Abstract: Microplastics in soil and sediment may affect the transport of contaminants in the environment. In this study, we examined the transport behaviors of tetracycline and triclosan in saturated quartz sand with an addition of 5% newly made or aged polypropylene microplastics. The breakthrough curves were fitted with a convection-dispersion model coupled with a two-site sorption (chemical nonequilibrium) model. The results showed that the transport dynamics of tetracycline and triclosan at different pH conditions were closely associated with their dissociation status. The transport of tetracycline was prohibited at neutral condition, but was almost unaffected at acid and alkaline conditions due to the electrical repulsion between tetracycline and porous media. Triclosan was least able to migrate in its molecular form under acidic conditions, but its transport ability was increased with increasing solution pH. The presence of microplastics in the media restrained the transport of tetracycline and triclosan by increasing kinetics sorption sites and reducing sorption rate. Particularly, the degree of nonequilibrium adsorption was promoted, and the retardation factor was increased when the aged microplastics existed in the porous media. As a consequence, the sorption and retention of tetracycline and triclosan were intensified due to the generation of oxygen functional groups in aged microplastics.

Key words: microplastic, tetracycline, triclosan, transport, sorption.