NATURAL AND MAN-INDUCED PHYTOREMEDIATION IN SEVERAL MINE RESIDUES CONTAINING HIGH CONCENTRATION OF CD - Management of Hazardous Residues Containing Cd - page 165

heap. Additionally, the strong slopes (10 to 100%) observed in some parts of
the tailing might also represent a risk of dissemination to the Pinus forest
established around the tailings.
Ortega-Larrocea et al. (2010) studied the fungal and plant biodiversity in
mine residues located at Zimapan, Hidalgo in Mexico. The Cd concentrations
ranged from 9.5 to 814 mg Cd/kg dry soil, but other metals were also in high
concentrations (Ni, As). These authors give an extensive list of plant families
and species found on these sites, which may be used for phytoremediation of
other similar contaminated sites, because of their tolerance to high heavy
metals concentration. They also observed that roots of almost all the collected
plants were consistently associated to AMF and other rhizospheric fungi. The
analysis of the possible roles of these microorganisms suggested that they are
an important component for the stabilization of areas under remediation and
may help for plant establishment in these extreme conditions, due to their
ability to assist them on abiotic stress, including metal stress.
Research followed in different metal polluted sites in Mexico have
confirmed that AMF and several other beneficial microorganisms are always
associated to roots of plants growing in these soils. Hence, in order to increase
vegetation in areas following natural attenuation, organic matter addition and
introduction of seedlings inoculated in the nursery with native AMF and other
rhizospheric microbes may favor and speed up revegetation. Microbial strains
isolated from long term metal polluted areas will often be the most efficient
way for bioremediation practices.
Other kinds of research looking for alternative plants to use in remediation
have been followed. Rodriguez-Elizalde et al. (2010a) studied the effect of
substrates containing mixtures of mine residues and agricultural soil (0, 20, 40
and 60% v:v) on the emergence and initial development of three ornamental
plants Dahlia x hortorum Willd. (dahlia), Tagetes erecta L . (marigold), and
Cosmos bipinnatus Cav. (cosmos). These growing substrates had high
concentrations of heavy metals (Cu, Zn, Cd, Pb and Mn). The authors
observed that the three ornamentals presented morphological and
physiological changes, but these were able to establish themselves in the
polluted substrates. Dahlia had better growth of cotyledons and roots, biomass
and metal tolerance index than the other two species; but accumulated less Cd
than cosmos and marigold.
In a longer research, Rodriguez-Elizalde et al. (2010b) examined the
response of dhalia and marigold and their antioxidant and photosynthetic
pigments response influenced by a mycorrhizal fungus ( Glomus mosseae BEG
25). The growth of both plant species was affected negatively by the toxic