Spatial distribution and age estimation of microplastics collected from rivers, seas, and sediment in Shizuoka Prefecture, Japan

Microplastics (MPs) have become a major concern for the general public. Although their sources and sinks have been studied, the fate of MPs in the environment remains unclear. Understanding their fate is essential for governments to develop effective countermeasures against MP pollution. In this study, MP pollution was investigated at 22 rivers and 11 beaches in Shizuoka Prefecture, Japan. Polyethylene (PE)-, polypropylene (PP)-, and polystyrene (PS)-MP concentrations in sediments ranged from 0.411 to 423 particles kg-1, 0 to 206 particles kg-1, and 0 to 45.1 particles kg-1, respectively. In river water and seawater, concentrations ranged from 0 to 14.7 particles m-3, 0 to 21.1 particles m-3, and 0 to 6.00 particles m-3, respectively. MP concentrations were rescaled to align with the 1 to 5,000-μm size range used to define the hazardous concentration for 5% of species (HC5). All aligned concentrations in this study were below the HC5 threshold. Population density was found to be significantly correlated with the PE-, PP-, and PS-MP concentrations in river water, and with PE- and PP-MP concentrations in sediments, suggesting that local pollution sources drive MP pollution. The estimated ages of PE-MPs in river water, seawater, and sediments ranged from 0.061 to 5.5 years, 0.25 to 0.63 years, and 0.0 to 4.3 years, respectively. No significant differences in age were observed among sample types or sampling sites. These findings suggest that effective measures to reduce MP emissions could significantly decrease MP pollution within one year in Shizuoka Prefecture.