Como as características quantitativas de microplásticos variam em um ciclo de maré durante o período chuvoso no estuário do rio Cocó (Fortaleza-CE)?

Abstract

Microplastics are synthetic polymers with sizes from 1 μm to 5 mm, which can be originated from the breakdown of larger plastic materials or even from direct production in industrial processes. MP have become one of the most discussed pollutants in recent years, being ubiquitous in the most diverse environmental compartments, including being reported in marine ecosystems and coastal environments. In these environments, MP vary dynamically in space and time, with the influence of several factors such as tidal fluctuations, seasonal periods, and the physical characteristics of MP themselves such as shape and density. However, MP pollution in estuaries has been poorly reported when taking into account the influence of daily tidal variations that dynamize estuarine environments. Therefore, the objective of this work is to evaluate the dynamics of MP in the waters of the Cocó River estuary (Fortaleza/CE), facing a tidal cycle. The estuary in question is subject to several anthropogenic impacts, such as the discharge of effluents and the disposal of solid waste, which are sources of MP. Water samples from the estuary were collected on May 30, 2022, over a complete tidal cycle, covering ebb and flood periods, under spring tide conditions, in the rainy season. The collection consisted of consecutive trawls every 2 hours, contrary to the direction of the current, using a 120 μm mesh plankton net with attached flowmeter. The collected samples were analyzed in the laboratory, counting on the steps of sieving, digestion of organic material, separation by density, filtration and inspection of the MP under a magnifying glass for counting and identification as to color, shape and size. The results showed that the abundance of MP increased from ebb to flood tide conditions, with mean values of 16.2 items/m3 at ebb and 27.0 items/m3 at flood. Such results may be related to the likely increase in current velocity under flood conditions, which favored the return of PMs that left at ebb, as well as the resuspension of plastic particles previously sedimented and trapped in the intertidal margins. Characteristically, the predominant forms of MP were fibers (53.7%), followed by films (20.8%) and fragments (13.0%), forms associated with the secondary origin of MP. The colors transparent (34.3%), white (20.1%) and blue (18.5%) stood out from the rest. A range of colors was found, possibly due to the complexity of sources around the estuary.