Insights acerca da deposição e da dinâmica molecular de microplásticos em ambientes estuarinos: um comparativo entre o teórico e o experimental

Abstract

Microplastics (MPs) are persistent and ubiquitous contaminants capable of interacting with various environmental components, particularly natural organic matter, such as humic acid (HA) present in sediments. In estuarine environments, this interaction is particularly critical, as estuaries are known to be areas of MP deposition, ant the presence of HA is frequently reported in extraction procedures. Thus, understanding the interaction between MPs and HA, and the mechanisms involved is highly relevant from an environmental perspective. In this study, experimental and computational approaches were employed to investigate the tendency of interaction between MPs of the types polyethylene (PE), polypropylene (PP), and polystyrene (PS) and HA. The experimental approach, associated with Principal Component Analysis (PCA), was applied to evaluate the correlation between MPs, HA, and different studied estuarine environmental parameters, such as granulometry (sand, gravel and silt), organic matter (OM), and organic carbon (OC). The PCA revealed a positive correlation between MPs and HA, evidencing their affinity and ability of HA to influence the distribution of MPs in estuarine sediments To further investigate these interactions, the Molecular Dynamics (MD) computational technique was applied. This method provided a important details about the interaction, such as the predominance of van der Waals interactions in the stabilization of the systems (HA-PE, HA-PP, and HA-PS), with a higher affinity between HA and PS compared to the others, due to the more negative IPE value. In addition, a more significant reduction in the number of hydrogen bonds involving HA-H2O was observed for the system containing PS, suggesting a more favorable HA-PS interaction. Through the Independent Gradient Model (IGM), it was possible to visualize the interactions and confirm the presence of van der Waals interactions in all systems, as well as to verify strong interactions between HA and PS, mainly near the oxygen atoms of HA. Therefore, the high affinity directly impacts the environmental dynamics of these contaminants in estuarine environments, favoring their retention and deposition in sediments. These results highlight the strong affinity between HA and MPs, especially PS, emphasizing the need to further environmental studies further environmental studies on MPs to better understand their impacts on estuarine environments.