Avaliação da poluição por microplásticos nas águas do Igarapé do Mindu, no ambiente urbano de Manaus

Abstract

When the plastic material is exposed to different environmental conditions and interaction with the local biota suffers fragmentation and originates debris, called microplastics that can be primary or secondary. However, there is still fragmentation in sizes less than 1 nanometer, giving rise to nanoplastics, which are considered potentially dangerous. In addition to size, other factors that influence its degradation are the origin and chemical composition. Despite the growing increase in information on the subject, there is little information about microplastics in freshwater systems. Hydrographic basins are important units of source, flow and destination of plastic pollution. Manaus with its hydrographic basins has great influence of deposition of pollutants in the Negro River. The Mindu stream is one of the most wellknown water bodies in Manaus whose watercourse is the most extensive in the urban site. Seven points were georeferenced for collecting water in the Mindu stream carried out in four phases of the hydrological regime. For the isolation of debris, adaptations were made to the laboratory methods developed by NOAA and methodologies used in scientific studies carried out in freshwater environments. The size classes were defined in 3 groups: Microplastics (> 5 mm to 0.3 mm), Microplastics (<0.3 mm to> 2 µm) and Nanoplastics (<2 µm). Quantitative data regarding sizes were obtained: microplastic (between 0.3 mm and 2µ) and nanoplastic (less than 2µ), with a greater predominance for the latter. Through the FTIR analysis it was possible to identify that the micro and nanoplastic samples were not exclusively a type of plastic polymer, but complex samples that presented spectral peaks of different materials. There was variation in concentrations in the different hydrological regimes and depth profiles, with higher concentrations of micro and nanoplastics in the drought and flood regimes, respectively.In addition to the isolation of micro and nanometric particles, it was also possible to measure through main spectra, the presence of signatures of monomers, elastomers and substances used in different plastic polymers, which are influenced by pollution by domestic effluents, depth and dispersion of contaminants in the column of water. The investigation of microplastic contamination in the Mindu stream has had a satisfactory effect, highlighting the importance of research in urban waters, whose anthropic pollution has a strong contribution of detritus, in the case of Manaus, the Mindu stream tributary contributes to plastic pollution of the river Black that therefore adds up to the quantity of 60,000 tons of plastics carried by the Amazon River to the ocean.