Microplastics are everywhere, but just how harmful are they to human health?

Plastics are everywhere. They gradually break down into (very) small particles, micro and nanoplastics, which eventually end up in the soil and oceans. They are deliberately added to a wide range of everyday products such as cosmetics and abrasive cleaners, get released every time we wash our clothes, or end up as contaminants in human and animal food products. So how are these plastics affecting our health and how can we minimise our exposure to them? MOMENTUM, a consortium of Dutch toxicologists, chemists, epidemiologists, biologists, knowledge institutes and industry, was established to explore this issue. ZonMw, Health~Holland and the Netherlands Organisation for Applied Scientific Research (TNO) are investing more than five million euros in the project. The sense of urgency is greater than ever, according to Juliette Legler (UU) and Dick Vethaak (Deltares, a research institute specialising in water and subsoil).

We know plastics end up in the environment, but how many of those particles ultimately accumulate in our bodies?

'Goats and sheep graze on fields where agricultural plastics are used on a regular basis. Tiny plastic particles end up in the soil and find their way into the animals' bodies. We then eat them, drink their milk, make cheese from it or wear clothes made from their wool, and the plastics end up accumulating in our bodies as well.'

Detecting particles in the bloodstream

Juliette Legler and Dick Vethaak effortlessly reel off a list of examples, each one more alarming than the last. For example, one of Legler's PhD students, Hanna Dusza, conducted a study last year using cell culture models. She discovered that plastic particles are easily absorbed by placental cells. 'The Faculty of Veterinary Medicine has now teamed up with colleagues at Farm Animals like Hilde Aardema. We're setting up exploratory studies to assess the effects of plastic particles,' explains project leader Legler, Professor of Toxicology at the Faculty of Veterinary Medicine. 'There's quite a bit of evidence to suggest they are being ingested in the human body, but we still don't know much about the health implications. That's why MOMENTUM will be developing measurement methods to detect these particles in human blood, tissue and placentas. We're also working with the industry to see if we can reduce or prevent exposure to plastics.’ 

The consortium was launched in June. So where do we currently stand?

'All the researchers and partners will meet up at the start of November to discuss the results of the fifteen ZonMw breakthrough projects that led to this wonderful consortium', Legler explains. 'MOMENTUM brings together virtually every Dutch researcher working in the field today, which is really unique. Co-project leader Vethaak, researcher at Deltares and now Emeritus Professor of Water Quality and Health at VU University Amsterdam, adds: ZonMw has also developed a knowledge agenda for the coming ten to fifteen years. We've basically kicked things off by setting up the necessary infrastructure for this research here in the Netherlands. MOMENTUM is a three-year project, but Juliette and I now realise that this research will definitely involve a long-term commitment. We'll barely have achieved any practically applicable results in three years' time.

Why is that?

Vethaak: 'We still don't have the analytical methods we need to measure the tiniest of the plastic particles, which is a major obstacle. As a result, we have no way of determining whether people are being exposed to them at all. Unfortunately, those minute particles are the most dangerous ones.’

So how did you figure that out then?

Vethaak: 'There's already been a lot of research into other, non-plastic particles in air pollution, such as soot. They've been linked to all sorts of diseases. In fact, the WHO recently announced that these particles are already harmful to our health at low concentrations. Not only do they cause all kinds of diseases, they're also responsible for seven million deaths a year worldwide'.

While there have also been various animal experiments involving exposure to micro- and nanoplastics, Vethaak says these are more difficult to interpret because the particles simply aren't comparable to those polluting the environment. 'However, we have known that textile industry workers were exposed to plastic dust particles for several decades now thanks to occupational toxicology, and we also know this has led to all sorts of illnesses including cancer. However, textile workers were exposed to extremely high concentrations. Animal populations are generally exposed to far lower concentrations. Micro/nanoplastic is an umbrella term for a class of diverse and highly complex contaminants – there are so many different types, forms and compounds out there. They can also absorb and release chemicals – such as pathogens – into your body. All in all, it's a very complex issue.

So how do you approach such a complicated puzzle?

'We had to decide what we wanted to focus on', Legler explains. What are the biggest gaps in our knowledge of microplastics and human health? Crucially, as Dick already mentioned, you need to be able to prove that we've actually been exposed to it. We know plastics end up in the environment, but how many of those particles ultimately accumulate in our bodies? That requires some incredibly complex analysis, and our current methods are still in their infancy. That's why we're focused on developing effective measurement methods that can detect these minute particles in human blood, lungs and placentas. Determining actual exposure levels is a crucial part of the project.'

Is that your main challenge at the moment?

'Yes. If there hasn't been any exposure, there's obviously no risk', Vethaak responds.

But I thought we had already proven that beyond any doubt?

'The thing is, we can basically only measure the larger particles at the moment. But those are the kinds you excrete or exhale if you've ingested them. The minute particles capable of penetrating deep into the lungs, passing through the intestinal wall and into the bloodstream still can't be accurately measured. Next, you need to answer two other crucial questions: how do they end up there, and where do they ultimately go? Do they accumulate in certain organs, or are they quickly excreted again? What level of risk is acceptable in the case of lifelong exposure? We still don't have solid answers to any of these questions. You'll need to conduct epidemiological studies if you want hard evidence of the effects in humans'. 

Cattle feed can also become contaminated with microplastics, and the same goes for fish feed

Could there also be some correlation between soot particles and plastic particles? Perhaps one type 'piggybacks' on the other?

'That's actually a relevant question – both types of particles are released when we burn plastic or wear out car tyres,' Vethaak continues. Legler: 'Although we unfortunately can't cover everything in this project, MOMENTUM will also examine the presence of pathogens on plastic particles and the potential for human ingestion. How important is that sort of ingestion?’

You said you'd mainly be developing measurement methods over the coming three years?

‘I think we'll definitely make some headway’, Legler says. 'In three years' time, we will have figured out whether our methods can be applied to large populations and identified any biological effects on the human body. After all, we're working with a large group of toxicologists, biologists and collaborating with physicians.’

Which types of plastics would you consider to be the most dangerous?

'We decided to focus on the plastics to which we are most commonly exposed, such as polypropylene and polyvinyl chloride (PVC). One of our partners produces very fine particles from both plastics, which we then use as base materials. We also produce nylon particles for testing purposes. The latter ties in with Dick's concerns about particles from the textile industry. Once they get into your lungs, they can cause some serious problems.’

Vethaak: 'We also need to devote more attention to the veterinary dimension – the problem is also affecting livestock farms. Cattle feed can also become contaminated with microplastics, and the same goes for fish feed. Every time you mow grass, you also end up grinding plastic waste which then ends up in the feed you give to pigs and cows. Plastic chemicals are also relevant in that regard. We should be more focused on that, don't you agree, Juliette?’

Legler: 'Definitely. We're also working with the Farm Animal division to determine how microplastics are affecting farm animals' environments. We conducted an initial study to determine the effects on cow ova, but we'd like to take a broader view. We want to identify all the sources of the plastics found at farms. Do they also end up in cows and their milk? While there are indications that this is the case, there hasn't been any sound, systematic research into microplastics in agriculture.

Plastic particles in shredded carpets

Microplastics are also a common occurrence at riding schools, Vethaak explains. 'Some riding schools use carpet shreds as a riding surface instead of wood shreds. Those shreds tend to be contaminated, and plastic particles get released every time the horses run on them. As a result, both the instructors and pupils are heavily exposed. The same goes for the face masks and food packaging. A lot of plastic particles are released when you microwave something in plastic packaging. The same thing happens when you open plastic bags with a pair of scissors. There's also the ongoing debate about non-stick layers in Teflon pans. Plastic particles are literally everywhere.'

It's good to hear you're working closely with the industry. I can imagine that might be challenging in light of their commercial interests?

'It is, but we've managed to get the largest umbrella organisations in the plastics industry on board, such as Plastic Europe and the American Chemistry Council,' Legler proudly explains. 'They're also worried and we assume they're genuinely interested in finding solutions. Industrial partners submit their products to us for testing and they're obviously aware we'll be publishing the results. We owe that to the world – our research is being funded by taxpayers.'

So, when will the project have succeeded, what's your biggest ambition?

Legler: 'If we manage to develop effective ways of detecting microplastics in humans. We can then apply those to larger human studies and launch studies on human exposure and its relationship with health problems. If we can make progress in those areas, the project has been successful.' Vethaak adds: 'Thankfully we're not the only ones working towards that goal – there are also other EU projects focused on microplastics.'

This is an article from Vetscience issue 12 (in Dutch).