Abstract
This work will be a study of microorganisms from an industrial research site which is contaminated with polyaromatic hydrocarbons (PAHs). The site has been populated with native plants through a process of natural succession over a period of 15 to 20 years. Chemical characterization of samples shows that PAH concentrations increase with depth, and in areas of the site which now contain mature trees the regions of lower concentration are deeper than in nearby grassy areas. The results lead to a hypothesis that trees and microflora have acted in concert to bioremediate soil contaminants in the root region, suggesting that it is critical to study what has happened and what is happening to the pollutants in the field. This contrasts to the approach of a pure laboratory study followed by attempts to introduce new technology to the field. Analysis of the native plant-microbe systems that have invaded and appear to have accelerated the biodegradation of PAHs, at this field site provides a more direct means to develop an ecologically-sound, sustained phytoremediation strategy to treat PAH-contaminated sites.
Studies on the microflora from a PAH-impacted site and their relationship to plants growing there will utilize both classical microbiology and molecular biology methods. Plant and chemical analysis work (Fletcher et al., 1997) is now being complemented by our extensive quantitative and qualitative characterization of bacteria in different vegetated regions and at different depths of the field site. To date, counts of total bacteria, as well as of bacteria capable of using PAHs (napthalene, phenanthrene, or pyrene) as carbon/energy source have been performed. Analysis of the data is not yet complete, but it is already clear that the number of bacteria decreases dramatically at the interface between the partially-remediated sludge in the root zone and heavily-contaminated, parent sludge beneath 4 feet. In bulk samples of soil beneath grassy or tree-containing regions there is no significant difference in total bacterial numbers between samples taken at corresponding depths. However, soil from the tree-root region had higher numbers of PAH-degraders than soil from the grasses. Yet to be tested is the local region around the tree roots themselves.
In year one we will: a) Thoroughly characterize the diversity of the PAH-degrading microorganisms isolated from the contaminated soil using classical microbial methods and molecular biology (quantitative polymerase chain reactions, PCR). This can be a powerful test of diversity, including that of organisms that can not be cultured. b) Begin to study the spacial location of PAH-degrading organisms by microsampling the soil adjacent to plant roots, using culture techniques and PCR to compare the number of PAH-degraders in closest proximity to that far removed from the roots. c) In year two, begin to characterize microflora in a pilot PAH phytoremediation site which has been planted for less than a year and may mimic early development of the site with mature vegetation.