TNT buster

BOSTON — Scientists aiming to clean up soil contaminated with TNT may get more bang for their buck if they call in the microbial cavalry.

A bacterium isolated from a Yellowstone hot spring aids in breaking down the explosive chemical, preliminary experiments suggest. Chemical engineer Catherine VanEngelen of the Thermobiology Institute at MontanaStateUniversity in Bozeman presented the work June 4 in Boston at a meeting of the American Society for Microbiology.

At various places in the United States and Europe, such as munitions sites where bombs, shells and grenades were made, soil and groundwater are polluted with TNT. The yellow, crystalline chemical is both stable and toxic, and has proven difficult to clean up, VanEngelen says.

Martina Ederer of the University of Idaho in Moscow notes that “With TNT, you usually have to scrape and pile it up somewhere and hope for the best.”

Attempts to convert TNT, or 2,4,6-trinitrotoluene, to a less-toxic form have mostly entailed mixing the stuff with large amounts of sodium hydroxide. This method is expensive and isn’t very environmentally friendly, says VanEngelen. Working with adviser Brent Peyton and collaborator Robin Gerlach, VanEngelen decided to see if microbes were up to the task.

The researchers turned to Anoxybacillus bacteria that they had collected from the Heart Lake Geyser Basin of Yellowstone National Park. They mixed a cocktail of the bacteria, TNT and liquid media and then manipulated the pH and temperature of the mix. At a highly alkaline pH, the TNT quickly converted to TNB, or 1,3,5-trinitrobenzene, which is still explosive, but less so than TNT. This chemical reaction occurred more quickly at 80° Celsius.

Then the Anoxybacillus began breaking down the TNB. VanEngelen found the bacteria work best at 60° C and without oxygen.

“There was a really big difference. You get a lot of degradation,” she says.

The researchers isolated one species from the mix — Anoxybacillus kualawohkensis — and found there was just as much degradation with the single species as there was with several. Now the scientists are focusing on A. kualawohkensis and trying to identify the compounds left in the microbe’s wake.