Spinach Enzymes Neutralize Explosives

RICHLAND, Wash. -- Spinach may have given Popeye brute strength, but enzymes found inside the green leaves soon may be used to neutralize dangerous explosives.

Researchers at the Department of Energy’s Pacific Northwest National Laboratory have discovered that nitroreductase enzymes found in spinach and other natural compounds can eat, digest and transform explosives such as TNT. This emerging biotechnology is called the Environmentally Benign Digestion Process (EBDP). It reduces dangerous explosives to low toxicity byproducts that can be used by industry or reduced further to harmless products such as carbon dioxide and water.

EBDP has been tested in the laboratory and soon will move to field-testing. The research project is in its first year and will receive a total of about $1 million over three years from the Department of Defense, the Department of Energy and companies involved with demilitarization.

This digestion process addresses a dire need of the U.S. military to eliminate, in a cost effective and secure manner, its nearly 500,000 tons of explosives stockpiled around the country.

"The primary risk of storing explosives at any site is explosions because they create panic, can cause injury and are a trigger to releasing biological and chemical agents stored nearby," said Dr. Manish M. Shah, the project’s principal investigator.

"The challenge is to have a process that is safe, easy to use, environmentally friendly and preferably mobile," Shah said. “EBDP destroys explosives in a very benign manner."

Enzymes -- proteins made of amino acids -- are an integral part of a human’s digestion within the stomach. But they also are a booming business. The enzyme industry is a $1.3 billion market that is growing 10 to 15 percent each year.

Enzymes are used by the detergent industry as supercleaners, by the beverage industry to make glucose and by the textile industry to stonewash denim. Until now, enzymes have not been used to neutralize dangerous explosives.

"If we can use enzymes to clean clothes or to make corn syrup, there’s no reason why we can’t use them for destroying explosives," Shah said. "It’s the best alternative to current technologies. It’s almost like a catalyst process."

The process is done without open burning, open detonation, fire, high temperature, high pressure or producing toxic waste byproducts. According to Shah, it could replace current methods of burning and incinerating explosives that are risky and expensive.

If as successful in the field as in the lab, EBDP would be more cost effective than other methods of explosives disposal. The process does not require any special equipment, hardware or software, and thus has very low capital costs. As a result, the enzyme digestive process may be done at sites such as military bases or explosives stockpile depots rather than moving explosives cross-country to incinerators. The process could be more energy efficient because it is done at room temperature, compared with other methods that require heating to extreme temperatures.

The digestion process would be safer than other alternatives, according to Shah. It would be conducted in a tank of water at atmospheric pressure, therefore reducing risk of explosion or fire. There would be no alkaline solutions to dispose of because the process is done at a neutral pH.

A variety of naturally occurring enzymes -- found, for example, in spinach, plants, fungi, bacteria and buttermilk -- have an apparent reactivity to degrade explosives.

These nitroreductase enzymes are mixed with a buffer solution and a reductant, such as lactic acid or ethanol. In that mixture, the reductant reduces the enzymes. Then those reduced enzymes further reduce, or digest, explosives in the enzyme solution in the water tank. The enzymes begin their natural process of "eating" the explosives, which are nitroaromatic compounds. The enzymes continue their natural process of digesting and recycling themselves like any other catalyst. During this recycling, the enzymes transform the explosives into another compound, a byproduct of the process.

Future research efforts will determine if the byproduct made by the enzymes is of lower toxicity. It may be possible to convert the byproduct for commercial use. Research to date suggests the byproduct could be used in chemical processes that use free radical chemistry. For example, researchers have determined the enzymes convert nitrobenzene into p-aminophenol, which is used in the pharmaceutical industry to make headache medicine.

The digested byproduct also could be reduced completely to a gaseous state, such as ammonia or carbon dioxide, through a second digestive process using microorganisms.

Pacific Northwest is one of DOE’s nine multiprogram national laboratories that conduct research in the fields of environment, energy, health sciences and national security. Battelle, based in Columbus, Ohio, has operated Pacific Northwest for the DOE since 1965.