Economic and Regulatory Factors That Affect the Phytoremediation of Contaminated Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 365

16

Economic and Regulatory Factors That
Affect the Phytoremediation of Contaminated
Groundwater

You're in charge of the last of the Truffula seeds. And Truffula
Trees are what everyone needs. Plant a new Truffula. Treat it
with care. Give it clean water. And feed it fresh air. Grow a
forest. Protect it from axes that hack. Then the Lorax and all of
his friends may come back .

accumulate in the soil after leaf drop. This concern of con-
taminant transfer from groundwater to other media is valid,
especially when the contaminants of interest are known or
suspected carcinogens. Moreover, there are concerns that the
contaminants will invoke a toxic response in the plants used
for phytoremediation.

The Lorax (Dr. Seuss 1971)

This passage from the end of the children's classic The
Lorax provides a solution to the overuse of natural resources
that was the central theme in the topic, in this case, the
removal of every last Truffula tree. But it also provides a
message that some environmental problems can be solved,
or at least left in a better condition, through the careful
management of plants. In this case, phytoremediation may
bring back cleaner groundwater, rather than the Lorax and
all his friends.
Although planting trees does not require regulatory
approval, their use as part of a remedial strategy to restore
contaminated groundwater does. There are many factors that
should be considered during planning a phytoremediation
system that will affect its use and acceptance by the regu-
latory community. Many of these factors involve economic
concerns as well. Some common economic and regulatory
factors are discussed in this chapter.

16.1.1 Natural Plant Toxic Compounds

When considering the legitimacy of stakeholder concerns
about potential negative plant and groundwater interactions,
particularly in determining whether or not a site is planted,
some of these concerns may be alleviated through the intro-
duction of stakeholders to the natural ecology of plants and
chemical compounds.
As was discussed in Chap. 11, plants such as those
implemented at phytoremediation sites are not helpless
creatures at the mercy of groundwater contaminants. Plants
have evolved external and internal defenses to prevent
predation and ensure survival. The most common and obvi-
ous external defense is thorns or spines, essentially leaves
that have been modified over time. As we saw earlier, some
plants produce raphides in cells that render their leaves
unpalatable to herbivores. Plants also can manufacture
secondary metabolites that can be used as offensive and
defensive chemicals. For example, alkaloids can be
extracted from almost all parts of plants. Most alkaloids
contain heterocyclic nitrogen compounds. Some of these
plant chemicals include alkenes, which are characterized
by a carbon-carbon double bond. These are all naturally
produced chemicals that can be analyzed in the emissions
of trees, as reported in the study by Martin et al. (1999). In
this same manner, these naturally produced plant chemicals
are part of the plant detoxification system that can be
leveraged through the installation of plants at sites with
contaminated groundwater.

16.1 Plant-Enhanced Contaminant

Phase Transfer

During phytoremediation, plants are purposefully placed in
contact with contaminated groundwater. Unlike the biore-
mediation or MNA of contaminated groundwater, there are
realistic concerns with phytoremediation regarding the fate
of contaminants in the treatment system itself—the plants.
For example, it is often assumed that plants will act as
conduits to bring subsurface contaminants to the surface
and necessarily increase exposure rates. This can occur
by contaminant volatilization or sorption to leaves that