Mt. Costigan mine, on the Western Slopes of the Great Dividing Range, NSW, was
worked intermittently (1887 - 1928) for copper, lead, zinc, silver and gold. The
entire mine site was originally cleared and contaminated with mining wastes, but
had naturally revegetated with eucalypt woodland in parts. However, a barren
section remains despite recent remediation efforts by the NS W Department of
Mineral Resources (DMR), and problems of metal contamination, acid saline
seepage, erosion and the threat of contaminated runoff into the catchment persist.
This study utilized the triad approach of field ecological and chemical-impact
assessment at the barren site, using revegetated woodland as a reference site, and
glasshouse toxicity trials of soils from both the barren and reference sites. Copper,
lead, zinc and cadmium levels in barren site soils all exceed NSW Environmental
Protection Agency (residential) limits in soil. Remediation by the DMR of the
barren site using biosolid amelioration while this project was being carried out
resulted in decreased metal contamination at the site, without significant changes in
salinity. Vegetation analysis of the barren site before and after remediation did not
indicate significant changes, though this may have been due to seasonal variation in
A glasshouse bioassay using neat site soils and several dilutions with river sand was
designed to determine the dose-response relationships in native plants Eucalyptus
sideroxylon, Acacia hakeoides and A. salicina, endemic to Mt. Costigan. The
objective was to evaluate soil toxicity and the potential of native species for
phytoremediation at Mt. Costigan. Avena sativa (oats) was included as a standard
test species for phytoxicity studies, and was the only species to survive in all soils.
A. salicina proved well suited to much of the barren site, but E. sideroxylon did not
grow well, and was better adapted to woodland soils. Acacias and eucalypts both
showed strong accumulator tendencies for copper, zinc and manganese in diluted
site soils. The reverse was true for cadmium, however, with plant-tissue
concentrations of this metal increasing in proportion to soil content. Most metals
were selectively concentrated in root tissue, but acacias leaves showed high copper
and manganese content.
Phytoremediation is likely to prove effective in a multifaceted program of physical,
chemical and biological characterization and remediation. It is suggested that
phytostabilization of the severely contaminated parts of the barren site be initiated
by planting adaptable species such as A. sativa, and that less-contaminated areas be
planted with A. salicina. This could be followed by amelioration with biosolid,
mixed into top layers, before further planting with the less-tolerant E. sideroxylon.
The resulting humic buildup and reduction in soil toxicity would allow other
indigenous plant communities to return and restore ecological balance at Mt.