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Microplastic loading, weathering, extraction, and environmental fate in estuarine systems
Summary
Rainstorms wash significant amounts of tiny plastic bits (microplastics) off streets and into rivers and estuaries, with more rain meaning more plastic pollution getting flushed into waterways that connect to our water supply and seafood sources. This research also found that the lab methods scientists use to measure microplastics can accidentally over- or under-count them, which matters because it means current pollution estimates may need refining before we can accurately judge health risks. While this study focused on tracking plastic movement in water rather than testing health effects directly, understanding how these particles travel and break down is a necessary first step toward figuring out our real-world ex
Microplastics (MPs, <5 mm) are ubiquitous anthropogenic pollutants that enter aquatic systems through multiple pathways linking terrestrial surfaces to freshwater and marine environments. MPs are an environmental concern because their small size increases the likelihood of interaction with aquatic organisms and potential adverse biological effects. Despite growing attention to MP pollution, important uncertainties remain regarding their pathways of entry, the influence of extraction methods on microfiber (MF) and MP quantification, the effects of photooxidation on polymer spectral characteristics, and the processes controlling MP fate and transport in estuarine systems. This dissertation addresses these gaps through an integrated investigation combining field observations, laboratory experiments, and numerical modeling. First, stormwater runoff was evaluated as a pathway of MP transport by quantifying MP loading during rainfall events in urban and suburban watersheds. MP abundance was expressed as particles per unit contributing drainage area (MP m-2), enabling comparison across storm events and catchments. MP loading increased with rainfall intensity and accumulated precipitation, indicating that rainfall events mobilize MPs from urban surfaces and transport them through stormwater runoff. Second, laboratory experiments evaluated how extraction procedures influence MF and MP recovery based on the ASTM D8333 protocol, focusing on particle characteristics after the cellulose digestion step with Schweizer’s reagent. Digestion efficiency and polymer integrity varied with exposure time and sample composition: regenerated cellulose materials were effectively removed at shorter contact times, whereas cotton-rich blends required longer exposure. Extended digestion could result in over-digestion and loss of target materials, indicating that pretreatment conditions influence MF recovery and reported MP abundance. Third, additional experiments examined how simulated solar radiation alters FTIR spectral characteristics and polymer identification. Laboratory weathering of polyethylene and polypropylene produced polymer-specific changes quantified using bond indices, with linear increases in carbonyl index for polypropylene and non-linear trends for polyethylene. In contrast, environmental MPs from stormwater and estuarine samples showed greater variability in these indicators, reflecting heterogeneous exposure histories and potential variability in initial composition, as polymers may contain pigments or additive formulations (e.g., UV stabilizers) that influence weathering and spectral interpretation. Finally, hydrodynamic simulations using the Regional Ocean Modeling System (ROMS) coupled with ROMSPath particle tracking were used to investigate MP fate and transport in the Hudson River and Estuary. Model results showed that freshwater discharge and particle buoyancy influence MP residence time, vertical distribution, retention, and export within the estuary. Overall, these results provide valuable insights into the pathways, extraction, characterization, weathering, and transport of MPs in aquatic systems. These findings contribute to improving the interpretation of environmental MP observations and may support risk assessment, development of fate and transport models, and the design of mitigation strategies aimed at reducing MP inputs to aquatic environments.