Microplastics deposited on the seafloor have tripled in 20 years

Over the past 20 years, the total amount of microplastics deposited on the seafloor has tripled, with developments corresponding to the type and amount of plastic products consumed by society
.
This is the main conclusion of a study carried out by the Institute of Environmental Science and Technology of the University of Barcelona (ICTA-UAB) and the Department of Built Environment of Aalborg University (AAU-BUILD), which is the first high-resolution reconstruction
of microplastic pollution in sediments in the northwestern Mediterranean.

Although the seafloor is considered to be the final sink of microplastics floating on the surface, the historical evolution of this source of pollution in the sediment chamber, especially the sequestration and burial rate of smaller microplastics on the seafloor, is unclear
.

The new study, published in the journal Environmental Science and Technology, shows that microplastics remain unchanged in marine sediments, and that the quality of microplastics segregated on the seafloor mimics global plastic production
from 1965 to 2016.
ICTA-UAB researcher Laura Simon-Sánchez explains: "Specifically, the results show that the number of plastic particles deposited on the seafloor has tripled since 2000 and, with the production and global use of these materials, their accumulation has not only not decreased, but has not stopped growing
.
"

The researchers explain that the sediments analyzed have remained unchanged
on the seafloor since they were deposited decades ago.
ICTA-UAB researcher Michael Gre Lauder explains: "This allows us to see how the accumulation of polyethylene and polypropylene particles in packaging, bottles and food films, as well as polyester particles in synthetic fibers in clothing fabrics, has increased since the 80s of the 20th century, and especially in the last 20 years
.
" The number of these three particles reached 1.
5 milligrams of sediment per kilogram collected, with polypropylene having the highest content, followed by polyethylene and polyester
.
Despite campaigns to reduce single-use plastics, data from the annual marine sediment record shows that we are still far
from achieving this goal.
Policies at the global level in this regard could help to improve this serious problem
.

Although smaller microplastics are abundant in the environment, limitations in analytical methods limit strong evidence
on levels of small microplastics in previous studies of marine sediments.
In this study, they quantified particles
up to 11 microns in size by applying state-of-the-art imaging techniques.

The researchers investigated the degradation state of buried particles and found that once trapped on the ocean floor, they no longer degrade, either due to lack of erosion, oxygen or light
.
"The process of fragmentation occurs mainly in beach sediments, on the surface of the sea or in the water column
.
Patrizia Ziveri, ICREA professor at ICTA-UAB, said: "Once deposited, degradation is minimal, so plastics from the 60s of the 20th century remain on the seafloor, leaving a character of
human pollution there.
"

The surveyed sediment cores were collected in November 2019 on board the oceanographic research vessel Sarmiento de Gamboa, which departed from Barcelona for the Ebro Delta coast
in Tarragona, Spain.
The team chose the western Mediterranean as the study area, particularly the Ebro Delta, because rivers are considered hotspots for several pollutants, including microplastics
.
In addition, sediment flowing from the Ebro River has a higher
rate of sedimentation than in the high seas.