DESIGN AGENDA FOR abandoned mines & their potential for phytoremediation

The current framework for dealing with contaminated site rehabilitation includes earthworks, soil extraction and capping; being all extremely expensive methods of remediation. Mining tenements are also usually surrounded by pastoral leases, meaning they must support a framework of agricultural land-use requirements following their closure. Nonhazardous mine waste is usually directly revegetated after excavation, with a  thin veneer “cap” of  plant-growth  laid down if necessary.  If the mine wastes are deemed hazardous, they are generally isolated in large tailings, which are later capped at considerable expense using various geologic  and  synthetic  materials. This must all take place before the site can be revegetated. 

Although the site has been capped, this does not ensure guaranteed safety of the site. Root  systems  of  these vegetated areas will invariably become exposed to the metals  and metalloids contained in the medium, and may accumulate in the tissues of above ground vegetation and ultimately pass contaminated material down the food chain.

'new hope'

‘New Hope’ is the energy company associated with the controversial mine situated on the lush Darling Downs. The release of glossy PR material showcasing the ‘rehabilitation of 300 hectares of land’ has caused speculation regarding the safety of the land which has evidently been returned for cattle to graze upon. Consumers are unknowingly buying and eating products coming from cattle that have been grazing on ‘rehabilitated’ land.

Another issue associated with the rehabilitation of contaminated land is when the site falls on private land. Without governmental monitoring, sites are often left untreated or not adequately remediated.

“Phytoremediation using vetiver grass (Vetiveria zizanioides) has been regarded as an effective technique for removing contaminants in polluted water and soils. Results showed that vetiver grass was effective in removing all the heavy metals, but removals greatly depend on root length, plant density and metal concentration. Longer root length and higher density showed greater removals of heavy metals due to increased surface area for metal absorption by plant roots. Results also demonstrated significant difference of heavy metals uptake in plant parts at different concentrations indicating that root has high tolerance towards elevated concentration of heavy metals.

CONTEXT OF abandoned mines & their potential for phytoremediation

Metalliferous mining has a worth of over $8.3 billion in Queensland, showing extreme high value as an industry (Department of Environment and Heritage Protection 2007). The north and north-west Queensland mineral provinces contain the majority of Queensland’s metalliferous mines, however over 15, 000 of these are abandoned (Willacy 2016). This has created thousands of potential environmental hazards with unknown levels of contamination. 

Current statistics show that out of all the land mined in Queensland, only 35%  has been successfully rehabilitated, which is predominantly due to the cost of rehabilitation. The cost of total rehabilitation has been predicted to amount to over $17.8 billion dollars.

Subsequently, the total cost of rehabilitation would amount to over 30% of the total income generated by Australia’s coal industry in the past seven years, being $55.4 billion (estimate by Cameron Amos at The Australia Institute). These figures put into perspective the sheer scale of the destruction taking place, making finding an alternative method of remediation of utmost priority

monitoring, maintenance & effectiveness

As a biotechnology, phytoremediation harnesses only natural plant processes that over time, remediate the site to a safe state. This is significantly less invasive than capping or earthworks, as it poses minimal disturbance to surrounding native plant communities and species. Not only is it less invasive, but it is also incredibly cost efficient. In comparison to to hiring an excavator, digging out a contaminated site and moving the waste to landfill, phytoremediation (despite being a slower process) can be up to ten times cheaper to implement. 

Despite the countless reasons for the implementation of this type of land remediation, the lack of research surrounding the field has meant that phytoremediation is used far less in Australia than overseas. This is something with heightening potential as the number of untreated mining sites increases, and we become more aware of the dangers associated with improperly treated sites.