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In the present research, the occurrence of contamination by microplastics in the water column was investigated in 15 sample sites along the rivers Guapimirim, Macacu and Maracanã—important rivers that flow into Guanabara Bay, a very polluted estuarine environment in Brazil. The correctidentified polymers were manually counted and classified as to their morphology and color using a binocular stereomicroscope and were characterized by ATR-FTIR spectroscopy. The total mean abundance of particles was 3651.5 items m−3, ranging from 3.6 to 51,166.5 items m−3. Plastic debris was identified in all samples, with a predominance of fibers (67.3%). Polyethylene, polyester fiber and high-density polyethylene (50%) were the major polymers, and the main colors were transparent followed by black and blue in all the water bodies studied. The highest quantities of microplastics were found in the Maracanã River. The figures show that microplastic concentrations are correlated to the level of urbanization.

Aim: Tyre wear particles (TWPs) have been indicated as one of the main sources of microplastics (MPs) in aquatic environments, yet they receive little attention in the published literature. They have never been reported in Guanabara Bay in spite of several published analyses of the abundance, distribution, type, chemical composition and color of MPs in this area. We aimed to develop a method to allow ready detection of these particles in sediments. Methods: Nine sediment samples were taken from locations over a wide geographic cover of the bay. They were collected from different depths using a Van Veen grab sampler. MPs were separated using peroxide degradation of organic matter followed by floatation and filtration. TWPs were identified using a binocular stereo microscope,Scanning Electron Microscopy (SEM) and Fourier transformed infrared spectroscopy. Results: The combined use of these MP detection methods allowed the visualization and identification of high numbers of TWPs in the bay. Exact quantification was impossible because of the large size range of the particles and the use of a sedimentation system already shown to be sub-optimal. Conclusion: High levels of TWPs were detected in Guanabara Bay sediments. Future studies to quantify these particles in coastal environments will necessitate the development of more robust methods, possibly using specific TWP markers. Various options are discussed.