Microplastic-water partitioning of two states halogenated PAHs: Solute and sol

The complex interactions of contaminants with microplastics significantly affect ecological risk assessments. Studies of the sorption behavior of freely dissolved hydrophobic organic contaminants (HOCs) on microplastics are common. However, concentrations of HOCs in the actual aquatic environment sometimes exceed their water solubility. A possible explanation is that a microplastic-sol-water three-phase medium (TPM) is formed in the actual water environment. Both states HOCs (in solute and sol) have the potential to migrate to particles suspended in water. To confirm this view, four kinds of microplastics and eight halogenated polycyclic aromatic hydrocarbons (HPAHs) were selected to examine the partitioning of HPAHs between microplastics and water (sol and solute). Both monolayer and multilayer coverage of HPAHs onto microplastics occurred, and chemical sorption dominated the pseudo-sorption mechanism. The microplastic-water partition ratios of HPAHs (0.12-0.74) were approximately four to five orders of magnitude lower than their corresponding KOW values, suggesting that mechanisms other than sorption were involved. Apparently, the sol HPAHs contributed almost identically large increments to both microplastics and water, and closed the gap. For microplastic-supported HPAHs, the contribution of the sol fraction was more than triple that of the dissolved fraction; the key influencing factor was the water solubility of HPAHs.

Automated summary

The interactions between microplastics and contaminants play a significant role in ecological risk assessments. Studies have shown that in some cases, concentrations of hydrophobic organic contaminants in the aquatic environment can exceed their water solubility due to the formation of a microplastic-sol-water three-phase medium. Research on the partitioning of halogenated polycyclic aromatic hydrocarbons between microplastics and water revealed that chemical sorption dominated the process and there were mechanisms other than sorption involved.