Just as with heavy metals in the ocean, it turns out that nanoplastics — plastic particles less than one micrometer in size — can also move up the food chain. These particles are primarily the result of large pieces of plastic being weathered due to natural processes – sometimes by ingestion by animals.
Researchers from Europe, led by biologist Fadel Munich of the University of Eastern Finland, demonstrated this process in the lab by feeding tiny 250 nanometer particles of polystyrene and polyvinyl chloride to lettuce (sativa lettuce).
After 14 days, the researchers fed this lettuce to the larvae of the black soldier fly (tightly shining), then gave those larvae to hungry cricket fish (red rutile) after another 5 days. Once the fish had been feeding on insects for 5 days, the team dissected and photographed tissues from each level of the food (food) chain.
Because these particles are difficult to detect and can be altered during their physiological journeys, the researchers encapsulated the rare element gadolinium inside microplastics to track them more easily. The team used a scanning electron microscope (SEM) to ensure that the plastic completely covers the metal to reduce its biological impact.
The good news is that biomagnification did not appear to have occurred with these types of nanoplastics in the species studied. Biomagnification occurs when chemicals taken up at lower trophic levels become more concentrated when they are exceeded in the food chain; This is a common problem caused by pollutants such as mercury and PCBs.
But the images revealed nanoplastics in the gills, liver, and intestines of fish, and in the mouth and intestines of insects, accumulating in lettuce leaves.
Furthermore, the two plastics behave differently during their journey through the food chain. Lettuce took a little less polystyrene, so less of this plastic flavor was passed on compared to PVC.
The researchers explained that properties such as the size, shape and surface chemistry of particles can all influence the different effects they have on life. For example, some earthworms may be more likely to break down polyethylene in the soil before the plant can eat it.
“Our results show that lettuce can absorb nanoplastics from the soil and transport them to the food chain,” says Munich. “This suggests that the presence of small plastic particles in the soil could be associated with potential health risks for herbivores and humans if these findings are found to be generalizable to plants and other crops and in field settings.”
Microplastics, including even smaller nanoplastics, are now ubiquitous in every environment, from the deepest ocean trenches, to the tallest mountains, to the isolate of remote Antarctica. They’re in the food we eat, the water we drink, and the air we breathe.
Microplastics pass through our bodies every day, but researchers say there is no need to panic, because there are clearly no immediate short-term effects on us; Long-term exposure and high concentration levels remain a concern.
A particular concern about these microparticles is that they are small enough to pass through many physiological barriers, unlike the larger particles of origin. Some of them have already been shown to cause potential toxicity in plants, invertebrates and vertebrates.
Monikh and colleagues also demonstrate how these plastics can attract a protein coating on their surface as they pass through various life forms. How this changes its effect is not fully known.
“Further research is still urgently needed,” Munich concludes.
This research was published in nano today.