How do 'forever chemicals' harm our ecosystems?

The health risks associated with PFAS are starting to creep into the light. Last year, it was found that exposing cancer cells to certain forever chemicals causes an increase in cell motility, making them more likely to metastasise. Also, a study from the Keck School of Medicine found that PFAS accumulation in adolescents has been linked to limiting their peak bone mass acquisition, leading to greater rates of osteoporosis. But there’s growing concern that PFAS exposure can play a part in increased risk of diseases from liver damage to decreased fertility to hormone interference. At the moment, the real limit to our knowledge is time. The majority of PFAS health studies are still in their early stages, so we haven’t had enough time to know enough about them. Whilst we can observe a potential link between exposure and health problems, the mechanisms involved are currently less understood. We also don’t know where the cutoff in dangerous dose is, and how it differs among different groups of people. But whilst evidence of PFAS’ effects on human health is an ongoing thing, if we look at other organisms with shorter life spans such as marine invertebrates, the effects of forever chemicals is much more well documented. Richard Thompson works at the University of Plymouth, and he has special attachment to this subject, as it has been almost 20 years to the day since research he was a part of coined the term ‘microplastics’.

Richard - We got evidence from quite early work that when you had 1% of plastic, it was PVC in this case, mixed with 99% beach sand that wasn't contaminated, that affected the ability of marine worms to get goodness from their food to put on weight in the normal way, if you like. And that might seem slightly trivial, but of course that's not killing them, but it's affecting them over their lifetime. That could potentially affect their growth, their reproductive output. And I think that points to where probably the greatest concern in my mind about these small bits of plastic is not that they're going to poison all of the marine life overnight. It's more these long-term chronic effects where you might see consequences over a lifetime. Of course, at higher doses we see more immediate effects. We've recently been working with tire particles for instance, which it's clear when you have to replace tires, they've lost quite a lot of tread, right? Well all of that material is going into the environment. And then we've got small pieces that have a range of chemicals in them that are potentially of concern and they can be entering in quite high quantities near to roadways where they will wash off when it rains heavily.

Chris - And these forever chemicals, they're presumably also part of the potential toxic cocktail that can stick to particles and then get into plastic particles and then get into all species across the different elements of the trophic levels you mentioned in this way.

Richard - That's right. And I think as we consider those, we need to consider the two possible pathways. Now, one is that the plastic in water has acquired those chemicals from the environment. The forever chemicals are already there from other sources. Many of these chemicals are hydrophobic in nature, so they will latch onto the surface of plastic. And that is quite a significant effect. In a matter of days plastics can concentrate some of these chemicals in orders of magnitude more than the concentration in the surrounding seawater. And some of the early work we did showed that when a creature ate those particles, it increased the rate of release of those chemicals. So you potentially got a mechanism of transfer. The rate of release into a warm blooded creature was up to 30 times greater, let's say, than if we transferred our piece of plastic with the chemical burden just back into clean sea water. So there's a mechanism there, but even that doesn't prove harm in itself. It establishes a mechanism. And there's subsequent work that we did, because of course if you picture a creature in a contaminated ocean, it's acquiring those chemicals directly from seawater or from the food that it eats as well as from the plastic. So the key question really with respect to the issue of transfer of chemicals by plastics is how much worse does the presence of the plastic make it for that creature? And with the chemicals that are already in the environment, probably the additional contribution of the plastic is quite small compared, let's say to picturing a fish or a filter feeding, taking the water, the seawater, over its gills and acquiring the chemical directly that way because it's passing far much more water over its gills than it is encountering plastic. Those studies were based, and this is the caveat that I think is going to be interesting going forward, they were based on assuming the plastic passes through the gut in a normal transit time. It goes in and it goes out. How much chemical could be released. Now since then, we've shown that the nano-sized particles of plastic litter will very rapidly circulate throughout all the tissues in the body. We used scallops, marine molluscs, and we showed that within six hours they'd passed from being ingested throughout the circulatory system to all of the tissues. But weeks later, some of those nanoplastic particles were still present in the scallop. And so I think in those scenarios there may be different potential for harm where you've got bits of plastic with a chemical burden lodging in specific tissue. So I think that the question about chemical transfer from water to creatures by plastic, there are also additive chemicals that are used at the time of manufacture. That's a slightly different pathway in that because these are additives in the plastic, their additions to the environment when the plastic enters the environment. So it's a different story to the plastic picking up a chemical burden that's already in the ocean and redistributing it, and you're asking the question, did the plastic make things worse with respect to that chemical that was already there? If you're talking about the plastic bringing a chemical into the environment with it, then it's clearly an addition to the environment. And some of those chemical additives can be present in the plastic product at really high concentrations, at higher doses if you like, than you would likely accumulate onto the plastic from seawater.

Chris - Could the plastics paradoxically be helpful in some respects? Because if they are good at sucking up the 'nasties', and we'll put to one side the nasties that they might bring with them, because they're oily and the oily chemicals would rather be on the plastic than in the sea water. If you put plastic in the water and it soaks up all these things and then sinks, does that mean actually the plastics might be helping to a certain extent to get rid of some of these forever chemicals or these other nasties that would otherwise end up in a fish?

Richard - I wouldn't see it or describe it like that. Certainly we can use plastics to mop up oil spills because of this affinity. So you can use them in a cleaning sense, but I certainly wouldn't think about putting plastics into the ocean to accumulate some of these chemicals. And it's all really about thinking about the kind of concentration gradient between the amount of chemical that's in the water, the affinity to the plastic, and the plastic can of course move around. If it sinks to the seabed, it's moving to a different compartment. And if there's a lower concentration of that forever chemical on the seabed compared to at the sea surface, then some of it will be released again. And one thing that is very different about plastics, in the same way that the oceans have the ability to move around particles of natural sediment, it can do the same with plastic particles so they don't become diluted and diluted and diluted. They can become redistributed and concentrated in some location.

Chris - And to finish, how worried are you about these forever chemicals, these various industrial substances which are pretty pervasive and appear to hang around for really long periods of time and are getting into the sea? How bothered are you by that?

Richard - I'm very concerned about anything that we're putting into the environment that is persistent. There's evidence of toxicity and it's potentially going to accumulate. And I think this has to be the way forward that we have to look at and screen in a much more responsible way the chemicals and the particulates that are entering the environment in order to make sure that we're not creating long-term effects. Because once these plastics are micro or nano plastics, there's no way of removing them. And it's a similar scenario with the chemicals that you're talking about.