Superfund Research Program

Processes Influencing the Natural Attenuation of Organic Contaminant Plumes: Transport, Enzymatic Regulation and Microbial Transformation Rates in Flowing Groundwater Systems

Project Leader: Linda M. Abriola (Tufts University)
Grant Number: P42ES004911
Funding Period: 1995 - 2006

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Final Progress Reports

Year:   2004  1999 

During this year, progress was made on the development of relationships between the desorption behavior and the microbial bioavailability of sorbed contaminants. Sorption and desorption equilibria of phenanthrene with respect to three different types of geosorbents were measured, as were the rates of desorption and biological mineralization of this representative hydrophobic organic contaminant. The chemical nature of the organic matter associated with each geosorbent was characterized using solid state C-13-NMR spectrometry. The results of these studies reveal that both the desorption behavior and the microbial bioavailability of the sorbed contaminant are influenced by the physicochemical character of the organic matter. The more reduced and condensed the organic matter, the greater the extent of sorption-desorption hysteresis, the slower the desorption rate, and the less readily bioavailable the sorbed contaminant. These observations are consistent with projections predicated on a dual reactive domain model introduced earlier to describe the sorptive reactivities of different types of soil/sediment organic matter with hydrophobic organic contaminants.

Progress has also been made on another aspect of the research--microbial degradation of NAPL mixtures and impact of the microbial degradation on the toxicity of these mixtures. Biodegradation of globules of the NAPL mixture composed of 10 components resulted in the removal of all but three heavy PAH components. Researchers used gap junctional intercellular communication (GJIC) as an epigenetic biomarker to assess the toxic effect of the original and biodegraded NAPL. The results suggest that bioremediation techniques that leave residual components of such NAPL mixtures in contaminated media can quantitatively but not qualitatively reduce their epigenetic toxic risk. Nonetheless, such bioresistant residuals may be environmentally less mobile than the biodegraded components of the precursor NAPLs.