Despite the seafloor being considered the final sink for microplastics floating on the sea surface, the historical evolution of this pollution source into the sediment domain, and particularly the sequestration and burial rate of smaller microplastics onto the ocean floor, is unknown.
A new study shows that microplastics are retained unaltered in marine sediments, and that the microplastic mass sequestered onto the seafloor mimics the global plastic production from 1965 to 2016. it provides the first high-temporal resolution reconstruction of microplastic pollution from sediments obtained in the northwestern Mediterranean Sea. Since 2000, the amount of plastic particles deposited on the seafloor has tripled, and that, far from decreasing, the accumulation has not stopped growing, which is mimicking the production and global use of these materials.
The sediments analysed have remained unaltered on the seafloor since they were deposited decades ago. Since 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. The process of degradation takes place mostly in the beach sediments, on the sea surface or in the water column. Once deposited, degradation is minimal, so plastics from the 1960s remain on the seabed, leaving the signature of human pollution. Although smaller microplastics are very abundant in the environment, constraints in analytical methods have limited robust evidence on the levels of small microplastics in previous studies. In this new study they were characterised by applying state-of-the-art imaging to quantify particles down to 11 μm in size.
Data from annual marine sediment records show that we are still far from reducing and/or banning single-use plastics that are discharged and accumulating in the marine environment. Policies at the global level in this regard could contribute to improving this serious problem.