In the shadowy underworld of soil, tiny plastic particles are lurking like molecular saboteurs. Researchers have long suspected they're sneaking into our crops, but the trail often goes cold fast. Why? Because tracking these microscopic misfits through plant tissues is akin to chasing ghosts with a magnifying glass.
So are nanoplastics silently infiltrating our food chain, or just stirring up trouble at the roots?
What we do know is that crops exposed to nanoplastics show signs of stress, including stunted growth, physiological hiccups, and a general botanical malaise. But whether this damage comes from plastics building up inside plant tissues or from root-level chaos like reactive oxygen species is still up for debate. And with experimental designs often vague about exposure zones, the story remains incomplete.
To solve the mystery of whether veggies are quietly hoarding plastic, researchers at the University of Plymouth ran a novel experiment. Their goal? To determine if nanoplastics can enter crops through their roots and contaminate the edible parts.
Researchers used a radiolabelling approach to demonstrate, for the first time, that polystyrene nanoplastics accumulate and move into the edible tissues of radishes (Raphanus sativus).
Plants have a built-in bodyguard called the Casparian strip that blocks nanoplastics from entering the xylem and traveling to edible parts. But when researchers try to trace nanoplastics into shoots and leaves, the evidence gets fuzzy.
Many experiments use hydroponic setups where seedlings are dunked into water with plastic particles, letting leaves and stems touch the mix directly. So that complicates the results, with critics claiming the plastic particles ultimately detected are just clinging to the surface like glitter on a party guest?
In this new study, published in Environmental Research, radishes were exposed hydroponically for five days, ensuring that only the thin, non-edible roots made contact with the plastic. Then, they checked if any of those particles had traveled into the edible parts.
Radishes were chosen because they grow quickly and have large, juicy roots, making them perfect for detecting plastic buildup.
Researchers discovered that about 5% of the tiny plastic particles stuck to or were absorbed by the thin, non-edible roots of radishes. But here's the twist: even though only those skinny roots touched the plastic-filled water, the edible root and leafy shoots still showed signs of plastic inside them. That means the particles didn't just hang around; they traveled through the plant, crossing the Casparian strip.
"This is the first time a study has demonstrated that nanoplastic particles could get beyond that barrier, with the potential for them to accumulate within plants and be passed on to anything that consumes them," explained Nathaniel Clark, an author on the new study. "There is no reason to believe this is unique to this vegetable, with the clear possibility that nanoplastics are being absorbed into various types of produce being grown all over the world."
Out of all the tiny plastic particles that stuck to the radishes, about 25% ended up in the edible root, which equals 1.1% of the total amount they were exposed to. Around 10% made it into the leafy shoots, which is 0.4% of the total exposure.
The data shows radishes can take in tiny plastic particles through their roots, and these particles can reach the edible parts in just five days. Once inside, the plastics stay stable for weeks, meaning they likely remain as solid particles.
Microplastics have previously been measured in soils reaching concentrations up to 4.5 mg/kg, but nanoplastic concentrations remain unknown due to analytical constraints. As a result, the focus of this research was to demonstrate the accumulation potential of nanoplastics in radishes in a hydroponic system.
These findings suggest that tiny plastic particles can hypothetically end up in parts of plants we eat. However, more research is needed to understand in what ways this could affect our health.
"To some extent, these findings shouldn't be a surprise – after all, in all our previous work we have found microplastic pollution everywhere we have looked for it," said Richard Thompson, another co-author on the new study. "This work forms part of our growing understanding of accumulation, and the potentially harmful effects of micro- and nanoparticles on human health."
The new study was published in the journal Environmental Research.
Source: University of Plymouth
