210Pb chronology assessing the historical microplastics dynamics and aging effects in urban areas with separate sewer systems and multiple-use reservoir.

This study uses the ²¹⁰Pb chronology to assess the historical dynamics and aging effects of microplastics (MPs) in urban areas with separate sewer systems and multiple-use reservoir for the first time, reconstructing their temporal deposition over multiple decades. The Sorocaba River basin, state of São Paulo, Brazil, was chosen as study area. Direct release of untreated urban sewage and stormwater runoff was the main source of MPs in riverbed sediments before 2006. The construction of wastewater treatment plants (WWTPs) post-2006 led to a decrease in fibres, films, fragments, and pellets. Despite the new WWTPs, the levels of tyre wear particles continued to rise, reaching ∼ 85,000 units/kg at SP4 in 2011, due to an increase of vehicle numbers circulating in impervious surfaces in the cities of this watershed. However, the total of MPs decreased along the multiple-use reservoir, from ∼ 43,000 to ∼ 6300 units/kg at SP1 and SP3, respectively. Using pollution load index, nearly all sediment cores were classified to have extremely high pollution levels. Combining ²¹⁰Pb chronology and sediment pollution of MPs has been useful in exposing historical deposition patterns of MPs in urban areas and multiple-use reservoir environments and relating them to interventions made to mitigate pollution.