The tiniest specks of plastic can enter the human food chain, finds study

There is growing concern about the environmental and health impact of plastic pollution, especially since it breaks down into smaller pieces that begin to accumulate in the environment. Now, researchers from the University of Eastern Finland have found that small pieces of plastic called nanoplastics can travel up the human food web, through plants, insects and even fish. Nanoplastics are tiny plastic debris that are smaller than 5 mm in length.

How the study was conducted

According to findings published in the journal Nano Today on September 12, the team of researchers developed a new, metallic fingerprint-based method to detect and measure the amount of nanoplastics in organisms.

For their study, they applied the technique to a model food chain that contains three trophic levels (trophic level is the position an organism occupies in the food chain) — lettuce, which was the primary producer, black soldier fly larvae, the primary consumer, and insectivorous fish (roach) as the secondary consumer.

For the study, the researchers exposed lettuce plants to nanoplastics from commonly found plastic waste in the environment — polystyrene (PS) and polyvinyl chloride (PVC) nanoplastics — through contaminated soil for 14 days. They were then harvested and fed to black soldier fly larvae, insects that are used as a source of protein in many countries, and are also used as feed for chickens and cattle.

After five days of feeding them the lettuce, the insects were then fed to the fish (roach) for five days. The roach, (Rutilus rutilus) is widely found in fresh and brackish water and is sometimes eaten and used as bait.

Traveling up the food chain

By using scanning microscopy, the researchers examined the dissected plants, insect larvae and fish. Images showed that the nanoplastics from the soil were taken up the roots of the plants and accumulated in the leaves. Subsequently, the contaminated lettuce transferred the nanoplastics to the insects. Imaging of the black soldier fly digestive system showed that both PS and PVC nanoplastics were found in the mouth and gut, despite allowing them to empty their guts for 24 hours. Both the lettuce and insects, however, contained a lower amount of PS particles, as compared to the PVC nanoplastics.

In the fish that had fed on the contaminated insects, particles were detected in the gills, liver and intestine tissues. The liver contained the highest concentration of nanoplastic, indicating that it is the primary target tissue for nanoplastics entering vertebrates, the study claimed.

No barriers against nanoplastics?

Due to their small size, nanoplastics can likely pass through physiological barriers and enter organisms. The researchers note that the measurement of the absorption of nanoplastics from the soil by vegetables and fruits, will help tell us whether and to what extent nanoplastics can enter our food chain and then our own bodies.

“Our results show that lettuce can take up nanoplastics from the soil and transfer them into the food chain,” said lead author, Dr Fazel Monikh of the University of Eastern Finland. “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,” Dr Monikh said.

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