Superfund Research Program
Beyond Parent Compound Disappearance in the Bioremediation of PAH-Contaminated Soil
Project Leader: Michael D. Aitken
Grant Number: P42ES005948
Funding Period: 1995-2018
Final Progress Reports
Polycyclic aromatic hydrocarbons (PAH) containing four or more rings are known to be degraded by naturally occurring microorganisms, but often are not removed extensively during the bioremediation of PAH-contaminated soils. The overall aim of this project is to elucidate the factors that influence the extent to which these compounds are degraded. The principal focus of the past year was in identifying and characterizing products from the bacterial transformation of the four-ring compounds pyrene and fluoranthene. A number of bacteria are able to metabolize these compounds only partially, but until now the products of such incomplete metabolism have not been identified. Depending on the specific organism, PAH-degrading bacteria were found to transform pyrene either to cis-4,5-dihydro-4,5-dihydroxypyrene or to pyrene-4,5-dione, as well as other unidentified products. The same organisms transform fluoranthene to fluoranthene-2,3-dione, fluoranthene-1,5-dione, and other unidentified products. Pyrene-4,5-dione strongly inhibits the bacterial mineralization of benzo[a]pyrene (BaP), and fluoranthene-2,3-dione was shown to inhibit the mineralization of BaP, benz[a]anthracene, and chrysene. Since PAH in contaminated environments always occur as mixtures, these findings suggest that the formation of o-quinones from the partial transformation of some PAH can impact the degradation of other PAH. There are potential consequences of these findings for health risks as well, since o-quinones derived from other PAH have been shown to be cytotoxic and mutagenic, and to form DNA adducts in mammalian cells.