Evaluating the adsorption and desorption performance of poly(butylene adipate-co-terephthalate) (PBAT) microplastics towards Cu(II): The roles of biofilms and biodegradation

The environmental risks associated with microplastics from biodegradable plastics are an emerging concern, but the roles of biofilm formation and biodegradation in the environmental behaviors of biodegradable microplastics have not been clarified. Here, we investigated the adsorption and desorption performance of Cu(II) on the poly(butylene adipate-co-terephthalate) (PBAT) microplastics and explored the roles of biofilms and biodegradation during the adsorption. The maximum adsorption quantities of Cu(II) by the pristine PBAT, the biofilm-covered PBAT, and the biodegraded PBAT were 140.547 µg·g−1, 192.197 µg·g−1, and 172.065 µg·g−1, respectively. The biodegradation increased the Cu(II) adsorption on the PBAT by 24.43%, which was due to the changes in physicochemical properties (e.g., a high surface area to volume ratio, high crystallinity, and more oxygenated groups). The surface of PBAT covered by biofilm contained oxygen- and nitrogen-containing functional groups, which could complex with more Cu(II), thus making the promoting effect of biofilm on adsorption stronger than that of biodegradation. The adsorbed Cu(II) on the surface of the biodegraded PBAT had a remarkable desorption hysteresis and was less impacted by the presence of FA, indicating that PBAT after biodegradation could transport the adsorbed heavy metals over long distances, which was not observed on the biofilm-covered PBAT. Our findings highlight the critical effects of plastic degradation on the environmental behaviors of petro-based microplastics, which helps assess the environmental fate of biodegradable microplastics in aquatic systems.