Biomedical Engineering Reference
In-Depth Information
with a number of the resulting techniques having been used subsequently in the
field to good effect.
In effect, phytoremediation may be defined as the direct in situ use of living
green plants for treatment of contaminated soil, sludges or ground water, by the
removal, degradation, or containment of the pollutants present. Such techniques
are generally best suited to sites on which low to moderate levels of contamination
are present fairly close to the surface and in a relatively shallow band. Within
these general constraints, phytoremediation can be used in the remediation of land
contaminated with a variety of substances including certain metals, pesticides,
solvents and various organic chemicals.
Metal Phytoremediation
The remediation of sites contaminated with metals typically makes use of the
natural abilities of certain plant species to remove or stabilise these chemicals by
means of bioaccumulation, phytoextraction, rhizofiltration or phytostabilisation.
Phytoextraction
The process of phytoextraction involves the uptake of metal contaminants from
within the soil by the roots and their translocation into the above-ground regions
of the plants involved. Certain species, termed hyperaccumulators, have an innate
ability to absorb exceptionally large amounts of metals compared to most ordi-
nary plants, typically 50-100 times as much (Chaney et al ., 1997; Brooks et al .,
1998) and occasionally considerably more. The original wild forms are often
found in naturally metal-rich regions of the globe where their unusual ability
is an evolutionary selective advantage. Ten years ago, the best candidates for
removal by phytoextraction were copper, nickel and zinc, since these are the
metals most readily taken up by the majority of the varieties of hyperaccumula-
tor plants and they arguably still remain the metal species most often addressed in
this way. New varieties of transgenic plants are also appearing which have been
shown to improve performance and may ultimately offer new avenues for real-
world, small scale applications in future (Gyulai et al ., 2005). Plants which can
absorb unusually high amounts of chromium and lead have also been success-
fully trialled in an attempt to extend the potential applicability of this approach
to phytoremediation.
There have also been some breakthroughs in current work, building on earlier
attempts to find suitable phytoextractors for nickel and cadmium, with practical
field successes in extracting cadmium from paddy fields using the two indica rice
cultivars MORETSU and IR-8 (Ibaraki, Kuroyanagi and Murakami, 2009). After
two years, the cadmium concentration in the local environment had decreased by
18%, which strongly suggest that phytoextraction using high-Cd accumulating
rice varieties could be used very effectively to provide a practical remediation
system for moderately cadmium-polluted paddy fields and might be suitable for
other similar applications also.
Search WWH ::




Custom Search