Adsorption of Tylosin and Tetracycline onto Microplastics: Behavior and Effects of Adsorbents and Salinity

Microplastic pollution is becoming one of the most severe threats to the entire earth surface ecosystem; moreover, it has the potential to act as a carrier for other chemical pollutants, introducing these pollutants in diverse environments. To evaluate this threat, this study investigated the adsorption of two antibiotics, tylosin (TYL) and tetracycline (TC), onto three common environmental microplastics, polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC), through batch adsorption experiments. Overall, the Freundlich model fitted the isothermal adsorption well, which indicated inhomogeneous distribution of adsorption sites involved in the adsorption. The fitted parameters indicated that the adsorption of TYL and TC onto PVC was highest relative to that onto the other two microplastics, which was attributed to the differences in functional groups and crystallinity of polymers. The adsorption efficiency decreased with increasing microplastic concentration. Owing to the salting-out effect, the increase in salinity promoted TYL adsorption onto the microplastics; salinity had no significant effect on TC adsorption onto microplastics. The results suggest that microplastics can be carriers of antibiotics in the environment, for which the physicochemical properties of microplastics and antibiotics as well as environmental factors are crucial influencing factors. This study further clarifies the adsorption mechanisms of contaminants onto microplastics under different environmental conditions.