Research reveals microplastic contamination in aquatic species

According to latest research, all aquatic species in the river mouths flowing into the Mediterranean Sea and Atlantic Ocean are contaminated with microplastics.

Carried out by scientists at the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB), the conclusions of the international project “i-plastic” revealed that molluscs were the “most affected due to their ability to filter water”.

Analysing the presence of micro and nanoplastics in estuaries and their adjacent coasts, the researchers observed that rivers are one of the main sources of pollution by microplastics (five to 0.0001 mm in size) and nanoplastics (smaller than 0.0001mm) in the oceans.

“Estuaries, as transition zones between rivers and the sea, are major hotspots for the accumulation of these particles, which are retained in sediments. They pose a threat to aquatic ecosystems given their ability to capture harmful chemicals from the surrounding environment, enter the food-web through ingestion, and bioaccumulate towards higher trophic levels, including valuable commercial species,” explained the team.

The findings of the project show that, of the bivalve species analysed, 85 percent percent of mussels and 53 percent of oysters had ingested microplastics. Meanwhile estuarine-dependent marine fishes (white mullet, silver mojarra and Brazilian mojarra) were 75 percent affected, while in coastal regions influenced by the estuarine outflow, 86 percent percent of European hake and 85 percent of Norwegian lobster contained microplastics or synthetic microfibers in their gut.

Scientists went on to explain that nanoplastic pollution may be even more serious than microplastics and may poses a greater risk to aquatic organisms, as they can pass through the cellular membrane and harm species living in estuarine and marine environments to a greater extent, as was detected in the case of mussels.

“Pollution is ubiquitous in estuaries and their adjacent coasts, in the Mediterranean, and in tropical and temperate zones,” says Patrizia Ziveri, Oceanographer at ICTA-UAB and coordinator of the project, who points out that the amount of accumulated particles in sediments has increased in recent decades at the same rate as global plastic production and that, since 2000, the particles deposited on the seafloor have tripled.

The researchers have warned that this pollution “poses a global threat to coral reef systems at all depths, causing a reduction in coral reef growth”.

In addition, the research notes that pollution is particularly high near urban centres and wastewater treatment plant outflows as this is where microfibres, the most common type of microlitter, are discharged into the estuaries.

“Plastics from the 1960s still remain on the seabed, leaving the signature of human pollution,” says Michael Grelaud, oceanographer at ICTA-UAB and coordinator of this JPI-Oceans-funded project, in which universities in Italy, Portugal, Brazil and Spain have participated.

Once trapped in the seafloor, the particles do not degrade due to lack of erosion, oxygen and light. Particles that are not deposited on the seabed can be transported by ocean currents and tides hundreds of kilometres in just a few months.

“A microplastic from the Ebro estuary in the Northwestern Mediterranean Sea can reach Sicily, in Italy, in six months,” continued Ziveri.

Considering methods to reduce microplastic pollution in coastal marine environments, the researchers stressed that bioremediation – the use of living organisms to remove pollutants from water – is one of the few viable options available, as laboratory experiments have showed that different species of filter-feeder communities removed almost 90 percent of the microplastics from surrounding waters.