Determinação da ocorrência de microplásticos no estuário do rio Pacoti, utilizando moluscos bivalves como sentinelas

Abstract

The global increase in plastic waste production is causing negative impacts on levels of biological organization. Plastics make up about 75% of marine litter, and their fragmentation results in particles ranging from 1 µm to 5 mm, known as microplastics (MPs). MPs are already present in all environmental compartments and can cause significant harm to coastal fauna, including bivalves. Monitoring MPs frequently uses sentinel species, such as bivalve mollusks, which are good environmental indicators due to their filter-feeding habits and broad distribution in various coastal environments. Although most studies on MPs in Asia and Europe use bivalves as a model, in Brazil, especially in the state of Ceará, such studies remain limited, despite being on the rise. The scarcity of research on MP contamination in bivalves may pose a significant biosafety risk locally, especially to communities that rely on these resources for their livelihood. This study aims to determine MP levels in the Pacoti River Estuary (PRE) using two bivalve species as sentinels, *Anomalocardia flexuosa* (Clams) and *Crassostrea rhizophorae* (Oysters), and to compare their performances. The collections took place in December 2023. Seven sampling points (P1 to P7) were selected in the lower, middle, and upper regions of the estuary. Ten individuals of each species were collected per point. The clams were collected manually, while the oysters were collected with the aid of a chisel and hammer. The samples were wrapped in aluminum foil and frozen (-5 ºC). In a sterile laboratory, the samples were thawed, measured using a digital caliper with 0.001 mm precision, and weighed on an analytical balance with 0.001 g precision. The tissues of the bivalves were digested in a 10% KOH solution and filtered in a vacuum system under laminar flow, using fiberglass filters with a pore size of 1.2 μm. The resulting filters were stored in Petri dishes and observed under a digital optical stereomicroscope for MP counting and characterization (size, shape, and color). Of the collected bivalves, 93.46% contained MPs in their tissues. In clams, the most common MPs were between 1000 and 2000 µm (29.6%), while in oysters, particles between 0 and 500 µm predominated (32%). The MP concentration was significantly higher in clams than in oysters (p < 0.0001). However, oysters showed greater shape diversity, with fibers being predominant (96.3%) but also containing fragments (5.06%) and films (1.34%). The most frequent colors were blue (50.44%), colorless (15.38%), black (7.14%), and red (6.41%). The highest MP concentration in clams was observed at point P4 (3.20±2.15), while in oysters, it was found at point P1 (4.00±3.30). There was no significant difference in contamination between the collection points for clams (p = 0.8156) and oysters (p = 0.2778). The two species used in this study have different MP accumulation rates and perform differently as sentinels. Therefore, both species are valid as sentinels, with oysters having the advantage of better assessing the variety of MP forms present in the estuarine environment.