A new study published on Tuesday estimates that some species of whales consume up to 10 million pieces of microplastic daily.
Microplastics are tiny fragments of plastic found all over the world, even in the deepest oceans.
The amount believed to be consumed by the world's largest mammals would amount to anything from 2.51 kilograms to 43.6 kilograms (96.1 pounds) of microplastic a day, the study said.
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Whales tagged and monitored near California
The research, published in the journal "Nature Communications", was conducted by a team of US-led researchers.
The study involved placing tags on 191 blue, fin and humpback whales which the scientists used to help monitor the whales movements.
"It's basically like an Apple Watch, just on the back of a whale," said the study's author, Shirel Kahane-Rapport, speaking to AFP news agency.
Research was conducted off the coast of California with feeding habits of the world's largest mammals being observed.
Whales feeding in pollution hotspots
The whales would feed at depths of between 50 to 250 meters (165-820 feet), which is also where there is the "greatest concentration of microplastics in the water column," Kahane-Rapport said.
The team of scientists estimated the daily number of mouthfuls whales made, with the most likely scenario being that blue whales were consuming 10 million pieces.
When considering the yearly feeding season took place over the course of 90-120 days, this meant that more than a billion pieces could be consumed during that period.
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Threat level still to be determined
According to the research, the vast majority of microplastics being ingested were already inside the krill the whales were feeding on.
Kahane-Rapport said this was concerning, because it means microplastics can also end up at our dinner table.
"We also eat anchovies and sardines," Kahane-Rapport said, adding that "krill is the basis of the food web."
The report stated that more research would be needed to determine the chemical composition of the ingested microplastics to understand to what degree filter-feeding megafauna were at risk.
AFP material contributed to this report.