In a presentation held by Lisbeth Van Cauwenberghe, a PhD student from the University of Ghent, it became very clear that these microplastics quite probably cause bigger problems than pollution alone. In a project carried out using mussels, she demonstrated that not only do invertebrates ingest the microplastics in their habitat; these tiny particles are able to move through the gut wall of sea animals and into other tissues.
Her project examined whether microplastics could be found in two widely cultivated marine species: the blue mussel Mytilus edulis and the oyster Crassostrea gigas, As these species are specifically cultivated for human consumption, it may be confidently assumed that microplastics detected in these cultured animals will end up in the human food chain.
The researchers carrying out the project acquired mussels raised in the North Sea from a German mussel farm and oysters that had been cultivated in the Atlantic Ocean from a oystersFrench supermarket. The animals were divided into two groups by the researchers. One group underwent an acid digestion procedure immediately, while the other was treated with clean water for three days to clear their gut – the water in the test vessels was renewed to ensure that previously egested material, including microplastic particles, would not be ingested again. – and then subjected to an acid digestion procedure. Afterward, a microscopic examination of the tissues took place in order to establish the presence of microscopes.
“We found an average microparticles load of about 0.36 particles per gram of mussel,” said Van Cauwenberghe. “This number was higher in oysters at about 0.47 particles per gram of oyster.”
Microparticles were also found in the animals subjected to depurefication prior to acid digestion. “Because they had had a three day period to clear their gut, we may presume that the microparticles found in these animals came from other tissues and were there permanently,” she said. To positively identify the microparticles as truly microplastics, she then also performed a spectroscopic analysis. The results showed that this was the case.
It was clear, therefore, that the microscopic plastic fragments had found their way out of the stomachs and into the rest of the animal’s system.
“We don’t know yet what the effects of this are,” Van Cauwenberghe said. “However, it is reasonable to assume that it could cause inflammation.”
What’s more, mussels and oysters are not the only living creatures in which microplastics can move through the gut wall. “The same thing has been found in vertebrates, such as rodents and dogs, and even in humans.”
She continued: “We have cautiously tried to estimate how much microplastic is ingested by the population of Europe. That is difficult, as shellfish is far more popular in some countries than others. However, we know that consuming an average portion of mussels means that we consume at the same time around 90 particles of microplastic. An average portion of 6 oysters contains around 50 particles. So, the minimum dietary exposure per individual is probably 1800 particles per year, although the top consumers may well be ingesting up to 11,000 pieces of microplastic per year.”
There is not enough research available to be able to state what the impact of this is on human health. “It has been suggested that it could be a contributing factor to diseases like Crohn’s, or intestinal cancer. However, more dedicated studies are needed to establish the potential risks for our health,” said Cauwenberghe.