Superfund Research Program

Mechanisms of Bioavailability Regulation in Soil

Project Leader: Frederic K. Pfaender
Grant Number: P42ES005948
Funding Period: 1995 - 2006

Project-Specific Links

Final Progress Reports

Year:   2005  1999 

During the last year, project investigators have made significant progress in four areas of research on the bioavailability of PAH in soil. The researchers have continued and expanded work on the biologically mediated transformations and sequestration of PAH to examine what happens under anaerobic conditions which occur regularly in all soils. Extensive disappearance of high molecular weight PAH occurred when anaerobic electron acceptors were provided. This work was expanded to include a larger array of potential electron acceptors and soils from different parts of the US. The results suggest a wide variability in the degradation capacity of anaerobic communities from different soils, and that prior exposure is an important determinant of the ability to breakdown PAH. Additionally, researchers are investigating the mechanism of increased solubilization of PAH that occurs under anaerobic conditions. It has been shown that the aqueous phase concentrations of many high molecular weight PAH can be over an order of magnitude greater than the solubility in pure water. Project investigators have shown that under anaerobic conditions the action of anaerobic microorganisms remove hydrogen ions that results in higher pH values. At increased pH the humic materials become more soluble and carry their sorbed PAH into solution. This solubilized PAH was shown to be biologically available. The third area of endeavor addresses methods for characterizing the solubilized PAH using 13C-NMR. Researchers are working with Dr. Pat Hatcher at Ohio State University to analyze samples incubated under a variety of conditions with 13C labeled PAH. Finally, molecular methods are being applied to the analysis of the microbial community in the soils from the Reilly Tar and Chemical Superfund site in St. Louis Park, MN. This is a highly exposed soil (1500 mg/kg total PAH) with an active community of degraders. Methods have been developed for extraction and amplification of DNA from these highly contaminated soils. Special preparation of soils and DNA extracts are necessary since the PAH interfere with PCR amplification. Investigators have now shown that the community is of low diversity but contains a mixture of aerobic and anaerobic degraders. Further characterization is currently underway.