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.

Microplastic pollution in aquatic ecosystems has drawn attention not only because microplastics are likely to accumulate anywhere but also because they cause negative impacts both to aquatic biota and, indirectly, to public health, as a result of their presence. The understanding of the distribution and accumulation patterns of this “new contaminant” is fundamental for the calibration of environmental risk studies. However, research on its migration pattern and consequent distribution is still limited. The present study has focused on the peculiar physical characteristics of plastic microparticles and the response to environmental factors such as hydrodynamics and physical chemistry of water on the diffusion dynamics of these pollutant agents. Therefore, we examined information about the vertical abundance distribution, the composition, and the sizes of microplastics, along with the varied aquatic environments existing on Earth. This study provides valuable evidence for the accumulation trend of microplastics across the environment and the peculiar particle characteristics that dictate their distribution patterns. The present study concluded that detailed studies should be carried out in order to add information about the behavior of plastic microparticles in aquatic environments and thus subsidize the calibration of existing information, thus increasing its accuracy in understanding the diffusion patterns of these polluting agents.

Although plastic is ubiquitous in marine systems, our current knowledge of its transport is limited. Recent studies suggest size-selective removal of small plastic particles (<5 mm) from the ocean surface as a result of the formation of a biofilm (the “plastisphere”) on the microplastic particle (MP) surface. This localized microenvironment can isolate the microcosm from the adjacent aqueous medium, and thus protect component alien species from the surrounding physico-chemical conditions. Apart from resulting in specific conditions for the transfer of alien species through the environment, the plastisphere can impact MP hydrodynamics and cause MPs to move through the water column, initially sinking. The importance of this phenomenon has not been previously considered for these particles. The size-dependent vertical movement of MPs through the water column determines their distribution, which will vary with time of exposure and colonization. Some plastisphere organisms have plastic-degrading activities, which could be harnessed in marine depollution strategies. This article seeks to increase our understanding of the role of biofilms in the biological dynamics and diffusion of plastic microparticles.

Guanabara Bay, located in Rio de Janeiro state. It is surrounded by the second most important metropolitan area of the country. Over recent decades, land disturbance and urbanization in the surrounding area has significantly increased sediment input to the bay and had a negative effect on its overall environmental. This is especially related to high volumes of untreated sewage and industrial effluents. This study evaluates the history of this human impact through detailed examination of a sediment core taken from the northern portion of Guanabara Bay. A geochronology is established using ²¹⁰Pb dating and related to organic carbon and heavy metal fluxes to the sediments. This gave a calculated net average sedimentation rate for the core of 0.67 cm.year^-1. The organic carbon and heavy metals flux started to increase at the beginning of the last century and the highest values was observed in the top of the cores.