A significant concern over plastic pollution is the release of plastic additives, especially plasticizers. Phthalates make up about 70% of the plasticizer market. These chemicals are known as endocrine disruptors and pose significant risks to both aquatic ecosystems and human health. Understanding the environmental behavior of phthalates is essential for evaluating their ecological risk. 

Since phthalates are not covalently bonded to the polymeric matrix and exist in a leachable form, they migrate into the environment easily upon disposal of phthalate-containing products through plastic aging and decomposition. In natural settings, the environmental behavior of additives in plastics may be influenced by biological activities, in addition to being regulated by various physical and chemical parameters. Biofilms inevitably form on plastic surfaces when plastic enters the aqueous environment. However, the study on the impact of biofilm growth on plastic surfaces in relation to phthalate release remains limited. 

In a study published in Environmental Science & Technology, a research group led by Prof. WU Chenxi from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences provided new insights into the environmental behavior of phthalates in plastics from the perspective of biofilm on plastic surfaces.  

In a microcosm experiment, researchers found that biofilm growth on plastic surfaces could increase the release of phthalates, employing polyvinyl chloride (PVC) plastics with varying levels of the di(2-ethylhexyl)phthalate (DEHP). By measuring the concentrations of DEHP in the aqueous solutions of the biofilm growth and biologically inhibited control groups, they found that except for the plastics without DEHP, the concentrations of DEHP in the aqueous phases of the biofilm growth groups for all types of plastics were significantly lower than those of the control groups during the whole experiment. 

In the biofilm growth groups, researchers found that biofilm attachment was evident on the plastic surface. Consequently, they quantified the contents of DEHP in the biofilm and its main metabolite monoethylhexyl phthalate (MEHP) in the experimental system. They found that the concentrations of MEHP in the aqueous solution of the biofilm growth groups were significantly higher than those of the control groups for all of plastics, and the contents of MEHP was significantly higher than the contents of DEHP, indicating that the biofilm on the surface plastic adsorbed and degraded the DEHP released from the plastic. 

Besides, researchers assessed the cumulative migration amounts of DEHP in the experimental system to explore the impact of biofilm on DEHP migration in PVC plastics. They revealed that the cumulative amount of DEHP in the system of the biofilm growth groups across various DEHP contents in PVC plastics was significantly higher compared to the control group.   

This study demonstrates that surface biofilms can significantly enhance the leaching of additives from plastics, and these surface biofilms exert influence on the transport and transformation of the additives released plastic through barrier, adsorption, and degradation in the environment. The significance of this emerging interface is especially crucial in natural environments, given that plastics entered aquatic environments will inevitably be attached to biofilms.