Insights About Interactions between Microplastics and Humic Acids: An Approach Theoretical Modeling and Experimental

Area of Science:

• Environmental Science
• Chemistry
• Materials Science

Background:

• Microplastics (MPs) are persistent pollutants found globally.
• MPs interact with organic matter, like humic acid (HA), in environmental matrices.
• Estuarine sediments are deposition zones where HA and MPs frequently co-occur.

Purpose of the Study:

• To investigate the interaction mechanisms between polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics and humic acid.
• To quantify the affinity and forces governing HA-MP interactions.
• To assess the influence of environmental parameters on these interactions.

Main Methods:

• Experimental analyses including statistical evaluation.
• Computational modeling to determine interaction potential energy (IPE) and hydrogen bonding.
• Visualizations to confirm interaction types and binding sites.

Main Results:

• Experimental data revealed clear correlations between HA-MP interactions and sediment parameters like organic carbon and organic matter.
• Computational analysis indicated that van der Waals forces predominantly govern HA-MP interactions.
• Polystyrene (PS) exhibited the highest affinity for HA (-316 kJ mol⁻¹), followed by PP (-254 kJ mol⁻¹) and PE (-195 kJ mol⁻¹).
• PS demonstrated a greater reduction in HA-water hydrogen bonds, favoring HA-PS interactions.

Conclusions:

• Humic acid shows a significant affinity for microplastics, particularly polystyrene.
• Van der Waals forces are the primary drivers of these interactions.
• Further research is crucial to understand the environmental risks associated with HA-MP interactions in estuarine environments.