Nanoplastics Can Travel From Lettuce To Larvae To Fish

It is well known that microplastics carried by water can accumulate in the tissues of fish and eventually be swallowed by people. However, there is another way these tiny particles can end up in the food chain: from earth to vegetation to insects to fish.

In a new study from the University of Eastern Finland, researchers applied the technique to a model food chain containing three trophic levels (positions on the food chain) cultivated lettuce in soil containing polystyrene and PVC (polyvinyl chloride) particles 250 nanometers in width. These materials were selected because they account for a sizable portion of the plastic pollution currently present in the marine environment.

The plants were harvested after fourteen days and fed to black soldier fly larvae, frequently used as a protein source in animal feed. After five days of eating lettuce, the larvae were fed to freshwater roach (insectivorous fish) for another five days. Then, the fish, larvae, and lettuce plants were dissected and analyzed using scanning electron microscopy.

It was discovered that the roots of the plants first absorbed both kinds of nanoparticles before building up in the leaves. Some of the particles from those leaves entered the larvae’ mouths and guts when they ate them. The particles persisted even after the larvae had been given 24 hours to empty their stomach.

The nanoparticles then moved from the larvae to the fish, where they were predominantly found in the liver but also the intestine tissues and gills. No particles were found in the brain tissue.

It's worth noting that none of the organisms—lettuce, larvae, fish—exhibited adverse effects from absorbing the nanoparticles. However, some investigations have hypothesized that plastic nanoparticles may, at the very least, accumulate pathogens from contaminated environments and subsequently transmit those pathogens to animals or plants.

Dr. Fazel Monikh, the study's lead author, concluded:

"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."

The study was published in Nano Today on September 9, 2022.