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Today’s presentation will discuss the complex challenges of PFAS contaminants in soil. With that, I’d like to introduce our presenters for today. We are pleased to have with us today, Dr. Christopher Higgins, University Distinguished Professor of Civil and Environmental Engineering at Colorado School of Mines. Dr. Higgins’ research focuses on the movement of contaminants in the environment. In particular, he studies chemical fate and transport in natural and engineered systems with a focus on PFAS. He has authored more than 130 peer-reviewed publications. His research has been supported by National Science Foundation, National Institutes of Health, the US EPA, US Department of Agriculture, and the Department of Defense. Dr. Higgins received a bachelor’s degree in chemistry from Harvard University and graduate degrees in civil and environmental engineering from Stanford University.

We’re also pleased to have with us today Dr. Paul Erickson. Dr. Erickson is the Director of Research and Development with Regenesis, overseeing the commercialization of new environmental solutions to address complex remediation challenges. During his time with Regenesis, Dr. Erickson has led the development of a number of remediation products and technologies, including Petrofix, Flux Tracer, and AquiFix. Dr. Erickson earned a Bachelor of Science degree in chemistry from Florida State University, a master’s in chemistry from the University of Minnesota, and a Ph.D. in environmental chemistry from ETH Zurich. He is an author on over 20 peer-reviewed scientific publications, mainly in the area of environmental chemistry.

All right, so that concludes our introduction, and now I will hand things over to Dr. Christopher Higgins to get us started.

Great. Well, thank you very much for the introduction, and good afternoon to everybody. It’s a pleasure to be here and to be talking about my favorite topic, which is PFAS’s, which I’ve been studying for a number of years, and particularly looking at them through the lens of soils. And I’ll focus, as you’ll learn today, on those impacted by firefighting foams. I like to start every talk by acknowledging the people who are actually doing the work, as opposed to myself, my graduate students and postdocs, and the army of undergraduates that have been working on this topic.

I’m listing here pretty much all the students and postdocs that have at times worked on the PFAS issue in my laboratory, as well as a number of collaborators. I’ll try to highlight the individuals whose work I’m talking specifically about as we go through it. But it is very much been a team effort. And even though I may be on the boat, at the end of the day, I’m not the one who’s paddling hard to make sure we miss that big hole in the rapids. So I probably for this audience don’t need to point out the importance of PFASs as environmental contaminants in terms of national attention.

Over the years there’s been a lot of attention but most recently the announcement of the proposal for the national primary drinking water regulations for some specific PFASs of interest, PFOS and PFOA, proposed MCLs at four nanograms per liter, and the combination of four different other compounds proposed using a hazard index approach, kind of illustrated here. I adapted this from a bar engineering graphic, which I thought did a very good job of this. But the point is that there’s a lot of interest in regulating these chemicals, and some states are already regulating these chemicals at very low levels. But I’m going to be talking about why even this list of compounds is really probably not sufficient when you’re looking at soils, because there’s a lot of these compounds out there.

It is certainly a national issue. This was a figure from a paper published a couple of years ago using data from UCMR 3, the Unregulated Contaminant Monitoring Regulation, from a number of years ago looking at all public water systems serving a large number of people and looking to see how many of these compounds were present in different water supplies. At the time, reporting limits were basically saying about 4% of large water systems had detections of these perfluoroalkyl acids greater than 20 nanograms per liter. More recently, a paper came out from the US Geological Survey suggesting that both public and private wells, when you started looking at them, that maybe a slightly larger number, you could say significantly larger number of drinking water samples were impacted by PFASs. And there’s likely this very clear urban versus rural differences in terms of what the sources are.

But certainly in the former study, in the Who It All paper, we saw some indications that the use of firefighting foam was at least a potential contributor to the presence of these compounds in different water supplies. And I’m gonna come back to that later because that’s been an overarching theme of a lot of the research that I’ve been doing is PFAS is derived from firefighting foam use. However, it’s not just a national issue here in the US, it’s a global issue. So this was a paper that surprisingly has had a quarter of a million views looking at the PFAS levels in rainwater around the globe and discussing that in the context of planetary boundaries of safe operating spaces, and basically making the argument that essentially all water on the planet has been contaminated to some extent, at least surface waters and rainwaters with these compounds and what does that mean in terms of issues for us as humans living in and drinking this water.

I’m going to be super clear about terminology because it’s really important for compounds I’m going to be talking about today. So poly and perfluoroalkyl substances is what we refer to PFASs, the class as PFASs. However, within that designation, there are perfluoroalkyl acids, PFAAs, which is the PFOS and PFOA to the most widely studied compounds and widely known. On the left here is an example of a perfluoroalkyl acid. This particular structure is PFOA. And for those who don’t know, the carbons are implied. Every intersection of those lines on the image on the left is a carbon atom. But all of these, what would normally be hydrogen atoms, are replaced with fluorines.

On the right is a polyfluoroalkyl acid. This is a fluorotylimer acid. And the reason why it’s polyfluorinated is that it’s not fully fluorinated. It has hydrogens on these two carbons where otherwise fluorines would be if it were perfluorinated. And that’s really important and a really important designation or differentiation between the poly and the per in that the perfluoroalkyl acids are the ones we for the most part ultimately care about. But the polyfluorinated compounds can potentially transform to form the perfluoroalkyl acids in soils and in groundwater over time.

So, what I’ve been talking to you about so far is the definition of PFASs as proposed by Buck et al. in 2011. These are defined as compounds that meet what I was just describing, but being aliphatic substances. They have a number of carbon fluorine bonds in them. They’re aliphatic, typically linear structures. I will point out that OECD proposed a definition of PFAS shown here on the left. And this is important in that it is a broader definition. And as detailed by Emma Shimansky, a colleague at University of Luxembourg in Europe, if you broaden that definition, OECD-based PFASs, you could have up to 6 million compounds. But the vast majority of those compounds would be things that contain a trifluoromethyl group. I mean, things like Prozac or Paxlovid, lots of pharmaceuticals, personal care products, and pesticides within that definition.

So for today, I’m going to stick with the historical buck-at-all 2011 definition, inclusive of ethers, but I’m not really going to talk about the perfluore ethers today. But I think what you define as a PFAS is really important because regulatory implications could be quite significant. So that’s just a quick disclaimer on this. This debate is what is actually defined as a PFAS is ongoing, but I’m going to stick with the bucket-all definition for today’s talk.

So again, perfluoroacryl acids are what everyone can agree is a PFAS. These are fluorofluorinated chemicals repel both oil and water. It’s actually the precursors, the polyfluorinated compounds to these perfluoroacryl acids, which were used in the vast majority of products, coatings for textiles, paper packaging products, firefighting foams, which I’ll spend a lot of time talking about today, were actually combination of both PFAA-based precursors, as well as PFAAs for some firefighting foam formulations. It turns out that the PFAAs are extremely environmentally persistent. Some of them are bioaccumulative and toxic, which is why we’re concerned about them. Widely detected in humans and wildlife all over the globe and in rainwater, as I’ve already discussed.

And one of the things that’s really interesting about this group of compounds and why they’ve garnered so much attention is that most of the time we’re talking about environmental contaminants, you can have contaminants that bioaccumulate, but are not particularly mobile, or things that are mobile, but are not particularly bioaccumulative. And PFAAs are a group that are relatively mobile and yet bioaccumulative, which is why they are causing so many problems in terms of trying to address them in terms of environmental context, adding to the fact that they’ve been detected and present all over the globe.

So again, what are these compounds? I’m showing another structure. I am an organic chemist. I do like structures. I apologize for those who are not. We showed PFOA before. This is the other poster child perfluoro octane sulfonate or PFOS. Eight carbon, 17 carbon fluorine bonds and a sulfonate head group. That tail imparts the oil and water repellency. It also makes it a great air water interface surfactants. These things love to stick at air water interfaces which we’ll come back to in a moment. The good news from aching these chemicals is that they’re very useful for various purposes because the carbon fluorine bond is one of the strongest bonds known.

The bad news is if it’s one of the strongest bonds known, that means they’re extremely persistent in the environment. So if they’ve been sprayed out there into the environment as part of these firefighting foams, they’re gonna stick around there for a very, very, very long time. Hence, they’ve been often referred to in the popular media as forever chemicals. And that one that we’re referring to are these specifically these PFAAs. So when I think about PFASs and their environmental challenges and the complexity of the challenges, I think about this in multidimensional space. And the first dimension I think is really important to think about is the chemical composition. And here I’ve tried to rank where I think PFASs sit relative to other organic contaminant classes. I won’t go into all of those today.

The one group that I think probably has more chemical complexity than PFASs is the pharmaceuticals and personal care products, simply because those are mainly grouped by their function as opposed to any particular structural feature. But PFASs do exhibit a very large diversity of structures, as I’ll talk about here in a moment. So it’s not just about PFOS and PFOA. This is, again, is a figure from a paper that has gotten a lot of traction over the years, showing the, at the time, family tree for PFASs. And I’ve highlighted here the PFAA precursors that I think are really important to the story I’m going to tell today.

But again, it’s not just about PFOS and PFA. And if you’re really interested in how this process of identifying what these chemicals are and how we use high-resolution mass spectrometry to identify the various precursors and the known compounds. There’s a great paper that was put out a number of years ago kind of discussing some of the work that we’ve done as well as some of the great work done by the US EPA to identify some of these compounds both in firefighting foam and in other locations again mainly using high-resolution mass spectrometry.

What I am going to spend most of my time talking about today is PFASs that originate from the use of aqueous film forming foam or AFFF and I will say that very quickly, but H-BLUF is something that I’ve been studying for a number of years and is essentially, I think, a major source of PFASs for groundwater impacted throughout the US and potentially throughout the world. It’s important to keep in mind that only 3% of fluorochemical production is estimated to be used for H-BLUF, so there’s a lot of other uses of PFASs and other types of products, but this is a form of the chemistry that was actually sprayed out directly into the environment during training exercises and in some cases in actual accidental releases or accidents where the fuel fire occurred and people were trying to put out that fire.

Most of that HBLUF is thought to have been used by the military. I’ve seen 75.25, I’ve also seen 50.50, the point being that the military sources are important but not the only sources of PFASs or users of PFAS-based HBLUF and releases to the environment. These different formulations of HFF are complex, the proprietary mixtures, at many sites where this was released, they didn’t use one formulation, they used multiple formulations over many years, and again, often directly released to the environment, sometimes directly sprayed onto soils, sometimes it was a volleyball court because it drained really well, but the point being these chemicals were directly added to soils as part of these training exercises, in some cases, actual accidents.

The thing to keep in mind is that these H-BLUF formulations, while again, only 3% of fluorocommel production, the PFAS is present in these, we’re present at gram per liter levels, which is really, really important. What that means is that if you have a bucket of H-BLUF and there’s a number of buckets of H-BLUF, this is one way they were sold in five gallon buckets, but also larger totes. If you had 3M light water based H-BLUF, that has enough PFOS in it, historical formulation, to contaminate the annual water supply for a town of 470 ,000 people, down to that 4 nanogram per liter. That’s one five-gallon bucket has enough PFOS in it for that amount, which is not much. It doesn’t take much to contaminate a water supply.

People often think about, you know, how many grains of salt in an Olympic-sized swimming pool is 70 nanograms per liter or 4 milligrams per liter, I like to flip that around a little bit and talk about Olympic-sized swimming pools filled with HBLUF. So if you had one US Olympic-sized swimming pool filled with 3M light water, that would have enough PFOS in it to contaminate 125 years worth of the entire US drinking water supply for the US population. And again, many Olympic-sized swimming pools of HBLUF were made over the years. And when you couple that with potential places where these might’ve been released, This is actually an incomplete picture of potential H-BLUF release sites.

Other organizations like EWG and others have put together site maps of places where it wasn’t just H-BLUF, but also landfills and wastewater. But this is just looking at H-BLUF potential release sites. There’s a number of places that could have very significantly impacted groundwater as a result of this H-BLUF release. So when I think about challenges of PFASs, one question I often get is, how many compounds should we be looking at, should we be worrying about, is my analytical suite of 40 compounds enough, should I be looking at more?

Well, the good news is a former postdoc from a group, Karen McDonough, who’s now at Carnegie Mellon, put this figure together, which I think does a nice job of summarizing all the different analytical tools that help answer this question. And most of the time we’re focusing on those compounds that we can measure using targeted LC tandem aspect, as are most commercial labs, we’ll focus in on this dot here. Honestly, we don’t know how big that dot is relative to everything else. There’s a lot of research trying to understand that. But when we do this work in my lab, we tend to focus on things that are amenable to LC mass spec and things that we can analyze using high resolution mass spec.

We also do a little bit of things related to the top assay, something I won’t talk about today, but I happen to take any questions about that later. But the point is, we’re trying to go beyond the target list of compounds in any one list. We’re trying to look for as many compounds as possible that are at least amenable to liquid chromatography mass spectrometry. So what does that look like? So this is an example of some of the structures that we observe when we look at either in firefighting foam or at H-bluff impacted sites, and they’re complex. So they aren’t just the perfluoroccal tail and a simple head group. These head groups are quite complex. They can be cationic, they can be zwitterionic, so they have both negative and positive charge.

But the head groups are typically polyfluorinated. That’s where we get the diversity of most structures is because of that polyfluorinated head group. And I certainly will reward anyone with a beer if you can come up with a good pronunciation of how to pronounce some of these names. These are acronyms meant to imply some information about the structures but the point is there’s a large variety of compounds that we look for when we’re going out to look at these foam-impacted sites. And there’s even a larger list maintained by NIST now of PFASs that may be of interest. But when we’re specifically focusing on those at H-bomb-impacted sites, any one site may have 100 or so different compounds, but we’re looking for over a thousand different compounds that might be present at these sites.

So I mentioned the complex challenges of PFASs and the fact that chemical composition is kind of the first dimension where PFASs are pretty important. There’s a lot of different compounds out there with different structures. They come at different chain lengths and different head groups. Where PFASs really start to differentiate themselves as environmental contaminants is when we think about environmental behavior. And so that’s where I think PFASs really start to be pretty unique in terms of the complexity of their behavior. And if I can focus specifically on soils, which I wanna do today, I’ll talk about this conundrum of soils, and particularly H. blef source-sown soils.

And the conundrum is that these compounds are relatively mobile. They have been detected in groundwater plumes that are 10 miles long. I’ve heard of a plume in one Midwestern state that’s 100 square miles of some compounds. So some of them are relatively mobile, but they’re also present at very, very high concentrations in what we call Veto-sown soils. So those are the soil above the groundwater table, but below the surface of the ground. And those are somewhat problematic in that, if they’re so mobile, why are they still sticking around in the soils?

And when we do site investigations and people have integrated across the site, they still come up to this conclusion that a large fraction of the mass, sometimes the majority of the mass is sitting in that source zone and in those soils. And so the working hypothesis as to why these compounds are sitting in soils is that the retention is a result of their air-water interfacial properties, I mentioned that before, but also the slow release and biotransformation of cationic and zwitterionic polyfluorinated compounds, or PFAA precursors. And I’m gonna talk a little bit about both of these, but mainly the second bullet, because that’s work that we’ve been doing in my lab, but we’ve also done a little bit of work related to their air-water interfacial retention.

So what we’re really talking about here is the fact that if you have precursors in a soil that they can transform to these perfluoroalkyl acids and be transported down gradient. So the related questions, you know, are these precursors a significant abundance in these impacted soils? Are they actually slowly released? You know, can we verify this hypothesis? Can we test it? And are they released more slowly than PFAAs? And do they have that ability to transform to these perfluoroalkyl acids as we expect they might? So this is a structure of one particular Cephatomyl ethanol, a precursor present in some products, actually not so much. There’s a little bit in some H-BLUF, but not so much in H-BLUF, but certainly in consumer products. But the idea is that can this compound slowly transform over time to form PFOS? Or other sorts of compounds with like C6-based structures transformed to things like PFHXA or PFHXS?

So to answer some of these questions, a number of years ago, another former postdoc of mine, Andrew Maisel, who’s now at NIST, started a study funded by the CERDEP program, the DOD program, to evaluate the releases of PFASs, particularly precursors from H-bluff impacted soils. And so what he did is we took field collected soils, we ran artificial groundwater through those soils, and analyzed all the water that came off over a number of four volumes for everything that we could via LC-QTOF-MS. So we did targeted analysis for the normal per-fluoroalkyl acids, but also looked for all these other compounds that I’ve been talking about and tried to identify if they were present and also if they were coming off.

Now, the key thing though, is that we needed to have some sense of what was present in the soils to begin with. And so another person in my group, Dr. Anastasia Nickerson, a former graduate student, actually went about validating a method to analyze all the diversity of compounds that we knew were present in HbF, in HbF-impacted soils. And so the soils were extracted using a slightly more complex extraction procedure than is proposed with the EPA method 1633. It’s both basic and acidic extraction. We combine the extracts, eventually analyzing by LC-QTOF-MS.

An important thing I want to point out is that what Anastasia determined is that we need to look for both compounds in ESI negative mode, which is looking for the negatively charged compounds, but also ESI positive mode, which looks for the positively charged compounds if you’re trying to get the full picture of compounds that are in these Hbf-impacted soils. The other thing we did is we took an approach and actually Dr. Maisel helped with this quite extensively to semi-quantify a lot of these compounds because we don’t have authentic standards for a lot of these cationic and spherionic compounds that we’re observing by high-resolution mass spectrometry in our soils.

So what Anastasia further did was say, okay, if I look at three different soils, how do these rank? What are the most abundant compounds in these soils? And these are ranked now for these soils A, B, and C, all collected from US Department of Defense H-bluff impacted sites. Left to right, high to low concentration. I note that some of these are semi-quantified in terms of the compounds. But what you’ll note is PFOS was highest in soils A and C. But soil B actually had these three other compounds, which are these precursor molecules, at higher abundance than PFOS. In fact, if you look down the list, all of these compounds in red are precursor molecules that we can only analyze in ESI-positive mode, which are things that most people are not looking for in their soils. And I will note the scale on the right, it basically just shows that we can get better extraction of these compounds if we do this more comprehensive extraction procedure.

But the point is, we need to make sure that we analyze for both the ESI-positive and ESI-negative compounds when we’re looking at these soils to see what is actually coming off. So back to Andrew’s study, what he found when he looked at the soils, I’ll look at the profiles more in a moment, but from these two different soils that he tested, we saw 167 different compounds present on the soils and or coming off. And again, I’ve highlighted in red all of the polyflournate compounds that are precursors to the perfluoroalkyl acids that were coming off the soils. And what you can see here is each line is just a subclass of compounds, and I’m showing the different chain links. So C3 to C8 facets, for example, are the fluoroalkylsulfonamides that were present in these soils, and we saw C3 to C8 being present.

But the point is there’s a lot of different compounds that are present in these soils and potentially eluting slowly from those soils. So looking a little bit more detail at the elution profiles from these, again, field-collected soils that Dr. Micell eluded the PFASAs from using artificial groundwater, we saw these pretty nice trends of perfluoroalkyl chain length. So the C5, C6, C7, C8, C9, C10, shown here, where the C5 is coming off first and slowly, eventually you get to the C10. Note here, the X axis is the pore volume. So essentially how much water has passed through, but that is in log scale. So it takes 100 times as long almost for some of these compounds to come off as some of the very short chain compounds. And that holds for the carboxylates, shown here in the upper left, as well as the sulfonates shown here in the upper right. And so it was chain-link dependent elution.

We expected this. That’s consistent with what we know about the fact that the long chains stick more strongly to the soils. But what was interesting is we still saw chain-link dependent behavior, even among the polyfluoridate compounds. So the bottom left down here is a subclass of PFASs where they all have the same head group, but they all have slightly different tails. so the C3, C4, C5, C6 tails. And we still see that chain-link dependent elution, but again, much later elution. So this one isn’t peaking to about 104 volumes as compared to some of the short-chain carboxylic which came off very quickly. And just to emphasize that even more, this bottom right is showing everything that has the same perfluoroalkyl tail as PFHXS, so perfluorohexane sulfonate, and essentially it’s precursors. And what you see is that PFHXS comes off relatively early, but a lot of these other precursors to PFHXS that can transform to form PFHXS come off much, much, much later. And that’s really important in verifying this idea that the polyfluoroid compounds are sticking much more strongly to the soils and are very, very slowly eluting from the soils.

The question is, are they all actually coming off? And what Andrew Maisel looked at was a fractional mass eluted for just the top 10 compounds. And the short answer for one of these soils shown in blue is that most of the mass was coming off except for some of these precursors down here. But for this other soil, a lot of the compounds weren’t even eluting. So even if we collected all the mass and estimated the concentration for all the compounds coming off in the water, most of the mass was actually sticking on the soil and not eluting. And even when the precursors do elute, if again, we just look at the compounds that can form PFH excess, The PFHXS is a small sliver down here of the mass of this PFHXS and its precursors.

The vast majority of the mass, essentially of PFHXS precursors, is coming off much later and is in the form of the C6-sophonamide, but also this other kind of more complex precursor. So one of the questions that Anastasia wanted to answer was, you know, do these precursors slowly transform to these perfluorocyl acids and elute from the sorzone soils? And so we went back and repeated a very similar experiments to what Andrew did looking at elution, but then tried to stimulate the biological activity in these columns and see how that affected the elution profiles. And what was interesting is that it actually didn’t matter a whole lot if we changed to oxide conditions or tried to keep things anoxic by just having nitrogen asparge through the groundwater that we were feeding through the systems. we did see some effect of the biological activity, but it really, there wasn’t a huge differences between being oxic or anox. And that’s interesting in that most of the transformations we expect for these polyploid compounds transforming to the perfluoroacryl acids are expected to be occurring under oxy conditions.

What we do see is when we look at the levels of what comes off the column versus what was on the column to begin with, we do see that for some compounds, as compared to the unaltered conditions down here on the bottom, we see a lot more coming off the soils and particularly a lot more of the sulfonamide compounds, the C6-sulfonamide, C5-sulfonamide here. Interestingly, the C6-sulfonamide, we even see greater elution under the unaltered conditions. But all of this does point to the fractional mass is similar in terms of a mass eluted from these oxygen-nitrogen-sparge columns, but is generally higher in the biologically active columns compared to unaltered columns.

And so this again suggests that the biology is contributing to the elution and potential formation of some of these compounds from the precursors in these H2F impacted soils. I did want to mention that it’s not just about precursors and slow elution and biotransformation. Here’s a nice summary of a study that John Stoltz, a former PhD student now working at CDMA Smith did, where we looked at unsaturated transport of PFASs. And what we’re seeing here on the top is the tracer data for a saturated column, an unsaturated column, and an unsaturated column where we had low flow. So this is where all of the pore spaces, the unsaturated columns, all of the pore spaces are not filled with water, there’s some air in there. And for the tracer, you see these nice breakthroughs, very normal kind of behavior for the tracers.

But when we looked at the PFASs in these columns, in the saturated, we see a little bit of retention, But when you go to unsaturated conditions, we see a lot more retention of these PFASs because of the sticking to that air-water interface. And what’s really interesting is the fact that when we ran unsaturated conditions under low flow conditions, so in other words, a lot slower pore water velocity, we saw even greater retardation. And that suggests to us that there’s likely some kinetic effects, even with air-water interfacial retention of these compounds. Now, obviously, a lot more study needs to happen on that. But it just gets to the complexity of trying to understand the transport of these compounds in the subsurface.

So I wanted to point out why these compounds are behaving so differently in terms of their environmental behavior in the subsurface. I do want to keep in mind where this is all going, and that is that ultimately we want to understand human exposure. And human exposure is actually where I think PFASs really take the cake in terms of complexity. And that’s because the pathways for human exposure are quite complex. We can be exposed through consumer product use and through the environment, and the environmental sources can both be drinking contaminated water, but also eating contaminated food. What I wanted to try and focus on is at least a little bit the complexity of the types of compounds that are eventually getting into our drinking water sources.

There’s lots of other folks sending some of the other things. We’ve done studies on some of the other sorts of exposure, but I want to focus for the moment drinking water exposure and why all of that complex chemistry matters even for drinking water exposures. So the question I often get, which compounds are in people’s drinking water, which compounds by accumulate, which compounds might be problematic and cause a hazard. And the working hypotheses are I’ve kind of listed here, you know, I think that for most Hbf-impacted water supplies it’s mainly going to be the perfluoroalkyl acids and some of the shorter chain anionic polyfluoridate compounds, which we’ll show in a moment. I think that’s generally supported.

We think the polyfluoridate compounds are much less bioaccumulative than perfluoroalkyl acids. The third one is also not really an exposure question, but does impact treatment goals. And so I’m gonna try and hit on a little bit of this before we end, just because I think that when you’re talking about soils, I wanna make sure you understand why we are concerned about all these polyfluoridate compounds. At the end of the day, we’re asking this question, you know, do all of these polyfluorine substances matter, particularly when we’re talking about drinking water exposure? Are we looking at just the tip of the iceberg or if we analyze for PFOS and PFOA, is that the vast majority of the compounds that we’re exposed to? The short answer is it’s not. There is a lot of compounds that might be present in H4F-impacted drinking water supplies.

What I’m highlighting first here is a figure from a paper that’s in Zhao, a visiting scholar. We visited my group a number of years ago, published looking at a very highly impacted, keep in mind, microgram per liter levels of PFOS and PFOA in this particular drinking water supply. And we saw not just PFOS and PFOA though, but a lot of these other compounds, including the sulfonamide compounds. And this was a point in time when we weren’t really semi-quantifying anything. We just saw that these compounds were present.

Kerry McDonough, again, former postdoc I talked about before, now Carnegie Mellon, followed this up with a study of the drinking water supply here in Colorado. And we looked at different wells in the security found in Whitefield aquifer, essentially arranged from the north to south, going from left to right here. And looking at the sulfonates with the sum of all the sulfonates we observed and the carboxylates in those water supplies. And then actually, I’m sorry, these are from south to north, opposite as the label here, security being kind of the north and fountain being the south. But then also looking at these sulfonamides here, and these are, again, these same compounds I’m talking about here, and we’re present in these Hbf-impacted soils. And when we estimate concentrations for these, because we don’t have authentic standards for all of them, we think that their concentrations are quite significant.

So again, several hundred nanograms per liter for some of these compounds being present in the water supplies. This is an example of a unsaturated PFOS molecule. It’s an analog or something very similar to PFOS, which is also present, but at very, very low concentrations in these H2O factor water supplies. So, you know, what does that matter if they’re present in the drinking water? Well, it matters in that we might be exposed to them, they might be accumulating in our bodies. And so one of the questions that we have been asking, just taking this kind of the next step is, you know, when we go to look at what’s in our bodies, you know, are we looking for the right compounds? Are we measuring the right PFASs when we look at human blood?

And I want to point out that most biomonitoring studies focus on human serum. So they take the whole blood, they separate the red blood cells and focus on serum. And serum is much more challenging to collect because you have to have a lot of this, collect the sample and then separate out the clotted red blood cells, but tends to be slightly more sensitive because most perfluoroalkyl acids bind to the serum albumin, and so you get an enrichment in serum as compared to whole blood.

Well, during the pandemic, we were challenged by going out and collecting samples of blood from people because, well, there wasn’t a lot of allowed human contact. And so a collaborator of ours at Eurofins said, well, we’ve got this idea of doing these volumetric absorptive micro-samplers, or VAMs, where you can collect a whole blood, and it can be just based on the finger *****. And so we said, OK, that would be great. Can we use that for monitoring PFAS in human blood and getting a better picture of what people are exposed to? And so the objective would not just evaluate whether we can use VAMs as a reliable means to measure PFAS exposure, but also, are we missing anything when we only look at serum as compared to whole blood? And again, this will tie back why We care about all these other compounds and soils and in groundwater in a moment.

So for this particular study, this was a part of the PFAS United Michigan cohort led by Courtney Kerrigan. This paper came out earlier this year in ES &T. This particular site was not an Hbuff impacted site, or I should say, we don’t think that was the vast majority of the contamination was more related to a paper coating facility. The town is parchment. So hopefully that makes sense. We had 130 people enrolled in the study. 100 people provided venous blood, and by the time we got the VAMs ready to go, we had 53 people that could collect both venous blood samples, essentially by phlebotomist, as well as VAMs. So we analyzed and compared serum and VAMs at urethans, reporting down to 0.1 nanograms per liter, which is pretty low for this type of measurement.

And what we observed is a very strong correlation, not surprisingly, between what we saw in serum versus capillary-collected VAMs, essentially finger ***** VAMs samples. And this is log scale with the Y-axis being log of the serum concentration, the X-axis being the capillary VAMs, very strong correlation. And if you look at the ratio of what’s in serum to what’s in the whole blood as measured by VAMs, it’s essentially a two to one. So some of the compounds are slightly less than two, but for most compounds, it tend to be about a two to one ratio, which is consistent with what others had shown in the past.

What is interesting though, and why I wanted to have this kind of sidebar about whole blood measurements and why we look at what people are exposed to, is that if we look at what the detection frequencies in terms of all the different compounds we looked for, and this wasn’t, I should say, this wasn’t high resolution mass spectrometry. This was targeted LC-MS. This is a relatively boring table. Most things are pretty consistent in between what we saw in serum and what we saw in VAMs, except for the FOSA. And this is a sulfonamide compound that is the C8 version of the C6 sulfonamide I was talking about before, being very present in soils and eluting from soils more slowly than the sulfonate analogs that have the same chain like. FOSA I should add is specifically the C8 version of this class of chemical.

When we were looking at the H-bluff impacted drinking water in Colorado Springs, we were actually looking at the shorter chain-link versions of that, which tend to be much more abundant in the H-bluff-impacted groundwaters. And what we observed for FOSA is that we don’t see it in the serum at all. It was all below the reporting limit, which was relatively low, but we saw it in almost half the VAM samples. And this is an example of a compound which may actually prefer, or appears to be, preferring to stick in the whole blood. And so, if you’re not looking for it in whole blood, you might be missing it.

And we don’t know to what extent this holds up for the other compounds in this class, but I think it really points to the need to maybe look at whole blood as an alternative to serum because you will get just the same sort of sensitivity in terms of seeing compounds for the most part, but you will perhaps see a broader diversity of compounds that may be particularly important, particularly for these H-bluff impacted communities. So, if I think about the challenges for PFASs, particularly the soil challenges for the global community, I like to say that these compounds are ubiquitous in the global environment, so they’re present in waters, and I didn’t talk about soils, but they’re also present in soils all over the globe.

We can’t treat all the water and soils, so what do we prioritize? I think that’s a good question that a lot of us are going to have to be asking and trying to answer over the next few years. I will say the chemical complexity, the compositional chemical complexity, can be daunting, particularly for non-chemists, but, you know, I do think there’s this need to go beyond the standard analyte list, particularly for these H-bluff-impacted soils, because you’re going to miss a large fraction of the mass if you don’t. The behavior of these compounds and soils is complex. I think there’s open questions about how we develop predictive models, given all the chemicals and the complexity of this, can we simplify things in a nice way to make more predictive models over the long term about these soils becoming long-term sources of PFASs to groundwater?

But I do think that these precursors are likely contributing to PFAA body burden. So the idea here, I haven’t described in great detail, but if these precursors are present in our drinking water, we may not be capturing them if we’re not looking at whole blood samples. And if they’re transformed in our bodies, which is, again, one way that these transformations can occur, you know, it may be contributing to the levels of the various PFAAs in our bodies. And so the bigger question is, how do we capture the full exposure of humans to PFASs, both from H. bluff, in fact, to drinking water, as well as all the other different potential sources. And with that, I will end my presentation and turn it over to Dr. Erickson.

Thanks, Chris, for the excellent presentation. And yeah, to wrap things up, what I’d like to do is just to follow on where I’ll highlight some of the work that we’re doing at Regenesis and also, you know, work that others are doing revolving around the remediation of particularly AFFF-impacted soils that we’re finding on sites at various locations. And so, you know, what I’ll do is just touch for a moment on some of the remediation activities that we have at Regenesis. And then I’ll do what I call roll the highlight reel of some of the research that has been looking specifically at some of the technologies that we have at Regenesis.

And then just more broadly, what’s being done within particularly the DOD to investigate you know, what are the appropriate measures that we should be taking to manage these impacted soils and aquifers that we’re finding. And so, one of the main impacts from AFFF and how it’s gotten into the environment is application through the use of either a training or incident response where AFFFs were used either at airports, DOD facilities, et cetera, and the impacts that they lead to. So, we heard about the compounds, both the perfluoalkyl acids as well as the precursors that are present in soils. And, you know, that sets up over time these situations where we’ve got contamination impacting our aquifers. And ideally, we can come up with ways to address both of them.

And so, Regenesis, a couple of the different technology classes that we have, I’m showing here, you know, they are adsorptive technologies in the form of a Source-STOP. This is a technology that we can use to immobilize, you know, these PFAS that are present on soils. And then we can install these permeable barriers so you can install this this line of points that as groundwater is moving through these areas where we put in an absorptive technology you know the PFAS are removed and you know sequestered for for a significant period of time and so you know now what I’ll do is just quickly touch on some of the the research activities that have been looking into these concepts and and how it fits into the the remediation world Because we know that, with a problem as large as what we’re facing, a good toolbox is really what we’re all after for building out.

And so before I do that, this is a technology that’s been applied now on nearly 50 sites across the US and abroad. And we’ve got almost 200 sites in the design and review phase. And so this is, again, one of the methods that we think is really going to play a role in mitigating the impacts that PFAS have had to soils and groundwater in the coming years here, as they become more and more widely regulated. So the first paper that I’ll touch on is one by Chuck Newell and his colleagues at GSI, looking at what’s on the table, what are the options that we have in the remediation space right now.

What Chuck does is he nicely outlines a number of scenarios to manage PFAS in soils and groundwater. And he outlines three different scenarios. You know, one of which is this idea that we find something that, you know, whether it’s an oxidative, reductive, or biological treatment that’s going to help, you know, degrade PFAS in situ, you know, that would be something that we’d like to see. But the more likely scenarios, at least in the coming years, are some combination of either pump and treat or pump and treat with plume stabilization methods using, you know, particulate absorbance or other forms of immobilization to really set up what they refer to as a triage, where given how widespread the issues are, one strong strategy that we can use today is that we can put absorbance in place that can help us to enhance the attenuation or enhance the retention of PFAS as they’re in these soils and groundwater.

And really, depending on where you are and what else is used, This is a viable technique that really reduces the amount of impacted groundwater that then makes it to receptors, whether that’s surface waters or drinking water, which is what Chris talked about a lot today. And so really, I’d say this publication really helped set the stage for one of the means that we will certainly be using to help address the challenges that PFAS and groundwater and soils are posing to us. And then the other publication, the next one I’ll talk about is, this is the first publication that was looking at what we lovingly refer to as the accidental site, a site that addressed PFAS using colloidal carbon in situ.

And so this was done by Rick McGregor in Canada. And the paper talks about a site where there was a former fire training area that was being initially remediated for hydrocarbons. After the fact, it was realized that there was also PFAS present. And so, you know, sampling was done before the application. And then, lo and behold, you know, after application, groundwater was showing that PFAS was removed, you know, at least the measured PFAS in that suite that Rick was measuring. And so this really set off the interest in this technology for us, at least, and some of the other papers that came along, you know, talking about the efficacy of this approach, and which kind of brings me to this next paper, which was a modeling look at the application of this particular site, and a modeling look at the longevity, the expected longevity of using colloidal carbon and other absorptive ideas to address PFAS in situ.

And so, you know, this was a good team that looked at, you know, a modeling approach. They looked at different, you know, if you take the isotherms of the carbon, and now the various components that are present in the groundwater along with your PFAS, what’s the expected longevity of a treatment of this nature? And so, and the conclusions are, and I’ve got the QR codes here for anyone that wants to follow up on these publications to check out, projected longevity on the order of decades. Moving forward, there’s been now a number of sites that we’ve done applications are, and that laid enough work there that they could take another look at the longevity and projected longevity of applications, particularly on airports in this case, so AFFF impacted sites.

And this publication reviews 17 different sites where Plum Stop was used. And they again looked at modeling of the different scenarios. And so the building on the longevity that we talked about, the publication gets into different doses of carbon in place and what the expected longevity would be under different scenarios, as you can see here. So, really, there’s a building case that this is a viable strategy, and it’s also one that’s garnered attention from the DOD. And so, those of you that are familiar with SERTEP and ESTCP, this is a big funding mechanism for the DOD to look at problems that they need addressing. And this table alone is the timeline of projects that they’ve had in the works looking at PFAS and how do they manage the situation that they have on their sites.

And the ones that I highlight here represent a number of sites, a dozen or more funded projects that are looking at various orbits, colloidal carbon, and other techniques in situ at this idea that this can be managed in part, at least from an in-situ stabilization standpoint. And so there’s, again, growing and increasing interest in this technique. And I’ll also point out that there’s a NESD project that is in its second year now of monitoring, that also is looking at colloidal carbon. So again, just coming on the heels of Chris, I wanted to highlight some of the research work that’s being done around the approaches that we’re using at Regenesis to address PFAS in situ.