Environmental Engineering Reference
In-Depth Information
I MPORTANCE OF R HIZOSPHERIC M ICROORGANISMS
IN R EMEDIATION OF M ETAL P OLLUTED S OILS
Several authors have drawn attention to the role played by soil
microorganisms in the processes underlying plant-based methods of
remediation (phytoremediation) of heavy metal contamination, including
phytostabilization. Arbuscular mycorrhizal fungi (AMF) and plant-growth
promoting bacteria have been the most interesting groups of microorganisms
because they appear to play a key role in soil development and successful
plant establishment (González-Chávez, 2005).
Our research group has focused on AMF effect and function, because
these fungi are integral and functional parts of plants roots, playing a central
role in ameliorating metal toxicity in their hosts. The mechanisms involved are
based on the extra-radical mycelium (EM), which binds and sequestrates
metals at cell wall level; and glomalin, a glycoprotein copiously produced by
all AMF tested. González-Chávez et al. (2004) showed that this protein,
extracted from polluted soil or from hyphae, strongly and irreversibly
sequestrates not only Cd, but also Cu, Zn and Pb. Therefore, AMF may
stabilize metals in the soil, reduce their availability and decrease the risk of
toxicity to other soil microorganisms and plants growing in polluted
substrates. Colonization of roots by these fungi, appears of great importance
for the establishment of the early plant community structure and is largely
responsible for the vegetation of such habitats.
In degraded soils, some authors have shown that several plant species
create resource islands or clusters, rich in organic matter, nutrients and spores
of AMF, which eventually form fertile soil. At the Temascaltepec mining site,
González-Chávez et al. (2009), observed that AMF and mesofauna were co-
occurring with plants, in vegetal patches. By thin slag sections analysis, these
authors showed that mesofauna and AMF were modifying some important slag
properties such as: organic matter, color, pH and structural development, and
forming A horizons. In addition, they observed that mycelium from AMF and
other fungi were abundantly produced in the vegetal patches and glomalin.
Unlike other tailing heaps, the one from Temascaltepec contains quartz as the
main mineral and Cd as the main contaminant. In consequence, remediation of
this tailing may be less complicated than others where different minerals and
multiple metals are involved. An interesting fact was that Cd concentrations
were higher at the bottom of the tailing than at the top. Authors suggested that
a possible Cd movement, through lixiviation, might be occurring in the tailing
Search WWH ::




Custom Search