Direct and non-direct transfer of phthalate esters from indoor sources to settled dust: Model analysis

Abstract Phthalate esters (PAEs), as a group of typical semi-volatile organic compounds (SVOCs) with excellent performance as plasticizers, are widely used in indoor products and have been found to harm human health. There are two migration pathways for phthalates from the source to settled dust, namely: direct and non-direct contact with the sources. Therefore, concentrations of phthalates in settled dust have exhibited significant differences in the source and non-source surfaces in past literature. In this study, a porous media model is proposed to characterise the mass transfer mechanism of phthalates from the source into settled dust via two migration pathways. We compared the simulation data with the experimental data in the literature to validate the model, and the simulation results were consistent with the experimental results within an acceptable degree. Based on the model, a certain thickness of settled dust was selected to simulate the dust-phase concentration change of DEHP within 500 days and the concentration difference between source (value of 21,687.33 μg/g) and non-source surfaces (value of 150.32 μg/g) was compared. Then, the difference in the concentration distribution in the dust layer of different mass transfer pathways was visually demonstrated. Dust loading can dominate the mass transfer of phthalates and influence the concentration in dust by affecting the characteristics of the dust layer (porosity and thickness of settled dust). In addition, the solid diffusion coefficient and Koa values of phthalates have a significant influence on the dust-phase concentration and time to reach a steady state.