### 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 FA R 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 pave ment 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. C OMPARISON OF P AVEMENT D EICING C HEMICALS

Airport avement deicers consist primarily of a freezing point depressa nt 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 mixtur e 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 de icer 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 b ecome 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 structur e of aquatic ecosystems. Although potassium acetate is more frequently used at U.S. airpor ts, its theoretical oxygen demand is less than half
that of urea. Urea is the sec ond largest chemical by usage and pr esents a greater environmental concern due to the larger oxygen dema nd 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 us age and exerts an e quivalent oxygen demand in the environment; however, propylene glycol do es not contribute to the same toxicity and nutrient loading issues associated with the decay of urea in receiving wa ters. Data on propylene glycol’s toxicity for aquatic organisms is li mited, though it is generally perceived as being relatively low. Available data indicate that pr opylene glycol may cause general chronic toxicity effects, including slower growth and inhibite d 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 causi ng acute mortality in many aquatic organisms
and can cause a host of chronic effects includ ing reproduction inhibition, diminished juvenile growth, and reduced embryo and ne onate survival. Ammonia is most toxic in its un-ionized form which is more likely to exist at higher temp eratures and pH levels . The National Recommended Water Quality Criterion for ammonia is dependen t on pH, temperature, a nd 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 criteri a 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 fu rther decays in aquatic environments to nitrates, a form of nutrients, which in excessi ve amount can produce ecological impacts such as nuisance algal blooms, death of underwater plan ts (due to reduced lig ht penetration through turbid waters), reduced dissolv ed oxygen levels, and impaired aquatic organism populations.

In comparison to urea, the ecological eff ects 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 e nvironment which can elevat e 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 organi sm functioning and surv ival (Public Sector Consultants 1993). Exposure to exce ssive 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 con centrations are high enough, exposure to excessive potassium concentrations can cause death throug h ionic imbalance. In lakes, increased salt
concentrations can also lead to increased dens ity of water layers, lead ing 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 chem ical with the lowest us age (see Table 2) and exerts approximately half of th e 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 th e remaining pavement deicer chemicals (i.e., sodium acetate and sodium formate) are primar ily limited to the oxygen demand exerted in the environment. Acetate-containing pavement dei cers (i.e., potassium acetate and sodium acetate) may be toxic at sufficiently high concentrations. Fo r example, specific toxicity values for sodium acetate range from a 48-hour lethal concentr ation for 50% of the sample population (LC 50 ) of 2,400 mg/L for the waterflea to a 120- hour LC 50 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 ex erted by acetate containi ng pavement deicers.

2. R EFERENCES

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. Works hop: 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_airtr affic/airports/resources/draft_a dvisory_circulars/media/draft_15 0_5200_30c.pdf . Accessed December 4, 2008.Memorandum 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 EP A). 2000. Preliminary Data Summary for Airport Deicing Operations. Office of Wa ter. 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.