The frequency of microplastic pollution in the oceans has likely been grossly underestimated. This is evident from research that suggests that there are at least twice as many particles as previously thought.
Scientists dragged water off the coasts of the UK and the US and found many more particles using fine-mesh nets than the coarser ones normally used to filter microplastics. Adding these smaller particles to global estimates of surface microplastics increases the range from 5 to 50 tons of particles to 12 to 125 tons of particles, the scientists say.
Plastic pollution is known to affect the fertility, growth and survival of marine life. Smaller particles are of particular concern because they are the same size as the foods eaten by zooplankton, which support the marine food chain and play an important role in regulating global climate. The new data suggests that some bodies of water may have more microplastic particles than zooplankton.
“The estimate of marine microplastic concentrations could be seriously underestimated at this time,” said Prof. Pennie Lindeque of the Plymouth Marine Laboratory in the UK, who led the research.
She said there may be even smaller particles than those caught by the fine mesh nets, meaning the numbers “could be bigger again”.
Another new study shows how microplastics found their way into the food chain in rivers. Birds consume hundreds of particles every day via the aquatic insects that they feed on.
Microplastic pollution has contaminated the entire planet, from arctic snow and mountain floors to many rivers and the deepest oceans. It is also consumed and inhaled by humans, and the health effects are not yet known.
Research published last month found microplastics on the ocean floor in greater quantities than ever before, suggesting that hundreds of thousands of tons of microplastics could blow ashore in ocean breezes every year.
The study by the Lindeque team, published in the journal Environmental Pollution, used nets with mesh sizes of 100 micrometers (0.1 mm), 333 micrometers and 500 micrometers. They found 2.5 times more particles in the finest mesh than the 333 micron mesh normally used to filter microplastics, and 10 times more than the 500 micron mesh.
The trawls off the coast of Plymouth in the UK and the coast of Maine in the US showed similar results, suggesting that they are representative of waters near populated land. The particles were dominated by fibers from textiles such as ropes, nets, and clothing.
“Using an extrapolation, we suggest that microplastic concentrations could exceed 3,700 particles per cubic meter – that’s far more than the number of zooplankton you would find,” Lindeque said. These tiny animals are among the most abundant species on the planet.
Dr. Ceri Lewis, a marine biologist at Exeter University who was part of the team, said, “Understanding more about the smaller microplastics is important because these smaller particles are more likely to be taken up by the zooplankton that form the basis of marine food webs. “
The study of microplastics in rivers, published in the journal Global Change Biology, analyzed the feces and vomit pellets of white-throated ladles at 15 river sites in South Wales. The scientists said the results were startling.
They found that the birds that feed on river insects ate around 200 pieces of plastic a day. These were mostly fibers and a quarter was larger than 500 microns.
The team also found that the dipper fed their nest-bound chicks thousands of plastic fibers as they evolved. Previous research by the scientists had shown that half of river insects contain microplastic fragments.
Professor Steve Ormerod of Cardiff University, who led the work, said: “In nearly 40 years of river and dipper research, I never thought that our work would one day endanger these spectacular birds by ingesting plastic. It’s a measure of how this pollution problem has crept on us.
“Dippers are the only songbirds in the world that are able to dive and feed on river insects. However, this wonderful adaptation also means that they cannot escape this pollution.”
The effects on bird health are not yet known. “It is imperative that we understand whether microplastics contribute to the other pollution problems affecting ladles and other river organisms, and we are using that knowledge to guide remedial action,” Ormerod said.