Phytotechnology and Photosynthesis 153having a secondary role in trapping wind-blown particulates. Depending on the
individual site, the bio-bund can be constructed in such a way that it can also act
as a buffer strip to control migrating chemical pollution, if required.
Plant Selection
It should be obvious that the major criteria for plant selection are the particular
requirements for the method to be employed and the nature of the contaminants
involved. For example, in the case of organic phytotransformation this means
species of vegetation which are hardy and fast growing, easy to maintain, have
a high transpiration pull and transform the pollutants present to nontoxic or less
toxic products. In addition, for many such applications, deep rooting plants are
particularly valuable.
On some sites, the planting of grass varieties in conjunction with trees, often
in between rows of trees to stabilise and protect the soil, may be the best
route since they generate a tremendous amount of fine roots near to the sur-
face. This particularly suits them to transforming hydrophobic contaminants such
as benzene, toluene, ethylbenzene, xylenes (collectively known as BTEX) and
polycyclic aromatic hydrocarbons (PAHs). They can also be very helpful in con-
trolling wind-blown dust, wash-off and erosion. The selection of appropriate plant
species for bioengineering is not, however, limited solely to their direct ability to
treat contaminants, since the enhancement of existing conditions forms as much
a part of the potential applications of phytotechnology as bioremediation. For
instance, legumes can be of great benefit to naturally nitrogen-deficient soils,
since they have the ability, via symbiotic root nodule bacteria, to directly fix
nitrogen from the atmosphere. With so much to take into consideration in plant
selection, the value of a good botanist or agronomist in any interdisciplinary
team is clear.
Applications
Phytotechnology has many potentially beneficial land uses, though for the most
part the applications are still in the development stage. Several have been tested
for the treatment of contamination, and in some cases successfully tried in the
field, but generally they remain in the ‘novel and innovative’ category, lacking
well-documented data on their performance under a variety of typical operating
conditions. As a result, some researchers have voiced doubts, suggesting that the
beneficial effects of plant utilisation, particularly in respect of phytoremediation,
have been overstated. Some have argued that the reality may range from genuine
enhancement to no effect, or even to a negative contribution under certain cir-
cumstances and that the deciding factors have more to do with the nature of the
site than the plants themselves. In addition, some technologies which have been