Scientists are becoming increasingly concerned about plastic pollution, particularly after they realized that mismanaged plastics that reach the environment break down into smaller pieces known as microplastics and nanoplastics. Due to their very small size, nanoplastics can break through physiological barriers and enter a variety of organisms.
However, despite the growing awareness of the potential toxicity of nanoplastics to plants and animals, the current scientific understanding of plastic transfer in food chains remains limited. For instance, little is known about the presence of nanoplastics in soil ecosystems and their uptake by soil organisms, even though agricultural soils are most likely polluted by nanoplastics from sources such as atmospheric deposition, wastewater irrigation, sewage sludge application, or mulching film use.
Now, a team of researchers from the University of Eastern Finland has developed a novel, metallic fingerprint-based method to detect and measure microplastics in organisms, and applied it to a model food chain consisting of three trophic levels: lettuce as a primary producer, black soldier fly larvae as primary consumers, and the common roach (an insectivorous fish) as a secondary consumer.
The researchers exposed lettuce plants to polystyrene (PS) and polyvinyl chloride (PVC) nanoplastics for two weeks via contaminated soil, after which they harvested and fed them to black soldier fly larvae. After five days of feeding with lettuce, the flies were fed to the fish. By using scanning electron microscopy to analyze the dissected plants, larvae, and fish, the scientists discovered that nanoplastics were taken up by the roots of the plants and, after accumulating in the leaves, were transferred to the insects and, eventually, the fish. The pollutants were found in the mouth and gut of insects even after allowing them to empty their guts for 24 hours, as well as in the gills, liver, and intestines of fish.
“Our results show that lettuce can take up nanoplastics from the soil and transfer them into the food chain. This indicates that the presence of tiny plastic particles in soil could be associated with a potential health risk to herbivores and humans if these findings are found to be generalizable to other plants and crops and to field settings. However, further research into the topic is still urgently needed,” concluded lead author Fazel Monikh, an expert in Nanotoxicology at the University of Eastern Finland.
The study is published in the journal Nano Today.