Land contaminated with toxic pesticide DDT could be cleaned up using small amounts of seaweed, according to research published in the Journal of Chemical Technology and Biotechnology.

It is eaten with sushi and put on gardens as fertiliser. Now another use for seaweed has been discovered - combating pollution.

Researchers have found that sprinkling just the right amount of powdered seaweed on contaminated soil can accelerate the breakdown of the deadly insecticide DDT.

DDT was introduced in the 1940s as a "wonder chemical" and used widely in Australia before being banned in 1987.

However, almost 20 years later thousands of sites around the country remain contaminated.

Hunting for an effective way to clean up DDT, the scientists, working with the CSIRO, Flinders University in Adelaide, the University of Adelaide and the University of Newcastle upon Tyne in Britain, explored the properties of seaweed.

They discovered the right dose of seaweed caused 80 per cent of the chemical to vanish within six weeks.

It works by helping micro-organisms in the soil to attack the toxin, said Megharaj Mallavarapu, an associate professor at the University of South Australia.

The organisms have enzymes that convert DDT into other substances that deteriorate quickly. But the scientists have had to grapple with the problem of building a big enough microbe army and getting it to the battlefield.

They found that the high levels of sodium in seaweed disperse clay in contaminated soil, allowing the micro-organisms to reach the insecticide. "The sodium makes the DDT more accessible to the organisms," Professor Mallavarapu said.

At the same time, the seaweeds high levels of carbon feed the micro-organisms, allowing their populations to boom, creating more troops to do battle against the chemical.

"DDT can last for years in the soil," said Professor Mallavarapu, who continues to work with the scientist who came up with the possibility of using seaweed, Professor Ravi Naidu, a research director of the University of South Australia.

DDT contamination is a particular problem in places where it was used with other deadly chemicals, such as arsenic.

"In cattle dips they used arsenic and DDT together," Professor Mallavarapu said. "It is persistent in these soils because very high levels were used and the other chemicals in the mixture kill micro-organisms. There are about 1600 cattle-dip sites in the country still contaminated with DDT."

He also noted DDT was still being used in many malaria-infested developing countries to fight mosquitoes.

The researchers suspect seaweed may help break down other contaminants. "But we need to establish that," Professor Mallavarapu said.

But he had no doubt seaweed could become an important weapon against DDT contamination. "Its very economical, it is a natural material and its simple."

Their findings were published in the Journal of Chemical Technology and Biotechnology.