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MILWAUKEE, Wis. — A USGS study has found that water samples collected downstream of a Wisconsin airport during freezing weather had phosphorus levels exceeding benchmarks for healthy aquatic ecosystems. The elevated phosphorus levels in downstream water samples were traced to common ice control products used at airports throughout the U.S. that experience freezing precipitation.

As winter approaches and temperatures get colder, removing ice and snow and preventing ice formation from aircraft and runways becomes essential for safe air travel. Airports use a variety of products to remove or prevent ice and snow, which can contain chemicals that can affect local ecosystems. Use of these deicing products is required by the Federal Aviation Administration during periods of ice and snow accumulation on aircraft. Stormwater runoff from airports is regulated by the states with guidance from the Environmental Protection Agency and managed by airports.

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“Monitoring ice control product runoff is an important part of an airport’s pollution prevention plan, and in many cases, these plans include monitoring of phosphorus runoff,” says USGS Physical Scientist Owen Stefaniak, one of the authors of the study, “But accounting for the true source of phosphorus observed in airport runoff can be a real challenge for airport managers. Since these products contain proprietary ingredients not disclosed by the manufacturers, the airlines have no way to know how much phosphorus they are applying when they deice a plane.”

The new study revealed that nine of eleven ice control product formulations used at airports contained phosphorus.

Airports take measures to reduce runoff from ice control products during freezing precipitation periods. For example, Milwaukee’s Mitchell International Airport uses extensive deicer collection systems such as deicing pads (areas that drain to recovery tanks) and vehicles with high-powered suction devices designed to capture ice control products from pavement. However, preventing all runoff from aircraft and runway deicing operations during inclement weather while maintaining flight schedules is not typically possible.

Phosphorus exists naturally in the environment, but high levels can drive overgrowth of algae and plants, depleting oxygen and causing harmful algal blooms, fish mortality and habitat loss. USGS scientists collected water samples during the deicing season as well as during the warmer months over a period of five years to see if airport ice control products were contributing to phosphorus pollution in local waterways.

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During deicing periods, USGS found that 84% of the samples that were collected downstream of the airport had phosphorus that could likely be traced to ice control products, and 70% of the water samples had phosphorus levels that exceeded the Wisconsin Department of Natural Resources phosphorus aquatic life guidelines for streams, indicating potential for harm to the aquatic ecosystems receiving airport runoff.

The study focused on estimating how much phosphorus might be entering the streams from the ice control products, but it is still unclear how phosphorous from this source affects local ecosystems or whether this phosphorus is in a form readily available to aquatic organisms. Ice control product applications occur during freezing weather and phosphorus may not have the same environmental impact as it would during warmer months, when plant and algae growth is much greater.

The study was conducted in the area around Mitchell International Airport in Milwaukee, Wis., but the deicing products examined are extensively used at airports that experience freezing conditions.

“There are more than 200 airports in the United States alone that conduct significant deicing operations every year, so this issue is not unique to this particular study site,” said Stefaniak.

The study, "Airport Deicers: An Unrecognized Source of Phosphorus Loading in Receiving Waters" was published in the journal Environmental Science & Technology.

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