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Open Access Publications from the University of California

Scholarly Works (12 results)

  • Article
  • Peer Reviewed
UC Santa Barbara Previously Published Works (2014)
A comprehensive assessment of the environmental risks posed by engineered nanomaterials (ENMs) entering the environment is necessary, due in part to the recent predictions of ENM release quantities and because ENMs have been identified in waste leachate. The technical complexity of measuring ENM fate and transport processes in all environments necessitates identifying trends in ENM processes. Emerging information on the environmental fate and toxicity of many ENMs was collected to provide a better understanding of their environmental implications. Little research has been conducted on the fate of ENMs in the atmosphere; however, most studies indicate that ENMs will in general have limited transport in the atmosphere due to rapid settling. Studies of ENM fate in realistic aquatic media indicates that in general, ENMs are more stable in freshwater and stormwater than in seawater or groundwater, suggesting that transport may be higher in freshwater than in seawater. ENMs in saline waters generally sediment out over the course of hours to days, leading to likely accumulation in sediments. Dissolution is significant for specific ENMs (e.g., Ag, ZnO, copper ENMs, nano zero-valent iron), which can result in their transformation from nanoparticles to ions, but the metal ions pose their own toxicity concerns. In soil, the fate of ENMs is strongly dependent on the size of the ENM aggregates, groundwater chemistry, as well as the pore size and soil particle size. Most groundwater studies have focused on unfavorable deposition conditions, but that is unlikely to be the case in many natural groundwaters with significant ionic strength due to hardness or salinity. While much still needs to be better understood, emerging patterns with regards to ENM fate, transport, and exposure combined with emerging information on toxicity indicate that risk is low for most ENMs, though current exposure estimates compared with current data on toxicity indicates that at current production and release levels, exposure to Ag, nZVI, and ZnO may cause toxicity to freshwater and marine species. © 2014 Springer Science+Business Media.
    Cover page: Emerging patterns for engineered nanomaterials in the environment: a review of fate and toxicity studies
    • Thesis
    • Peer Reviewed
    UC Santa Barbara Electronic Theses and Dissertations (2016)

    Engineered nanomaterials (ENMs) are a relatively new class of material for which the risks of negative environmental impacts are still being determined. A comprehensive assessment of the environmental risks of ENMs entering the environment is essential, in part due to the continued increase in ENM production and release to the environment. The technical difficulty in measuring ENM fate and toxicity in complex and dynamic environmental media necessitates the use of mathematical models. In this research, the environmental risks of ENMs are assessed through: (i) the collection and analysis of emerging information on significant fate and transport processes; (ii) development of an ENM-specific fate and transport model to predict the accumulation of ENMs and their exposure to organisms in the environment; (iii) development of a statistical model to predict the distribution of species toxicity from specific ENMs in freshwater; and (iv) development of a bioaccumulation model to predict the long-term accumulation of ENMs through a food chain.

    The NanoFate model, which was developed as part of the research described in this paper, is used to predict the temporal variability in fate across a broad range of complex environmental media at various spatial scales using both traditional fate and transport processes such as advection, deposition, and erosion, but also using ENM-specific processes and transformations such as heteroaggregation, sedimentation, and dissolution. A case study on San Francisco is then used to explore how fate and accumulation may vary among 4 different metallic ENMs, n-CeO2, n-CuO, n-TiO2, and n-ZnO, because the rates of fate processes and the toxicity are known to vary among these four ENMs.

    Chapter 1 specifically explores how these processes and toxicities vary among different types of ENMs. Chapter 2 explores how species sensitivities vary between different ENMs within a freshwater ecosystem. A species sensitivity distribution (SSD) is a cumulative probability distribution of a chemical’s toxicity measurements obtained from single-species bioassays that can be used to estimate the ecotoxicological impacts of that ENM. The SSD results indicate that size, formulation, and the presence of a coating can alter toxicity, and therefore the corresponding range of toxic concentrations. Chapter 3 describes the development of the NanoFate model and explores the implications of the San Francisco case study. By investigating both the range in rate processes and release scenarios, ENM fate was found to vary by multiple orders of magnitude among different environmental media and that even with an improved understanding of ENM fate, predictions of environmental concentrations are still very uncertain. We compare the predicted environmental concentrations for San Francisco Bay across many different release scenarios with the results of the SSDs and found that while CuO, TiO2, and ZnO are likely to exceed No Observed Effect Concentrations (NOEC) in freshwater, this is not the case for soils. The worst-case scenario, where the predicted concentrations would exceed lethal concentrations (LC50), was not found in any scenario explored within the case study. Chapter 4 explores the range in bioaccumulation that could result from the NanoFate predictions for a freshwater ecosystem. A toxicokinetics model, using as much species-specific and ENM-specific uptake, biotransformation, and elimination rates as were available for CuO, TiO2, and ZnO is used to predict the likelihood of bioconcentration and biomagnification through a simple food chain. Though bioconcentration was found for most species, biomagnification was not predicted to be significant with increasing trophic levels. Uncertainty analysis indicates that these results may vary by as much as two orders of magnitude. A parameter sensitivity analysis highlights key biological and environmental parameters that can be used to focus future research. While further developments will improve these predictions as our understanding of ENM fate and toxicity progresses, current understanding indicates that risk is likely low for most ENMs at predicted environmental concentrations though there is some concern that under high and localized release scenarios, toxic impacts will occur.

    • 2 supplemental files
    Cover page: Assessing the Risk of Engineered Nanomaterials in the Environment: Modeling Fate, Exposure, and Bioaccumulation
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2017)
    We developed a dynamic multimedia fate and transport model (nanoFate) to predict the time-dependent accumulation of metallic engineered nanomaterials (ENMs) across environmental media. nanoFate considers a wider range of processes and environmental subcompartments than most previous models and considers ENM releases to compartments (e.g., urban, agriculture) in a manner that reflects their different patterns of use and disposal. As an example, we simulated ten years of release of nano CeO2, CuO, TiO2, and ZnO in the San Francisco Bay area. Results show that even soluble metal oxide ENMs may accumulate as nanoparticles in the environment in sufficient concentrations to exceed the minimum toxic threshold in freshwater and some soils, though this is more likely with high-production ENMs such as TiO2 and ZnO. Fluctuations in weather and release scenario may lead to circumstances where predicted ENM concentrations approach acute toxic concentrations. The fate of these ENMs is to mostly remain either aggregated or dissolved in agricultural lands receiving biosolids and in freshwater or marine sediments. Comparison to previous studies indicates the importance of some key model aspects including climatic and temporal variations, how ENMs may be released into the environment, and the effect of compartment composition on predicted concentrations.
      Cover page: Assessing the Risk of Engineered Nanomaterials in the Environment: Development and Application of the nanoFate Model
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2015)
      Engineered nanomaterials (ENMs) are a relatively new strain of materials for which little is understood about their impacts. A species sensitivity distribution (SSDs) is a cumulative probability distribution of a chemical's toxicity measurements obtained from single-species bioassays of various species that can be used to estimate the ecotoxicological impacts of a chemical. The recent increase in the availability of acute toxicity data for ENMs enabled the construction of 10 ENM-specific SSDs, with which we analyzed (1) the range of toxic concentrations, (2) whether ENMs cause greater hazard to an ecosystem than the ionic or bulk form, and (3) the key parameters that affect variability in toxicity. The resulting estimates for hazardous concentrations at which 5% of species will be harmed ranged from <1 ug/L for PVP-coated n-Ag to >3.5 mg/L for CNTs. The results indicated that size, formulation, and the presence of a coating can alter toxicity, and thereby corresponding SSDs. Few statistical differences were observed between SSDs of an ENM and its ionic counterpart. However, we did find a significant correlation between the solubility of ENMs and corresponding SSD. Uncertainty in SSD values can be reduced through greater consideration of ENM characteristics and physiochemical transformations in the environment.
        Cover page: Species Sensitivity Distributions for Engineered Nanomaterials
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2023)
        Global changes, including climate and land use changes, can result in significant impact to water resources. Planning for these changes requires making projections, even in the face of considerable uncertainties, to make informed management and policy decisions. A number of climate change scenarios and projections at global and regional levels are available that can be used to predict the likely range of outcomes. However, there is a need to translate these projections into potential implications for hydrology and water quality. Since there are dozens of hydrologic models, there is a need to evaluate them critically and to develop guidance regarding selecting the appropriate model for a given objective. We conducted a review of 21 different models commonly used for modeling hydrology (8), water quality (6) or both (7) at the watershed scale. Six of the models are strictly water quality models that depend on a separate model or observed data for hydrology. Seven additional models are useful for estimating hydrology and water quality simultaneously. The models were then evaluated based on ten different criteria, including functionality, scope, ability to model extreme events, data requirements, availability, and technical support, among others. The models were ranked Low, Medium or High in each of the criteria. The results indicate that three hydrologic models, MIKE-SHE, HEC-HMS, and MODHMS, as well as two full hydrology and water quality models, SWAT and WARMF, stand out in terms of functionality, availability, applicability to a wide range of watersheds and scales, ease of implementation, and availability of support. Modelers should carefully select the best model for their application, in part guided by the criteria discussed herein.
          Cover page: Hydrological models for climate-based assessments at the watershed scale: A critical review of existing hydrologic and water quality modelsCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2018)
            Cover page: Linking Exposure and Kinetic Bioaccumulation Models for Metallic Engineered Nanomaterials in Freshwater Ecosystems
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2023)
            Water resources managers must increasingly consider climate change implications of, whether the concern is floods, droughts, reservoir management, or reliably supplying consumers. Hydrologic and water quality modeling of future climate scenarios requires understanding global climate models (GCMs), emission scenarios and downscaling GCM output, since GCMs generate climate predictions at a resolution too coarse for watershed modeling. Here we present theoretical considerations needed to understand the various downscaling methods. Since most watershed modelers will not be performing independent downscaling, given the resource and time requirements needed, we also present a practical workflow for selecting downscaled datasets. Even given the availability of a number of downscaled datasets, a number of decisions are needed regarding downscaling approach (statistical vs. dynamic), GCMs to consider, options, climate statistics to consider for the selection of model(s) that best predict the historical period, and the relative importance of different climate statistics. Available dynamically-downscaled datasets are more limited in GCMs and time periods considered, but the watershed modeler should consider the approach that best matches the historical observations. We critically assess the existing downscaling approaches and then provide practical considerations (which scenarios and GCMs have been downscaled? What are some of the limitations of these databases? What are the steps to selecting a downscaling approach?) Many of these practical questions have not been addressed in previous reviews. While there is no “best approach” that will work for every watershed, having a systematic approach for selecting the multiple options can serve to make an informed and supportable decision.
              Cover page: Downscaling approaches of climate change projections for watershed modeling: Review of theoretical and practical considerations
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2016)
              The application of nanotechnology in drinking water treatment and pollution cleanup is promising, as demonstrated by a number of field-based (pilot and full scale) and bench scale studies. A number of reviews exist for these nanotechnology-based applications; but to better illustrate its importance and guide its development, a direct comparison between traditional treatment technologies and emerging approaches using nanotechnology is needed. In this review, the performances of traditional technologies and nanotechnology for water treatment and environmental remediation were compared with the goal of providing an up-to-date reference on the state of treatment techniques for researchers, industry, and policy makers. Pollutants were categorized into broad classes, and the most cost-effective techniques (traditional and nanotechnology-based) in each category reported in the literature were compared. Where information was available, cost and environmental implications of both technologies were also compared. Case studies were also provided where traditional technologies were directly compared with nanotechnology-based technologies for the similar pollutants. Although nanotechnology-based methods are generally believed to be more expensive, we found instances where they offer cheaper and more effective alternatives to conventional techniques. In addition, nano-based techniques may become extremely important in meeting increasingly stringent water quality standards, especially for removal of emerging pollutants and low levels of contaminants. We also discuss challenges facing environmental application of nanotechnology and offer potential solutions.
                Cover page: Engineered nanomaterials for water treatment and remediation: Costs, benefits, and applicability
                • Article
                • Peer Reviewed
                UC Santa Barbara Previously Published Works (2017)

                A dynamic life cycle impact assessment model demonstrates a non-constant intake fraction of inhaled nano-TiO2 as total emissions changes.

                  Cover page: Modeling human health characterization factors for indoor nanomaterial emissions in life cycle assessment: a case-study of titanium dioxide
                  • Article
                  • Peer Reviewed
                  UC Santa Barbara Previously Published Works (2015)
                  Local increases in sea level caused by global climate change pose a significant threat to the persistence of many coastal plant species through exacerbating inundation, flooding, and erosion. In addition to sea level rise (SLR), climate changes in the form of air temperature and precipitation regimes will also alter habitats of coastal plant species. Although numerous studies have analyzed the effect of climate change on future habitats through species distribution models (SDMs), none have incorporated the threat of exposure to SLR. We developed a model that quantified the effect of both SLR and climate change on habitat for 88 rare coastal plant species in San Luis Obispo, Santa Barbara, and Ventura Counties, California, USA (an area of 23,948 km2). Our SLR model projects that by the year 2100, 60 of the 88 species will be threatened by SLR. We found that the probability of being threatened by SLR strongly correlates with a species’ area, elevation, and distance from the coast, and that 10 species could lose their entire current habitat in the study region. We modeled the habitat suitability of these 10 species under future climate using a species distribution model (SDM). Our SDM projects that 4 of the 10 species will lose all suitable current habitats in the region as a result of climate change. While SLR accounts for up to 9.2 km2 loss in habitat, climate change accounts for habitat suitability changes ranging from a loss of 1,439 km2 for one species to a gain of 9,795 km2 for another species. For three species, SLR is projected to reduce future suitable area by as much as 28% of total area. This suggests that while SLR poses a higher risk, climate changes in precipitation and air temperature represents a lesser known but potentially larger risk and a small cumulative effect from both.
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