How could microplastics affect human health?

What might be the health impacts of microplastics on us humans? How heavily are we being exposed, and when we are, what happens? Studies have shown plastics entering human lungs, and intestines, and getting into the heart, our brains, the walls of blood vessels, and even being present in semen. This suggests there may be potential consequences such as increased stroke risk, dementia and fertility costs. But is it too early to tell? Tamara Galloway is Professor of Ecotoxicology at the University of Exeter…

Tamara - There are all sorts of different ideas about how microplastics might impact human health. Some of those relate to the presence of the small pieces of plastic themselves, also physical damage, and others relate to the presence of different chemicals, particularly plastics additives that might be present in those plastic particles and then might leak out into the body. And most of the suggestions relate to things like oxidative stress and inflammation. The presence of those tiny little bits of plastics cause inflammatory changes to different tissues in the body.

Chris - The other thing that people have worried about is that plastic is made from oil and it will go around collecting up a cargo of other oil-based molecules. And when you put these into your body, it might offload that cargo into your tissue. So although there is a physical plastic effect, there may also be chemical damage going on as well.

Tamara - That's right, the so-called Trojan horse effect. The suggestion is that that can happen based on lots of hydrophobic chemicals or contaminants in the environment, and also metals that might be floating around, particularly in things like combustion from cars or air traffic.

Chris - How do we think, though, that these particles replete with their cargo get into the body in the first place?

Tamara - The most obvious route into the body is that most microplastics are ingested with food or drink. They pass from the gut. There is evidence to suggest that the smaller particles can pass across the gut and to the circulatory system and circulate through the blood.

It's also becoming obvious that there are plastics floating around in the air, so particularly fibrous microplastics. These can be inhaled and enter the body through the lungs and then enter from the lungs into the bloodstream.

Chris - And what sort of level of exposure do we all have? Are we talking about a handful of particles here and there, or are we talking about significant burdens of this stuff that we are breathing in and also eating?

Tamara - The suggestion is that the vast majority of the microplastics that we ingest are in things that we eat, and they're passed into food substances from packaging. So packaging is most likely a much larger source than, say, ingesting seafood that might already have microplastics in it. As to exactly how much we're exposed to, well, that's one of the problems because we're not entirely sure.

It's very difficult, it's very technically challenging to do those kinds of measurements and know exactly how much there is in any particular human body at any particular time. Just about all of us have microplastics in our bodies or are ingesting them and excreting them at any particular time.

Chris - Is it a one-way street then? Once it's in, does it stay in, or does it come and go?

Tamara - The suggestion is that it comes and goes. Particles that are taken up across the gut pass into the lymphatic system and the blood system, and then they can circulate through the body. And ultimately, they'll be cleared through the liver and the kidneys, and they'll be excreted in faeces and urine. So although they might circulate in the body, the vast majority will be excreted after a certain period of time. What we don't really quite understand is what happens to the particles that might be retained within the body, particularly the smaller-sized particles that are much harder for us to measure.

Chris - And what organs are we particularly concerned about?

Tamara - Well, a lot of the organs that have been studied have been highly vascularized organs, so that means organs that have a high blood flow. So things like the liver, the heart, even the testes and the ovaries, these have all been studied and shown to have tiny pieces of plastic present in them. What we don't know is whether that has any significance yet for human health.

Chris - Indeed, it must be a hard one to prove, because I suppose we've got different people alive in different places for different lengths of time with different levels of exposure, getting different diseases. So trying to tie this together and show a kind of causal relationship must be really, really tricky.

Tamara - Absolutely, and you've got to the heart of the problem there, because we're not talking about one individual thing that people are exposed to. We're talking about lots of different kinds of plastics of different shapes and sizes. We're talking about people in the general environment who are exposed to all sorts of different things at any particular time. They'll be eating different food, they'll be living different lifestyles. And a lot of the ill effects that we are expecting or we are predicting might occur due to plastics and microplastics are very diffuse things. They're chronic disorders.

We're not talking about acute toxicity here, where you could definitely say somebody's collapsed from plastic poisoning, say, in the same way that you might look at lead or arsenic or highly toxic substances. We're looking at very subtle effects and they're very hard to identify in population studies.

Chris - Do you think it's the new asbestos?

Tamara - I think there are all sorts of things that we don't yet know about microplastics. And one of the most interesting things that we can try to understand is how plastics relate to other particles that we might have in our body. So what is our exposome? How are we exposed to different particles? How are we exposed to different chemicals? How many of those might we be able to avoid? Is it an issue that we're breathing in all sorts of different things altogether? And what can we do to reduce our risk? I think those are the most important things to focus on.