Nontarget Analysis Reveals a Bacterial Metabolite of Pyrene Implicated in the Genotoxicity of Contaminated Soil after Bioremediation.

ABSTRACT

Bioremediation is an accepted technology for cleanup of soil contaminated with polycyclic aromatic hydrocarbons (PAHs), but it can increase the genotoxicity of the soil despite removal of the regulated PAHs. Although polar biotransformation products have been implicated as causative genotoxic agents, no specific product has been identified. We pursued a nontarget analytical approach combining effect-directed analysis (EDA) and metabolite profiling to compare extracts of PAH-contaminated soil from a former manufactured-gas plant site before and after treatment in a laboratory-scale aerobic bioreactor. A compound with the composition C15H8O2 and four methylated homologues were shown to accumulate as a result of bioreactor treatment, and the C15H8O2 compound purified from soil extracts was determined to be genotoxic. Its structure was established by nuclear magnetic resonance and mass spectroscopy as a heretofore unidentified α,ß-unsaturated lactone derived from dioxygenation of pyrene at an apical ring, 2H-naphtho[2,1,8-def]chromen-2-one (NCO), which was confirmed by synthesis. The concentration of NCO in the bioreactor was 11 µg g-1 dry soil, corresponding to 13% of the pyrene removed. It also accumulated in aerobically incubated soil from two additional PAH-contaminated sites and was formed from pyrene by two pyrene-degrading bacterial cultures known to be geographically widespread, underscoring its potential environmental significance.