in its newest document suggesting that concentration limits in composts and biosolids might be appropriate or even that use restrictions for these products might be merited.
My big question is would any of these bans reduce exposure to these compounds for the general public? Would the bans/rules/limits make a difference? Here a critical thing to remember is the whole notion of pathways. In order for a compound to get into you, you have to have a path of contact. There has to be a way for the compound in whatever media it is in to get from it into you. In order to understand pathways and probability of entry let’s take a walk around the house and the compost pile. The graphics and explanations on our tour (see boxes throughout this article) give you a sense of whether primary exposure for almost all individuals is from the compost/biosolids or from another source.
One of the other recommendations that the EPA document made was that source control, or banning/restricting/limiting use of these products in the first place is a potential solution. This recommendation was the one section of the report that actually made me give EPA a fist pump or equivalent sign of approval. Let’s put it this way. If the PFAS in the food scraps/biosolids are coming from your food, your bathroom or your dust rag, there is a far higher exposure potential for you in your home than in any compost pile. If there are concerns about PFAS from commercial sources, pretreatment has worked well for every other class of contaminants. Stopping that rug manufacturer from discharging into your system would likely have the same effect.
Then there is the real question of how necessary these compounds are in so many of the products that they are used in. We have seen that the bans of the longer chain compound, the PFOA and PFOS, have decreased over time in human blood and in biosolids. That isn’t a coincidence. It is the direct result of the ban in their manufacture. If we are truly concerned about this class of compounds then the appropriate action is source control. Lipstick will still come in lovely shades if it is manufactured without PFAS. Pizza may stick to the top of the box a little more but it will still be deliciously gooey and greasy. The data very strongly suggest that restricting concentrations of PFAS in composts and biosolids or restricting use of some of these materials will have no impact on human exposure. If that is really the goal, stop making and using them in the first place. That we know will have an impact.
Sally Brown, BioCycle’s Senior Adviser, is a Research Professor in the College of the Environment at the University of Washington.