Once deposited, degradation is minimal so plastics from the 1960s onwards remain on the seabed.
In just two decades the amount of microplastics has tripled on the seafloor
Microplastics make for an insidious form of pollution with vast quantities of tiny particles, invisible to the naked eye, permeating the environment from mountaintops to the bottom of the seas.
On the seafloor alone the amount of microplastics has tripled in the past two decades, says a team of researchers from the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB) and the Department of the Built Environment of Aalborg University.
The scientists discovered this troubling fact by examining microplastic pollution from sediments obtained in the northwestern part of the Mediterranean Sea. The threefold increase they found was in tandem with the growth of the growing global production of plastics from 1965 to 2016, they say.
“Specifically, the results show that since 2000 the amount of plastic particles deposited on the seafloor has tripled and that, far from decreasing, the accumulation has not stopped growing mimicking the production and global use of these materials,” explains Laura Simon-Sánchez, a researcher who was an author of a new study on the findings.
The seafloor is the final resting place of microplastics that first float on the surface of the sea and then filter down to the bottom over time to accumulate in sediments there. Earlier research has found that as much as 14 million tons of microplastics are deposited on the seafloor.
The environmental impacts of this relentless pollution have yet to be fully understood although it has been well established that microplastics have contaminated our food and water supplies.
“[S]ince the 1980s, but especially in the past two decades, the accumulation of polyethylene and polypropylene particles from packaging, bottles and food films has increased, as well as polyester from synthetic fibres in clothing fabrics,” notes Michael Grelaud, one of the researchers behind the new study.
The amount of these three types of particles together reaches 1.5mg per kilogram in collected samples of marine sediment, with polypropylene being the most abundant, followed by polyethylene and polyester, the experts say.
“Despite awareness campaigns on the need to reduce single-use plastic, data from annual marine sediment records show that we are still far from achieving this. Policies at the global level in this regard could contribute to improving this serious problem,” they observe.
Importantly, once trapped in the seafloor microplastics no longer degrade. “The process of fragmentation takes place mostly in the beach sediments, on the sea surface or in the water column,” says Patrizia Ziveri, a professor at ICTA-UAB’s Department of Animal Biology, Plant Biology and Ecology.
“Once deposited, degradation is minimal, so plastics from the 1960s remain on the seabed, leaving the signature of human pollution there,” Ziveri adds.