Not the basic chemicals for ice removal or prevention, but proprietary chemicals added by manufacturers are responsible for the toxicity they observed, agency researchers said after comparing nine different formulations.
Neither of the primary ingredients - ethylene glycol and propylene glycol - nor the known additives accounted for all observed toxicity of these formulations.
Additives are used in de-icers and anti-icers to facilitate product application, ensure that the product will adhere to aircraft wings and fuselage, and enhance its overall effectiveness. Those that are proprietary have compositions known only to the manufacturers.
Study results indicated that anti-icers are more toxic than de-icers due to the larger percent of additives contained in anti-icers.
Some additives are of special concern not only due to the toxicity of the additive, but because they can become increasingly toxic as they degrade in the environment.
'Airports in cold climates throughout the world use de-icers or anti-icers nearly every day during the winter, and those in warmer climates also must use them periodically. The most intensive de-icing and anti-icing application often occurs during extreme weather conditions including periods of snow, freezing rain, and high winds,' said Steve Corsi, USGS scientist and lead author of this study.
'This occasionally makes it difficult to contain the spent fluids and they are released to the environment. While they are a necessity for aviation safety, these products are potential environmental contaminants,' said Corsi.
For this study, completed in cooperation with Milwaukee's General Mitchell International Airport and the Dallas-Fort Worth Airport, formulations were collected directly from storage tanks and de-icing vehicles and tested on minnows, water fleas, green alga, and marine bacterium.
The sensitivity of tested organisms varied according to formulation of the product. Concentrations of deicer and anti-icer components previously observed in airport effluents have, at times, exceeded the toxicity levels shown in results of this study.
The U.S. EPA acknowledges that there is environmental impact from aircraft de-icers and anti-icers and is studying possible guidelines in consideration of national regulation to limit its runoff from airports.
Many airports have implemented measures to reduce runoff of chemicals into the environment, so the fate of these substances varies depending on the individual airport and weather conditions during their use.
The report, Aquatic Toxicity of Nine Aircraft De-Icer and Anti-Icer Formulations and Relative Toxicity of Additive Package Ingredients Alkylphenol Ethoxylates and 4,5-Methyl-1H-benzotriazoles is published in the journal 'Environmental Science & Technology,' and is online. Click here.