Research Goals: The goal of this project is to understand the mechanisms surrounding the use of phytoremediation as a means of degrading or containing contaminants such as PAHs and metals.

Progress to Date: This project evaluates plant uptake and plant exudation as a means of remediating soil contaminated with both metals and PAHs.   Measurements of PAH uptake, as well as the effect of PAHs on metal uptake, is a new and significant contribution to our understanding of how plants may actually perform under realistic contaminant scenarios.  In addition, the evaluation of these same parameters under conditions of varying soil metal and PAH bioavailability, provides a means of predicting the effectiveness of phytoremediation on a particular site and soil.  Although the results of studies on the above are important, it is the work on root exudates that will likely have the greatest impact on the development of phytoremediation as a technology.  Separating the chemical effect of root exudates from any root surface phenomena is an important step in isolating the mechanism behind the observation that degradation of organic contaminants is enhanced in the presence of plants .  Many studies have speculated on the involvement of root exudates in rhizosphere degradation, but very few studies have gone beyond adding simple carbon substrates in short pulses.  The published study employed a system that exposed the microbial community to real root exudates in concentrations - and over a time period - that mimicked actual conditions.  Ongoing work in this area is identifying the specific factors in the exudates that are responsible for enhanced degradation of PAHs in the rhizosphere.

Application of Knowledge: The information gained from these investigations will be useful in determining how effective (both in terms of cost and remediation) phytoremediation will be when applied to actual contamination sites.

Techniques Incorporated:
EPA standard methods are used for metal and PAH extraction/analysis of soils and plant tissue. Rhizosphere degradation is determined by measuring mineralization of radiolabelled PAHs. A sterilized system allows separation of soluble exudates from the intact plant root. Microbialculturing techniques were used to determine bacterial growth with root exudates as a carbon source. Biomass of microbial communities are determined by using an analysis of lipid phosphate content (PFLA).

Keywords:
Phytoremediation
Contaminated soil
Polycyclic aromatic hydrocarbons (PAHs)
Metals
Mixtures
Rhizosphere degradation
Root exudates
Bioavailability
Superfund