Ocorrência e caracterização de microplásticos no período de estiagem na foz do Rio Cocó (Fortaleza - CE).

Abstract

The microplastics (MPs) are particles between 1 µm to 5 mm which can be found in different environmental compartments. In the aquatic environment, MPs can be ingested by small organisms, such as plankton; which leads to the gastrointestinal system obstruction of these animals or the bioaccumulation and biomagnification in the trophic web of the possible MPs attached pollutants, for example persistent organic pollutants (POPs) and heavy metals. MPs usually come from bad solid waste management and from effluents, which paired with their dispersion capacity, impacts the fresh water courses and the seas they flow into. Estuaries being the meeting point of fresh river water and salty sea water, which makes them suitable locations for microplastic presence. Therefore, the objective of this study is to evaluate the occurrence of microplastics in the superficial waters of the Cocó river mouth, Fortaleza, Ceará, in the dry season, through the determination of MPs abundance, form, color, size and polymer composition. The sampling was done in triplicate, in October 2021, on a spot located at the Cocó river mouth, using a plankton net with a 120 μm mesh. During the trawls, the net was placed at the side of the boat, with buoys and a flow meter attached. The retained material inside the collection cup was washed, transferred to glass pots and taken to laboratory where it was stored at -20 ºC. In the laboratory, samples went through the stages of sieving in 5 mm and 63 μm meshes, organic matter digestion with KOH 10%, density separation with a ZnCl2 concentrated solution (d = 1.6 g/cm3 ) and filtering in glass fiber filter (0.7 μm). The filters were analyzed under stereomicroscope and the quantity, forms, colors and sizes of the MPs were determined. The polymer analysis was done using Raman spectroscopy. 334 suspected MPs were found and the average abundance was 1.87 ± 0.54 particles/m3 . The forms found were fibers (75.4%), fragments (20.7%), films (2.1%) and rubbers (1.8%). The colors observed were transparent (70.7%), white (9.3%), blue (5.4%), green (5.1%), black (4.2%) and red (3.0%). Regarding the size, the majority measured between 0.5 to 2.0 mm (62.7%). The polymers detected by the Raman analysis were: polypropylene (45.5%), polyethylene terephthalate (18.2%) and polyethylene (18.2%). When comparing the results with previous studies, it was observed a tendency from the Cocó estuary to retain MPs instead of exporting them in the drought season. It was also possible to trace an initial profile of the MPs general and polymer characterization in the Cocó river mouth.