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.

Disruptors cause hormonal function disturbances and adverse effects in animals and humans, even at low concentrations in the micro and nanogram range, and have become a serious environmental concern. In this sense, this study aimed to determine the estrogenic activity and toxicity of sediment samples from the Cunha Channel watershed, a major contributor of micropollutants to Guanabara Bay, the most polluted but most productive estuarine system in Rio de Janeiro, southeastern Brazil. Estrogenic activities were determined by the in vitro Yeast Assay Estrogen Screen (YES) and acute toxicity was determined using the Vibrio fischeri bacteria assay, in samples processed with protocols for wet and dry sediments. The wet test was the most efficient, with values ranging from 3.4 to 17 ng.g-1,while sample drying led to no detectable estrogenic activity and with toxicity in all samples except one (0.16 ng.g-1). All samples were categorized as very toxic or toxic in the acute toxicity assessment, suggesting high Ethylene Dichloride contamination in the Cunha Channel. This is due to anthropogenic and Vibrio fischeri the lack of local sanitation policies, indicating major environmental concerns in one of the most productive estuarine sites in the state of Rio de Janeiro, southeastern Brazil. This assessment contributes to studies in estuaries estrogenic compounds, which are still extremely scarce worldwide.