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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Santa Barbara Electronic Theses and Dissertations (2016)

Nanoparticles have had a large impact and driven a growing commercial industry of nano-enabled products. Nanoparticles’ small size causes large changes in physicochemical properties compared to their “bulk” states, and this has been utilized for a wide variety of applications, ranging from biomedical to electronic, to cosmetic use. However, these novel properties also carry with them unknown effects on our environment. Numerous laboratory studies have found deleterious effects of nanoparticles on aquatic organisms, but we are missing key knowledge on how these toxic effects amplify in ecological systems. The aim of my dissertation is to investigate the effects of nanoparticles on freshwater systems through a series of experiments on phyto- and zooplankton and the development of quantitative models to explain these empirical results and extrapolate effects to other systems. My work has identified the importance of ecological feedbacks in nanotoxicology, specifically two novel feedbacks: algae produce dissolved organic carbon (DOC) that mitigates the toxicity of nanomaterials (silver and iron nanoparticles) to the cells themselves and a concentration of silver nanoparticles (AgNPs) that is toxic to individual Daphnia has no effect on populations of zooplankton due to population-level feedbacks.

The development of quantitative models of both of these feedbacks has enabled the estimation of the strength of both nanomaterial toxicity and of the mitigating feedback. Through the development of models of algal growth, DOC production, and nanoparticle toxicity, I estimated the strength of both the inactivation of toxicity by DOC as well as the toxic strength of the various contributors to nanotoxicity (nano versus ionic, different transformations of nanoparticles). Estimating the relative contributions of different forms or products of nanoparticles to their overall toxic effect can be useful in ecological risk assessment, as it could identify toxic factors that are already regulated (such as ionic silver) along with those that are currently unregulated (nanosilver) and allow for direct comparison of their toxicity. The development of models of daphnid growth and reproduction, parameterized with individual-level data of AgNP exposure of Daphnia at multiple food rations, allowed me to identify the feedback that seemingly disrupts extrapolation between levels of biological organization. A concentration of AgNPs that is toxic to individual Daphnia has no effect on small populations of Daphnia due to population-level feedbacks in which the zooplankton population equilibrates at a lower consumer and higher resource biomass. This increase in the amount of food per individual allows the zooplankters to survive AgNP exposure. Overall, my dissertation work highlights the importance of ecological and environmental complexity when estimating the impacts of nanoparticles on freshwater systems.

    Cover page: Ecological feedbacks and engineered nanomaterials in freshwater environments
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2016)
    Nanoscale zerovalent iron (nZVI) and its derivatives hold promise for remediation of several pollutants but their environmental implications are not completely clear. In this study, the physicochemical properties and aggregation kinetics of sulfide/silica-modified nZVI (FeSSi) were compared in algal media in which Chlamydomonas reinhardtii had been cultured for 1, 2, or 11 days in order to elicit the effects of organic matter produced by the freshwater algae. Furthermore, transformation of FeSSi particles were investigated in C. reinhardtii cultures in exponential (1-d) and slowing growth (11-d) phases while monitoring the response of algae. We found evidence for steric stabilization of FeSSi by algal organic matter, which led to a decrease in the particles' attachment efficiency. Transformation of FeSSi was slower in 11-d cultures as determined via inductively coupled plasma and X-ray analyses. High concentrations of FeSSi caused a lag in algal growth, and reduction in steady state population size, especially in cultures in exponential phase. The different outcomes are well described by a dynamic model describing algal growth, organic carbon production, and FeSSi transformations. This study shows that feedback from algae may play important roles in the environmental implications of engineered nanomaterials.
      Cover page: Influence of Phytoplankton on Fate and Effects of Modified Zerovalent Iron Nanoparticles
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2017)
      Nanozerovalent iron (nZVI) is widely used for its ability to remove or degrade environmental contaminants. However, the effect of nZVI-pollutant complexes on organisms has not been tested. We demonstrate the ability of a sulfidized derivative of nZVI (FeSSi) to sorb cadmium (Cd) from aqueous media and alleviate Cd toxicity to a freshwater alga for 32 days. FeSSi particles removed over 80% of the aqueous Cd in the first hour and nearly the same concentration of free Cd remained unbound at the end of the experiment. We found that FeSSi particles with Cd sorbed onto them are an order of magnitude more toxic than FeSSi alone. Further, algal-produced organic material facilitates safer remediation of Cd by FeSSi by decreasing the toxicity of FeSSi itself. We developed a dynamic model to predict the maximum Cd concentration FeSSi can remediate without replacing Cd toxicity with its own. FeSSi can remediate four times as much Cd to phytoplankton populations when organic material is present compared to the absence of organic material. We demonstrate the effectiveness of FeSSi as an environmental remediator and the strength of our quantitative model of the mitigation of nanoparticle toxicity by algal-produced organic material.
        Cover page: Remediation of Cadmium Toxicity by Sulfidized Nano-Iron: The Importance of Organic Material
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2013)
        The vast majority of nanotoxicity studies measures the effect of exposure to a toxicant on an organism and ignores the potentially important effects of the organism on the toxicant. We investigated the effect of citrate-coated silver nanoparticles (AgNPs) on populations of the freshwater alga Chlamydomonas reinhardtii at different phases of batch culture growth and show that the AgNPs are most toxic to cultures in the early phases of growth. We offer strong evidence that reduced toxicity occurs because extracellular dissolved organic carbon (DOC) compounds produced by the algal cells themselves mitigate the toxicity of AgNPs. We analyzed this feedback with a dynamic model incorporating algal growth, nanoparticle dissolution, bioaccumulation of silver, DOC production and DOC-mediated inactivation of nanoparticles and ionic silver. Our findings demonstrate how the feedback between aquatic organisms and their environment may impact the toxicity and ecological effects of engineered nanoparticles.
          Cover page: Environmental Feedbacks and Engineered Nanoparticles: Mitigation of Silver Nanoparticle Toxicity to Chlamydomonas reinhardtii by Algal-Produced Organic Compounds
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2018)
            Cover page: Incorporating Suborganismal Processes into Dynamic Energy Budget Models for Ecological Risk Assessment
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2021)
            Nutritional and contaminant stressors influence organismal physiology, trophic interactions, community structure, and ecosystem-level processes; however, the interactions between toxicity and elemental imbalance in food resources have been examined in only a few ecotoxicity studies. Integrating well-developed ecological theories that cross all levels of biological organization can enhance our understanding of ecotoxicology. In the present article, we underline the opportunity to couple concepts and approaches used in the theory of ecological stoichiometry (ES) to ask ecotoxicological questions and introduce stoichiometric ecotoxicology, a subfield in ecology that examines how contaminant stress, nutrient supply, and elemental constraints interact throughout all levels of biological organization. This conceptual framework unifying ecotoxicology with ES offers potential for both empirical and theoretical studies to deepen our mechanistic understanding of the adverse outcomes of chemicals across ecological scales and improve the predictive powers of ecotoxicology.
              Creative Commons 'BY' version 4.0 license
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