Adsorption of Model Micropollutants to Polymer Films After UV Light Exposure

Abstract

Plastics have proven to be useful in a myriad of applications due to properties like chemical resistance. However, this also makes them a problematic, persistent environmental contaminant. In the environment, plastics are known to degrade from environmental factors including UV light irradiation. Previous studies have shown that plastics have an ability to sorb organic compounds, causing plastics to act as vectors for contaminant transport through the environment that ultimately causes accumulation within various aquatic organisms. Yet, little work has evaluated if plastic weathering impacts its behavior in the environment. This work aims to quantify sorption of coumarin, a model pollutant molecule, onto photodegraded polymers. The main polymers studied for this work are polyethylene (PE) and polyethylene terephthalate (PET) since they are abundantly found as waste in marine environments. Photo-transformations of polymer films were characterized by ATR-FTIR and SEM after irradiation with 254 nm UV light to understand molecular and structural changes. Coumarin adsorption to non-photolyzed and photolyzed plastic films were evaluated with liquid chromatography (UPLC) and the monitored data was fit to the Freundlich and Langmuir sorption isotherms to quantify pollutant partitioning. Correlations between distribution coefficients and plastic phototransformations affecting hydrophobicity and crystallinity were analyzed. The distribution coefficient of coumarin was higher for 0 h UV PET than PE. For both types of plastic, distribution coefficients of coumarin initially decreased then increased from either 24- or 48- time points. The trend for the distribution coefficient therefore cannot be only related to changes in polymer hydrophobicity and crystallinity. This work has contributed to a better understanding of the interaction between plastic debris and organic pollutants found in water.