Microplastic properties and their interaction with hydrophobic organic contaminants: a review

Microplastics (MPs) have been defined as particles of size < 5 mm and are characterized by hydrophobicity and large surface areas. MPs interact with co-occurring hydrophobic organic contaminants (HOCs) via sorption-desorption processes in aquatic and terrestrial environments. Ingestion of MPs by living organisms may increase exposure to HOC levels. The key mechanisms for the sorption of HOCs onto MPs are hydrophobic interaction, electrostatic interaction, π-π interactions, hydrogen bonding, and Van der Waals forces (vdW). Polymer type, UV-light-induced surface modifications, and the formation of oxygen-containing functional groups have a greater influence on electrostatic and hydrogen bonding interactions. In contrast, the formation of oxygen-containing functional groups negatively influences hydrophobic interaction. MP characteristics such as crystallinity, weathering, and surface morphology affect sorption capacity. Matrix properties such as pH, ionic strength, and dissolved organic matter (DOM) also influence sorption capacity by exerting synergistic/antagonistic effects. We reviewed the mechanisms of HOC sorption onto MPs and the polymer and matrix properties that influence the HOC sorption. Knowledge gaps and future research directions are outlined.