by Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Apologies but we are back to PFAS again this month. As with last time, this one was triggered by another new publication. This time the US EPA (article 1) came out with an analysis of PFAS in food scrap based digestates and composts that also includes references to biosolids. The report was prepared by consultants who talked to a lot of knowledgeable people. Nevertheless, you read the report and once again you catch yourself looking up to see if the sky really is falling.
Me- I look at the cover of the publication and the contaminants that scream out to me are the bits of plastic you can see on the surface of the compost.
It just so happens that at the recent Biofest (held on line so no excuses if you missed it) we had a full day of PFAS. One of the speakers and also one of the experts consulted by EPA on their document was Linda Lee. She is perhaps the world’s expert on PFAS in organics and an exceptional soil chemist based at Purdue University. A presentation on the topic is article #2 in the library. It is very similar to the talk that she gave at our conference but the hosts for this one gave her more time so it has a few additional slides. This is high level chemistry that really gives you solid information on properties and transformations of these compounds in a soil environment. A few main points- short chain compounds can transform to longer chain versions in the WWTP and in the soil. High carbon and higher chain length restrict movement of the PFAS compounds in the soil. So, one good and one bad. The point here is that PFAS are an interesting class of compounds and Linda is eminently qualified to study them.
From Dr. Lee we move on to Dr. Pepper. Ian also spoke in the PFAS section of the conference. He has a new paper out (#3). The impetus for this research was a ban on land application of Class B biosolids in Pima County based on concerns over PFAS. Ian and his team took samples from long-term application sites that have been used to grow cotton, a high irrigation demand crop in the AZ desert. The graphical abstract from the paper pretty much tells the story:
It turns out that the irrigation water used on the site also contained PFAS. It wasn’t just the biosolids. This had also been the case at the Kern County site years back. This stuff is everywhere and that is the main reason we can detect it in the biosolids and the food scrap compost. As a result of his work, Pima County has again started to apply biosolids. Ian spent a portion of his talk at Biofest describing a proposed study where he is hoping to replicate the realism that got Pima County back from the ban. Hopefully that will come to fruition.
Ian’s study highlighted the fact that PFAS is everywhere. A laser focus (and that is what it feels like) on composts and biosolids will do little if the compounds are everywhere. To bring home this point (as I have done in multiple libraries- last July on lipstick for example) we turn to article #4. This article shows that concentrations of PFAS in carpets and dust in childcare centers are about double or higher than in most biosolids and even more than that for food scrap composts. I challenge you to find me a childcare center where kids aren’t crawling around on the carpets! Here is a picture of our couch with a glimpse of the new carpet- we got the special dog resistant kind. We decided the potential for accidents from our 90 pound girl outweighed the risks from whatever type of PFAS was used to make the carpet Sophie proof.
We end with a diatribe from me on this topic, just published in Biocycle. Here I go into detail on the EPA report and whether it makes realistic recommendations. Two of those- to restrict use of composts and biosolids based on PFAS concentrations or to set limits on PFAS in these products are likely to have no impact on human exposure. The other- source control aka stop making these and putting them into every product imaginable- is highly likely to have an impact. In the article I go through a typical home with associated PFAS exposure routes and concentrations to make the point clear.
I am tired of talking about PFAS, likely you are tired of reading about PFAS. Hopefully this article will help put the risk into perspective. I can promise that next month’s library will be a big departure and a lot more fun.