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鈥攖heir major component鈥攊s not highly toxic. But the
additives are far more toxic than glycol. 鈥淭he toxicity measures [of the
de-icer] didn鈥檛 match up with the known toxicity of the glycols themselves,鈥�
says Devon Cancilla of the Western Washington team. 鈥淲hen you start to test the
whole solution, things just jump off the scale.鈥�
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.
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Cancilla has since found tolyltriazoles in the groundwater beneath an airport
in Milwaukee, Wisconsin (Environmental Science & Technology, vol
32, p 3834). 鈥淲e found it in very high concentrations,鈥� 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. 鈥淚t鈥檚 quite
apparent that de-icer runoff is causing toxicity in the stream,鈥� Corsi says.
What鈥檚 worse, Cancilla says, is that current regulations for de-icing fluids
only monitor glycol levels and thus ignore the major sources of toxicity. 鈥淓ven
at the guideline levels, there鈥檚 significant toxicity,鈥� 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.