Release, Transformation, and Effects of Polymer-Associated Chemicals in the Aquatic Environment

Plastic, while incredibly useful to both industrial and commercial products due to its flexibility and durability, has created a global waste management issue. In 2020, roughly 368 million tons of plastic was produced for packaging, textiles, consumer products, transportation, construction, electronics and more. Due to the lack of a circular economy for plastic, a large majority will be used once before being taken to landfills, incinerators, and recycling facilities. A fraction of this waste is also mismanaged and disposed of in the environment. Plastic debris in the environment is found within freshwater lakes, rivers, and streams where sedimentation can occur or transport to the marine environment. Plastic waste in aqueous environments has the potential to undergo abiotic and biotic weathering that will cause fragmentation to the polymer result in the release of microplastics and potentially hazardous polymer associated chemicals. Polymer associated chemicals (PACs) include polymer additives and monomers that are intentionally incorporated into the polymer to imbue the material with certain properties along with non-intentionally added substances like processing impurities. Some PACs have previously demonstrated toxicity including being mutagenic, carcinogenic, and estrogenic. PACs are not physically bound to the polymer and can be released into aqueous environments. Thus, plastic pollution introduces a risk of harm to marine and freshwater organisms via ingestion of microplastics that will result in exposure to potentially hazardous chemicals. The objective of this dissertation aims to further characterize the risk of polymer associated chemicals released into aqueous environments by answering these three questions: (1) What is the leaching behavior of PACs within various simulated aqueous environments? (2) How are PACs chemically transformed in simulated aqueous environments? (3) To what extent do released PACs and mixtures of PACs contribute to the estrogenic activity in a polymer leachate? In chapter 2, I studied the influence of carbon nanotube loading and various abiotic factors on the release of the monomers bisphenol A (BPA) and 4-tert-buylphenol (TBP) from epoxy and polycarbonate nanocomposites submerged in simulated freshwater environments. Single walled carbon nanotube (SWCNT) loading within the polymer nanocomposites (PNCs) demonstrated a decrease in monomeric concentrations released into water. Temperature, pH, UV light, and polymer size were found to be the most significant factors influencing release of TBP and BPA from PNCs. Additionally, the relative leaching behavior demonstrated differences by polymer type and chemical over the 5-day leaching experiments. These results provided important data to assess the risk posed by SWCNT polymer composites as they age in the environment. In chapter 3, I examined the release and fate of PACs from polypropylene (PP) and polyurethane (PU) microplastics during 12-month freshwater wetland mesocosm experiments and 3-month freshwater laboratory photolysis and leaching studies. Liquid chromatography coupled to high-resolution mass spectrometry (HRMS) is a powerful analytical technique used to characterize soluble organic pollutants in complex aqueous matrices. I utilized the data acquired from our HRMS with a non-targeted mass spectrometry workflow to identify novel polymer additives (Tinuvin 770), monomers (4-(4-formamidobenzyl)phenyl) formamide), and non-intentionally added substances (ricinine). Additionally, I was able to use this information to structurally annotate abiotically driven transformation products of two PACs. Leaching behavior of PACs quantified in both studies varied significantly where mesocosm PAC concentrations decreased over 12 months and laboratory-controlled PAC concentrations increased over 3 months. Further, UV pretreatment to the microplastics highlighted the difference in PACs that were UV labile or photo transformed. This work demonstrated the importance of utilizing both laboratory and mesocosm based studies in analyzing the fate and occurrence of PACs released from microplastics into freshwater environments. In chapter 4, four polymers (latex (LX), polyethylene (PE), polypropylene (PP), and polystyrene (PS)) were submerged in simulated freshwater, seawater, fish gastric fluid, seabird gastric fluid and solvent extracts to characterize leachable and potentially endocrine disrupting PACs. Suspect screening and targeted analysis were employed to quantify known PACs and structurally annotate PACs. In vitro bioassays were utilized to determine estrogenic responses of individual chemicals and chemically representative mixtures of the seabird digestate. Suspect screening characterized 20 polymer associated chemicals in the PE shopping bag, PS foam and PP string functioning as catalysts, antioxidants, lubricants, colorant intermediates, and surfactants. Additionally, in silico fragmentation workflows were employed to structurally annotate unknown sulfurous containing polymer associated chemicals released from PS foam samples. Of the four compounds quantified in the leachates, Tris(2,4-di-tert-butylphenyl) phosphate demonstrated significant estrogenic response at relevant concentrations found within the samples. Further, chemical mixtures of previously quantified phenols and phthalates explained 20% of the estrogenic activity within the PE shopping bag seabird digest samples. The implications of this work highlight the necessity of coupling non-targeted screening tools to in vitro assays for predicting the risk of polymer associated chemicals in the environment. In summary, this dissertation coupled targeted and non-targeted mass spectrometry workflows to characterize the broad diversity of leachable PACs. This work additionally highlighted the importance of analyzing environmental PAC transformations to understand the fate of PACs in water. Further, toxicity studies combined with identification of potentially hazardous chemicals further characterized the risk of endocrine disruption from PACs released into simulated marine stomachs. Taken together, my work represents significant progress in characterizing the behavior and risk of polymer associated chemicals in aqueous environments.