Sulfidogenic and methanogenic biodegradation of coal tar constituents from the subsurface of a former manufactured gas plant

Ground water impacted by former manufactured gas plants (MGPs) is most often contaminated with coal tar leachate that includes monocyclic and polycyclic aromatic hydrocarbons. Intrinsic bioremediation may be an important component of organic contaminant attenuation in the subsurface at MGP sites. However, many contaminated ground waters are characterized by low redox conditions and little is known about aromatic biotransformations in these environments. The primary objective of this work was to examine microbial transformations of the model compounds benzene, toluene and naphthalene under sulfate-reducing and fermentative/methanogenic conditions using subsurface materials obtained from the largest MGP site in North America.; Laboratory microcosms were established using soils and sediments from depths up to 30 m below a former MGP site with a documented history of subsurface coal tar contamination. Samples from three aquifers were enriched for aromatic-degrading microbial consortia and provided with each of the model compounds as a sole carbon source. Monitoring of compound degradation by HPLC and GC methods indicated that bacteria indigenous to the site are able to transform the model compounds under both sulfidogenic and methanogenic conditions. These results provided laboratory documentation of anaerobic transformation of contaminants as previously suggested by indirect field evidence.; This study provides the first laboratory evidence of naphthalene degradation under sulfate-reducing conditions in ground water. Radioisotope experiments confirmed that naphthalene was mineralized to carbon dioxide with the simultaneous reduction of sulfate to sulfide. Molybdate inhibition of sulfidognesis and a concomitant reduction in naphthalene oxidation provided evidence that naphthalene mineralization was directly coupled to sulfate reduction. GC/MS analyses of a stabilized naphthalene-degrading microbial consortium suggest that naphthalenol may be the first intermediate in the sulfidogenic transformation of naphthalene.