ESTCP Project #1011, Rhizosphere
2. Technology Description
2.1 Technology Development and Application
Phytoremediation is an umbrella term covering a number of different plant-based methods that
can lead to contaminant degradation, removal (through accumulation or dissipation), or
immobilization. Terminology is still evolving, yet some uses and terms are now becoming more
commonly used. Pivetz (2001) reviewed phytoremediation and defined various phytoremediation
methods to include:
1. Degradation (for destruction or alteration of organic contaminants).
A. Rhizodegradation: enhancement of biodegradation in the below-ground root zone by
B. Phytodegradation: contaminant uptake and metabolism above or below ground,
within the root, stem, or leaves.
2. Accumulation (for containment or removal of organic and/ or metal contaminants).
A. Phytoextraction: contaminant uptake and accumulation for removal.
B. Rhizofiltration: contaminant adsorption on roots for containment and/or removal.
A. Phytovolatilization: contaminant uptake and volatilization.
4. Immobilization (for containment of organic and/or inorganic contaminants).
A. Hydraulic Control: control of ground-water flow by plant uptake of water.
B. Phytostabilization: contaminant immobilization in the soil.
Rhizosphere-enhanced remediation (or rhizodegradation in 1A above) is a form of
phytoremediation based on root exudation of excess plant-produced carbon compounds. The
rhizosphere is the zone of soil surrounding a plant root and influenced by the plant root.
Typically, the root releases excess carbon molecules produced by the plant and the excess carbon
stimulates the nearby soil microbial ecology. Researchers generally agree that the stimulated
microbial activity near the root in turn results in enhanced biotreatment.
Field implementation of rhizosphere-enhanced remediation includes selecting and adding
appropriate seeds and nutrients to the contaminated soil to stimulate rhizosphere activity. It
requires minimal equipment and costs for set up, operation and maintenance, or shut down.
Demonstration plots at the Campion Air Force Station are shown in Figures 1 and 2.
The constraint to application is having defensible field data. Our approach to obtain defensible
field data was to conduct replicated, statistically balanced field demonstrations and to obtain
meaningful soil samples from the field. Although choosing the appropriate sample analysis is
important, research overwhelmingly and clearly demonstrates that, due to the spatial variability
of contaminants in the soil, a much greater error arises from field sampling. In brief, the success