Tamanho de rede faz a diferença?: densidade de microplásticos em um estuário tropical raso (Rio Piranji, Ceará, Brasil)

Abstract

Plastics are among the most common materials in production, consumption and inadequate disposal in current society. Once in the environment, it goes through various physical, chemical and biological processes, fragmenting into smaller parts called microplastics (MPs). For estuaries, scientific knowledge about the presence and density of MPs has grown, although it is still scarce for Brazilian tropical estuaries. Methodologies using plankton nets vary, without the consolidation on which net sizes are more efficient in sampling MPs. This work aims to compare the density of microplastics collected with 65, 120, 200, 300 and 500 μm nets in a shallow tropical estuary (Rio Piranji, Ceará, Brazil), as well as to characterize the MPs in terms of shape and color. Collections were carried out in the estuary region during the year 2015. Sampling was carried out during the ebb tide with subsurface horizontal hauls made on board a vessel. In the laboratory, the screening of MPs was performed using a stereoscope. The samples were fractionated in a laminar flow hood, using a beaker, a filter mesh sieve and petri dishes. Statistical analyzes were performed using the STATISTICA 7 program. Samples from each mesh size were used as replicates to perform the non-parametric Kruskal-Wallis test. Relative abundance was calculated as percentages of total MPs sampled from each mesh size. The total density of MP collected with the 65 μm net showed higher density and was significantly different from the other nets (Kruskal-wallis, p<0.05). The 120, 200 and 300 μm nets had statistically similar densities (Kruskal-wallis, p> 0.05), while the 500 μm net had the lowest total MP values. The collected MPs were characterized in fiber (orange, black and blue), fragment (gray, black, white, blue and yellow) and paint particle (yellow, blue, orange and white colors) formats. The density of MPs collected for the tropical estuary varied according to the mesh size used, with smaller nets being more effective compared to larger ones. The gray fragment, the orange paint particle and the blue paint particle showed the highest relative abundance in all mesh sizes. Further studies with chemical analysis and identification will help to better understand the microplastics present in this estuarine environment.