POISONOUS additives from fluids used to de-ice aircraft are polluting groundwater near airports, say researchers from Western Washington University in Bellingham. The team has found the additives in high concentrations in groundwater under an airport, and their toxic effects are being felt in watercourses downstream.
Until recently, the de-icing fluids were thought to be relatively harmless because glycol-their major component-is not highly toxic. But the additives are far more toxic than glycol. "The toxicity measures [of the de-icer] didn't match up with the known toxicity of the glycols themselves," says Devon Cancilla of the Western Washington team. "When you start to test the whole solution, things just jump off the scale."
De-icer manufacturers do not reveal what additives they use, because they regard this as proprietary information. So Cancilla decided to isolate the toxic component. Using a microorganism test, he identified the culprit as a family of chemicals called tolyltriazoles, which are also used as corrosion inhibitors in car antifreeze.
Cancilla has since found tolyltriazoles in the groundwater beneath an airport in Milwaukee, Wisconsin (Environmental Science & Technology, vol 32, p 3834). "We found it in very high concentrations," Cancilla says. This made the water extremely toxic to the test bacteria, Vibrio fischeri.
Steven Corsi of the US Geological Survey in Madison, Wisconsin, verified that water taken from the stream that drains the airport can be highly toxic to aquatic life. On three occasions when heavy de-icing had been carried out, all of the fathead minnows and water fleas he put in the water died. On a fourth occasion, less de-icer washed into the streams because an ice storm froze the runoff, but half of the organisms still died. In the summer, when de-icer is not used, more than 80 per cent of the organisms survived in all tests. "It's quite apparent that de-icer runoff is causing toxicity in the stream," Corsi says.
What's worse, Cancilla says, is that current regulations for de-icing fluids only monitor glycol levels and thus ignore the major sources of toxicity. "Even at the guideline levels, there's significant toxicity," he says. Some airports, including the Milwaukee airport, have begun to collect the excess fluid when planes are sprayed, but it is impossible to prevent de-icer dripping off the aircraft as they taxi down the runway and take off.
The US Environmental Protection Agency is currently deciding whether to tighten current regulations on de-icing fluids. But at the same time, an alternative de-icing technology is emerging. Radiant Energy, a company in Buffalo, New York, has developed a way of focusing ice-melting infrared radiation on aircraft as they taxi through a hangar. The company says this slashes the amount of de-icer needed by 80 per cent, and cuts the cost by three-quarters. But some glycol is still needed to keep the aircraft ice-free after it has taken off.
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