A Risk Assessment of Coastal Nanoplastic Particles: Enzymatic Pre-Treatment and Analytical Approaches at the Nanoscale

Thesis (Master's)--University of Washington, 2023Anthropogenic impacts on marine ecosystems have developed into a dominating and formative force within coastal regions. One of the strongest influences within these coastal anthropogenic zones is the deposition and life cycle of marine plastic waste. Macroplastic, mesoplastic, and microplastic waste fields have undergone significant growth in both study and remediation yet given the various mechanisms of degradation within the marine environment, all plastic waste categories without intervention will degrade onto the nanoscale, a class of waste termed nanoplastics. The field of nanoplastics remains in its infancy, it lacks both standardized definitions and operating procedures for sampling and analysis, however inferences on activity and environmental relationships can be derived from current and former literature on engineered nanomaterials. This work provides several approaches for addressing a risk assessment for coastal micro and nanoplastic particles within the coastal zone scenario, with specific scoping towards the developmental endpoint. This risk assessment incorporates ranges of i) plastic concentrations, ii) plastic exposures through incidental marine ingestion and ingestion of seafood, iii) and constituent compound contents to better assess plastic risk from a holistic view. There is insufficient toxicological data to conduct a thorough quantitative risk assessment. Using available environmental monitoring data, we were able to apply the mixtures-based risk assessment developed within this work and we believe that coastal micro and nanoplastic mixtures pose low to no level of risk to the public regarding the developmental endpoint at present environmental concentrations. Although this study has determined low to no risk at present, we emphasize that this assessment and the data availability relating to hazard and exposure characterizations is underdeveloped and believed to be increasing in magnitude leading to a relevant yet likely inaccurate model. This study also addressed some of the analytical deficiencies identified through conducting a review of the literature relating to sample treatment and analysis for environmental nanoplastic particles from various media. This review revealed complex analytical considerations applied within the pretreatment schema we put forth for seafood and marine media. A methodological study and approach is applied here in where polyethylene (PE, 200-1000 nm), polyethylene terephthalate (PET, 60-500 nm), polymethyl methacrylate (PMMA, 150 nm), and carboxylated polystyrene (PS, 120 nm) self-synthesized and commercially procured nanoparticles underwent an enzymatic digestion to progress the state of viable pretreatment methods for marine micro and nanoplastic particle samples. Post-digestion particle size when assessed via spectroscopic methods yielded statistically significant increases of 23% (PS), 51.7% (PMMA), 43.9% (PE), 380.2%(PET) diameter across all polymers, while assessment through microscopic techniques yielded a statistically significant increase and decrease of 65.7% and -72.4% for PS and PET respectively