Browsing by Subject "Microplastics"
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Item Open Access Modeling Releases of Polymer Additives from Microplastics into the Aqueous Environment(2020) Feng, SiyuanMicroplastics (MPs) are becoming an emerging problem due to increased consumption of plastic. Despite research on MPs acting as sinks of contaminants, the potential of leaching additives out of MPs has been given little attention. Given challenges like the slow release rates of additives and the variety of physical chemical properties of MPs, mathematical models are great tools to explore this problem. In this study, the internal controlled diffusion model was used to describe release behaviors of additives from MPs into aqueous environments. This model was then applied to study Bisphenol A (BPA) and 4-t-butylphenol (TBP) leaching from epoxy MPs. Simulations on the influence of properties of microplastics and various temperatures were completed. Calculated diffusion coefficients of BPA and TBP based on leaching experiments data range from 10-13.3 cm2/s to 10-14.3 cm2/s and 10-12.1 cm2/s to 10-12.7 cm2/s, respectively. Though at low release rates, the release process was accelerated significantly by smaller sizes and irregular shapes of MPs. With a particle radius reduced from 1mm to 100 nm, the half-life of BPA changes from 3000 years to several minutes, and from 30 years to several seconds for TBP. Also, temperature dependence of migration obeys the Arrhenius equation and activated energies for BPA and TBP are 48.9 kJ/mol and 27.0 kJ/mol, respectively. To sum up, simpler plastic structures, smaller sizes, rough surfaces, smaller additive molecules, and the higher temperature facilitate the release process. This model contributes to the risk assessment of additives releasing from MPs. Yet the real problem might be far more complex considering special properties of plastics materials and environmental conditions. Thus, more research is required for a deeper understanding of this problem.
Item Open Access Multisector Mitigation of Plastic Pollution: Approaches from Biology, Policy, Law and Industry(2023) Diana, Zoie TaylorPlastic pollution is ubiquitous in the ocean. Researchers are actively determining how plastic pollution harms marine animals and which measures should be used to reduce pollution. I use the four pathways to global sustainability (created by Folke et al., 2021) as a guiding framework for this dissertation because this framework outlines how society can develop sustainable practices to address environmental challenges, in this case, plastic pollution. I identify risks posed by plastic pollution to marine animals and characterize government and corporate responses to plastic pollution. My overarching goal is to use these results to inform stakeholders of gaps or mismatches in plastics governance and chart a path toward global plastics sustainability. In Chapter 1, I investigate plastic consumption in marine animals, using the sea anemone as a model animal. I find that anemones readily consume plastic (polyethylene and polyvinyl chloride) pellets and can extract metallic additives, specifically lead and tin, from plastic. More broadly, this research suggests that plastic pollution may be a novel pathway for heavy metals to enter the marine food web. In Chapter 2, I examine government responses to plastic pollution by qualitatively analyzing public policies at all levels of government, from local to international, adopted between the years 2000 and 2019. I show that governments are increasingly adopting policies over time. Policies frequently target plastic bags and macroplastics and infrequently target microplastics. In Chapter 3, I qualitatively analyze voluntary commitments to reduce plastic pollution made by the world’s largest companies. I report that most companies are aware of the unsustainability of plastic and responding, albeit insufficiently given the scope of the challenges. Company commitments often lack concrete deadlines and frequently focus on recycling, despite low global recycling rates, which obscures corporate accountability. In Chapter 4, I provide insight into the role that emerging technologies may play in plastics sustainability. I synthesize literature on the use of plastic waste in road construction and highlight key knowledge gaps such as plastic additive leaching, microplastic and nanoplastic generation, and road recyclability at end-of-life. The dissertation closes with Chapter 5, which summarizes articles from the special issue “Emerging Challenges and Solutions to Plastic Pollution,” published in Frontiers in Marine Science, and contextualizes my dissertation findings in the broader scientific literature. I close Chapter 5 by synthesizing key dissertation findings and suggesting areas of future research. I highlight that societal responses to plastic pollution have not prioritized addressing the plastics that pose the greatest risks to aquatic ecosystems, resulting in negative environmental consequences. This dissertation contributes to the field by demonstrating the harms posed by plastic pollution to sea anemones and qualitatively characterizes public and private sector measures aiming to reduce plastic pollution. More broadly, I highlight the role of interdisciplinary research in environmental problem-solving and charting a path toward global plastics sustainability.
Item Open Access Release, Transformation, and Effects of Polymer-Associated Chemicals in the Aquatic Environment(2021) Walker Karega, Imari IyanaPlastic, 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.