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Short-term Chronic Toxicity of Photocatalytic Nanoparticles to Bacteria, Algae, and ZooplanktonEPA Grant Number: R831721
Title: Short-term Chronic Toxicity of Photocatalytic Nanoparticles to Bacteria, Algae, and Zooplankton
Investigators: Huang, C. P. , Cha, Daniel K. , Ismat, Shah S.
Institution: University of Delaware
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2005 through September 30, 2007
Project Amount: $334,881
RFA: Exploratory Research to Anticipate Future Environmental Issues: Impacts of Manufactured Nanomaterials on Human Health and the Environment (2003) RFA Text | Recipients Lists
Research Category: Health , Safer Chemicals , Health Effects , Nanotechnology
The overall goal of this proposed research project is to assess the short-term chronic aquatic ecotoxicity of photocatalytic nanoparticles. Upon the irradiation of photocatalysts at a wavelength equivalent to the bandgap energy, electrons will jump over from the valance band to the conduction band, leaving behind positive holes. The holes are strong oxidation agents, and the electrons are strong reducing agents. Depending on the level of band gap energy, photocatalysts can exhibit both reduction and oxidation reactions, only oxidation reactions, or only reduction reactions. It is expected that chemical reduction-oxidation reactions play an important role in the aquatic ecotoxicity of nano-photocatalysts. The specific objectives of this research project are (1) to determine the acute toxicity of photocatalytic nanoparticles to mixed bacterial cultures, (2) to determine the short-term chronic toxicity of photocatalytic nanoparticles to pure bacterial culture exemplified by E. coli, (3) to determine the short-term chronic toxicity of photocatalytic nanoparticles to daphnia exemplified by Ceriodaphnia dubia, (4) to determine the short-term chronic toxicity of photocatalytic nanoparticles to algae exemplified by Selenastrum capricornutum, (5) to determine the short-term chronic toxicity of copper (II) to Selenastrum capricornutum in the presence of photocatalytic nanoparticles, (6) to determine the short-term chronic toxicity of chlorinated phenols to E. coli and Ceriodaphnia dubia in the presence of photocatalytic nanoparticles, and (7) to determine the short-term toxicity of photocatalytic nanoparticles to freshwater algal assemblages.
To achieve these objectives, a group of nano-photocatalysts and aquatic microorganisms will be selected for study. The nano-photocatalysts to be studied include infrared (IR) sensitive, e.g., CdSe and MoS2; visible light sensitive, e.g., GaP, CdS; and ultraviolet (uv) light sensitive, e.g., TiO2, ZnO and SnO2. The testing organisms will cover three trophic levels including bacteria, algae, and primary consumer. E coli and a mixed commercial bacterial culture, Selenastrum capricornutum (green algae) and Cericodaphnia dubia (daphnia), will be selected as testing organisms. The mixed bacterial culture is commercially available and will be used to test for the acute toxicity of the selected nano-photocatalysts by measuring the respiration rate during glucose oxidation with and without the presence of selected nano-photocatalysts. Two pure bacterial cultures, e.g., E. coli K-12 strain ATC27325 and TB1, will be studied. The short-term chronic toxicity of selected nano-photocatalysts to these pure bacterial cultures will be determined in terms of cell viability, lipid peroxidation, and cellular respiration rates. Additionally, changes in DNA sequencing of the pure bacterial cultures upon exposure to nano-photocatalysts will be investigated. Renewal static bioassay using less-than-24 h neonates of Ceriodaphnia dubia will be used to assess the short-term chronic toxicity of selected nano-photocatalysts. The endpoints of toxicity tests are based on survival and reproduction. Green algae, Selenastrum capricornutum, which is a feed for Ceriodaphnia dubia also, will be used as a test organism for the toxicity of selected nano-photocatalysts. The algal population is exposed in a static system to nano-photocatalysts at a series of concentrations for 96 h. The response of the population is measured in terms of change in cell density, biomass, chlorophyll content or light absorbance. Statistical analysis of the green algae growth data will follow that proposed by EPA. The synergistic and/or antagonistic effects of selected nano-photocatalysts and toxic chemicals, namely heavy metals and organics, are to be assessed. It is expected that nano-photocatalysts may reduce heavy metal ions to their elemental state, which in turn will reduce the ecotoxicity of heavy metals. The effects of selected nano-photocatalysts on modifying the acute toxicity of heavy metals will be studied using Selenastrum capricornutum and copper (II). Likewise, nano-photocatalysts may mineralize toxic organic chemicals, which in turn may decrease the ecotoxicity of these organic chemicals. To assess the effects of nano-photocatalysts on the ecotoxicity of hazardous organic chemicals, the toxicity of chlorinated phenols to Ceriodaphnia dubia and E. coli will be studied. Finally, the ecotoxicity of nano-photocatalysts will be assessed with algal assemblages collected from local and regional streams.
This proposed research project has four unique features: (1) evaluating the general ecotoxicity of nanoparticles, (2) evaluating the additional effect of photocatalysis of nanoparticles to aquatic organisms, (3) studying the ecotoxicity of organisms of three subsequent trophic levels, and (4) assessing the response of a natural algal community to nanoparticles. Information obtained from this project will serve a wider purpose to the regulatory and scientific communities. Specifically, the information to be obtained in this research includes the EC50, IC25, and IC50 values of various nanophotocatalysts for E. coli, green algae Selenastrum capricornutum and Ceriodaphnia dubia. The mutagenicity of photocatalysts to E. coli will be assessed using the direct DNA sequencing technique. This information will shed much light on the toxicity mechanism of nanophotocatalysts. The synergistic and antagonistic effects of nanoparticles to toxicity will also be examined by copper toxicity to green algae and the toxicity of chlorinated phenols to Daphnia. Since the three test organisms represent three successive trophic levels, the toxicity effect displayed by these three test organisms can be extrapolated readily to species of higher orders in trophic scale. For instance, based on the feeding capacity of each organism and the information obtained in this research such as EC50 and IC50, it is possible to estimate with first approximation the tolerable amount of uptake of the corresponding nanoparticles by organisms of higher order in trophic structure. We will also assess the response of natural algal community to nanoparticles. As algal communities are most sensitive to environmental contaminants, this information will prove to be most useful to the public and the private sectors.