A new study has suggested plastic accumulation in foods may be underestimated, with concerns that microplastics (MPs) could carry potentially harmful bacteria such as E. coli – commonly found in coastal waters, up the food chain. 

Researchers from the University of Portsmouth tested a theory that MPs covered in a layer of microbes, (called a biofilm) were more likely to be ingested by oysters than clean micro plastics. Despite the experiment being 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.

Up until now, studies to test the impacts on marine life have typically used clean, virgin microplastics. However, this is not representative of what happens to MPs in the marine environment as microbes readily colonise MPs that enter the ocean. In this study, scientists compared the uptake rates of clean MPs versus those with an E.coli biofilm coating – and the results were worrying.

The oysters contained 10 times more MPs when exposed to the biofilm coated beads. It is believed that these coated MPs appear to be more like food to the oysters, which explains their preferential ingestion over clean MPs.

The scientists say the implications for the food chain are concerning, because the ingestion of MPs is bad for both the oyster and human health. This is because the plastic does not break down in the marine animal and is then consumed when we (humans) eat it.  

“We found 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,” commented lead researcher, Dr Joanne Preston, Reader in Marine Ecology and Evolution at the University of Portsmouth, who described MPs as the “Trojan Horse of the marine world”. 

Dr Preston further stated that when the oysters ingested more MPs, it affected their health – and despite being unsure on how much this can really affect the food chain, she suggests that this can have a negative effect on the health of humans as the creatures are ingesting more plastic and, therefore, “potentially disease causing organisms”.

She continued: “We know MPs 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.

“We have successfully tested a hypothesis – this opens the door for more research on environmentally relevant studies of the long-term impacts of biofilm coated MPs on a wider range of marine life. We also need to study the transfer of microbes up the food chain via plastics in much greater detail.”

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