Microplastics in water and bed sediments from the Baluarte River Basin: Occurrence, behavior and composition

Given the concerning alert about the potential high toxicity of microplastics in the environment, in recent years, significant efforts have been made to understand more about the occurrence and behavior of microplastics on Earth. Focuses of these efforts include where they are found, mainly in higher concentrations; their transport pathways; their occurrence in a diversity of organisms; their toxicity; their relationship with other pollutants; and many other questions that still need to be answered. The present work is the first one to focus on the study of microplastics in a lotic exoreic environment in the tropical Mexican Pacific region. In this study, the occurrence, temporal variation, and chemical composition of microplastics found in the surface water and bed sediment of rivers of different orders from the Baluarte River Basin were investigated. In surface waters, an average of 0.23 microplastic-like particles per liter were found during both seasons, showing no significant differences between them. During the rainy season, there was an average concentration of 0.11 particles per liter. On the other hand, in sediment, the results showed average concentrations of 139.2 and 66.7 microplastic-like particles per kilogram for the dry and rainy seasons, respectively, with significantly higher concentrations during the dry season. Most of the analyzed microparticles were fibers and had light blue and transparent colours. Polyethylene terephthalate (PET) was the most found polymer in both environmental compartments, followed by cellophane and rayon. It is concluded that, in general, the microplastics found in the fluvial system of the Baluarte River Basin may come from the discharge of domestic wastewater, agriculture, fishing, garbage dumped on land, as well as the construction of a hydrological infrastructure in the area. For future more detailed studies, it is recommended to increase the number of sampling sites at varying distances from human settlements and to explore better methods for microplastic separation. If possible, it would be interesting to implement control measures in first-order rivers of the Baluarte River Basin.