Meet the hyperaccumulators: plants that can mine metals

Most heavy metals are toxic to humans and animals, but some plants have adapted to live with high levels in their environment. Meet the hyperaccumulators - plants that can accumulate heavy metals such a nickel, zinc and arsenic from the soils in which they’re growing.
Dr Antony van der Ent is studying hyperaccumulator plants at the sustainable minerals institute of the University of Queensland. He says the plants have devised ways of living with these otherwise toxic elements in their leaves and shoots.
There are heavy metal hotspots around the globe, many of which Antony has visited, including New Caledonia, where there are more than 3000 plants, most of which are endemic (only found in New Caledonia). It was here that he saw Pycnandra acuminata, which has up to 25% nickel in its latex, turning the sap a blue-green colour.
“It’s probably the most metallic tree or plant known in the world,” says Antony. “It’s extremely rare.”
He also discovered a tree in Borneo - Phyllanthus balgooyi - that has 20% nickel in its sap.
Hyperaccumulators have adapted to these small outcrops of minerals, which is what makes them so rare. Because many of these minerals are valuable, the plants have the ill fortune of growing in areas that are well suited to mining, making some of them hyperendemic - not just to a region, but to a specific site where the metals are found.
Australia has its share of hyperaccumulators too. These include:
Neptunia amplexicaulis, a legume that hyperaccumulates selenium
Gossia fragrantissima, which hyperaccumulates manganese and cobalt
Crotalaria novae-hollandiae, which hyperaccumulates zinc
In the hot house, the plants are ‘dosed’ with metals in solution.
Antony hopes that these plants could be grown on the waste mounds from mines to stabilise the soil as well as accumulating the residual mineral from the tailings. As well as revegetating the mine site, these perennial “metal crops” such as the Crotalaria can even be harvested and processed to extract the mineral, a process known as phytomining.
The researchers are still learning about Australia’s hyperaccumulators and Antony says it’s “a race against time” to identify them before mining companies work the specific sites that they are restricted to growing in.
Gastrolobium parviflorum and Gastrolobium parvifolium both accumulate fluoride and make fluoroacetate, which is the compound used to make the poison known as 1080. The hope is that these plants might be able to extract poisonous fluoride from contaminated waste water created by some industrial processes, such as coal mining.
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