Deep-sea fish contaminated with plastic

Researchers have found plastic particles in three out of four fish in the depths of the Northwest Atlantic Ocean. As these fish are often a food source for other marine animals, this microplastic waste could easily make its way up the food chain to our plates, reports Elke Bunge.

Plastic waste was found in the stomachs of 73% of fish living in the depths of the Northwest Atlantic Ocean. (Image credit: Kevin Krejci via Flickr)

It’s well known by now that the world’s oceans are contaminated with plastic waste. And that these tiniest of these plastic particles – known as microplastics – make their way from our wastewater into our oceans via streams, rivers and lakes, polluting everything along the way.

We also know that microplastics ingested by seabirds and fish are entering the food chain and ending up on our plates. But less is known about the mesopelagic fish living in the depths of our oceans.

A team from the National University of Ireland in Galway has now conducted a survey of fish stocks in the deep sea and uncovered shocking data: fish living in areas normally untouched by humans are also contaminated with microplastic, with these tiny plastic particles found in three out of every four fish in the Northwest Atlantic Ocean.

Microplastic in the deep sea

The researchers led by Alina Wieczorek from the university’s Ryan Institute examined an area 1,200 kilometres west of Canada’s Newfoundland on fish living at depths of 200 to 1,000 metres.

Altogether, the researchers looked at the stomachs of 233 fish from 7 different species. Fourier-transform spectroscopy was used to detect alkaline organic substances in the fish. Microplastic particles smaller than 0.7 micrometres in size were clearly detected in 35 other preparations.

The laboratory conditions were designed in such a way that special air filters were used to prevent any microplastics from entering the preparations via the laboratory air. As such, the presence of plastic particles can only be due to the fact that the animals had already consumed them in the sea.

Isolated from human influence

“We were surprised by this as these fish normally live in mesopelagic areas in the ocean,” said Wieczorek. “These fish inhabit a remote area, so theoretically they should be pretty isolated from human influences, such as microplastics.

Typically, these fish swim to the surface at night to feed before returning to deeper waters during the day. The researchers suspect that they may ingest microplastics when they migrate to the surface.

Three-quarters of all fish species affected

The researchers found that a whopping 73 per cent of the fish have ingested the pollutants. One species of bristlemouth even had a 100% ingestion rate.

On closer examination, the researchers discovered that the microplastics originate from plastic fibres, such as those used in textiles like fleece jackets. These fibres break down when the garments are put in the washing machine and then enter the water system via the wastewater.

Particles in the food chain

Mesopelagic fish serve as a food source for a large variety of marine animals, including herring and tuna. As this new research shows high levels of plastic contamination in the fish, the researchers warn that mesopelagic fish could be spreading microplastic pollution throughout the entire marine ecosystem: from the surface down to deeper waters and ultimately affecting deep-sea organisms.

“Our research was able to demonstrate that even zones previously considered untouched are now subject to the negative influence of humans,” said Wieczorek.

The researchers are calling for a worldwide ban on the use of microplastics in cosmetics and toothpastes.

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