Tire-derived microplastics accumulate in marine and lake sediments with potential for wide-scale dispersal in strong currents

A research group led by Researcher Kosuke Tanaka, at the Material Cycles Division of the National Institute for Environmental Studies; Group Leader Atsuko Amano at the Research Institute of Geology and Geoinformation of the National Institute of Advanced Industrial Science and Technology (AIST); and Senior Assistant Professor Kei Nakayama at the Center for Marine Environmental Studies of Ehime University, announced on August 22 that they had clarified the contamination status of tire-derived microplastics (MPs) across Japan. The researchers examined the concentration of MPs in sediments at 36 sites across 11 prefectures from Hokkaido to Okinawa, including coastal marine areas and lakes, detecting MPs at 32 sites. They also found that these particles are transported through rivers to seas and lakes, where they settle and accumulate in sediments along with mud and organic matter that flow out from terrestrial areas. The findings are expected to serve as foundational knowledge for countermeasures. The results were published in Water Research on July 24.

Sources of microplastics include synthetic fibers and artificial turf, among others, but tire-derived MPs generated by tire abrasion from automobiles and other vehicles are thought to account for a large proportion of the total volume produced. The annual release of MPs in Japan is estimated at approximately 11,000-24,000 tons, of which tire-derived particles are estimated to account for 24-85%. However, knowledge about actual contamination conditions was limited, and environmental behavior remained unclear.

Therefore, in this study, the researchers conducted quantitative analysis of tire-derived MPs in sediments from 36 sites across 11 prefectures and investigated their environmental behavior.

Bottom sediment samples (sand and mud) were collected from coastal areas of Hokkaido, Iwate, Yamagata, Tokyo, Hiroshima, Kochi, Fukuoka, Miyagi, Yamaguchi, and Okinawa, as well as Lake Suwa (a freshwater lake) in Nagano Prefecture, to investigate the actual contamination status by tire-derived MPs.

The analysis used pyrolysis gas chromatography/mass spectrometry to quantify natural rubber and synthetic rubber, which are representative components of tires, and determined the weight of particles generated by friction between tires and roads.

As a result, tire-derived MPs were detected at 32 of the 36 sites. The concentration averaged 182 µg/g on a dry weight basis. At 30 sites, concentrations exceeded the threshold concentration considered to have no toxicity to organisms (predicted no-effect concentration threshold), indicating a risk that ecosystem health and biodiversity could be compromised.

In water bodies with significant mud deposition (particles ≥ 63 µm in diameter), tire-derived MP concentrations showed positive correlations with mud content, total organic carbon, and terrestrial organic carbon. This suggests that tire-derived MPs generated on roads and flowing into rivers and other waterways are transported by water flow together with mud and organic matter and distributed in sediments of coastal marine areas and elsewhere.

Conversely, in water bodies with strong currents where mud deposition is minimal, tire-derived MP accumulation was limited, indicating that MP contamination may be dispersed over a wide area through diffusion.

There is a vast accumulation of knowledge regarding the deposition status of mud and organic matter across Japan from geological surveys conducted by the AIST and other institutions. Such knowledge could potentially be utilized to clarify the overall picture of contamination including the spatial distribution and accumulation patterns of tire-derived MPs.

Future evaluation using both field measurements and modeling

Tanaka stated: "While this study clarified contamination conditions in aquatic environments, we hope to conduct comprehensive evaluations in future research using both field measurements and modeling, including processes from the generation of tire-derived MPs on roads to their release into the environment. Additionally, the behavior of chemical substances such as additives contained in tires is important when considering toxicity to organisms, and we believe it is necessary to advance research in this area."

Journal Information
Publication: Water Research
Title: Distribution and accumulation patterns of tire-derived particles in coastal and lake sediments
DOI: 10.1016/j.watres.2025.124278