Chris Hughes discusses biodegradation and environmental persistence on The Eco Well podcast
Are you interested to learn more about the topic of chemical biodegradation and environmental persistence?
If so, then my conversation with Jen Novakovic back in October 2024 on The Eco Well podcast is a good place to start.
Our discussion covers:
What is biodegradation and persistence? Why is this important?
How we test for biodegradation and assess persistence.
The history and latest developments, including PFAS, microplastics, PMT/vPvM, polymers and EU policy changes.
Data availability and quality issues, plus other challenges.
Biodegradability claims and greenwashing.
Differing perceptions of the term 'persistence'.
Implications for the cosmetics sector and the future of chemicals management.
Prefer to read? Here is a transcript:
Jen: Welcome to The Eco Well Podcast. This is a show about the science of cosmetics. My name's Jen, and I'll be your host. With the greater awareness of issues of persistence for chemicals — for example, with all the press regarding 'forever chemicals' — the topics of biodegradation and persistence are becoming increasingly important for brands to understand.
With all the regulatory movement and noise, I figured it was a good time to do a deep dive. This episode is a 101 on biodegradation and persistence. To help me unpack this topic, I was joined by Chris Hughes from Embark Chemical. Disclaimer: this episode definitely got a bit into the weeds, but if you're interested in really understanding what it all means, especially in the context of cosmetics, I think it's important.
Jen: So I'm here with Chris Hughes, who does a lot of work around ecotoxicology and biodegradation, and that's going to be the focus of this podcast. It might be a little in the weeds — I don't know where this conversation is going to go — but I wanted to have it anyway, maybe for my own selfish purposes. Anyhow, this podcast is going to be about biodegradation. But before that, Chris, would you mind introducing who you are and what you do?
Chris: Sure. Thanks, Jen. Thanks very much for having me on — it's a pleasure to be talking with you. My name's Chris Hughes, and I'm the founder of Embark Chemical Consulting.
We've been in business now for just over a couple of months. Prior to that, I was working as an industry scientist and then as a consultant for six years with the consulting company Ricardo. My background is in environmental hazard and risk assessment of chemicals, specialising in the European regulatory frameworks such as REACH and CLP.
I've got a particular focus on biodegradation and the environmental persistence of chemicals, which is really taking off at the moment in terms of the level of interest — both from the public and the regulatory community — all linked to the global sustainability agenda. So recently I decided that it was the right time to establish Embark Chemical Consulting. My mission is to help organisations to navigate the path to the sustainable and circular economy, with a particular focus on biodegradation and persistence, but also helping them with the many cross-disciplinary challenges they might face.
Jen: Okay, so I guess for some groundwork, maybe it makes sense to ask: what does biodegradation mean? And also maybe how does it relate to persistence?
Chris: Going back to basics, biodegradation is about the breakdown of chemicals by naturally occurring microorganisms. Typically, organic chemicals will break down to CO2, water, and other salts and simple molecules. That's called mineralisation, and that's the desired end goal for the chemicals we use in day-to-day life — particularly if we are releasing them down the drain, which is the main route by which cosmetics might potentially be released into the environment.
We want chemicals to mineralise, but chemicals can sometimes take time to fully mineralise, or they can get stuck partway down the pathway. You can think about biodegradation as a series of steps from the molecule that you place on the market — every reaction transforms it into something else, and ultimate degradation is the culmination of all those reaction steps. Biodegradation is by far the most important means by which chemicals degrade in the environment, but they can also degrade through physical processes such as hydrolysis and through the action of light — photodegradation.
When we get onto the topic of persistence, this is about how long chemicals are likely to reside in the environment. The longer they're in the environment, the greater the chance they have to cause harm or to get back to people through drinking water, the air, or the food that we eat. Obviously, persistence — once chemicals are past the end of their life cycle — is not a positive property. The concern is that chemicals that are more persistent can build up to higher concentrations in the environment than non-persistent chemicals, and those concentrations can be difficult to reverse if we were ever to stop emitting that chemical.
Jen: So we hear phrases like 'readily biodegradable'. What does that mean, and what are the other kinds of terms used to describe the rate of biodegradation?
Chris: Ready biodegradability is kind of the main classification that we're looking for with chemicals. It corresponds to the performance of the chemical in what is called a biodegradation screening test — the so-called ready biodegradability test.
This is where you take the chemical, you incubate it at a set concentration using a standardised inoculum. You have a set mineral medium, and you take your inoculum from, say, a sewage treatment plant and do some preparation of it before you incubate the chemical. Then you observe degradation of the chemical, normally by an indirect measurement like the consumption of oxygen or the production of carbon dioxide.
What we're looking for when we talk about ready biodegradability is that the chemical is observed to degrade above a certain threshold — normally 60% in the test. If you get above 60%, you're considered to have passed, and the chemical can be considered readily biodegradable. There's another criterion: that degradation needs to take place within 10 days following the start of degradation, and that's called the 10-day window. Normally what we see in these tests is the chemical will sit in solution in the vessel with not a lot happening, and then all of a sudden you'll get a lag phase followed by an exponential growth phase of the inoculum as the bacteria grow on the chemical. What you want to see is that the degradation hits 60% within that 10-day window.
Ready biodegradability is used across all kinds of different legislative frameworks and eco-labels — it's a kind of universal standard, and we have OECD standardised tests to assess this. There are a number of different tests that account for different properties of chemicals, since certain properties can cause issues with certain kinds of tests. That's kind of our universal language for talking about the biodegradability of chemicals — or at least it was until quite recently, when the global sustainability agenda arrived and a few other issues threw everything up in the air, to be honest.
Jen: Before we get to that conversation — which is important — to continue laying the groundwork: what kind of chemicals biodegrade? And if something doesn't biodegrade, does that mean it doesn't necessarily degrade at all?
Chris: Yeah, I mean, this goes to the properties of chemicals and how that impacts their fate in the environment, and also their tendency to degrade and what reactions they can undergo. The question of whether a chemical is going to degrade is very multifaceted.
We also need to think about the situation that the chemical's in — the environmental conditions — because those can be really important too. The presence of light, the pH, oxygen, redox conditions, things like that. One thing that's often quite important is whether the chemical is in what we call an available form — a freely dissolved form. That's kind of a prerequisite to biodegradation taking place, in order for enzymes to gain access to the chemical to do the work.
What we find with certain chemicals is that if they're very large molecules, or if they're very hydrophobic, they will have a tendency not to want to be dissolved in water. They might be sorbed to particulate matter, they tend to prefer to stick to surfaces, or they'll dissolve in fats rather than water — and in those cases they can have a more difficult time being degraded simply because they're not available to the organisms that might degrade them. It's a balancing act and quite a nuanced picture.
It's important as well for biodegradation screening tests, because in those tests you have fixed conditions — a set concentration of your inoculum, a relatively low concentration of inoculum, and a set concentration of your test chemical, which is relatively high. If you have a chemical that's poorly soluble in water, you can end up with a case where a lot of your chemical is not actually dissolved in the medium, and therefore you're not seeing degradation — but that may well be because the chemical's not bioavailable rather than because it's not biodegradable.
When we're looking at biodegradation and persistence — if we take the REACH regulation, for example, and the requirement to do a persistence assessment — the scope is limited to organic chemicals. So that's the first step: if the chemical's not organic, it's not really of interest from a persistence assessment standpoint. Then you're looking for chemicals that are really persistent and therefore potentially causing a problem.
The one that everyone's talking about right now is the family of PFAS chemicals — the per- and polyfluoroalkyl substances. Those molecules have carbon-fluorine bonds, which are extremely strong bonds, and these molecules tend not to break down in the environment. As a result, they're being found pretty much everywhere, and there's growing alarm that these chemicals are accumulating. You'll have heard the term 'forever chemicals'. You can see this groundswell of public concern, and there's a huge amount of scientific research and regulatory activity as well.
That's one of the reasons why persistence of everything else has really risen to the fore — because we had these regulatory frameworks for chemicals, companies had to comply with regulations to place these chemicals on the market, but the majority of us didn't really anticipate the issue of PFAS, which is turning into quite a runaway issue now.
Jen: Coming back to the biodegradability topic — are there some conditions that might confuse results for biodegradability? What's that landscape like?
Chris: There certainly are issues that can arise that affect the reliability of your studies and can also lead you to over- or underestimate the degradability of a substance.
The two that come to mind for overestimating degradability: the first one is if you have a chemical with a positive charge — a cationic substance — that will tend to be quite a sticky material that can stick to the surfaces of your vessel and things like that. Depending on how you're running your test, one of the ways you can run it is to measure what's called dissolved organic carbon — you measure the change in dissolved organic carbon over time. If you don't account for the amount of chemical that's sorbing to the glassware, you might interpret that as being degradation, when in reality the chemical is just sticking to the glassware.
It's also important when you get to the higher-tier testing, which I think is going to become more and more important. For the past 20 or 30 years we've been happily working in this area around ready biodegradability and biodegradation screening, but there are also higher-tier tests which are designed to measure the rates of degradation in different environmental compartments — and those are more commonly used in plant protection products and biocides. But we're seeing more and more that this kind of data is now being required for other regulations. In those tests you measure the disappearance of your chemical, rather than, say, the production of carbon dioxide. So if your chemical is sticking to a surface and you can't recover it, or if it's volatile and it's escaping from the vessel, that's another way you can misinterpret the data — attributing loss from the system to degradation when it isn't.
One final example: bacteria are very clever, in that if you expose them to a chemical for a long enough period, they will find a way of degrading it — they're continuously turning over and, in effect, evolving. This process is called microbial adaptation. For regulatory assessment of chemicals, adaptation is considered a big no-no — you shouldn't be using an inoculum that's either been pre-exposed to that chemical or has had an opportunity to adapt to it prior to starting the test. If you have data generated with an adapted inoculum, you might be showing more degradation than you otherwise would, and that would be another reason why the results would be questionable.
Jen: So there are two questions I wanted to ask, and I'm not sure what makes sense to ask first. One is about common misconceptions around biodegradation. But the other is, because you were talking about testing and some of the new tests that are coming out — the evolution of biodegradation testing from where we started to where we currently are. Maybe let's start with the evolution of tests, just because we were kind of talking about it there.
Chris: Yeah, it's probably good to go back to the history really — how did we end up looking at biodegradation in the first place? Why do we care about this?
You can chart this back to the 1950s or even earlier. One of the big revolutions in chemicals was the development of detergent surfactants, which replaced soaps — prior to that, soaps were used for cleaning in pretty much every application. We had these alkylbenzene sulfonate surfactants that were not very degradable, and that was the first time that chemical biodegradability really came to mind as an issue. These surfactants weren't degrading in water treatment infrastructure, and as a result we were seeing foaming — in sewage treatment plants and even in water bodies as well. This was obviously a problem. It led to the development of the linear alkylbenzene sulfonates that are still in use today, and it also drove the development of tests around biodegradation.
That really started things, and then we had the Silent Spring period — Rachel Carson's 1962 book — which focused on organochlorine pesticides and the issues those could cause to both people and wildlife. One of the main reasons they were such a problem was their environmental persistence. Chemicals like DDT and the drins were in the focus here. That's how we started on this journey of identifying the chemicals that were really problematic — chemicals with persistence and bioaccumulation potential and also toxicity. Long-range transport potential is also a property of concern, in focus for example under the Stockholm Convention.
That really took us to where we've been up to about 10 years ago. Different countries around the world adopted the so-called PBT or POP frameworks to identify these problematic chemicals. As part of that, if a chemical was suspected to be a PBT, then you needed to investigate its persistence in more detail — and you can't really get at that with a ready biodegradability test, because a ready biodegradability test is only intended to assess the high potential for degradation. If it fails that test, it's considered not readily biodegradable, but generally you would just stop your assessment there.
There are many reasons why a chemical might not pass that test — it's a very stringent test and you can often not have the right microorganisms in your inoculum to allow the chemical to degrade. But generally, ready biodegradability is the goal there, and you can't get at the question around persistence. To assess persistence, you normally have half-life criteria for different compartments: water, soil, and sediment. So you need a way of getting half-life data, and you can't get that from a ready test.
What we generally use instead is a class of tests called simulation tests, which are very different to the screening tests because here you're trying to get a realistic measurement of how quickly a chemical degrades in each of those compartments. When you have that data, you can model the degradation kinetics, get a half-life, and compare that to the criteria.
If you think about it, the way we've managed chemicals to date: we've had the screening tests looking for the readily biodegradable chemicals, and we've had the simulation tests looking for the PBT chemicals. That's generally been our domain for industrial chemicals — chemicals used in cosmetics and other domestic applications. For plant protection products and biocides, they go into a lot more detail on the risk assessment side and routinely use those tests. So generally for those chemicals, that sort of data exists. But for other chemicals, very few have it. That seemed to be okay because we were looking for PBTs, and if things weren't PBT, then we were pretty relaxed about it.
But more recently, with the issue of PFAS in particular — and also to an extent microplastics and plastic pollution — we've got these two big global issues linked to chemicals that are largely driven by the issue of persistence, in that both these materials are extremely persistent. So it's not just a matter of whether a half-life is greater than a certain cut-off — in effect, these materials don't appear to degrade at all.
What that's caused in Europe, at least, is something of a contagion effect. One of the big concerns with PFAS was that these chemicals are getting into drinking water and causing harm to people as a result. The follow-on from that has been a new concept called PMT — persistent, mobile, and toxic. As a result, that's now in law in the European Union, in the CLP regulation. There's a new hazard class that's been added to the European version of GHS for persistent, mobile, and toxic, and even very persistent and very mobile — so you don't actually need the toxicity element to meet the criteria.
What this has done in effect is elevate persistence as the most important property out of the three. We have PBT chemicals — the ones that are bioaccumulative, the ones that are fat-soluble, that prefer to be in fat rather than water. But now we've got PMT: the mobile chemicals are more water-soluble, less fat-soluble, more likely to pass barriers, less likely to stick to surfaces, and more likely to get into drinking water. You can think about this as a hydrophobicity scale: we had PBT at one end of the scale, and we've now got PMT at the other end. The two properties are in effect cancelling each other out, which means that, really, we're looking at persistence across the full spectrum. Not many chemicals are likely to be neither bioaccumulative nor mobile — so we're now looking at persistence for essentially all of them, which means we need to understand this property much more deeply and we need a lot more data.
That's how the testing is evolving, because we're seeing now under the REACH regulation that the European Chemicals Agency has issued clarifications to say substances should have data on simulation tests. Most of them don't currently, but what ECHA has basically clarified is: yes, we know there's not much data here, we know that waiving conditions have been used to avoid doing these tests, but we're telling you now that you need to do them, and we are going to make you do them.
That's what we're seeing: ECHA runs this dossier evaluation process where they review dossiers and issue decision letters saying, 'You've got this, this, and this gap in your dossier. We want you to run these tests. Come back in two years with the data, and if you don't, then you're subject to regulatory enforcement.' We've seen a huge increase in the number of simulation tests being requested as part of this activity. What this is in effect doing is changing the way we manage chemicals in the EU, significantly increasing the importance of persistence, and it's going to cause a lot of chemicals to have new regulatory impacts because they'll either be PMT, vPvM, or they'll fall foul of a false positive from the simulation tests.
I should say that simulation tests are very expensive, very complex, and challenging to perform, and there are also some issues with the robustness of some of the methods. For example, the OECD 309 test in surface waters — there's been a lot of literature published recently suggesting that this test, as it has to be set up according to the regulation, has some issues around the reliability of the data you're going to get at the end of it.
Jen: That seems like a concern. So maybe before the misconceptions question — I'm just wondering, what's the impact? What's the impact to chemical industries, and also how does this impact finished products? Probably a pretty big economic impact based on what we understand, especially if there are reliability issues. Is this going to make products more environmentally friendly? Is this going to be a net positive?
Chris: It's difficult to say right now. I think there are certainly going to be changes afoot, that's for sure. I will say as well that specifically for the cosmetic sector, it's a little bit nuanced, because at the moment you don't need to classify cosmetic products according to GHS in the EU. In effect, they're not going to be carrying these labels, unlike other sectors like home care products that will have to have these additional labels.
But it is part of the European Chemicals Strategy for Sustainability. The intention is to include these hazards as categories of substance of very high concern under the EU REACH regulation, and we're already seeing the PMT and vPvM hazard classes being included under other regulations as well — as substances of concern. The Corporate Sustainability Reporting Directive and the Ecodesign for Sustainable Products Regulation both mention these hazards as things that need to be declared or things that will impact products in the future. Ultimately, there will be lots of chemicals currently in use that may fall out of suitability.
There will certainly be disruption. It remains to be seen whether there will be suitable substitutes for all the chemicals that end up with these labels. And as I said, there's likely to be some collateral damage too, because at the moment we're generating a lot of data from tests that have some apparent limitations, but the rules are still there for how the data should be interpreted. So it's not really clear what the long-term outcome is going to be in terms of the chemicals that are impacted.
Also, the overall impact of introducing the policy measure itself is still quite uncertain, because a chemical can undergo a transformation into something else — and normally what that does is make the chemical more polar. If the chemical progresses to mineralisation, then it's fine. But if the chemical gets stuck partway along its degradation path, you could end up with a transformation product that meets the criteria for vPvM — in which case the parent substance would also have to be classified vPvM.
It's still very uncertain as to what the long-term implications of this new hazard class are. It remains to be seen whether it will be adopted in other regions of the world as well. The UK hasn't adopted it and the US hasn't adopted it, as far as I'm aware, but it is being discussed at GHS level, so it's an ongoing matter.
Jen: Will this impact ingredient suppliers — because a lot of ingredient suppliers sell to household care products as well. Will this have a kind of global impact, given that many ingredient suppliers also manufacture globally? And is there an issue with where they're manufactured — is this specific to ingredients manufactured in the EU rather than imported?
Chris: So it's an EU regulation, so it affects substances that are placed on the market in the EU. Whether you manufacture them in the EU or you place them on the EU market, your product will need to comply. For listeners who are producing some of these chemicals outside the EU but want to sell into the EU market — you need to be aware of these developments, because even if you're not sharing the cost of doing the tests, you might ultimately be caught by the classification that comes through.
Jen: And so maybe this will have repercussions globally, because we're a global market in cosmetics — most large companies want to sell into the EU.
Chris: I think so as well. People are looking around at what's happening, and if a chemical is being banned or found to be unwelcome in the European market, it's not a great leap of the imagination to think there's likely to be some impact on demand elsewhere, especially in these consumer-facing sectors. So much of the pressure comes from the customer as well as from regulation.
We saw this probably most clearly — and again going back to the importance of persistence — when Unilever recently made an announcement that all of its ingredients were going to be biodegradable. That's caused big ripples through supply chains, because everyone is asking: how can we either get the data we need to demonstrate this, or how do we innovate to come up with alternatives that are more degradable?
Another example of where this is becoming clearly more important for the cosmetics sector is the new organisation — the International Collaboration for Cosmetic Safety — whose main focus is around animal testing, but there's also a big environmental safety component to it. For example, we developed a persistence assessment software tool which was co-funded by ICCS along with Concawe and CEFIC LRI. They have more projects now looking at standards for biodegradability of formulations, and also two additional projects on biodegradation of polymers, because polymers are another really important class of chemicals used in all kinds of different products — and there are question marks around how you even assess the biodegradability and persistence of those materials compared to all the standards that have been developed for smaller molecules.
Jen: Yeah. So a lot of uncertainty with respect to the outcomes of these regulations considering the reliability issues, and a ton of innovation happening right now to improve the methods used to test biodegradation. I'm reminded of something somebody in environmental risk assessment — who I really admire — told me. Coming from the finished product side of things, they said the biggest challenge for producing more environmentally responsible products, especially considering biodegradation, is data.
Chris: Mm-hmm.
Jen: Data reliability, but also just the absence of data from different ingredient suppliers. What would your comment be on that? And what are some of the other challenges that you see for finished product suppliers — specifically for cosmetic product producers?
Chris: Yeah. Absence of data has been a big problem. As I've alluded, this is a huge issue now. Before, it was possibly arguably less of an issue, so maybe it wasn't given quite the same attention as some of the other endpoints like toxicity. As a result, data that people thought were good are not actually as reliable as was thought, or regulations and guidance continue being updated, so what was good before maybe isn't considered so good any more.
A good example is if you have a substance with a complex composition. Many substances are not actually a single molecule — they are a mixture of different molecules, but still considered one substance. Naturally derived substances, surfactants, and things like that are often what we call UVCBs — substances of unknown or variable composition, complex reaction products, and biological materials. It's a big, broad class of chemicals, and about a third of chemicals on the market are UVCBs.
It's basically been declared in Europe that you need to assess the whole composition. You can't use a ready biodegradability test to unequivocally rule out concern for persistence on a UVCB, because you have a complex composition and in principle every constituent of that UVCB is going to behave in a different way. So this is part of the evolution of the regulatory practice for classification. For the old classification system, there was a kind of benefit of the doubt given to that kind of data, but now as we're moving into the persistence assessment space it's much more stringent — and we might find that chemicals which we thought were okay aren't, because we don't have enough to substantiate that there isn't 0.1% of that ingredient that might fulfil the criteria.
When you get into the minutiae of it, it really starts to feel quite unworkable in terms of getting the robust assessment that's required on paper. It really will remain to be seen how it all plays out in practice. But I think there's going to be some collateral damage, with certain substances being caught as UVCBs that haven't quite got the data to substantiate that they're not persistent.
I keep going back to the sustainability agenda and how it's really changing the way that people are looking at chemicals. While I was at SETAC — just to highlight how this issue is growing — we established a new interest group on persistence. They have interest groups for all these different matters, but they've never had one on persistence before. When you're in that kind of environment you can just see how people are continually pulling at threads. And that's what's happening now with this whole area — there's something there which doesn't quite line up, but people kind of said, 'Well, it's probably okay.' Now it's like, well, no, it's not okay, because we're looking at things in a different way. That's the kind of thing that industry really needs to be aware of — what was okay before is probably not okay any more, and they need to be prepared for disruption and new issues to arise where they didn't before.
Jen: On the other side of this conversation are claims around biodegradability on finished products. That's kind of a hot topic — the FTC considers it a deceptive claim. Now I've had conversations with people from finished product companies who feel that's too strict, because they feel that they have tests that can verify the biodegradability of the formula. Now with all this uncertainty around reliability — do we actually have the ability to verify biodegradability for finished products? What's that landscape like?
Chris: I would certainly say that yes, in principle, a biodegradability claim should be able to be made. If you have a substance with robust ready biodegradability data to support it, then I would have no issue with making that claim.
But this goes back to some of the uncertainties I was mentioning before — those loose threads that are now being pulled — which is raising concerns that some of these biodegradability claims are not going to hold up in the future. I understand that some of this is linked to a general backlash against bogus claims. There were the green claims issues in Europe as well. And I understand that part of this is driven by the issue of packaging, in that everyone was saying 'this packaging is biodegradable and compostable, don't worry about it.' I'm not fully up to date on what's happening in the US, but I understand that in California there was a law passed that kind of banned biodegradability claims — driven by packaging, but it caught formulations in the net too, so you could no longer make a biodegradability claim about your formulation.
Things like that are really quite dangerous, because you can see how a contagion effect can take place — other states will pick it up — and if it's not based on sound science at the policy development stage, then before you know it, you've thrown the baby out with the bathwater in terms of what you can say about products. There is a real advantage to using a product with readily biodegradable ingredients versus one without, and I would hate to see companies no longer allowed to innovate for biodegradability, because that's one of the key ways we reduce impacts on the environment.
A similar thing is happening in Europe as well. I think we're all facing the same questions, and I think it's important that at this point we remind ourselves of the science that underpins these assessments and what we've been using for several decades — because if we're not careful, we'll throw the baby out with the bathwater and end up having to ban everything.
Jen: And now coming back to the question I said I would ask earlier and didn't forget about — what are some of the common misconceptions you hear with respect to biodegradation and persistence?
Chris: So it's not really a misconception per se, but there's one thing I think is important to flag. One of the things we were discussing in the new interest group was that we don't have a good shared understanding of definitions.
When I say 'persistence' to you, it means something very specific to me, because I work in the area of prospective hazard assessment of chemicals — I'm thinking of persistence criteria, half-lives greater than 40 days in fresh water, greater than 120 days in soil, for example. But if I said that to a remediation specialist — somebody who deals with contaminated land — they would have a completely different perception of the term. Their consideration would be how long the land is staying contaminated and whether their remediation efforts are bearing fruit. There are also set conditions to my kind of 'persistent' — we're talking about diffuse pollution of the environment and very low-level concentrations of chemicals. That's what we're trying to look for in regulatory persistence assessments.
Now let's talk about PFAS, forever chemicals — they're persistent, right? But they're way more persistent than the P cut-offs of a PBT assessment. They're essentially not degrading at all, but people still call them persistent. So as long as everyone means something different when they say the same term, we're in trouble, because we can't get on the same page. That's been part of the issue with persistence, because everything's being tarred as a 'forever chemical' when people say it's persistent, because people are thinking about PFAS.
I would say: just because a chemical is not readily biodegradable doesn't necessarily mean it is a forever chemical. There's a big, broad spectrum there, and chemicals have got to be pretty degradable to meet those criteria. Bear in mind also that the environment is very variable — if you have a result from a biodegradation study that's not particularly good, that doesn't mean that's the end of the story. If you repeated the test, you might find you got a much better result, either by setting the test up in a more appropriate way to deal with the properties of your substance, or if it's poorly soluble by using what are called bioavailability improvement methods — and you can actually get a better result by going down that route.
The way ready biodegradability tests work is that they're designed to be very stringent, so positive results should supersede negative results. If you did two tests and one was a pass and one was a fail, generally if there's nothing wrong with the passing study, you would consider the chemical to be readily biodegradable. So I would say to people: if you have data in hand that's disappointing or surprising — if the chemical's not degrading as you'd expect — it's always worth setting up another test, maybe working with someone who understands how to set the tests up to get the best out of them, and trying to improve on the data you have.
The thing I'd want to leave people with is: all bets are off in terms of where things are going with persistence. There is change coming in terms of how chemicals are being assessed. It's important that people are aware that things might change in the future. One of the big issues with this is that we're dealing with differences in worldviews linked to sustainability — we're thinking about things in a new light, thinking about humans' impact on the planet. Perhaps all the things that people gave the benefit of the doubt to before are now being challenged.
Ultimately, persistence rings true to people when they look at microplastics or PFAS, because it relates to how chemicals are able to modify and degrade the environment. If you come from a worldview of wanting to preserve the environment, then persistence is going to be a really important issue, whereas maybe 20 years ago we were thinking more about how to minimise risk through day-to-day activities. That's a different question, and that's part of the reason why we are where we are today. There's more to come on this topic, for sure.
Jen: And now I just have to ask — just on the off chance that one of my consumer listeners got to the end of this podcast: if that's you, congratulations, I commend you. For the average consumer who's interested in supporting more biodegradable formulas, or maybe just wants to know more about this topic — is there anything you would want to leave them with?
Chris: I would say that generally, people are working hard to manage the risks of the products you're using in day-to-day life. Not all chemicals are forever chemicals. We have good infrastructure in place — if you're connected to wastewater treatment, for instance — to prevent or limit the release of chemicals into the environment.
Don't despair when reading the headlines. A positive note is that the environment is truly wonderful and amazing in the way it can work to remove chemical contamination. A lot of the tests we use don't fully capture the complexity and the real power of the environment to sort of heal itself. That's another thing to bear in mind when we look at this sort of data — the environment is far more complex than a vessel used in some of these tests, and it can really surprise you in terms of what it can do.
Jen: I hope you found that conversation as informative as I did. Big thank you to Chris for agreeing to be part of this podcast episode. Another thank you again to our Patreon supporters. A final reminder to please subscribe to our podcast and write a review — and that's all I've got. Thanks for tuning in.
