Quantifying Adsorption of Model Pollutants onto Various Weathered Plastics
Plastics in the environment are a global environmental problem and once in the environment, these plastics are exposed to various environmental stressors and begin to weather or chemically transform. While in the environment, plastics, including microplastics, can act as a substrate for small molecule organic pollutants to absorb to, which may ultimately be ingested by fish or be suspended in water bodies that are used for drinking water. The aim of our research is to quantify the adsorption of coumarin, diuron and bisphenol A (BPA) on the surface of photodegraded polyethylene (PE) and polyethylene terephthalate (PET) that have been weathered with UV light. The polymers were photolyzed with 254 nm UV light for 24, 48 and 72 hours to simulate different degrees of environmental weathering observed in natural samples. Plastics were placed in aqueous solutions with differing concentrations of either coumarin, diuron or BPA and the solution concentration was quantified with liquid chromatography (UPLC). The adsorption was observed as a decrease in the solution concentration of the pollutant and the change in concentration was modeled with a Langmuir isotherm to determine equilibrium distribution coefficients. Changes in the distribution coefficient were related to the materials properties, including hydrophobicity and surface area, and it was observed that adsorption of model pollutants is affected by a balance between chemical changes in the polymer and sites for adsorption. Through this work, we can better understand the implications for plastic waste in our environment.