Distinguishable adsorption interaction of virgin and biofilm covered polyethylene and polylactic acid for antibiotics

Microorganisms easily colonize microplastics in aquatic environment, forming microplastic circles with a high affinity for contaminants. However, the mechanism of antibiotic adsorption by biodegradable and non-biodegradable microplastics under biofilm loading is unclear. Here, virgin polyethylene (V-PE) and virgin polylactide (V-PLA) are non-biodegradable and biodegradable microplastics, respectively, and we investigated their biofilms formation in an aquatic environment. And the adsorption interaction of tetracycline hydrochloride (TCH) or ciprofloxacin (CIP) using biofilm covered polyethylene (B-PE) and compared it with biofilm covered polylactic acid (B-PLA). The biofilms changed the surface properties and morphology of the microplastics and enhanced their adsorption capacity for antibiotics. The order of adsorption capacity was B-PE > B-PLA > V-PE > V-PLA. Compared with V-PE and V-PLA, the adsorption capacity of B-PE and B-PLA for TCH increased by 0.346 and 0.267 mg/g, and adsorption capacity for CIP increased by 0.308 and 0.111 mg/g, respectively. The adsorption behaviors of B-PE and B-PLA fitted the pseudo-second-order kinetic equation well, and also fitted the Langmuir isotherm equation and the Freundlich isotherm equation, respectively. In addition, hydrogen-bond interaction, electrostatic interaction and hydrophobic interaction were found to dominate the adsorption of antibiotic by biofilm covered microplastics. Our study revealed the adsorption interaction between biofilm covered microplastics and antibiotics and provided basic information for ecological risk assessment of different biofilm covered microplastics.