Carvalho, D.G.de; Gaylarde, C.C.; Lourenço, M.F.de P.; Machado, W.T.V., and Baptista Neto, J.A., 2025. Seasonal variations in microplastic pollution in beach sediments along the eastern coast of Rio de Janeiro State, Brazil. Journal of Coastal Research, 41(2), 291–304. Charlotte (North Carolina), ISSN 0749-0208.

Microplastics (MPs) have become a pollutant of intense global concern. Sandy beaches represent fragile ecosystems facing this new threat, since these environments have become deposits for large amounts of plastic waste. Despite this, current knowledge about MP distribution on beaches and the scale of pollution is still lacking, especially in South America. For the first time, the distribution and features of MPs in the sand of 27 beaches along the eastern sector of Rio de Janeiro State shore were studied. MPs were present on all the beaches, but the quantities varied with the season. During the summer, 562 particles were found, whereas in winter, this number exceeded 2987 MP particles. Polymers were identified by attenuated total reflectance–Fourier transform infrared spectroscopy as polyethylene, high-density and low-density polyethylene, polypropylene, polystyrene, and acrylonitrile butadiene styrene. MPs in fragment form comprised almost 50% of the total, with fibers being the next most common form. Calculation of the carbonyl index allows the detection of aging in a selected number of MPs of different polymer types. The summer/winter variation indicated sea and wind forces to be the main determining factors for MP distribution.