The effects of substrate concentration and temperature on the biodegradation of five different aircraft deicing fluids was examined in soil samples obtained from an area adjacent to an airport runway. The principle organic constituents, which included ethylene, propylene, and diethylene glycols, were shown to be mineralized to carbon dioxide in soil microcosms incubated at temperatures ranging from -2 to 25 degrees C. No lag period was observed, and biological transformation of the test chemicals began immediately after addition to the soil. Glycol biodegradation was observed in soil at concentrations ranging from 392 to 5278 mg/kg, suggesting that high levels of the deicing fluids are unlikely to be inhibitory to soil microorganisms. All three glycols were readily degraded in soil at 8 and 25 degrees C, regardless of whether the compounds were present singly or as a component of a mixture. In addition, the biodegradation rates for the three compounds were very similar. Average rates were in the range of 19.7 to 27.0 mg/kg soil per day at 8 degrees C and 66.3 to 93.3 mg/kg soil per day for soil samples incubated at 25 degrees C. The soil biodegradation rates were reduced in soils at -2 degrees C to between 2.3 and 4.5 mg/kg per day. Based on these results, biodegradation is expected to play a major role in removing residual levels of glycols from soils adjacent to airport taxiways and runways.