The amount of microplastics settling to the ocean floor has surged, showing a threefold increase over the last twenty years. This finding comes from the press service of the Autonomous University of Barcelona and underscores the quiet but steady accumulation of plastic residues in the deepest corners of marine environments.
Traditionally, the seafloor is viewed as the final resting place for plastics that enter the sea. Yet researchers remain uncertain about how quickly these bottom sediments accumulate debris of different sizes, ranging from bulky items like bottles and bags to the tiniest particles that slip through the mesh of conventional cleanup efforts. Understanding this deposition is essential for assessing long-term environmental impacts and the behavior of plastics as they move through marine ecosystems.
In response, a team of Spanish scientists designed a focused study to quantify microplastic deposits and determine the deposition rate for particles as small as 11 microns. They extracted sediment cores from the seabed of the Ebro River delta, a site chosen because it is a major gateway for plastic input into the Western Mediterranean. The research relied on the Sarmiento de Gamboa, a oceanographic vessel well suited for deepwater sampling, to retrieve cores from beneath the delta’s shallow shelves to capture a representative record of sediment accumulation over time.
Analyses of the collected sediments revealed a remarkable stability in the seafloor composition over many decades. This constancy is significant because it provides a stable baseline from which changes can be detected. The researchers observed that since the 1980s, and with particular acceleration in the last twenty years, textiles shed synthetic fibers that contribute polyester particles to the seabed, alongside larger polymer fragments from packaging, bottles, and food films made of polyethylene and polypropylene. One of the study’s authors, Michael Grelod, notes that the three most prevalent polymer types accounted for about 1.5 milligrams of plastic per kilogram of sludge in the samples, with polypropylene being the most common, followed by polyethylene and polyester. This pattern illustrates how the composition of deposited plastics has shifted in step with evolving consumer products and packaging materials. Despite the presence of these plastics near the surface or within the water column in other parts of the marine environment, the deeper seafloor appears to retain a relatively unchanged legacy of earlier deposition, with some particles persisting for decades before breaking down significantly.
Beyond cataloging composition, the study emphasizes a clear connection between production, consumption, and seabed deposition. The rate at which microplastic particles accumulate on the ocean floor mirrors the broader trends in plastic manufacture and use across the economy. The researchers found that plastic deposition on the seabed tripled in a little more than two decades, a statistic that aligns with the global surge in plastic production during the same period. This correlation underscores how shifts in design choices, product lifecycles, and waste management practices translate into measurable changes in deep-sea sediments. The results highlight the importance of considering the fate of plastics at every stage—from consumer use to disposal—and suggest that reduction in material loss and improved end-of-life handling could influence even the most remote marine layers.
In light of these findings, scientists stress the value of continuing long-term monitoring of seabed sediments to track microplastic deposition over time. Such monitoring helps clarify how different particle sizes behave under the pressure of currents, bioturbation, and sediment mixing, as well as how they interact with biological processes in the deep sea. The observed tripling of deposition since 2000 serves as a stark reminder that plastic pollution is not confined to beaches or surface waters; it penetrates far beneath the waves and into the very ground of the ocean floor. By building a robust, time-resolved record of sediment composition, researchers can better predict future trends, guide policy decisions, and inform public awareness about the enduring legacy of plastic in marine environments.