Ocorrência, variabilidade espaço-temporal e fontes de microplásticos em córregos urbanos da Grande Cuiabá – Brasil

Abstract

Microplastics are plastic particles smaller than 5 millimeters. They have been found in high concentrations in freshwater environments around the world, affecting the biota of these ecosystems. In watersheds, cities have been shown to be the main sources of microplastics, but in urban watercourses, the sources and dynamics of microplastics need to be further investigated. Common sources include pellets used in the plastic industries, microspheres from toiletries and cosmetics, fibers from synthetic clothes, breakage of larger plastic items, among others. The main objectives of this research are to characterize the concentrations and discuss possible sources of microplastics in surface water of the urban streams of the Greater Cuiabá. The specific objectives are to define the spatial and temporal variability of microplastic pollution in the region and how the characteristics of the stream basins influence the concentrations of microplastics. Water at the mouth of the main urban streams of Cuiabá and Várzea Grande-MT were sampled with a plankton net in the rainy and dry seasons. The microplastics were counted and classified visually using a stereomicroscope. Microplastics were classified in fiber, fragment, pellet, styrofoam, and film. Microplastics were found in all 19 streams sampled. In the study area, their average concentration is 14,6 items of microplastics per 100L-1

, ranging from 2,2 to 62,4 per 100L-1

. The most abundant category was fiber (54%), followed by fragment (35%), film (7%), pellet (2%) and styrofoam (1%), similar to other studies in urban rivers. Fibers predominance, in almost all the sampled streams, suggest an important contribution of the washing of synthetic clothes as a source of microplastic pollution in the region. However, the highest concentration of microplastics was observed in the Industrial District region, where the largest number of fragments was recorded, suggesting that industrial activity is their main source. Among the basin characteristics, it seems that only demographic density can explain the observed spatial variation in microplastic contamination, even though the correlation coefficient was found not to be statistically significant. The total concentration of microplastics was higher in the dry season (mean of 15,9 n 100L-1

) than in the rainy season (mean of 14,2 n 100L-1 ), but differences in total concentrations and composition between periods were not significant. The results of this research demonstrate the need for further investigation of microplastic pollution in the region to understand the factors that influence its variation in river basins as well as to eventually curb this contamination that can impact human health, ecosystems, and biodiversity.