And researchers estimate there's another 3 trillion pieces in surface sediments.
For years, marine scientist David Hastings took Eckerd College students on annual research cruises in Tampa Bay to collect water samples and plankton. Along with the things one would expect to find in a large natural harbor, Hastings and his students were finding something else as well: Small pieces of plastic.
"We were looking at plankton, which form the base of the marine food web," Hastings recounts. "But when we put the samples underneath the microscope, we were astonished to find many brightly colored pieces of microplastic."Wanting to learn more, Hastings teamed up for a study with Kinsley McEachern, a recent Environmental Science and Policy graduate student at the University of South Florida St. Petersburg (USF). The small task at hand? Counting the bay's microplastics.
The team created 24 collection stations in the bay, Florida's largest open-water estuary which extends over 400 square miles. The stations were located at the mouths of major rivers, near industrial facilities and in relatively pristine coastal mangroves. Particles believed to be plastic were probed with a hot dissecting needle. If the material quickly melted or disfigured, the sample was classified as a microplastic, explains the University
What they found is this: On average, four pieces of microplastic per gallon of water, and more than 600 pieces of microplastic per pound of dry sediment. Calculating off of those figures for the entire Tampa Bay estuary, they estimated there are approximately four billion particles of microplastics in the water and more than 3 trillion pieces in surface sediments.
And they say that the numbers could be much higher, since collection in the bay was done only several feet below the water surface, meaning they would have missed buoyant microplastics at the surface.
"Very little is known about how much microplastics are out there and the full consequences of these particles on marine life," said McEachern, the first author of the study. "But emerging research indicates a wide range of impacts on marine ecosystems from the large accumulation of microplastics."
The University explains that plankton-sized plastics are consumed by filter feeders such as oysters, clams, many fish and some birds, allowing them to enter the food chain. "Persistent organic pollutants, including toxic pesticides, and metals can stick to their surfaces, making ingestion potentially that much more damaging. Effects include cellular damage, reproductive disruption and even death."
When the researchers looked at what kind of plastics were in the Tampa water and sediment, they found they were predominantly from thread-like fibers shed from fishing lines, nets, and washed clothes made of synthetic fibers. The next most common source was fragments broken down from larger pieces of plastic.
"These plastics will remain in the bay, the gulf and ocean for more than a lifetime, while we use most plastic bags and bottles for less than an hour," said Hastings. "Although it is tempting to clean up the mess, it is not feasible to remove these particles from the water column or separate them out from sediments."
"Only by removing the sources of plastics and microplastic particles can we successfully decrease the potential risks of plastics in the marine environment," added McEachern.
This was the first time scientists have measured microplastic abundance and distribution in the bay. The team hopes that the findings will provide necessary data to fuel the dialog around policies to reduce plastic in the marine environment.
The study was published in the Marine Pollution Bulletin.