Ocean Pollution: New Study Reveals Quick Rate of Nanoplastic Absorption

Earth’s oceans contain over 150 million tonnes of plastic. That is not a final count: An estimated eight million tonnes of plastic are added to the ocean each year. These growing heaps of pollution not only gravely endanger ocean life, new research shows. They pose a threat to many of our favorite foods — and they do it quickly.

In the November issue of Environmental Science & Technology, scientists show that scallops — delicious, filter-feeding bivalve mollusks — can absorb extremely small pieces of plastic throughout their body within a matter of hours.

After six hours of being exposed to nanoplastics in a laboratory setting, billions of tiny pieces of plastic, measuring at about 250 nanometers, accumulated within the scallop’s intestines. (For comparison, the width of a human hair is about 2.5 nanometers.) In the same time interval, even smaller pieces — measuring closer to 20 nanometers — had spread throughout their bodies, settling within their kidneys, gills, and muscles.

“This is is a groundbreaking study, in terms of both the scientific approach and the findings,” co-author and professor Richard Thompson, Ph.D., announced Monday. “We only exposed the scallops to nanoparticles for a few hours and, despite them being transferred to clean conditions, traces were still present several weeks later.”

This study is the first to show that nanoparticles can be rapidly be absorbed by a marine organism and then spread across their organs within hours. It’s also one of the few experiments to evaluate the relationship between nanoparticles and ocean creatures in a laboratory setting that mimics the concentration of plastics these animals encounter in the wild.

Subsequent experiments revealed that up these particles stuck around. It took 14 days for the 20-nanometer pieces to disappear and 48 days for the 250-nanometer pieces to no longer be detectable.

Filter-feeding marine organisms, like scallops, are especially susceptible to absorbing plastics because of the the way they ingest nutrients. They eat by passing water through a specialized filtering structure, which strains out food particles. Unfortunately, plastic particles also get taken up via this filtering system, accumulating within internal organs as a result. This process also holds true for barnacles, tube worms, sea-squirts, and mussels, which all have been shown to absorb nanoplastics.

Ingesting nanoplastics is not only harmful for these small ocean organisms. There is a serious risk of nanoplastics moving up the food chain, from filter feeder, to fish, to human, much in the same way mercury in small fish can build up to higher concentrations in bigger fish and the people who eat them. For example, in 2017 a Scientific Reports paper showed that nanoplastics accumulate in fish brains, which causes the fish to eat slower and explore their surroundings less often. This was thought to occur because the the fish were eating animal plankton, which also absorbs nanoplastics.

There’s no question that the nanoplastics absorption process needs to be better understood, before they further harm ocean wildlife as well as the people who eat them. With only 7 percent of the ocean protected, some scientists argue that for the health of the ocean and for humankind, targeted conservation needs to happen on a global scale.