Estudo teórico da interação de microplásticos polietileno (PE) e policloreto de vinila (PVC) com os pesticidas 2,4-d, tiametoxam e clotianidina

Abstract

Microplastics (PMs), plastic fragments smaller than 5 mm, have been recognized as potential carriers of contaminants in the environment. In this work, computer simulations were based on the Density Functional Theory (DFT) to evaluate the interaction of polyethylene (PE) and polyvinyl chloride (PVC) PMs with three widely used pesticides: 2,4-D acid, Thiamethoxam and Clothianidin. The calculations included geometric optimizations, interaction energies, and Electrostatic Potential Map (MEP), Boundary Molecular Orbitals (FMOs), and Non-Covalent Interaction Analyses (NCI) analyses. The MEP showed sites concentrated in functional groups such as nitro and carboxyl, while the FMOs showed moderate chemical reactivity for pesticides (Egap 4.1-5.4 eV) and high stability for polymers (Egap 7.5 - 8.1 eV). The structural optimizations presented 19 stable complexes, with interaction distances ranging from 2.432 to 2.995 Å, and the PVC presented stronger interactions with contaminants. The binding energies (∆Ebind < 0) confirmed favorable adsorption, and the enthalpy values ∆H < 0 indicated exothermic processes; however, Gibbs energies (∆G > 0) demonstrated that the adsorption between the pure polymers and the pesticides was not spontaneous under standard conditions. The analysis of non-covalent interactions (NCI) showed that PVC bonds hydrogen and also interacts by electrostatic forces, while PE showed predominantly weak van der Waals interactions. According to these results, PVC showed greater potential to adsorb pesticides, consequently, it demonstrates a greater propensity to transport them in the environment. Thus, these results collaborated to demonstrate the relevance of PM in the dynamics of pollutant transport, evidencing the contribution of computational chemistry as a predictive tool for environmental risk assessment.