"There's no such thing as an impermeable landfill or a container that is insoluble enough not to release metal," said Dr Eva Valsami-Jones, who heads the environmental mineralogy programme at Britain's Natural History Museum in London.

Tailings are usually stored in large pits, but a spate of serious accidents involving toxic spills will force the mining world to review its waste management policy.

"The only safe tailings dam is one that doesn't exist. You can store a couple of weeks' worth of water but basically you cannot go on storing billions of litres of water, because sooner or later, whether by accident or carelessness or natural disaster, it's going to fail," said Professor David McConchie, of the Australian green-technology firm Virotec.

Rather than neutralising the tailings with acid, the new remedies use the chemical powers of natural waste to trap heavy metal atoms, and slowly release them into the environment in such tiny amounts that they no longer pose a threat.

"The key questions are - do these methods work, are they cost-effective, are they better than what already exists and can operations be carried out in a way that minimises environmental harm?" said Charles Secrett, head of the British-based environmental lobby Friends of the Earth.

In a reflection of the ancient Greek practice of homeopathy - treating like with like - researchers have come up with three methods utilising waste products that promise to be cheap and sustainable to remediate, or clean, contaminated soil and water.

Caustic red mud can make acidic mine water clean enough to drink, while bonemeal and seaweed could one day be used together to clean the most polluted old mine sites.

LOCK UP THOSE ATOMS!

The Natural History Museum's team is currently studying the effectiveness of bonemeal, used as a common garden fertiliser because of its high phosphate content, in treating soil contaminated by inorganic material like heavy metals.

The bonemeal dissolves in the soil and its alkaline phosphate binds with the metal to form a chemical micro-barrier.

"The metal phosphate is very insoluble. Once it forms, it is no longer available as a contaminant, it's as if it is locked up in a mineral cage," Valsalmi-Jones said.

"The first stage of our research actually demonstrated in the lab that there was a wide range of metals we could remediate, which included the standard nasties like lead, cadmium and also things like uranium, nickel and cobalt - all the metals one would want to remediate," she added.

Research is still at an early stage, but this method may one day provide a safe, sustainable solution to waste and could even be used in tandem with other ecological methods to treat areas polluted by both organic and inorganic substances, she said.

"Anything that is safe for environmental or human health and closes the loop in terms of residue is in principle a good thing. But all too often we class residues as 'waste' that actually have demonstrable uses," said FOE's Secrett.

CLOSING THE LOOP

McGill University in the Canadian city of Montreal is also moving closer to closing the environmental loop with the use of dead plant life to rid tailings water of metal.

Professor Bohumil Volesky of McGill's department of chemical engineering found biomass such as dead seaweed removed heavy metals from water and like a sponge, was then easily rinsed out and reused and the metals could be recovered and resold.

"Heavy metals are toxic and the problem with them is that they are persistent. A metal is a metal is a metal. It doesn't change and the only way to remove the toxicity associated with it is to remove the metal from the environment," he said.