Microplastics can carry dangerous pathogens into oceans but unclear if they may cause disease outbreaks: Study

Researchers raise questions on whether microbes carried by microplastics threaten the fish farming industry, which has played an instrumental role in improving global food security


                            Microplastics can carry dangerous pathogens into oceans but unclear if they may cause disease outbreaks: Study
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Disease-causing microorganisms can hitch a ride on plastics that enter the world's oceans. But its effects on human and animal health are unclear. In a new study, researchers raise questions on whether microbes carried by microplastics can cause disease outbreaks, especially in the fish farming industry, which has played an instrumental role in improving global food security.

Plastics are known to carry metals, pollutants, and pathogens -- bacteria, viruses, and other microorganisms that can cause disease -- into the oceans. In this study, researchers from the University of Exeter found numerous aquaculture regions with high amounts of micoplastics. But the question of whether these microbes are capable of causing outbreaks still linger, they said. 

Studying the impacts that microplastics leave on marine life is no easy task. This is because of other stress-inducing factors such as climate change and chemical pollutants. All of them "can affect an animal's health and behavior. So much of what we know about the impacts of ingesting plastics come from controlled laboratory studies," Dr Ceri Lewis, from the College of Life and Environmental Sciences at the University of Exeter, told MEA WorldWide (MEAWW).

Understanding threats to food security

Aquaculture makes low-cost fish more available in the markets, thereby contributing to food security. But "disease is one of the biggest issues faced by the industry," said lead author Jake Bowley of the University of Exeter. Therefore, it is crucial to understand if pathogens carried by microplastics threaten the fish farming sector.

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According to the Food and Agriculture Organization (FAO), disease outbreaks have challenged the sector, affecting food production. It has also caused economic losses. "One estimate puts annual losses of the global aquaculture industry to the disease at around 6 billion US dollars a year. In some sectors such as shrimp aquaculture, up to 40% of global production can be lost in a year due to aquatic diseases," Dr Lewis said.

To learn more about the link between ocean plastic abundance and fish farming regions, the team of researchers used computer modeling. Here, they combined data on global sea surface microplastics concentration and aquaculture production regions to highlight potential hotspot areas. Their analysis showed numerous areas of high aquaculture production in microplastic hotspots. Pathogens might infect marine dwellers in these areas, they speculate. "One such hotspot is in China, where 57 microplastic particles per individual have been reported in the commercially important Yesso clam," Bowley explained.
 
Some studies have found that ocean microplastics contain bacteria capable of causing food-borne infections. The Vibrio bacteria sickens about 80,000 people and kills over 100 in the US every year, according to the Centers for Disease Control and Prevention (CDC). Eating undercooked seafood causes infection.

The threat applies to aquatic organisms as well. Dr Craig Baker-Austin, of Cefas, added: "Some Vibrio bacteria are known to contribute to disease in bivalves (mussels and oysters), often causing mass mortality among larvae and in some cases mortality within adult populations."

"Ultimately, we want to determine whether microplastics might act as a vector of disease transport for aquaculture species in order to support the aquaculture industry in mitigating this risk if it exists, Dr Lewis noted.

The study is published in Trends in Microbiology.

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