Toxicity of Polycyclic Aromatic Hydrocarbons Pre- vs. Post-Bioremediation

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants implicated in negative human and ecosystem health outcomes, including but not limited to carcinogenicity and teratogenicity. Bioremediation using PAH-degrading bacteria and fungi is a noninvasive, relatively low-cost technology capable of reducing environmental occurrence of PAHs. Employing analytical chemistry methods to detect the extent of degradation of PAHs, while insightful, is insufficient as the sole determinant of efficacy of bioremediation. Metabolites created during bacterial degradation of PAHs can be equally toxic or more toxic than parent compounds. Thus, toxicological assays of samples undergoing bioremediation are a crucial component for monitoring risk. The first objective of this project was to develop methods for toxicological assays that could be employed to determine the efficacy of bioaugmentation strategies currently being developed with microbial strains isolated from the heavily PAH-contaminated sediment at the former Republic Creosoting site in the Elizabeth River, VA, USA. The second objective was to use those methods to test three recently isolated PAH-degrading bacterial strains to determine their suitability for use in bioaugmentation. Experimental design included incubation of PAHs with bacteria; extraction of metabolites; analytical chemistry analysis to determine extent of degradation; then subsequent toxicological assays of extracted metabolites, including Ames assays to determine mutagenic potency and zebrafish morphological assays to determine teratogenicity. Four different PAHs were incubated with three strains of PAH-degrading bacteria in monoculture and co-culture. Significant degradation of only phenanthrene was observed, accompanied by a slight increase in mutagenicity and a significant decrease in teratogenicity. Visual inspection of cultures indicated potential fluoranthene degradation with a concomitant increase in mutagenic potency in monocultures, but not in co-cultures. Results for teratogenicity in fluoranthene cultures were inconclusive. Fluoranthene incubation conditions must be optimized to allow more complete degradation and to achieve more definitive results. Once optimization is attained, these assays can be employed in future studies to test additional strains of bacteria as well as fungi that may have capability of degrading a wider range of PAHs.