Scientists have detected microplastic particles even thousands of metres underwater in deep-sea ecosystems far from sunlight, a discovery that sheds more light on the pervasiveness of the polluting plastic particles.
It has been estimated that over 11 million tons of plastic enter the oceans each year.
Studies have shown that large plastic debris breaks down into tiny microplastic particles, which are transported throughout marine environments by ocean currents, threatening ocean life and entering the human food chain.
While previous research has extensively documented microplastic contamination of coastal and surface waters, very little is known about plastic pollution and its impacts on deep-sea habitats.
In particular, researchers say the impact of plastic pollution on underwater volcanic vent systems remains unknown.
These are unique deep-sea habitats which support diverse life despite the absence of sunlight.
Now, Korean scientists have conducted the world’s first comparative study revealing how microplastics accumulate in animals inhabiting deep-sea thermal vents in two different oceans.
“Plastic pollution has now spread even to deep-sea hydrothermal vent ecosystems that were once considered among the most isolated environments on Earth,” said Se-Joo Kim, an author of the study published in the journal Water Research.
In the study, researchers examined snails and mussels collected from thermal vents located more than 2,000m below the surface in the North Fiji Basin of the southwestern Pacific Ocean and the Central Indian Ridge in the Indian Ocean.
Scientists found microplastics in 92 per cent of all animals examined, with an average of 3.42 particles per individual.
Polystyrene, which is widely used in consumer products and packaging materials, was found to be the most abundant.
The findings show that even remote deep-sea thermal vent ecosystems are already contaminated by plastic pollution.
The feeding behaviour of these deep-sea creatures seems to play a key role in determining where microplastics accumulate in their bodies.
For instance, microplastics were concentrated mainly in the digestive organs of snails that feed on microbial mats covering the seafloor.
In comparison, filter-feeding mussels exhibited a relatively even distribution of microplastics throughout their tissues.
Researchers also found that animals collected from the Indian Ocean had significantly higher concentrations of microplastics in their bodies than those from the southwestern Pacific.
The Indian Ocean life forms analysed in the study had up to 15 times higher microplastic concentrations than the southwestern Pacific ones, after normalising for body weight.
Overall, the study shows conclusively that plastic pollution generated at the ocean surface can be transported thousands of meters downward, reaching one of Earth’s most remote and extreme marine ecosystems.
“Our findings provide important scientific evidence for establishing future deep-sea environmental monitoring systems and conservation policies,” Dr Kim said.