Richard Thompson: What harms are microplastics inducing?

Richard Thompson and Chris Smith discuss the evidence that microplastic pollution is causing damage to plant, animal and human health...

Richard – There's now a substantial body of laboratory evidence that microplastics have the potential to cause harm, and I say potential because it's always the dose that's the poison. There’s been recent modelling work done in the Netherlands that’s looked at all of the studies – and you know, there are now over 4,000 studies using the term microplastics. Back in 2004, there was only one that used it in this context.

So, there's a whole range of studies, lab experiments, that have demonstrated harm – that could be reduced growth, reduced ability to put on weight, reduced reproductive output. I mean, only the week before last we heard about potential effects of really small particles on photosynthesis. So there's been a wide range of adverse effects demonstrated.

A key question there is: are those lab experiments done at environmentally realistic concentrations? And the challenge here is that we don't know with absolute certainty what the environmental concentrations of microplastics are. Why? Because they're particles of a whole range of different sizes, and when you get to below a few microns in size, they're almost impossible to pull back from an environmental sample – of sediment or seawater or whatever it might be – and confirm that, hey, I’ve got a piece of polystyrene.

Picture a small piece of plastic that you could see in your hand the size of a sugar cube breaking into two pieces, then four, eight, sixteen, thirty-two, etc. You can predict how many nanoparticles there are, but we don't know with absolute certainty how many there are, or the size distribution down to those really small pieces. But where I'm going with this is that the modelling predictions, based on the best estimates of environmental concentrations – and of course those estimates vary from one place to another, some habitats are more contaminated than others – suggest, linking to the lab studies, that what we're probably seeing in the natural environment at the minute is fairly isolated harm from microplastics.

We already know that larger plastic litter is causing harm, but from microplastics at current concentrations, we're probably seeing harm in the natural environment in a smallish number of isolated places. But the interesting thing is that the modelling predictions suggest if we don't change our ways in the next 70 to 100 years, that problem will escalate – and what we will see is adverse effects in the natural environment on a very wide scale.

Chris – If it's in the fish and I eat that fish, does that mean that I'm at risk? Is this going up the food chain? We often talk about things concentrating up food chains – mercury, and so on, is one classic example people point to, isn't it?

Do microplastics and nanoplastics behave like mercury?

Richard – No. They'll certainly pass from one creature to another, so they'll pass along the food chain, but there doesn't seem to be any evidence of biomagnification – which is what you're referring to with mercury – that larger creatures are accumulating more than the amount, kilo for kilo. So it's not that as the creature gets bigger the relative amount of plastic is bigger. There's no evidence at the minute of magnification.

But absolutely, microplastics are in the water we drink, they're in the food we eat, and they're in the air we breathe. So they're in us as humans. People ask me, of course, about the harm to humans. At the minute, the evidence that we have is correlative evidence that's pointing towards the potential for adverse effects on humans. What I would say – and I'm not a medical scientist – is that the number of experiments we've got across the rest of the animal kingdom pointing to adverse effects… We are just another animal.

So why would we be surprised to see that evidence of harm to humans, as well as to the rest of nature that’s been studied? Because we could spend a decade trying to establish that direct causal link between micro- and nanoplastics and adverse effects on humans. It could cost millions to establish that, and when we've shown it, what do we do with that information? We're still going to need to address the problem.

So my question is: where is the tipping point here? We've shown that there is harm from plastics of a range of these sizes – particularly the larger stuff – to wildlife, economic harm, and potential harm to human health and well-being. How much more evidence do we need before we start to take action?

And I stress the importance of these larger items of plastic, because once they're in the environment, they fragment progressively over time. So the larger items of plastic litter of today are some of the microplastics of tomorrow. We need to make those changes now. We don’t need to wait for further evidence about effects on humans.

Chris – At least people are beginning to explore new forms of plastic that are more biodegradable, and won’t have this hundreds-to-thousands-of-years-long lifetime where they have the chance to fragment into tiny particles with potentially pathogenic effects. Is that the answer, do you think? Do we just have to make a big shift away from making plastics the way we have, and surrender what is a wonderful material – but one with a toxic legacy – in favour of ones that are much better?

Richard – The biodegradable plastics have a role in this, but they're not in any way centre stage as a solution. If you think of the things that have made plastic materials so successful – it's the fact that they're lightweight, they're inexpensive, they're versatile, and they're very durable. A lemonade bottle – you need to rely on it to hold that lemonade as long as you want it, on the supermarket shelf, on the back of your car on a hot summer's day, or on a cold rainy day.

How is that lemonade bottle going to magically know the minute you've consumed the drink, and it’s somehow become litter in the environment, and now it's time to self-destruct in a meaningful timescale?

If we can make them biodegrade rapidly and harmlessly, and not accumulate in the soil, if we can design polymers in those settings where we’ve got a very specific life expectancy of the polymer – it doesn’t need to be durable beyond a few months in the growing season, for example. Or another example: perhaps where we’ve got food wrappers, maybe served at a large venue – a pop concert, football stadium – where the time the food is needed is quite short-lived, over a few hours. You've got a big venue, with a single organisation controlling the food that comes in, the wrappers that come in, and critically, also the waste that goes out.

There, there’s the possibility for wrapping the hamburgers in a compostable wrapper, and the half-eaten hamburgers and the wrapper can go to a commercial composter. But unless those plastics can get into the right waste stream, they're not going to achieve any beneficial effects.