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Each year, more than 10 million tonnes of plastic debris enter the oceans and are found in almost every oceanic layer. They start with large floating objects and eventually break down into much smaller pieces called microplastics. These particles are ubiquitous and have been found in the digestive tract of more than 100 different species, causing physical, chemical and even biological damage to these animals. Mussels and other bivalves, such as oysters and clams, are eaten whole without removing the gastrointestinal tract and thus represent a pathway for microplastics into the human food chain.
In contrast to previous research, an original study by a team of scientists suggests that mussels are not a reliable indicator of the presence of microplastics in the marine environment because of their inherent ability to feed selectively. in fact, difficult consumers. Instead, marine aggregates, also called "marine snow", have much more to say about the future of microplastics in the environment.
Marine aggregates are a predominant form of absorbent carbon in the marine water column and form the basis of the ocean food chain. These aggregates also represent a transport mechanism of microplastics on the seabed. The study shows that they play an important role in the removal of microplastics from the ocean surface, by transferring them vertically through the water column and facilitating their transfer into marine food webs.
Using a powerful tool called spectroscopy, researchers from Florida Atlantic University, Eastern Normal University, the Woods Hole Oceanographic Institution, the University of Connecticut and the University of New England are the first to identify a link between microplastics and aggregates and mussels (Mytulis edulis). Results of the study, published in the journal Science and technology of the environment, have important implications for the fate of plastic particles in marine environments.
"We suspected that plastic-laden marine aggregates were gumming up suspended bivalves like mussels," said Tracy J. Mincer, Ph.D., co-author and research professor at the FAU Harbor Branch Oceanographic Institute and FAU Harriet. Wilkes Honors College. "We wanted to better understand the link between marine aggregates, microplastics and marine animals, especially bivalves, in the environment."
For this study, researchers collected marine aggregates and blue mussels at Avery Point, Connecticut, and used microscopy and microspectrometry to measure the spectra of these microscopic samples. They found that 73% of the marine aggregates sampled contained plastic particles. More than 90% of these microplastics measured less than 1 millimeter.
In the mussels, researchers detected microplastics in the biodeposits or digestive glands / intestines of almost all the mussels collected at the Avery Point wharf. More than 40% of the microplastic particles were either released into the pseudofeces of the mussels, or were emitted (rejecting undigested material) in the stool. Normally, mussels can digest their food in minutes. In contrast, the plastic particles pbaded to the digestive diverticula of the mussels took days to digest.
The characteristics of microplastics in marine aggregates and mussels were similar, providing further evidence of the role of marine aggregates in the trophic transfer of plastic particles to bottom suspension feed systems.
The uniformity of sizes and shapes of microplastics identified in the molds indicated that selective ingestion of certain types of plastics occurred. The mussels preferentially ingested particles of smaller size and having a relatively larger form factor.
"The good news is that molds are difficult to handle and have well-developed mechanisms for particle discrimination," said Mincer. "They sort the particles according to physical characteristics such as size, shape, flexibility and density, as well as chemical and nutritional properties.Parts selection is one of the strategies used to improve the quality of the particles. their diet and optimize their energy intake. "
The chemical composition of these marine aggregates was diverse and included a wide range of domestic and industrial uses. Polypropylene, polyester and cellulose acetate, commonly used in cigarette filters, hygiene products and clothing, accounted for nearly 76.3% of all plastic particles identified in the aggregates sampled seamen. Cellulose acetate is mainly introduced into marine environments through wastewater discharges, and cigarette butts also provide a major mechanism for penetrating coastal oceans.
An unexpected finding of the study was that fragmented plastics constituted the predominant type of synthetic particles identified in marine aggregates and accounted for 65.9% of all microplastics.
The researchers compared the abundances of plastic particles in marine aggregates with other reports in the world. They also found that the concentration of microplastics in the sampled mussels was about three times lower than that found in the wild mussels of Chinese coastal waters.
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