Microplastics as vectors of organic pollutants in aquatic environment: A review on mechanisms, numerical models, and influencing factors

Abstract

Microplastics (MPs), a new class of emerging pollutants, have attracted exponentially increased attention due to the adverse ecological impacts on biota, not only by themselves but also by the combined corrosive substances. However, the occurrence mechanisms, numerical models and influencing factors of MPs adsorbing organic pollutants (OPs) show a significant variation with literatures. Therefore, this review is focused on the adsorption of OPs on MPs, including mechanisms, numerical models, and influencing factors, to obtain a comprehensive understanding. Research shows that MPs with strong hydrophobicity have high adsorption capacity for hydrophobic OPs. Hydrophobic distribution and surface adsorption are considered to be the main mechanisms by which MPs adsorb OPs. The available literature suggests that the pseudo-second-order model describes the adsorption kinetics of OPs on MPs better than the pseudo-first-order model, while the choice of Freundlich or Langmuir isotherm model depends mainly on the specific environmental conditions. Moreover, the characteristics of MPs (composition, particle size, aging, etc.), the nature of OPs (concentration, polarity, hydrophilicity, etc.), the environmental conditions (temperature, salinity, pH, ionic strength, etc.), and the substances co-existing in the environment (e.g., DOM and surfactants) are all important factors affecting the adsorption behavior of MPs for OPs. Environmental conditions can also indirectly affect the adsorption of hydrophilic OPs adsorbed on MPs by causing changes in the surface properties of MPs. Based on the current knowledge, the perspective shortening the knowledge gap is also suggested.

Keywords: Mechanisms; Microplastics; Numerical models; Organic pollutants.