By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
PFAS concentrations in soils: Background levels versus contaminated sites
Extending the knowledge about PFAS bioaccumulation factors for agricultural plants – A review
Characterizing and Comparing Per- and Polyfluoroalkyl Substances in Commercially available biosolid and organic non-biosolid-based products
Landfill leachate contributes per-/poly-fluoroalkyl substances (PFAS) and pharmaceuticals to municipal wastewater
A framework for regulation of new and existing PFAS by EPA
Just when you thought that with all of the COVID frenzy and the cool stuff about wastewater- based epidemiology that people might forget about PFAS- it rears its’ ugly head. I got a copy of an article in Waste Dive all about the evils of PFAS and how it is going to stop biosolids and compost use. While I can’t bring myself to read it, I took it as a sign to do a PFAS library update. Here is the link if you are braver than I am
All of the papers in this library are new- published in 2020. Hopefully they’ll broaden the understanding of PFAS in the environment, the role of biosolids and composts and what to do about it (not have a nervous breakdown). The first article is a survey on soil concentrations of PFAS, PFOA and related compounds. The authors went over all of the published literature and also did a deep dive into US Airforce records. Articles included in the survey are from all corners of the globe and ALL of the sampled soils had PFAS and PFOA above detection limits. Granted detection limits were very low. But you find this sh**t in the Arctic. They separate the soils into three general categories; non- contaminated sites, primary contaminated sites and secondary contaminated sites. Primary include direct source contamination such as fire fighting foam and manufacturing. Secondary include land applied biosolids, contaminated wastewater, or proximity to manufacturing. They reported the highest concentrations from each study. The paper itself has the details on sources, locations and paper references but here is the grand summary:
The authors have 3 papers sited for the secondary manufacturing that include biosolids applications. One of them has biosolids and paper sludge. The two biosolids only range in PFOS from 0.4-878. The one that has the combo has 1692.
The paper also has a section where they compare soil concentrations to groundwater concentrations. Based on data from Air Force sites the ratio of soil to water varies by 9 orders of magnitude. 13% of the sites had higher water than soil concentrations. The remainder had the reverse pattern with a peak ratio of 2- (log scale here) meaning 100x more in soil than in the water. Here is their conclusion:
In summary, the results of this study demonstrate that PFAS are present in soils across the globe, and indicate that soil is a significant reservoir for PFAS. A critical question of concern is the long-term migra- tion potential to surface water, groundwater, and the atmosphere. This warrants increased focus on the transport and fate behavior of PFAS in soil and the vadose zone, in regards to both research and site investigations.
The next paper is a review of plant uptake. The authors have looked at the studies done in hydroponic systems but used only the ones done in soil systems. This is very important as hydroponics often greatly overestimate uptake in comparison to soils. There is an amazing diagram- like one of those posters you hung on your dorm room in the 70s that shows the number of studies by plant group and length of carbon chain.
The take-home of this paper is that the longer chain compounds are not taken up into plants but that the shorter chain compounds are. Almost all uptake is limited to the vegetative part of the plant and not the reproductive part. That is great if you are eating wheat but not so good for lettuce.
The third paper reports on concentrations in biosolids and compost products. It comes from Rooney Kim and Linda Lee from Purdue- so a very capable research group. The authors tested a range of products with an emphasis on biosolids based products. These included a number of heat dried biosolids, biosolids compost and biosolids – based blends. Only one food/ yard compost was tested. One would expect that food/ yard materials (a below) would have elevated concentrations relative to mushroom composts. The biosolids based materials had higher concentrations with high variability across the different products.
Concentrations also decreased over time -
So with all the fuss, things are improving as use of the longer chain compounds is being phased out.
The 4th article addresses a potentially unexpected source of these compounds into the wastewater stream: landfills. Makes sense. All of that old carpet has to go somewhere. Those old Scotchgard clothes, popcorn bags, Teflon pots and pans. In other words, all of those old PFAS impregnated items from our homes that make home exposure the biggest pathway of concern also makes landfills a major repository. Perhaps instead of sampling soils like in the first paper, scientists should be sampling landfills. Turns out that landfill leachate is a major source to treatment plants:
PFAS were detected more frequently in leachate (92%) than in influent (55%). Total PFAS concentrations in leachate (93 100 ng L−1) were more than 10 times higher than in influent (6950 ng L−1) and effluent samples (3730 ng L−1).
Time to get the pretreatment staff out on patrol.
So, these compounds are in all soils. The short chain ones, the ones that are still being made and used, are also much more plant available than the longer ones. Because they are so ubiquitous, they are entering treatment plants from landfills.
Do you ban the biosolids?
The final article in the library says that what you do is you regulate the compounds from the source. This is a policy paper that describes that regulation of the compounds. Don’t just ban the big ones, consider all of them as a single class. Prohibit their use when they are deemed non- essential. This is an answer that makes sense. It will take time to get past the age of non stick but this is the pathway to do it.