Microplastics are probably in your diet. But should you be worried?

Posted on September 17, 2019 by DrRossH in Plastic & Wildlife

You’ve probably got microplastics in your poo.

They were found in the stool samples of all eight participants of a study published last week in the Annals of Internal Medicine.

The eight healthy adults from Europe, Russia and Japan had between 18 and 172 microplastic particles in their faeces, with nine different types of plastic recorded overall.

Andit’s not the first study to confirm that most of us are probably ingesting plastic semi-regularly.

The question is, should we be worried?

Plastic bottles are one of the biggest sources of microplastic ingestion. (Getty Images)

Previous research has foundthe most common ways we take in microplastics are via airborne particles, shellfish, tap water, and even more so from bottled water,which contains an average of between 118 and 325 microplastic particles per litre.

“Bottled water may be a strong contributor to microplastic ingestion,” the authors wrote.

“A total of 90,000 microplastic [particles would be consumed] annually if the person’s recommended water intake comes entirely from bottled sources.”

Table salt is another big source, according to Thava Palanisami from the University of Newcastle, who wasn’t involved in the latest study.

“You’re evaporating the salt from the sea water and the seawater contains microplastics,” Dr Palanisami said.

His research, yet to be peer-reviewed, found we could be eating up to 5 grams of microplastics each week.

And because there’s a lot of microplastics in seawater, that means sea creatures like fish, shellfish, and krill are absorbing them too.

As bigger animals eat the smaller ones, you get a process of “trophic accumulation”, where the amount of microplastics increases in animals up the food chain.

What does it do to animals?

Marine biologists cut into a giant whale.
Scientists can’t study the effects of plastic on larger animals in labs. (AFP: Marine Biology and Cetacean Research Centre of national Cheng-Kung University)

We know that larger plastics hurt animals directly. Turtles choke on plastic bags and whales have been found with kilos of plastic waste in their stomach.

The stomachs of thousands of seabirds on Australia’s Lord Howe Island last year were found to be so full of plastics and microplastics that there was no room left for food.

But microplastics are classified as less than 5mm wide, and aren’t a choking hazard for larger animals.

The issue is that microplastics can leach potentially disruptive chemicals into the body after they’ve been eaten.

And while we might think that plastics that have weathered for a long time in the environment have leached outmost of their chemicals already, that’s not always the case.

“Chemicals can leach out in the environment, but [they] can also increase during weathering — plastic can absorb chemicals from the environment,” Dr Palanisami said.

In research published last week, scientists added three different types of microplastics (including plastics from clothing fibres) to soil and then added earthworms and planted ryegrass in it.

They found the worms in the microplastic soil were smaller than the control plots, and the ryegrass-shoot height was smaller than in the control as well.

Other research has found microplastics disrupt photosynthesis in marine bacteria and that they can act as potential vectors for microbes with antibiotic resistant genes.

How do we study humans?

Chemicals can actually accumulate in plastic after it enters the environment. (Getty images: Daniela Dirscherl)

Because this is stillan emerging field of research, there is a lot that is unknown about what impacts microplastics may have on the ecosystem, according to Jennifer Lavers from the University of Tasmania.

While small animals like sea-cucumbers and aquarium fish are easily kept in labs, it’s much more difficult for researchers to get long-term data for bigger species.

“If you want to monitor the impact of plastics or chemicals on an animal over time, you need to be able to capture and study that animal many, many times,” Dr Lavers said.

“So say tuna — you can catch that tuna once, but how are you going to catch a tuna many times?

“Then if you think of something like a blue whale or a humpback whale, it’s just not going to happen.”

Instead, researchers are limited to studying the impacts on smaller animals, and can only assume that the same mechanisms apply to larger ones.

And the same goes for humans. For us, there’s even less data on the potential health effects of microplastics.

That’s partly because the field of research is new, and because we can’t ethically give people doses of microplastics to see what happens.

So what do we know?

A plastic cup with small bits of plastic in the bottom.
Like all things, it’s the dose that makes the poison. (Supplied: University of Newcastle, Maddision et al., 2018)

In the latest paper, the authors conclude that “further research on the extent of microplastic intake and the potential effect on human health is needed”.

The fact that microplastics were detected in human faeces in the study suggests that they’re passing through the body.

But it’s what happens when they’reinside usthat is unknown.

Bisphenol A (BPA) in plastics is one of a number of compounds that poses potential health risks, according to Dr Palanisami.

“BPA was considered a potential carcinogen. And then phthalates — they can be endocrine disruptors,” he said.

“There are a few more chemicals too — there’s actually about 10 chemicals [in plastics] that can have an effect on human health.”

Like anything though, the dose makes the poison.A

And the amount we actually absorb is probably very low, according to a World Health Organisation (WHO) report from last month.

“Microplastics larger than 150 micrometres (a micrometre is a millionth of a metre) are unlikely to be absorbed in the human body, while the uptake of smaller particles is likely to be limited,” the report stated.

“Based on the limited information we have, microplastics in drinking water don’t appear to pose a health risk at current levels.”

However, the report concedes that the absorption of nano-sized [a thousandth of a micrometre] particles may be higher.

WHO Director Maria Neira said finding out more about the potential impacts is a top priority.

“We urgently to know more about the health impact of microplastics because they are everywhere,” Dr Neira said.