UC Santa Barbara

Contemporary contaminants of consequence to the health of aquatic ecosystems are dispersed in the environment owing their widespread use. Some are highly toxic yet cannot be monitored at concentrations which induce severe impacts, such as mortality, to aquatic organisms. In this research, the focus is on addressing the pressing need for accessible and practical tools to perform screening-level ecological risk assessments in the face of an increasing number of chemicals used by society. The challenge of obtaining field data for calibration and validation, particularly in data-limited conditions, forms the backdrop of this research. The first chapter delves into the application and evaluation of OrganoFate, showcasing its effectiveness in making screening-level predictions that align with observed concentrations in surface water. This chapter highlights the model's capability to assess potential aquatic health risks associated with CECs and pesticides. The second chapter shifts the focus to pesticides, acknowledging their significant impact on aquatic and terrestrial ecosystems. It introduces the Environmental Release Tool, a sub-tool of the Pesticide Mitigation Prioritization Model, designed to address critical challenges in evaluating pesticide toxicity over large extents, tracking spatiotemporal pesticide use, assessing cumulative toxicity, and identifying the contributions of different pesticide application sites. The chapter reveals key insights into the applied toxicity of pesticides and underscores the importance of considering cumulative applied pesticide toxicity for effective risk assessment. The third chapter introduces the Environmental Fate Tool (EFT), a novel tool with the unique ability to quantify aquatic risks for numerous pesticides and watersheds across expansive landscapes, pinpoint spatially explicit source contributions, and scale up analyses. This tool represents a significant advancement in identifying and prioritizing strategies to mitigate risks associated with dispersed chemical pollution in surface waters. Overall, this dissertation offers an exploration of tools and methodologies for ecological risk assessment in the context of a growing and changing chemical landscape. It underscores the importance of modeling approaches to restore and safeguard our water resources and provides valuable insights into the ecological risks posed by emerging contaminants in various aquatic ecosystems.