Caracterização de microplásticos em águas de drenagem urbana de uma área residencial da cidade de Fortaleza-CE.

Abstract

Microplastics (MPs) are synthetic polymers ranging size from 1 μm to 5 mm, considered contaminants of growing global environmental concern due to their wide distribution in the environment and their threat to marine life. Urban drainage water can be a potential source of MPs for the oceans, since it collects rainwater, carrying waste and contaminants from the streets into the rainwater galleries of cities. However, studies on the contamination of rainwater galleries by MPs are still scarce, especially in Brazil. In this context, the aim of this research is to preliminarily assess urban drainage water in Fortaleza - CE as a potential source of MPs to the ocean. Sampling took place in a rainwater gallery in the Meireles neighborhood, using two sampling methods: on-site sieving (63 μm) and surber net (330 μm). In the on-site sieving method, 5L of sample were filtered through a 63 μm sieve, while the collection with the surber net consisted of positioning the net at the mouth of the gallery for 2 minutes. The samples were collected in triplicate.The material retained on the mesh was washed with filtered distilled water and transferred to glass vials. The samples were processed in the laboratory by sieving them through a 5 mm and 63 μm mesh, digesting the organic matter with 30% H2O2, separating the particles by density difference with ZnCl2 (1,6 g/cm3

) and filtering them through glass fiber filters (0.7 μm pore size). The filters were viewed under a stereomicroscope to count and classify the MPs in terms of shape, size and color. The average abundance using the in situ sieving method was 13,5 ± 2,0 items/L, while in the surber net sampling this value was only 0,43 ± 0,59 items/L. The disparity between the values obtained can be attributed to the size of the mesh and the volume filtered, which leads us to believe that on-site sieving is the most effective method for quantifying the contribution of rainwater to the discharge of MPs into the ocean. The predominant forms of MPs were fibers (37,9%), rubber (32,5%) and films (20,2%). The predominant size ranges were 0,063 - 0,3 mm (48,4%), 0,5 - 1 mm (20%) and 0,3 - 0,5 mm (17,9%). The main colors were black (42,4%), blue (30,5%) and transparent (12,3%). The results show that urban drainage water has levels of MPs similar to those found in estuaries, highlighting its relevance as a source of MPs for the ocean.