MEMORANDUM 

TO: Bill Swietlik, EPA 

FROM: Kristi Bubb, ERG 

DATE: February 17, 2011 

SUBJECT: Comparison of the Ecological Effects of Urea to Other Pavement Deicer 

Chemicals

 In response to comments received during FAR from the Office of Policy, EPA requested 

that ERG provide a brief discussion to explain more thoroughly why urea pavement deicers are 

worse than the alternatives EPA will allow to be used under the final regulation for the Airport 

Deicing Point Source Category. The following memorandum summaries the oxygen demand and 

toxicity data presented for pavement deicer chemicals in the Final Environmental Impact and 

Benefit Assessment for the Final Effluent Limitation Guidelines and Standards for the Airport 

Deicing Category and the Technical Development Document for the Final Effluent Limitation 

Guidelines and Standards for the Airport Deicing Category. 

1. COMPARISON OF PAVEMENT DEICING CHEMICALS

 Airport avement deicers consist primarily of a freezing point depressant ingredient and, 

in many formulations, various additives. The pavement deicer freezing point depressants most 

widely used at U.S. airports are potassium acetate, urea, sodium acetate, sodium formate, 

propylene glycol, ethylene glycol, or a mixture of ethylene or propylene glycol and urea. 

Potassium acetate, sodium formate, and sodium acetate formulations are known to contain 

corrosion inhibitors, as well (Switzenbaum et al. 1999; Shi 2008; USDOT 2007) though the 

corrosions inhibitors’ chemical identity is not known. Table 1 presents EPA’s national estimate 

of commercial airport’s airside pavement deicer chemical use and shows that potassium acetate 

is the most frequently used pavement deicer at U.S. airports followed by urea. 

Table 1. U.S. Commercial Airports - National Estimate of Pavement Deicer Chemical Use 

Pavement Deicer Chemical 

Estimated Total 

Airport Use 

(tons/year) 

Potassium acetate 22,538 

Airside urea 4,127 

Propylene glycol-based fluids 3,883 

Sodium acetate 3,100 

Sodium formate 1,117 

Ethylene glycol-based fluids 774 

Source: US EPA Airport Deicing Questionnaire (2006). 
Memorandum 

February 17, 2011 

Page 2 

 Of particular and well-known concern is the oxygen demand exerted by all pavement 

deicer chemicals as they decay; however, the oxygen demand can vary significantly among the 

different chemicals as shown in Table 2. Oxygen demand is an environmental concern due to the 

potential for the level of dissolved oxygen to become too low and either impair or kill aquatic 

organisms present in receiving waters. Chronic low oxygen conditions can eventually change the 

biochemistry and overall community structure of aquatic ecosystems. Although potassium 

acetate is more frequently used at U.S. airports, its theoretical oxygen demand is less than half 

that of urea. Urea is the second largest chemical by usage and presents a greater environmental 

concern due to the larger oxygen demand it exerts in the environment. 

Table 2. Theoretical Oxygen Demand for Pavement Deicer Chemicals 

Pavement Deicer 

Chemical 

Theoretical Oxygen 

Demand 

(Moles of O2 per Mole of 

Deicing Compound)

Propylene glycol 4.0 

Urea 4.0 

Ethylene glycol 2.5 

Potassium acetate 1.75 

Sodium acetate 1.75 

Sodium formate 0.25 

Source: US EPA 2011. 

 Propylene glycol usage is similar to urea usage and exerts an equivalent oxygen demand 

in the environment; however, propylene glycol does not contribute to the same toxicity and 

nutrient loading issues associated with the decay of urea in receiving waters. Data on propylene 

glycol’s toxicity for aquatic organisms is limited, though it is generally perceived as being 

relatively low. Available data indicate that propylene glycol may cause general chronic toxicity 

effects, including slower growth and inhibited reproduction, as well as acute mortality at 

concentrations greater than 5,000 mg/L (US EPA 2000). Urea is not particularly toxic to aquatic 

life; however, in the environment urea degrades to ammonia which is highly toxic to many 

aquatic organisms. Ammonia is capable of causing acute mortality in many aquatic organisms 

and can cause a host of chronic effects including reproduction inhibition, diminished juvenile 

growth, and reduced embryo and neonate survival. Ammonia is most toxic in its un-ionized form 

which is more likely to exist at higher temperatures and pH levels. The National Recommended 

Water Quality Criterion for ammonia is dependent on pH, temperature, and organism life stage. 

Acute criteria for ammonia can range from 0.885 to 48.8 mg N/L, depending upon the pH and 

the presence of salmonids in the waterbody. Chronic criteria for ammonia are also pH 

dependant, but do not vary according to salmonid presence or absence, range from 0.254 to 3.48 

mg N/L (US EPA 1998). Additionally, ammonia further decays in aquatic environments to 

nitrates, a form of nutrients, which in excessive amount can produce ecological impacts such as 

nuisance algal blooms, death of underwater plants (due to reduced light penetration through 

turbid waters), reduced dissolved oxygen levels, and impaired aquatic organism populations. 

 In comparison to urea, the ecological effects presented by the other pavement deicer 

chemicals are minimal. Potassium acetate, the largest pavement deicer chemical by usage, 

releases potassium in its ionic form to the environment which can elevate salinity, conductance, 
Memorandum 

February 17, 2011 

Page 3 

or total dissolved solids in surface waters. High potassium loadings can create surface water ion 

balance issues that can impact aquatic organism functioning and survival (Public Sector 

Consultants 1993). Exposure to excessive potassium concentrations can interfere with essential 

fluid regulation in both freshwater and saltwater fish, requiring fish to expend more energy to 

maintain necessary osmotic pressures. If concentrations are high enough, exposure to excessive 

potassium concentrations can cause death through ionic imbalance. In lakes, increased salt 

concentrations can also lead to increased density of water layers, leading to or exacerbating 

stratification during cold or still weather to the point that normal seasonal overturn does not 

occur (D’Itri 1992). 

 Ethylene glycol is the pavement deicer chemical with the lowest usage (see Table 2) and 

exerts approximately half of the oxygen demand of urea. Similar to propylene glycol, toxicity 

data for ethylene glycol is relatively limited; however, available data indicates ethylene glycol 

may cause general chronic toxicity effects at high concentrations (>3,400 mg/L), including 

slower growth and inhibited reproduction and is known to cause acute mortality at excessive 

levels (US EPA 2000). The ecological effects of the remaining pavement deicer chemicals (i.e., 

sodium acetate and sodium formate) are primarily limited to the oxygen demand exerted in the 

environment. Acetate-containing pavement deicers (i.e., potassium acetate and sodium acetate) 

may be toxic at sufficiently high concentrations. For example, specific toxicity values for sodium 

acetate range from a 48-hour lethal concentration for 50% of the sample population (LC50) of 

2,400 mg/L for the waterflea to a 120- hour LC50 of 13,330 mg/L for the fathead minnow 

(Pimephales promelas) (US EPA 2000). However, toxicity is a secondary environmental concern 

when compared to the potential oxygen demand exerted by acetate containing pavement deicers. 

2. REFERENCES

D’Itri, F.M. 1992. Chemical Deicers and the Environment. Lewis Publishers, Inc. Chelsea, MI. 

Public Sector Consultants Inc. 1993. “The Use of Selected Deicing Materials on Michigan 

Roads: Environmental and Economic Impacts. Conducted for the Michigan Department of 

Transportation.” Available at: http://www.michigan.gov/mdot/0,1607,7-151-9622_11045-57246-

-,00.html. Accessed June 24, 2008. 

Shi, X. 2008. Impact of Airport Pavement Deicing Products on Aircraft and Airfield 

Infrastructure. Transportation Research Board, Airport Cooperative Research Program Report. 

Available at: http://onlinepubs.trb.org/onlinepubs/acrp/acrp_syn_006.pdf. Accessed December 4, 

2008. 

Switzenbaum, Michael S., Veltman, Shawn, Schoenberg, Theodore, Durand, Carmen M., 

Mericas, Dean, and Wagoner, Bryan. 1999. Workshop: Best Management Practices for Airport 

Deicing Stormwater. United States Department of Interior, Geological Survey. 173. July 29. 

U.S. Department of Transportation (USDOT). 2007. Advisory Circular: Airport Winter Safety 

and Operations. AC 150/5200-30C. Available at: 

http://www.faa.gov/airports_airtraffic/airports/resources/draft_advisory_circulars/media/draft_15

0_5200_30c.pdf. Accessed December 4, 2008. 
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February 17, 2011 

Page 4 

U.S. Environmental Protection Agency (US EPA). 1998. 1998 Update of Ambient Water Quality Criteria 

for Ammonia. Office of Water. Available at: http://www.epa.gov/ost/standards/nh3_rpt.pdf. 

U.S. Environmental Protection Agency (US EPA). 2000. Preliminary Data Summary for Airport 

Deicing Operations. Office of Water. EPA-821-R-00-016. Available at: 

http://www.epa.gov/guide/airport/airport.pdf. 

U.S. Environmental Protection Agency (US EPA). 2006. U.S. Environmental Protection Agency 

Airport Deicing Questionnaire. 

U.S. Environmental Protection Agency (US EPA). 2011. Technical Development Document for 

the Final Effluent Limitation Guidelines and Standards for the Airport Deicing Category.