The impact of microplastics on the adsorption of 2,4,6-tribromophenol in soils: Competitive adsorption

Soil is a major sink for microplastics (MPs) which can interact with organic contaminants affecting their transport behavior. The impact of MPs in soil matrix is complicated depending on soil-MPs, soil-contaminants and MPs-contaminants interactions, however the study on their interactions is limited. In this study, polyethylene (PE) was selected to investigate its effects on 2,4,6-tribromophenol (TBP) adsorption in soils. TBP adsorption on soils with/without MPs followed pseudo-second order kinetics, and the adsorption isotherm data fitted well with Langmuir and Freundlich models. Compared to pure soil, the presence of PE and aged PE (APE) in soil (1 %, w/w) reduced the adsorption capacity of TBP by 29.4 % and 32.4 %. Meanwhile, the TBP desorption efficiency from soil with PE and APE exceeded that observed in pure soil 31.5 %, which were 36.3 % and 35.7 %, respectively. Consequently, the mobility of TBP in soil could be enhanced increasing its risk to groundwater. With the increment of environmental pH, MPs dosage and ionic strength, the TBP adsorption amount decreased. MPs could compete with TBP for adsorption on soil particles exhibiting an inhibitory effect, since the adsorption energies of MPs-soil and TBP-soil from DFT calculation are strong and on the same level, while the interactions between TBP and MPs are mainly due to van der Waals force. Moreover, the inhibitory effect of APE was weaker than PE, because APE carried more negative charge, resulting from the oxygen-containing functional groups generated during aging, which reduced its affinity towards soil, consequently more vacant sites on soil were left for TBP adsorption.