Kyushu Study Finds 1,000–10,000 Microplastic Particles per m³ From Surface to 1,000 m — Biofouling Keeps Plastics Suspended for Decades

A team at Kyushu University has developed a novel sampling method that reveals small microplastics are widespread throughout the water column — from the surface down to 1,000 meters (3,280 feet). The research, published in Environmental Science & Technology and summarized in a university press release, provides higher-resolution depth data than previous net- or pump-based approaches.

New sampling approach and key findings. By collecting water at multiple depths, the researchers measured concentrations of roughly 1,000 to 10,000 small microplastic particles per cubic meter at observation sites included in the study. This confirms that tiny plastics are ubiquitous, not confined to the surface layers alone.

How microplastics behave in the ocean. Most small plastic particles start out buoyant because their density is lower than seawater. However, a natural process called biofouling — colonization by bacteria, algae and other organisms — alters particle density. The study found that some particles accumulate enough biological growth to reach near-neutral buoyancy and remain suspended at intermediate depths (about 100–300 meters / 328–924 feet). Others accrue heavier biofilms and sink to the seafloor, distributing plastic pollution vertically through the marine environment.

Longevity and ecological risks. The researchers estimate that suspended small microplastics can persist in the water column for roughly 20–40 years. Because these particles are non-biodegradable and can adsorb chemical contaminants, they present multiple hazards: physical ingestion and digestive harm to marine organisms, toxic effects from adsorbed pollutants, and potential transfer of contaminants through food webs — with implications for fisheries and drinking-water sources.

Implications and next steps. Professor Atsuhiko Isobe, who led the project, said a clearer understanding of depth distribution and particle behavior can improve sampling techniques and help quantify ecological impacts. He warned that while full environmental consequences will require more study, the evidence points to a long-lasting and growing contamination that "necessitates urgent countermeasures." The team plans to extend their work to examine effects on marine organisms and to better map particle transport distances.

What You Can Do

Researchers and environmental groups recommend reducing single-use plastics, choosing refillable bottles, and recycling responsibly to cut inputs of plastic waste to oceans and coastal communities. Policy measures, improved waste management and expanded monitoring are also essential to limit future pollution.

Bottom line: Kyushu's method gives a clearer picture of how pervasive and long-lived microplastics are through the ocean depth profile, underscoring both scientific uncertainties and the need for immediate mitigation.