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.

Marine debris constitute a global concern that pollutes the world’s oceans, including deep benthic habitats where little is known about the extent of the problem. SideScan Sonar systems are able to provide near-photographic high-resolution images of underwater areas, for a wide variety of objectives, including production of nautical charts and detection of underwater bathymetric features. Lately this technology has been used as a tool to detect debris on the seafloor that may be hazardous for living organisms and finally for humans. Harbor activities were the most common contributors of benthic debris. Little is known about the extent of the problem in the Guanabara Bay, Rio de Janeiro, regarding benthic debris distribution and their influence in the bottom sediment. The present study analyzes the spatial distribution and type of marine benthic debris in the area of Niterói Harbour. The study identified great amount of benthic debris, including tires, anchors, cables or linear features, sunken vessels, wooden or metal bars and pillars.Keywords: anthropogenic marine debris; benthic habitats, marine debris, estuarine pollution, Guanabara Bay O uso de sonar de varredura lateral para detectar grandes detritos marinhos bentônicos no Porto de Niterói - Baía de Guanabara/SE BrasilResumo. Os detritos marinhos são uma preocupação global que poluem os oceanos do mundo, incluindo habitats bentônicos profundos, onde pouco se sabe sobre a extensão do problema. O sistema de sonar de varredura lateral é capaz de fornecer imagens quase fotográficas de alta resolução de áreas subaquáticas, para uma ampla variedade de objetivos, incluindo a produção de cartas náuticas e detecção de características batimétricas subaquáticas. Ultimamente, essa tecnologia tem sido usada como uma ferramenta para detectar detritos no fundo do mar que podem ser perigosos para os organismos marinhos vivos e, finalmente, para os humanos. As atividades portuárias foram as que mais contribuíram para os detritos bentônicos. Pouco se sabe sobre a extensão do problema na Baía de Guanabara em relação à distribuição de detritos bentônicos e sua influência no sedimento de fundo. O presente estudo analisa a distribuição espacial e o tipo de detritos bentônicos marinhos na área do Porto de Niterói. Na área estudada foi observada grande quantidade de detritos bentônicos, incluindo: pneus, âncoras, cabos ou feições lineares, embarcações afundadas, barras e pilares de madeira ou metal.Palavras-chave: detritos marinhos antropogênicos; habitats bentônicos, detritos marinhos, poluição estuarina, Baía de Guanabara