Understanding Microplastic Pollution in Riverbed Sediments: Special Emphasis on a Medium-Sized City in the State of São Paulo, Brazil

Several studies have been carried out to characterize and quantify microplastics (MPs), including tyre wear particles (TWPs), in diverse environmental systems worldwide. In the state of São Paulo, the most important economic state in Brazil, there are several medium-sized cities that play an important role in territorial structuring and regional development. The city of Rio Claro is typically a medium-sized city located in this state, making it an ideal area to study MPs pollution in urban riverbed sediments. For this purpose, riverbed sediment samples were collected at two sampling points (P1 and P2) along the Wenzel Stream, where MPs were characterized and quantified. The average MPs concentrations were 18,033 ± 5,060 and 5,800 ± 1,679 units/kg at P1 and P2, respectively, values higher than those described for urban sediments in Brazil and elsewhere. Fibers were the most abundant type of MPs characterized in these materials, followed by TWPs, fragments and pellets. The release of untreated urban sewage through sources of clandestine connections in the drainage network, associated with surface runoff in highly impermeable areas occurring during heavy precipitation events, were the main sources of MPs. Regarding the environmental risk associated to MPs, the pollution load index (PLI) was used, and the values of 100 at P1 and 57 at P2 suggested an extremely high level of MPs pollution in the riverbed sediments of the Wenzel Stream, indicating that these values are substantial and should be included in global discussions on MPs pollution.