Deicing Aircraft and their Pollution Contributing to Dead Zones

 The following has been excerpted from the USGS study and press release:

Airport Deicers: An Unrecognized Source of Phosphorus Loading in Receiving Waters
Owen M. Stefaniak, Steven R. Corsi, Troy D. Rutter, and Greg G. Failey
Environmental Science & Technology 2023 57 (44), 17051-17060
DOI: 10.1021/acs.est.3c03417

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. My husband and I met in Washington DC in the 1970’s and were a young married couple when just minutes after takeoff when in January 1982 Air Florida Flight 90 to Florida crashed into the 14th Street bridge killing 78 people. The cause was inadequate deicing and pilot error in responding to the problem. Had we not left DC for my husband's graduate work, we would have likely been on that bridge commuting into the District. 

Airports use a variety of products to remove or prevent ice and snow. Commonly used aircraft deicer and anti-icing fluids (ADAF) to remove ice, and anti-icers for inhibiting the formation of new ice on the aircrft. Use of these deicing products is required by the Federal Aviation Administration after a series of disasters in the last decades of the 20th century. during periods of ice and snow accumulation on aircraft.

These deicing agents usually contain chemicals that can affect local ecosystems. Stormwater runoff from airports is regulated and managed by airports. “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, lead author 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 USGS study found that nine of eleven ice control product formulations used at airports contained phosphorus. Airports often take measures to reduce runoff from ice control products during freezing precipitation periods. In the coldest climates deicing pads drain to recovery tanks. 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 what is called a dead zone and is typically seen in summers. 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.

The extent of each year’s dead zone is dependent on several factors, including how much nitrogen and phosphorus pollution enters waterways. High precipitation can contribute to the dead zone because it leads to more polluted runoff washing into rivers and streams from agriculture. In the Chesapeake Bay watershed we have had several warm winters in a row as well as lower than average dead zones. Precipitation was below average for most of 2023 delivering less nutrient pollution especially during the critical spring season, but it is unknown what impact if any the warm winters have had. 

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 nationally. 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.