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US Army to compost surplus explosives

But are your exploding vegetables organic?

University of Arizona researchers are studying the environmental effects of insensitive munitions compounds, or IMCs, which are new, more stable explosives that won't detonate in response to heat or shock.

"The idea is that if you're driving in a caravan and get hit, the munitions in your truck won't detonate," said James A. Field, head of the UA College of Engineering's department of chemical and environmental engineering. IMCs are mixed with conventional explosives to make them more stable.

"The Army is taking a very proactive role here," Field said. "They're trying to discover the environmental consequences before deploying these new compounds. No one really knows what their effect will be on the environment. So we're looking at their fate and toxicity, how they interact with the soil, their degradation pathways, and whether they may pose a threat to surface water or groundwater."

Bacteria play a large part in breaking down compounds in the soil, Field explained. They do this directly by metabolizing (eating) the compounds, or indirectly through co-metabolism, which occurs when the bacteria consume other food sources, such as plant material, and provide energy to convert IMCs to intermediate compounds.

Eventually, these intermediates either further degrade or become locked up in stable organic matter called humic polymers that are relatively safe.

"In fact, the Army has found that the safest way to clean up TNT, for instance, is to compost it, and that mostly promotes polymerization into humus," Field said.

The trick now is to discover which of the millions of organisms found in soil will break down IMCs. This needle-in-a-haystack search starts with soil from military sites where specialized organisms may already have evolved in the presence of explosives.

"We will take a bit of this soil and supply only one food source – a nitro-aromatic compound – and then see if there is a bacterium that knows how to do something with it," Field said. "There may be [100,000] different species and maybe one can have just the right enzyme to knock off the nitro groups or just the right enzyme to break open the IMC's chemical bonds and initiate an attack.

"Then we'll use molecular ecology techniques to identify the bacterium," he added. "That's the exciting part of scientific discovery."
Source: University of Arizona


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