GIVEN a choice between two sea snail shells, hermit crabs know which will make a better home. That is, unless their thinking has been muddled by ingesting microplastics. Then, they struggle with a decision that could be crucial for survival. They aren’t alone: across the animal kingdom, it appears, tiny bits of plastic change behaviours and mess up cognition. Exposure to these particles makes mice more forgetful and less social. Bees have trouble learning. Zebrafish act more anxious.

Such discoveries sound a warning bell for people, too. These so-called microplastic fragments are everywhere, from Arctic snow to the Amazon rainforest. Perhaps worse, they are in our foods: from beer and table salt to seafood and honey. “If you turn the top of your plastic bottle, you shower tiny pieces of plastic down into the water,” says Tamara Galloway, an ecotoxicologist at the University of Exeter, UK, whose work focuses on the environmental and health effects of pollultants like microplastics. People consume around 52,000 microplastic particles per year – or around 121,000 if you include those we inhale. What’s more, recent research shows that some of these can cross the barrier designed to stop toxins from getting from blood vessels into brain tissues.

Exactly if and how this might mess with our minds is unclear because we can’t subject people to the sorts of experiments we do with the likes of mice – though Galloway’s opinion is that the effects on humans could be serious.

We do however, have animal studies to illuminate how microplastics affect the brain…