Endocrine Disruptor Found in
Aircraft De-Icer

BRITT E. ERICKSON / Environmental Science and Technology 28aug03

With a little bit of detective work and some “reverse engineering”, scientists have discovered what may be contributing to the toxicity of aircraft deicing fluids. In the September 15 issue of ES&T (pp 4031–4037), Steven Corsi of the U.S. Geological Survey (USGS) in Middleton, Wis., and colleagues report finding alkylphenol ethoxylate surfactants in various aircraft deicers and one of their breakdown products, nonylphenol, a known endocrine disrupter, in streams receiving airport runoff.

Although the main ingredient in aircraft deicers is either propylene glycol or ethylene glycol, numerous studies have shown toxicological effects of deicer solutions that cannot be attributed to these two chemicals. Manufacturers are reluctant to disclose what kinds of additives are in their deicer formulations, which often include surfactants, corrosion inhibitors, flame retardants, dyes, and foam suppressors. “All of the additives are proprietary, which makes it real difficult for us to determine what is causing the true toxicity,” Corsi says.

Using a technique called fast atom bombardment mass spectrometry, coauthor Jennifer Field of Oregon State University screened nine different aircraft deicers for numerous surfactants. Nonylphenol ethoxylates showed up in three of them, and octylphenol ethoxylates showed up in two.

Alkylphenol ethoxylates are nonionic surfactants widely used to reduce surface tension in numerous products, including detergents, paints, pesticides, and now aircraft deicers. The chemicals have been shown to break down during wastewater treatment processes into more toxic alkylphenols, which have estrogenic properties. Even though octylphenol is 10–20 times more estrogenic than nonylphenol, most of the concern has centered around nonylphenol and its parent compounds because they are more abundant in the environment.

It is unclear whether airport runoff is likely to be a major source of alkylphenols. In a stream near General Mitchell International Airport in Milwaukee, Wis., the researchers found nonylphenol at a concentration of 3.89 micrograms per liter (µg/L) after an intense aircraft deicing event on January 31, 2002. For comparison, in a recent USGS study, Dana Kolpin and colleagues found nonylphenols in 43 out of 85 U.S. rivers, with a median concentration of 0.8 µg/L and a maximum concentration of 40 µg/L (Environ. Sci. Technol. 2002, 36, 1202–1211). In laboratory studies, nonylphenols have been shown to cause endocrine-disrupting effects in rainbow trout exposed to levels as low as 8.3 µg/L (Environ. Sci. Technol. 2001, 35, 2909–2916).

Wastewater treatment plants (WWTPs) are likely to be a much bigger source of alkylphenols, believes Alba Torrents, an associate professor of civil and environmental engineering at the University of Maryland, College Park, who has been investigating nonylphenols in WWTP discharge near Washington, D.C., and Baltimore, Md. “As a source, WWTPs probably contribute higher loads to the receiving streams, because they operate constantly and discharge large volumes. At airports, deicing occurs only a few times a year, and the amount of runoff, even if concentrated, will not match that of a WWTP effluent,” she says. Nonetheless, biota living in streams near airports are exposed to concentrations of nonylphenols that could be toxic, even if it is for a short period of time, she adds. The U.S. EPA estimates that 21 million gallons of aircraft deicing fluid (50% concentration) are discharged annually into U.S. surface waters, according to a 2000 report.

Alkylphenol ethoxylates and their breakdown products add to a growing list of toxic compounds hidden in aircraft deicers. Proprietary additives make up about 1–5% of deicer fluids, according to coauthor Devon Cancilla of Western Washington University, who previously reported finding tolyltriazoles in aircraft deicers (Environ. Sci. Technol. 1998, 32, 3834–3835). Tolyltriazoles are anticorrosion chemicals used extensively in paints, cooling towers, car radiator fluids, and anywhere metal and water are together, Cancilla says. The chemicals are much more toxic to fish and other organisms than glycols. Cancilla and colleagues have detected tolyltriazoles in groundwater near airports and in fish and are currently investigating their cellular effects in fish.

“We know triazoles are in aircraft deicers, but there are a lot of other compounds as well. We still don’t know what they are,” Cancilla adds. “The triazoles can’t account for all of the toxicity that we observe. One of these days, we’d like to come up with more funding to do some more fractionation of the material itself,” he says. “There is the potential for these things to have long-term low-level effects that nobody knows about.”

Meanwhile, airports such as General Mitchell International are taking a proactive approach to improve the quality of their discharge, according to the airport’s environmental manager, Greg Failey. Unlike many other airports that use high volumes of aircraft deicers, General Mitchell International is one of the few that is aggressively trying to understand what is causing toxicity in the receiving waters, he says. “We are taking an extra step that a lot of other airports would not in order to understand the actual chemistry of the problem,” he says.

source: http://pubs.acs.org/subscribe/journals/esthag-w/2003/aug/science/be_deicer.html 30aug03