University of Florida researchers investigating algae in southern Biscayne Bay and northeast Florida Bay over the last two years made an unexpected discovery halfway through their work: high levels of tiny shards of blue-tinted microplastics.
The microplastics appeared in dense amounts, like an algae mat, that the researchers fear could be consumed by wildlife.
“The ones that we saw in this study fall within the same size range as micro planktonic algae,” said Edward Phlips, a UF fisheries professor and lead author of the study published in Scientific Reports last month.
The plastics were found in amounts of 10,000 to 20,000 particles per liter, a concentration similar to plankton that could be consumed by oysters, clams, sponges and a host of small fish that eat plankton, he said. The plastics could clog some filter feeders or get absorbed as they and other wildlife consume the particles. That plastic could then make its way up the food chain.
“Very small plastic particles can be taken up in the food web and we're part of the food web,” Phlips said. “We don’t often think of it that way, but we’re part of the marine food web.”
Researchers originally set out to study micro plankton, an algae that provides an important source of food in the bay. They wanted to look at the impact of freshwater flowing off land in the upper end of Florida Bay, which gets water from the Everglades where ongoing restoration work on the wilted marshes is increasing the amount of water flowing south.
In southern Biscayne Bay, around Barnes Sound, the C-111 canal dumps water drained from farm fields and industrial areas. Researchers picked 10 locations to see if pollution and water quality was influencing the plankton that can support valuable fisherines including shrimp, lobster and stone crab.
But about 10 months into the study, between May 2018 and April 2020, they unexpectedly detected microplastics.
“The densities peaked in the summer and then dissipated by the fall,” Phlips said.
Researchers, he said, still aren’t certain where the plastics came from, but they suspect they may be from debris deposited by Hurricane Irma. A material science professor who looked at the plastics identified them as polystyrene, and coming from a specific kind. Polystyrene is used to make styrofoam cups and food containers.
“It's hard to pinpoint what the plastic was, because what we're seeing is fragments. We're not seeing the original plastic material. But it was very consistent,” he said. “There was one type of plastic. It wasn't like multiple different kinds.”
Larger pieces of plastic debris can often get trapped in mangroves along shores, he said, and then quickly degraded to the barely visible size the researchers detected.
What’s not clear is how often the plastics appear or even what other parts of the bays may have plastics. Environmental regulators and other scientists have long monitored the bays for chemicals that harm wildlife, setting limits for nutrients like phosphorus and nitrogen that might tip the balance since the bays thrive with very little nutrients. Monitoring for microplastics also requires a more complicated filtering process.
With the findings, Phlips said it might be time to add plastics monitoring and set limits. Other studies have turned up plastics in fish and even in sand, heating up beaches and altering the sexes of nesting sea turtles.
“It highlights the fact that maybe we're not looking enough,” he said. “Macroplastic contamination is certainly very evident, very visible. People are doing beach cleanups, which is great. It's really important. But at the same time, you're not going to have a beach cleanup for microplastics.
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