Introduction to Phytoremediation - CLU-IN

leaves typically creates more exposure than accumulation
in stems and roots. Most organic contaminants do not accumulate
in significant amounts in plant tissue.
Some plant-eating animals have been shown to avoid
eating plants with elevated metal levels (Pollard 1996). In
addition, the increased habitat provided by the plants may
in some cases offset any potential localized impacts.
If some organisms (e.g., caterpillars, rodents, deer, etc.)
seem likely to ingest significant amounts of the vegetation,
and if harmful bioconcentration up the food chain is a
concern during the life of the remediation effort, appropriate
exposure control measures should be implemented
including perimeter fencing, overhead netting, and pre-flowering
harvesting. Phytoextraction techniques aim to harvest
metal-laden crops just as the plants translocate metals
into shoots, thereby limiting availability of contaminants
for consumption.
Transfer of the contaminants or metabolites to the atmosphere
might be the greatest regulatory concern. Transpiration
of TCE into the atmosphere has been measured
(Newman et al. 1997a), but little information is available
that would indicate any release of vinyl chloride.
Research being done on the bioavailability of contaminants
and on human health and environmental risk assessment
is directly related to phytoremediation. Studies
are underway to determine if contaminants that are not
available to plants for uptake or that are not vulnerable to
plant remediation are less of a risk to human health and
the environment.
2.2 Technical Considerations
Several key factors to consider when evaluating whether
phytoremediation is a potential site remedy are described
below.
1. Determine whether evidence of the potential effectiveness
of phytoremediation is specific to the site
matrix and contaminants. If laboratory studies on the
plants and contaminants of interest are the primary
evidence used to support the use of phytoremediation
at the site, the studies should at least show that the
plants to be used at the site are capable of remediating
site contaminants.
2. Consider the protectiveness of the remedy during the
time it takes the plants associated with phytoremediation
to establish themselves at the site to a point where
they are containing/degrading the contaminants of interest.
3. Consider whether phytoremediation is likely to clean
up the site in an acceptable time frame.
4. An adequate backup or contingency technology
should be identified in the event that phytoremediation
is attempted and does not succeed.
Additionally, monitoring the efficacy of any innovative
treatment may be more extensive than would be required
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for a more accepted technology. Monitoring needs to address
both the decrease in the concentration of the contaminants
in the media of concern, and examine the fate
of the contaminants. The monitoring plan must be tailored
to the site and plants.
2.2.1 Prior Applications of
Phytoremediation
One indication of acceptability of a technique is previous
successful applications on similar sites. Because it is
a relatively new technology, phytoremediation does not have
a long history of completed cleanups. Table 2-3 lists 12
Superfund sites where phytoremediation has been accepted
or is being field-tested for possible remediation of
soil or groundwater contamination. Appendix B lists approximately
180 sites where the technology has been applied
or is being field-tested. The peer-reviewed field data
that are available on these projects are limited. More data
should become available in the next few years through the
efforts of programs such as the Superfund Innovative Technology
Evaluation (SITE) program, the Remediation Technologies
Development Forum (RTDF), and others.
Results of studies done in greenhouses and on field test
plots can be used to show proof of concept, and some of
that data may be directly applicable to site-specific consideration.
If time and funding permit, soil or water from the
site should be used in lab or greenhouse studies. Such
treatability studies can confirm the effectiveness of the sitespecific
treatment. Chapter 5 provides more information
on treatability studies.
2.3 Economic Considerations
Because phytoremediation is an emerging technology,
standard cost information is not readily available. Subsequently,
the ability to develop cost comparisons and to
estimate project costs will need to be determined on a sitespecific
basis. Two considerations influence the economics
of phytoremediation: the potential for application, and
the cost comparison to conventional treatments. Care must
be taken to compare whole system costs, which may include:
Design costs: Operating costs:
Site characterization Maintenance
Work plan and report preparation Irrigation water
Treatability and pilot testing Fertilizer
Installation costs pH control
Site preparation Chelating agent
Facilities removal Drainage water disposal
Debris removal Pesticides
Utility line removal/relocation Fencing/pest control
Soil preparation Replanting
Physical modification: tilling Monitoring
Chelating agents Soil nutrients
pH control Soil pH
Drainage Soil water
Infrastructure Plant nutrient status
Irrigation system Plant contaminant status
roots, shoots, stems,
Fencing leaves)
Planting Tree sap flow monitoring
Seeds, plants Air monitoring (leaves,
Labor branches, whole tree, area)
Protection Weather monitoring