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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2015)

The overall goal of this dissertation was to determine the effects of an emerging contaminant, nanomaterials, on microbial communities in engineered systems. Specifically, communities within a simulated human colon and model septic system were studied. Microbial communities in their natural environments represent realistic scenarios for toxicity testing versus assays with enriched growth media and single cell cultures; the two engineered systems used in this work approach “real” scenarios communities would experience.

This dissertation work has allowed for the following observations. The simulation of metal oxide nanomaterials ingestion with the model colon demonstrated these particles do significantly alter the phenotype of the gut microbial community within the model colon reactor. Next, dosing experiments with copper materials in the septic system established that the effluent had pulses of improper waste treatment and that incomplete organic breakdown was likely occurring. However, even with weekly fluctuations in water quality caused by the particles, data suggest that 100% of the time, water quality parameters and microbial composition were recovering towards baseline conditions. This indicates the system could maintain baseline conditions after perturbances, regardless of the particle type.

Finally, effluent containing copper emitted from the septic system was tested in a high throughput toxicity screening assay with zebrafish embryos. While “as-received” nanoscale copper materials caused the greatest embryo hatching interference, all three “processed” copper materials emitted from the model septic system demonstrated a decline in embryo toxicity, regardless of particle composition/size. Thus, the zebrafish screening in combination with the septic system, provide a novel way to study hazard potentials of commercial Cu-based particulates during partitioning, transformation, and speciation.

This collection of studies provides critical insights into the importance of understanding microbial communities more holistically and in realistic environments. These studies demonstrate the need to update toxicity tests such that they more accurately reflect real exposure scenarios simulating environmental conditions. This research also confirms the invalidity of using “as received” nanoparticles; toxicity tests must use particles reflective of those materials transformed in the environment. Future directions for toxicological studies need new useful testing combinations that provide additional information for complex matrices and microbial communities.

    Cover page: Impacts of Nanomaterials on Microbial Communities in Engineered Systems
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    This research is part of a multidisciplinary research program to develop a bioremediation protocol for a solid waste management (SWM) site in Northern California - a site which is heavily contaminated with petroleum hydrocarbons. In this initial study, 30 bacterial strains were isolated and evaluated for their efficiencies to deplete crude oil. The 3 most efficient bacterial isolates for crude oil depletion were designated as S1BD1, OPKDS2, and OSDS1; they were identified as Serratia proteamaculans, Alcaligenes sp. and Rhodococcus erythropolis, respectively, based on partial 16S rRNA gene sequences. Determination of crude oil depletion efficiency by gas chromatography–mass spectrometry (GC-MS) revealed that Serratia proteamaculans S1BD1 was the most efficient (68.0 ± 1.78%), followed by Alcaligenes sp. OPKDS2 (63.7 ± 3.28%), and Rhodococcus erythropolis OSDS1 (54.9 ± 5.07%). S. proteamaculans S1BD1 was able to deplete a wide spectrum of carbon compounds within the individual components of crude oil. Alcaligenes sp. OPKDS2 was the most efficient at depleting BTEX (91.2 ± 1.90%), and R. erythropolis OSDS1 exhibited a substrate preference of n-alkanes. All three strains exhibited unusually high crude oil depletion efficiencies and tolerated a wide range of salinity and pH levels, which makes them excellent candidates for bioaugmentation of the SWM site.
      Cover page: Crude oil depletion by bacterial strains isolated from a petroleum hydrocarbon impacted solid waste management site in California
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2015)
      Although copper-containing nanoparticles are used in commercial products such as fungicides and bactericides, we presently do not understand the environmental impact on other organisms that may be inadvertently exposed. In this study, we used the zebrafish embryo as a screening tool to study the potential impact of two nano Cu-based materials, CuPRO and Kocide, in comparison to nanosized and micron-sized Cu and CuO particles in their pristine form (0-10 ppm) as well as following their transformation in an experimental wastewater treatment system. This was accomplished by construction of a modeled domestic septic tank system from which effluents could be retrieved at different stages following particle introduction (10 ppm). The Cu speciation in the effluent was identified as nondissolvable inorganic Cu(H2PO2)2 and nondiffusible organic Cu by X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), diffusive gradients in thin-films (DGT), and Visual MINTEQ software. While the nanoscale materials, including the commercial particles, were clearly more potent (showing 50% hatching interference above 0.5 ppm) than the micron-scale particulates with no effect on hatching up to 10 ppm, the Cu released from the particles in the septic tank underwent transformation into nonbioavailable species that failed to interfere with the function of the zebrafish embryo hatching enzyme. Moreover, we demonstrate that the addition of humic acid, as an organic carbon component, could lead to a dose-dependent decrease in Cu toxicity in our high content zebrafish embryo screening assay. Thus, the use of zebrafish embryo screening, in combination with the effluents obtained from a modeled exposure environment, enables a bioassay approach to follow the change in the speciation and hazard potential of Cu particles instead of difficult-to-perform direct particle tracking.
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2022)
        Pharmaceuticals and personal care products (PPCPs) are found in wastewater, and thus, the environment. In this study, current knowledge about the occurrence and fate of PPCPs in aquatic systems-including wastewater treatment plants (WWTPs) and natural waters around the world-is critically reviewed to inform the state of the science and highlight existing knowledge gaps. Excretion by humans is the primary route of PPCPs entry into municipal wastewater systems, but significant contributions also occur through emissions from hospitals, PPCPs manufacturers, and agriculture. Abundance of PPCPs in raw wastewater is influenced by several factors, including the population density and demography served by WWTPs, presence of hospitals and drugs manufacturers in the sewershed, disease burden of the population served, local regulations, and climatic conditions. Based on the data obtained from WWTPs, analgesics, antibiotics, and stimulants (e.g., caffeine) are the most abundant PPCPs in raw wastewater. In conventional WWTPs, most removal of PPCPs occurs during secondary treatment, and overall removal exceeds 90% for treatable PPCPs. Regardless, the total PPCP mass discharged with effluent by an average WWTP into receiving waters (7.35-20,160 g/day) is still considerable, because potential adverse effects of some PPCPs (such as ibuprofen) on aquatic organisms occur within measured concentrations found in surface waters.
          Cover page: Abundance, fate, and effects of pharmaceuticals and personal care products in aquatic environmentsCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2017)
          Given increasing use of copper-based nanomaterials, particularly in applications with direct release, it is imperative to understand their human and ecological risks. A comprehensive and systematic approach was used to determine toxicity and fate of several Cu nanoparticles (Cu NPs). When used as pesticides in agriculture, Cu NPs effectively control pests. However, even at low (5–20 mg Cu/plant) doses, there are metabolic effects due to the accumulation of Cu and generation of reactive oxygen species (ROS). Embedded in antifouling paints, Cu NPs are released as dissolved Cu+ 2 and in nano- and micron-scale particles. Once released, Cu NPs can rapidly (hours to weeks) oxidize, dissolve, and form CuS and other insoluble Cu compounds, depending on water chemistry (e.g. salinity, alkalinity, organic matter content, presence of sulfide and other complexing ions). More than 95% of Cu released into the environment will enter soil and aquatic sediments, where it may accumulate to potentially toxic levels (> 50–500 μg/L). Toxicity of Cu compounds was generally ranked by high throughput assays as: Cu+ 2 > nano Cu(0) > nano Cu(OH)2 > nano CuO > micron-scale Cu compounds. In addition to ROS generation, Cu NPs can damage DNA plasmids and affect embryo hatching enzymes. Toxic effects are observed at much lower concentrations for aquatic organisms, particularly freshwater daphnids and marine amphipods, than for terrestrial organisms. This knowledge will serve to predict environmental risks, assess impacts, and develop approaches to mitigate harm while promoting beneficial uses of Cu NPs.
            Cover page: Comparative environmental fate and toxicity of copper nanomaterials
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