Biological scavengers for radwastes.
Radioisotope-laced medical wastes are usually buried in clay-capped trenches. Over time, decaying organic materials -- which make up the bulk of these interred wastes -- will decompose, creating methane ([CH.sub.4]). This volatile gas can then seep through any fissures that eventually develop in the landfill's cap. And because tritium ([sup.3.H]) -- a radioactive form of hydrogen -- constitutes at least 90 percent of the radioisotopes contaminating these waste sites, much of the methane they emit is also radioactive, observes Lenore S. Clesceri, a microbial biochemist at Rensselaer Polytechnic Institute in Troy, N.Y. It's a potential problem that could jeopardize air quality, she says.
But clesceri's recent studies suggest there's a simple and inherently natural solution: harnessing several types of methane-loving bacteria, ubiquitous in soil, to transform the radioactive pollutant into water. Though still radioactive, most of the tritium-based water would ultimately drain into collection systems surrounding the monitored landfills.
Clesceri has confirmed the presence of methane-degrading bacteria in the thin layer of soil atop the trench caps at the West Valley low-level nuclear waste site near Buffalo, N.Y. However, she says, these bacterial communities appear malnourished. Though they crave methane as a dietary staple, they need additional nitrogen and phosphorus in order to work efficiently, her studies show. By fertilizing trench-covering soil with both nutrients, Clesceri has succeeded in doubling or tripling the rate at which indigenous microbes convert methane to water.
She recommends topping the thin soil layer now covering low-level radioactive wastes with another 18 inches of dirt, then adding fertilizer regularly. This lengthening of methane's escape route, she says, would ensure that plenty of microbes get a chance to prey upon the pollutant.
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|Date:||Jan 27, 1990|
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