Nickel - best known for its uses in coins, stainless steel and industrial products - isn't your normal garden fertiliser, but it sure gets the senses salivating (metaphorically speaking) for an obscure plant which grows near Rockhampton in Queensland.

The obscure Stackhousia tryonii plants look like a "bunch of stems with narrow leaves", said Dr Naveen Bhatia, a researcher from the Australian Nuclear Science and Technology Organisation (ANSTO).

Growing naturally in serpentine soils, they have a bad reputation among farmers. If cattle eat these small herbs they get sick and can die.

Stackhousia flowers seeds.

Naveen, an Australian Synchrotron Research Fellow at ANSTO, is one among a number of international scientists who are in the race to unlock the secrets of these and other metal 'hyperaccumulators'.

There are around 450 hyperaccumulator plants, said Naveen, a plant ecophysiologist, ranging from groundcover to trees. Each species has evolved in soil containing specific metals. Most of these plants absorb one type of metal, but a few can absorb two or even three metals "without showing any signs of toxicity".

"They can hyperaccumulate arsenic, boron, cadmium, cobalt, copper, lead, manganese, nickel, selenium, thallium or zinc," Naveen said. Less than 10 percent of the hyperaccumulators have been studied.

Across the world, scientists are experimenting with the metal munchers to find species suitable for environmentally-friendly mining. They plan to grow the plants on ore-rich soil, harvest them and then extract metals from their leaves and stems. The process is known as phytomining.

Naveen said all hyperaccumulator plants could potentially provide a cheap, "green" method of cleaning contaminated agricultural and industrial sites. In the United States and elsewhere, some species are already being used to remove toxic wastes from polluted soil in mine dumps and around smelters.

The hyperaccumulators can also be used to clean pasture and croplands contaminated by heavy metal from fertilisers and industrial pollution. In Asia tests are being conducted on a plant that can remove cadmium from rice fields.

Naveen began studying Stackhousia six years ago for his science doctorate. Trained in agriculture, he said: "I was interested in finding out how this plant takes up metal from the soil. Up to four percent of its leaf dry weight is pure nickel metal. I wanted to find out how it copes with such poisonous material. Most other plants would die with just a fraction of the metal."

He explains that immediately after the nickel is absorbed, the plant roots detoxify it by forming an organo-metallic complex.

Now he is about to take some of his rare Stackhousia plants to the United States to study their physiology with a synchrotron. His other subjects are the Python Tree, an Australian rainforest species that absorbs manganese, and a Congolese plant that absorbs copper and cobalt.

The synchrotron is a football-field size machine that accelerates electrons through magnetic fields to produce photons, a very bright light. "By exposing specimens to this light we can detect the organo-metallic complexes formed in the plants," explained Naveen.

Mature Stackhousia plant.

He said the problem with most metal-absorbing plants is they grow very slowly. By isolating the genes that enable these plants to absorb metals, it will become possible to insert these specific genes into faster-growing species.

Naveen believes that in 10 to 15 years time scientists will have created "transgenic hyperaccumulators". Seeds from these robust plants could be scattered in fields contaminated with heavy metals from fertilisers or industrial pollution. The plants could be left to clean the soil. "Then we could harvest them, incinerate them and cement the ash in waste disposal sites."

Naveen envisages transferring genes from super metal-absorbing plants into crops like rice or wheat to create nutrient-rich foods. For example you could create an iron-rich cereal crop that prevents anaemia.

With that glittering promise, it is no wonder that Naveen and others are so keen to study the rare metal munchers.