Insights into adsorption mechanisms of nitro polycyclic aromatic hydrocarbons on common microplastic particles: Experimental studies and modeling

Nitro polycyclic aromatic hydrocarbons (NPAHs) and microplastics (MPs) are emerging contaminants that pose a threat to the aquatic ecosystem. Knowledge of the NPAHs and MPs interaction will help the understanding of their fate and risks in natural environment. Here, the adsorption behavior and mechanism of typical NPAHs on microplastics were investigated. The adsorption kinetic and isotherm data showed that the adsorption of NPAHs was controlled by chemical adsorption and hydrophobic partition, because of excellent fit of kinetic and isothermal equations (R2 > 0.9). The adsorption capacity (587-744 μg g-1) was largely dependent on the hydrophobicity of NPAHs. The experiment of environmental factors confirmed the important role of pollutant hydrophobicity, with 1-Npyr of the highest hydrophobicity having the greatest adsorption on MPs (adsorption rate >90%) and less affected by solution pH and ionic strength (changer <5%). In the mixture system, MPs displayed high adsorption capacity for each compound; Interestingly, because compounds with smaller size were easy to occupy the adsorption sites in the pores of MPs, the adsorption of 2-Nflu (724 μg g-1) was even greater than that of 9-Nant (713 μg g-1) and 1-Npyr (703 μg g-1). The model calculation of adsorption also shows that there is surface adsorption and hydrophobic distribution in the adsorption process. The findings provide new insights into the interactions of MPs with organic pollutants in complex environments.