How Microplastics Are Infiltrating the Food You Eat
Isabelle Gerretsen | January 3, 2023 | BBC
Microplastics have infiltrated every part of the planet. They have been found buried in Antarctic sea ice, within the guts of marine animals inhabiting the deepest ocean trenches, and in drinking water around the world. Plastic pollution has been found on beaches of remote, uninhabited islands and it shows up in sea water samples across the planet. One study estimated that there are around 24.4 trillion fragments of microplastics in the upper regions of the world's oceans.
But they aren't just ubiquitous in water – they are spread widely in soils on land too and can even end up in the food we eat. Unwittingly, we may be consuming tiny fragments of plastic with almost every bite we take.
In 2022, analysis by the Environmental Working Group, an environmental non-profit, found that sewage sludge has contaminated almost 20 million acres (80,937sq km) of US cropland with per- and polyfluoroalkyl substances (PFAS), often called "forever chemicals", which are commonly found in plastic products and do not break down under normal environmental conditions.
Sewage sludge is the byproduct left behind after municipal wastewater is cleaned. As it is expensive to dispose of and rich in nutrients, sludge is commonly used as organic fertiliser in the US and Europe. In the latter, this is in part due to EU directives promoting a circular waste economy. An estimated 8-10 million tonnes of sewage sludge is produced in Europe each year, and roughly 40% of this is spread on farmland.
Due to this practice, European farmland could be the biggest global reservoir of microplastics, according to a study by researchers at Cardiff University. This means between 31,000 and 42,000 tonnes of microplastics, or 86 trillion to 710 trillion microplastic particles, contaminate European farmland each year.
The researchers found that up to 650 million microplastic particles, measuring between 1mm and 5mm (0.04in-0.2in), entered one wastewater treatment plant in south Wales, in the UK, every day. All these particles ended up in the sewage sludge, making up roughly 1% of the total weight, rather than being released with the clean water.
The number of microplastics that end up on farmland "is probably an underestimation," says Catherine Wilson, one of the study's co-authors and deputy director of the Hydro-environmental Research Centre at Cardiff University. "Microplastics are everywhere and [often] so tiny that we can't see them."
And microplastics can stay there for a long time too. One recent study by soil scientists at Philipps-University Marburg found microplastics up to 90cm (35in) below the surface on two agricultural fields where sewage sludge had last been applied 34 years ago. Ploughing also caused the plastic to spread into areas where the sludge had not been applied.
The microplastics' concentration on farmland soils in Europe is similar to the amount found in ocean surface waters, says James Lofty, the lead author of the Cardiff study and a PhD research student at the Hydro-environmental Research Centre.
The UK has some of the highest concentrations of microplastics in Europe, with between 500 and 1,000 microplastic particles are spread on farmland there each year, according to Wilson and Lofty's research.
As well as creating a large reservoir of microplastics on land, the practice of using sewage sludge as fertiliser is also exacerbating the plastics crisis in our oceans, adds Lofty. Eventually the microplastics will end up in waterways, as rain washes the top layer of soil into rivers or washes them into groundwater. "The major source of [plastic] contamination in our rivers and oceans is from runoff," he says.
One study by researchers in Ontario, Canada, found that 99% of microplastics were transported away from where the sludge was initially dumped into aquatic environments.
