Coarse-grained simulations of sulfanilamide and hexachlorobenzene mobility in soil organic matter

Abstract

Soil organic matter (SOM) is a complex and heterogeneous molecular system, crucial for soil health and ecosystem functioning. Therefore, the release of pollutant molecules into the environment poses a significant environmental threat. Mechanisms that are governed by the interactions of these pollutants with SOM at the molecular level remain largely unexplored. In this study, coarse-grained molecular dynamics simulations were employed to investigate the behavior of hexachlorobenzene (HCB) and sulfanilamide (SAA) in humic substance (HS) systems with varying compositions. Diffusion coefficients indicated a strong influence of water on SAA, with SAA displaying higher mobility, whereas HCB exhibited greater accumulation in the HS phase. Calculations of spatial distributions supported these observations, showing that SAA is predominantly situated in the water phase, while HCB's interaction was influenced by the hydrophobicity of the SOM system. Simulations in the microsecond range, which were possible by the coarse-grained representation, revealed temporary trapping of SAA in the SOM matrix. These were anti-correlated with water diffusion, while HCB's behavior was dominated by direct pollutant–SOM interactions. In general, the coarse-graining approach provides novel insights into the trapping processes of pollutants in SOM and offers a realistic representation of molecular interactions at larger spatial and temporal scales. The proposed method enhances the understanding of pollutant mobility in soil systems, thus enabling future studies on the ecological impact of pollutant–SOM interactions.