CHAUDHRY, TM & ABDUL G. KHAN.
Department of Biological Sciences, Faculty of Business & Technology, University of Western Sydney, Macarthur, PO. Box 555, Campbelltown, NSW 2560. AUSTRALIA.
Metal contaminated land is increasingly becoming an important
environmental, health, economic and planning issue in the world. Organic and
inorganic contaminants are persistent in the soil environment and current remediation
technologies are highly variable, complicated and costly. The use of certain
plants which can accumulate or biodegrade contaminant is a relatively new approach
to the problems of contamination of soil and water, i.e., phytoremediation.
Some plants naturally survive in heavy metal contaminated soils because of their
ability to either filter the toxic metals or absorb and accumulate them into
their tissues. The abilities of these plants to remove contaminants from the
soil has been the subject of various recent studies in the Europe and USA. These
plants are normally slow growing producing a small biomass but they accumulate
heavy metals in their tissues lowering the quantity and controlling the migration
of heavy metals through the soil profile. Symbiotic fungi and bacteria adapted
to heavy metals can be utilized to enhance the growth of such plants.
In this study some plants have been identified as metal accumulators or tolerant
and their associated symbiotic microorganisms such as mycorrhizal fungi and
nitrogen fixing Rhizobia from the spoil heaps of the BHP steelworks at
Port Kembla and the abandoned silver mine at Sunny Corner in New South Wales,
Australia. At both sites, plant species richness was poor. For the BHP spoil
heaps, vegetation was observed on older filtercake only. Those species for which
accumulation was most significant were Ricinus communis (Zn) and Sonchus
oleraceus (Cd). No plant was identified as a hyperaccumulator. For the Sunny
Corner mine the most efficient accumulators were Baeckea utilis (Cu,
Pb and Zn), Poa labillardieri (Cu, Pb and Zn), Pinus radiata (Pb
and Zn), Lomandra longifolia (Pb and Zn) and Acacia melanoxylon
(Zn), the first three species displayed greatest abundance. Poa labillardieri
was classified as a hyperaccumulator of lead. At both the sites, rhizosphere
of all plants harboured same form of mycorrhizal strains, i.e., Gigaspora
and Glomus spp. Roots of Pinus radiata possessed both VA and
EC mycorrhizae. Acacia melanoxylon roots were heavily VA mycorrhizal
as well as studded with nitrogen-fixing rhizobial nodules.
It was concluded that the mycorrhizal strains in the BHP filtercake and Sunny
Corner mine sites are more tolerant to metals (and have developed resistance)
compared with the reference soil strains. More importantly, the presence of
these microorganisms in the soil rhizospheres are likely to play a vital role
in the metal tolerance and accumulation exhibited by the host plants.
(Phytoremediation - an innovative green clean technology for Australia)