Microbial metabolites of polycyclic aromatic hydrocarbons: genotoxicity and relevance to contaminated soils

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  • March 21, 2019
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  • Park, Joanna Zielinska
    • Affiliation: Gillings School of Global Public Health, Department of Environmental Sciences and Engineering
Abstract
  • Soils at hazardous waste sites contain complex mixtures of chemicals and are often difficult to characterize in terms of risk to human and ecological health. Over time, biogeochemical processes can decrease the apparent concentrations of pollutants, but can also lead to accumulation of new products whose toxicity and behavior in the environment are often not considered. The first part of this study evaluated the toxicity of two bacterial transformation products of polycyclic aromatic hydrocarbons (PAHs), pyrene-4,5-quinone (P45Q) and fluoranthene-2,3-quinone (F23Q). Both quinones caused oxidative DNA damage in vitro by the production of reactive oxygen species (ROS). Hydrogen peroxide and copper were essential for causing oxidative DNA damage. F23Q was toxic to HeLa S3 cells, but did not produce measurable levels of ADL or base oxidation. P45Q caused both ADL and base oxidation in cells. Neocuproine reduced the amount of ADL caused by P45Q, indicating that copper was still important for the intracellular generation of damaging oxidants. P45Q is a novel metabolite and its effects on DNA have not previously been investigated. To assess the significance of redox-active bacterial metabolites on the toxicity of PAH-contaminated soil, a bioassay-directed fractionation technique was employed for the detection of mutagens in organic soil extracts. The bacterial tryptophan reverse mutation assay with E. coli WP2 uvrA/pKM101 (IC188) and E. coli WP2 uvrA oxyR/pKM101 (IC203) was used to screen fractions for genotoxicity. Strain IC203 carries the [delta]oxyR30 mutation which prevents the expression of anti-oxidant proteins in response to oxidative stress and increases its reversion by ROS-generating compounds. Polar fractions of PAH-contaminated soil extracts were mutagenic to strain IC203, but not to the OxyR-proficient strain, IC188. Catalase was able to reduce IC203 reversion, further implicating the involvement of reactive oxygen species. Oxidized PAHs, including quinones, were identified in the mutagenic fractions, but were not by themselves mutagenic to either strain. Transition metals were detected in mutagenic as well as non-mutagenic fractions, but no clear relationship between metal content and oxidative mutagenicity could be established from the data. Interactions between chemicals or complex organic molecules may have contributed to the oxidative mutagenicity of the fractions.
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  • In Copyright
Advisor
  • Aitken, Michael
Degree granting institution
  • University of North Carolina at Chapel Hill
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  • Open access
Date uploaded
  • October 19, 2010

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