Plastic is typically thought of as an ocean-based problem. That’s partially because the beach is where the research began. Richard Thompson, professor of marine biology at the University of Plymouth and coiner of the term “microplastic”, kept stumbling across plastic waste along the coastline, and subsequently found smaller, microscopic pieces in the sand and seabed. Since then, we’ve learned all about the Great Pacific Garbage Patch (located somewhere between California and Hawaii) and the fact that microplastics linger in seafood.
Then there’s the soil. In fact, the earth beneath our feet may contain more microplastic than the ocean, with agricultural land particularly plasticky. Researchers estimate that between 31,000 and 42,000 metric tonnes of microplastics are applied to European soils annually via the recycling of sewage sludge.
It gets there via our wastewater, which is full of tiny plastic particles. Tires are a big part of this problem: They wear away as we drive around, then the shreds get washed into the sewage system when it rains. Clothing is another major contributor, with 70 per cent of all apparel made from synthetics such as polyester and elastane, which shed tiny fibers when they’re being made, worn and washed. Human waste is also a microplastic source, aided by kimchi if the Korean study is correct.
We’re very good at removing microplastics from wastewater. What’s left is a nutritious mulch of biowaste and plastic, 80 per cent of which ends up on agricultural land in the UK.
A study from the James Hutton Institute looked at archived soil samples from a sewage sludge experiment that ran between 1994 and 2019. It found that after just four years of sewage sludge application, microplastic levels in soil rose by up to 1,450 per cent. The researchers also found that even after the plots of land were no longer fertilised with sewage waste, levels of microplastics remained the same for more than two decades and counting.