Temperature not key to biodegradation.

Environmental cleanup experts often contend that organisms living in warm soil and water degrade chemicals faster than microbes that reside in cold climes. After all, microorganisms become less active when their surroundings get cooler.

On the other hand, reasoned Paul M. Bradley and Francis H. Chapelle of the U.S. Geological Survey in Columbia, S.C., microbes adapt to their environment, so organisms living in constantly cool regions may perform as well in these cold environments as those accustomed to warm areas do in theirs.

To test their idea, the scientists examined microbes from aquifers in Adak, Alaska, that were contaminated with jet fuel and had a men temperature of 5*C and from aquifers in Hanahan, S.C., that were contaminated with petroleum and had a mean temperature of 20*C. The researchers clocked the speed at which the soil microbes created carbon dioxide by digesting toluene, a compound in petroleum. The Alaskans won, by a hair.

"There's going to be a lot of variability in the environment that's going to control the [degradation] rate, but temperature itself is not particularly important," Bradley contends. The type and quantity of nutrients, toxins, and microbes in the soil or water help determine degradation rates.

This new finding could change how bioremediation experts tackle cold, contaminated sites, says James M. Tiedje of Michigan State University in East Lansing.

In their experiment, Bradley and Chapelle added radiolabeled toluene to soil from the aquifers. They then measured the rate at which the microbes produced radiolabeled carbon dioxide at several temperatures. For each sample, the rate at 20*C was greater than at 5*C.

At the mean temperature for their respective aquifers, the Alaskan population turned 16.3 percent of the toluene into carbon dioxide per day, while the South Carolinian microbes converted 5.1 percent, the team reports in the November Environmental Science and Technology. They consider this difference to be small. The researchers demonstrated that the overall metabolism in the soil samples was similar, so none had an unfair number of microbes on the job.

Local oil-eating bacteria and fungi helped clean Alaskan beaches in 1989 after the Exxon Valdez spill (SN: 4/17/93, p.253). However, that example did not demonstrate the superiority of cold-dwelling microbes, because organisms from more southern climes were not tested.