Plastic accumulation in seafood increases risk of dangerous bacteria

Researchers from the University of Portsmouth tested a theory that microplastics covered in a layer of microbes called a biofilm were more likely to be ingested by oysters than microplastics that were clean.

Although the experiment was carried out on oysters under laboratory conditions, scientists believe similar results could be found in other edible marine species that also filter seawater for food.

“We know microplastics can be the mechanism by which bacteria are concentrated in coastal waters and this shows that they are more readily taken up by shellfish and can be transferred to humans or other marine life,” said lead researcher Dr Joanne Preston.

Microbes have been known to readily colonise microplastics that enter the ocean. This study makes a comparison between the uptake rates of clean microplastics versus microplastics with an E.coli biofilm coating. 

The results showed that oysters contained 10 times more microplastics when exposed to the biofilm-coated beads. This could be because the coated plastics appeared to be more like food to the oysters, the scientists said.

The ingestion of microplastics is not only bad for the oysters, it also affects human health as it does not break down in the marine animal and is consumed when we eat it. 

“What we’ve discovered is that microplastic really is the Trojan Horse of the marine world,” Preston added. “We discovered that clean plastics had little impact on the oysters’ respiration and feeding rates, but did have an impact when you fed them the microplastic hidden in the biofilm. 

“The oysters took in more and it affected their health. It is unsure exactly how much this could affect the food chain, but the likelihood is because the creatures are ingesting more plastic and, potentially, disease causing organisms, this will ultimately have a negative effect on human health.

“We know microplastics can be the mechanism by which bacteria are concentrated in coastal waters and this shows that they are more readily taken up by shellfish and can be transferred to humans or other marine life.”

Professor Steve Fletcher, director of Portsmouth University’s Revolution Plastics initiative, said: “The findings in this research give us further insight into the potential harm microplastics are having on the food chain. It demonstrates how we could be vastly underestimating the effect that microplastics currently have. It is clear that further study is urgently needed.”

In June, another team of researchers developed self-propelled microrobots capable of swimming, attaching themselves to plastics and breaking them down.