Poluição além do visível: microplásticos em ecossistemas lênticos tropicais e seus fatores ecológicos determinantes

Abstract

Microplastic (MP) pollution represents an emerging threat to the integrity of aquatic ecosystems, particularly in tropical lentic environments that remain poorly studied. This study investigated the occurrence, distribution, and ecological drivers of MP abundance in sediments and marginal soils of tropical artificial lagoons located at the Federal University of Lavras (UFLA), Minas Gerais, Brazil. An initial methodological validation step was conducted for MP extraction, in which sediment samples of different textures were sequentially processed through: (1) organic matter digestion; (2) density separation using water (H₂O), sodium chloride (NaCl), and zinc chloride (ZnCl₂) solutions; (3) filtration; and (4) optical microscopy analysis, including morphological characterization of particles (shape, color, and size). The most efficient methodology was then applied to environmental samples. Environmental and anthropogenic variables (visible plastic debris, soil texture, surrounding land use, hydrological position, and distance from roads) were incorporated into statistical models to identify factors associated with MP abundance. The protocol achieved an average recovery efficiency of 87.2%, with higher rates in sandy sediments and the best performance observed with ZnCl₂ among the tested solutions. MPs were detected in 100% of environmental samples, totaling 9,244 particles and an average abundance of 14,006 ± 17,043 particles·kg⁻¹. The composition was dominated by fragments (73.2%), black particles (81.9%), and sizes <500 µm (94.7%). Although no significant differences were found between margins and lagoon bottoms, high spatial variability was observed across lagoons, with concentrations exceeding 30,000 particles·kg⁻¹ in some and falling below 8,000 in others. Principal component analysis revealed distinct patterns in particle composition among lagoons, suggesting different sources and depositional processes. Regarding hydrological connectivity, lagoons closer to headwaters exhibited higher abundances, whereas more distant or disconnected ones showed reduced values, indicating a filtering effect of hydrological flow. Statistical models identified forest cover (positive relationship) and visible plastic debris mass (negative relationship) as the main predictors of MP abundance. The results confirm that apparently preserved environments, such as headwater areas with greater forest cover, are not free from contamination, possibly due to diffuse inputs such as atmospheric deposition. Conversely, the absence of visible macroplastics did not indicate low contamination, suggesting that visually “clean” sites may conceal high loads of microscopic particles. The predominance of small, dark fragments highlights ecological and health concerns, given their high bioavailability to aquatic organisms and potential for trophic transfer. Overall, tropical lagoons act as important sinks for MPs, reflecting the interaction between anthropogenic and environmental factors. This study helps to fill knowledge gaps on MP pollution in freshwater ecosystems, providing insights for monitoring, mitigation, and public policies aimed at waste management and water quality conservation.