Digging in the dirt: chemical and biological sensors could aid the search for hidden land mines

Science News, March 28, 1998 by Corinna Wu

Organisms that can be added to soil also play a part in explosives detection. At Oak Ridge, researchers have genetically engineered bacteria to light up in the presence of TNT

When certain bacteria ingest organic molecules, they turn on the production of regulatory proteins. By inserting a gene for a luminescent or fluorescent protein next to the gene for the regulatory protein, the researchers can induce the bacteria to produce both proteins whenever they come into contact with organic molecules (SN: 6/4/94, p. 358). In this way, glowing bacteria signal the presence of the explosive in the environment.

Robert S. Burlage and his colleagues at Oak Ridge have engineered several strains of the bacterium Pseudomonas putida to glow with visible or fluorescent light when they scavenge TNT and dinitrotoluene, a related chemical (SN: 11/9/96, p. 150). Burlage is presenting the results of this project at the Third International Symposium on Technology and the Mine Problem to be held at the Naval Postgraduate School in Monterey, Calif., next week.

Later this year, the group will test the bacteria on a small simulated minefield, spraying the plot of land with the bacteria and waiting 3 hours for them to produce the glowing proteins. Luminescent bacterial strains should be visible to the naked eye, whereas fluorescent ones will require ultraviolet light in order to be seen.

Burlarge expects eventually to apply the technique to real minefields, using a crop duster to shower an area with the engineered bacteria. Where the bacteria contact explosives, they will give off light that can be mapped from the air or viewed on the ground.

Burlage's team had previously engineered bacteria to report the presence of several environmental pollutants: toluene, naphthalene, and mercury. In 1996, the Environmental Protection Age, proved the use of these organisms cleaning up polluted areas.

Mines lie buried in so many different environments that no single method can deal with them all. Researchers are therefore developing a variety of technologies. In some places, deminers may need to apply a combination of techniques, each based on a different physical principle, in order to reveal a minefield's secrets. Discovering how to use advanced data analysis to combine these disparate lines of information adds another layer of complexity to the challenge.

Some land mines create a shorter-term hazard than others. So-called smart mines self-destruct after a set period of time. The United States makes an effort to use only smart mines, says Bottoms. However, a country like China, which has a stockpile of 50 million conventional mines, probably won't replace them in the near future.

At the upcoming conference, a representative from the U.S. Army has been invited to speak on the Army's efforts to find alternatives to antipersonnel land mines, Bottoms says. "Offhand," he adds, "I can't think of what those would be."