Caracterização dos resíduos plásticos em águas superficiais de um estuário antropizado

Abstract

Plastic pollution is a global concern due to the constant presence of these pollutants in aquatic environments and their adverse effects on biota. This work aims to evaluate the occurrence, distribution and degradation stage of plastic waste in surface waters of the Capibaribe River estuary, located in the city of Recife, Pernambuco (Brazil). The abundance of plastic waste present along this estuary was quantified considering the i) spatial (upper, middle and lower estuary) and ii) temporal distribution, taking into account the local rainfall, seasons: beginning of drought (September-November), end of drought (December-February), beginning of rain (March-May) and final rain (June-August). The samples were collected by superficial horizontal hauling, using a net with a 500 μm mesh from upstream to downstream. Retained plastics were counted, measured, identified and classified according to size, type and color. The stages of physical degradation of plastic waste of different sizes up to the microplastic level (MP = <5 mm) were identified. For the microplastic category, the particles retained in the net cup were used. The fish larvae collected were fixed in a 4% buffered formalin solution, neutralized with calcium carbonate (CaCO3) and preserved in 70% alcohol in 500 mL containers. Microplastics and fish larvae were analyzed using tweezers and a stereoscopic magnifying glass (Zeiss, Stemi 2000 C), photographed and measured with the aid of a digital microscopic camera using Belview software. A significant difference (p = 0.011) was observed when considering the amount of plastic waste (480 items) and the stage of degradation over the different seasons of the year, with the final rainy season showing greater abundance (54.1%) of the total of plastic waste found. Considering the degradation stage of macro and mesoplastics, the advanced stage (3) was the most frequent (90% compared to the others). Microplastics were found along the Capibaribe estuary, with a concentration of 19.71 part./m3, with an average size of 2.2 mm ± 1.01. Soft fragments were the most abundant type (69%), with a predominance of the transparent color (29%). Most microplastics have a very degraded physical condition (78.9%) with color change, weathering aspects, and incrustations. In all, 106 fish larvae were identified, with an abundance of 1.5 individuals/m3, with the larvae belonging to the order Gobiiformes being the most frequent in the Capibaribe estuary. During all the monitoring carried out, plastic residues were found in all regions of the estuary, as well as the number of microplastics exceeded the number of fish larvae, reaching an approximate ratio of 1.0 fish larva: 13.5 microplastics. These results are worrying, noting that the greater the availability of microplastics in the environment, the greater the probability of their ingestion by fish and, therefore, increase possible impacts on these communities.