By: Cristen Hemingway Jaynes
Published: November 17, 2023
Microplastics — tiny fragments of plastic products and industrial waste — are now so pervasive in Earth’s environment that they are found everywhere from the highest mountain peaks to the deepest parts of the ocean.
According to a new report, all aquatic species in the mouths of rivers that flow into the Atlantic Ocean and the Mediterranean Sea are contaminated with microplastics; mollusksare the most affected because they are capable of filtering large volumes of water.
Rivers are a main source of microplastics and nanoplastics pollution in the world’s oceans, according to the Universitat Autònoma de Barcelona (UAB). Microplastics are plastic pieces that range from 0.0001 to 5 millimeters, while nanoplastics are those smaller than 0.0001 millimeters.
Microplastics are prevalent in the waters and sediments of estuaries, where a freshwater stream or river meets the ocean. Chemicals can be retained by these tiny plastic particles and threaten aquatic ecosystems when animals ingest them.
“Pollution is ubiquitous in estuaries and their adjacent coasts, in the Mediterranean, and in tropical and temperate zones,” said Patrizia Ziveri, oceanographer at Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB) and coordinator of the international project “i-plastic,” which analyzed the presence of these plastics in estuaries and adjacent coastlines, reported UAB. Ziveri pointed out that the number of sedimentary particles has increased in recent times, alongside global plastics production. In fact, since 2000, the amount of particles deposited on the ocean floor has tripled.
The findings of the i-plastic project were that 53 percent of oysters and 85 percent of mussels had ingested microplastics. Of marine fishes dependent on estuaries, such as white mullet, Brazilian mojarra and silver mojarra, 75 percent had ingested the plastic particles. In regions along the coast that were influenced by estuarine outflow, 85 percent of Norwegian lobster and 86 percent of European hake were found to have synthetic microfibers or microplastics in their stomachs.
According to scientists, nanoplastic pollution may be an even more serious concern than microplastics and pose a greater threat to aquatic organisms, as nanoplastics are able to penetrate the cellular membrane and cause more harm to species in marine and estuarine environments, as was seen with mussels.
Microplastics and nanoplastics pollution poses a worldwide threat to all coral reef systems, as they cause a reduction in the growth of coral reefs.
Microplastics pollution is especially high near outflows from wastewater treatment plants and urban centers, from which microfibers, which are the most common kind of microlitter, are discharged into estuaries
“Microplastics and nanoplastics are mostly formed by the fragmentation of larger plastic items. Polyethylene, one of the most common plastic polymers produced, is more susceptible to surface oxidation, the first step in the fragmentation process. Investigating these processes under different environmental conditions is of paramount importance because they can suggest the types of synthetic polymers that are less prone to fragment into microplastics,” the report said.
Once they are trapped in the seabed, these plastic particles do not degrade from exposure to oxygen, erosion or light.
“Plastics from the 1960s still remain on the seabed, leaving the signature of human pollution,” said project coordinator Michael Grelaud, who is also an ICTA-UAB oceanographer.
Particles that do not settle on the seafloor could be transported by ocean tides and currents many miles in only a few months.
“A microplastic from the Ebro estuary in the Northwestern Mediterranean Sea can reach Sicily, in Italy, in six months,” Ziveri said.
Filter-feeders of various species were able to remove nearly 90 percent of microplastics found in surrounding waters, according to lab experiments. The researchers emphasized that using living organisms to remove pollutants from the water, known as “bioremediation,” is one of the only viable options for reducing microplastic pollution found in coastal marine environments.