Microplastics in the food chain: How harmful are they?

This article was first published in June 2022 and updated in January 2023.

There's a growing body of evidence about how widespread microplastics have become, across land, sea and air.

In 2019, researchers found that we consume thousands of these plastic particles every year, while further research published in May 2022 found the presence of microplastics in human blood.

But the problem isn't new. The UN Environment Programme explains that plastics - for example, microbeads - have been used in cosmetics and toiletry products for more than half a century.

Indeed, in 2015, US President Barack Obama banned the use of such microbeads in personal care and cosmetic products.

Microplastics are pieces of plastic debris under five millimetres in length, explains the US National Ocean Service.

Some - such as the microbeads mentioned above - are designed to be this small, while other plastic gradually breaks down to this size.

These tiny particles are often small enough to make it through water filtration systems. From here they can end up in the ocean and other water systems.

Equally, research has suggested that such microplastics can be transported in the atmosphere, spreading themselves into even some of the remotest corners of the Earth.

In the ocean, these particles can be eaten by marine life - from fish to shellfish. And, although Food Standards Australia and New Zealand says that ingestion is much less likely while eating finfish, exposure from shellfish could be higher.

Indeed, a study earlier this year found broken-down microplastics in blue mussels off the Australian coast. Researchers warned that the finding means that microplastics are ending up in human food supplies.

“By investigating microplastic load in the mussel, we call attention to the implications of microplastic pollution on South Australia’s unique marine ecosystems and on the local human food chain,” said lead author Janet Klein. The research added to the findings of an earlier study that concluded, 'if you eat muscles, you eat microplastics'.

And it's not just marine life that could be affected. The Guardian reports that microplastics have been found in foodstuffs including honey, tea and sugar, while Greenpeace warns they could be found in fruit and vegetables and salt.

Microplastics are also making their way onto farmland as a result of the use of sewage sludge being used as fertilizer, according to a new Cardiff university study. The BBC reports that much of this will then end up in waterways as a result of runoff from the top layer of soil.

It's still unclear what the environmental and health impacts of microplastics could be, according to a news release from the American Chemical Society.

Indeed, as Professor Mark Taylor of Macquarie University in Sydney told The Guardian last year, "nobody really knows". However, as he stressed, "absence of evidence is not evidence of absence".

But, there's research ongoing, according to the American Chemical Society, although lots more work is needed if we're to understand the effects. A Nature news feature in May 2021 explained that the first step underway at the moment is understanding levels of exposure.

For example, in California, work is underway to test and report levels of microplastics in drinking water.

In addition to regulation, for example in the US, there are some more eye-catching approaches too.

For example, a team of researchers at Sichuan University has developed a tiny robot fish that can collect microplastics.

And, last year, the BBC reported on a removal method using vegetable oil, iron oxide and magnets. Following 5,000 tests, the method was found to be 87% effective at extracting microplastics from water.