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Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics (2010)

Chapter: Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics

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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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Suggested Citation:"Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics." National Academies of Sciences, Engineering, and Medicine. 2010. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. Washington, DC: The National Academies Press. doi: 10.17226/14370.
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INTRODUCTION Discharge of spent aircraft and airfield deicing and anti-icing fluids to receiving waters is an environmental concern at air- ports across the United States. The presence of these fluids in storm water runoff can increase both aquatic toxicity and biochem- ical oxygen demand (BOD) in the receiv- ing waters, making expensive collection and treatment of the fluids necessary at many U.S. airports. Airport Cooperative Research Program (ACRP) Project 02-01, “Alternative Air- craft and Airfield Deicing and Anti-Icing Formulations with Reduced Aquatic Tox- icity and Biochemical Oxygen Demand,” was conducted to examine the potential to develop aircraft and airfield deicing and anti-icing formulations with lower aquatic toxicity and reduced BOD. Such products could reduce infrastructure costs to airports, provide aircraft operators and airports with greater operational latitude in deicing and anti-icing operations, and improve the overall reliability of the air transportation system. To accomplish this objective, the Proj- ect 02-01 team was tasked with: 1. Defining the present state of the art of deicing and anti-icing products with respect to minimizing their aquatic toxicity and biological oxy- gen demand. 2. Identifying components of deicing and anti-icing products causing aqua- tic toxicity and biological oxygen demand. 3. Identifying promising alternative for- mulations and components for deic- ing and anti-icing products with reduced aquatic toxicity and biolog- ical oxygen demand. 4. Evaluating the performance, effi- ciency, material compatibility, and environmental, operational, and safety impacts of these alternative formulations and components com- pared with current commercial products. 5. Describing the fate and transport of deicing and anti-icing formulation components and their degradation products. ALTERNATIVE AIRCRAFT AND PAVEMENT DEICERS AND ANTI-ICING FORMULATIONS WITH IMPROVED ENVIRONMENTAL CHARACTERISTICS This digest summarizes the results of ACRP Project 02-01, “Alternative Aircraft and Airfield Deicing and Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxygen Demand.” The research was conducted by a project team consisting of the University of South Carolina, U.S. Geological Survey, Wisconsin State Laboratory of Hygiene, Molecular Knowledge Systems Inc., Infoscitex Corporation, CH2M HILL, and Western Washington University. The digest was prepared from the project final reports authored by George Bowman, Steven R. Corsi, Lee Ferguson, Steven W. Geis, Harris Gold, Kevin Joback, and Dean Mericas. Research Results Digest 9 April 2010 Responsible Senior Program Officer: E. T. Harrigan AIRPORT COOPERATIVE RESEARCH PROGRAM Sponsored by the Federal Aviation Administration

This Research Results Digest summarizes the key results, findings, and conclusions of ACRP Project 02-01. The complete two-volume project final re- port is available as ACRP Web-Only Document 3,1 Formulations for Aircraft and Airfield Deicing and Anti-Icing: Aquatic Toxicity and Biochemical Oxygen Demand, and ACRP Web-Only Document 8,2 Final Report: Alternative Aircraft Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxy- gen Demand. In this digest and the project final re- port, the term “deicer” is used to refer generally to aircraft deicing fluids (ADFs), aircraft anti-icing flu- ids (AAFs), and airfield pavement-deicing materials (PDMs), which may be in liquid or solid form. LITERATURE AND DATA REVIEW An extensive library of policy documents, patent literature, professional literature, project reports, and other data was compiled and reviewed as well as a collection of deicer manufacturer literature. This extensive review helped to define the current state of public (non-proprietary) knowledge regarding deicers. Federal Aviation Administration and SAE International Policies Regarding Toxicity and Biochemical Oxygen Demand in Deicers SAE International (formerly the Society of Automotive Engineers) develops and issues stan- dards for aircraft and airfield pavement deicers. The Federal Aviation Administration (FAA) recom- mends these standards in Advisory Circulars. SAE International provides the only numerical limits related to environmental characteristics through its Aerospace Material Specification (AMS) 1424, which requires Type I fluids to have 50% lethal concentrations (LC50) greater than or equal to 4,000 mg/l for several organisms.3 No guidance is provided for the BOD content of deicers. Characterization of Components in Commercial Deicer Products A wide range of chemicals potentially used in deicers was identified in the literature, including 25 freezing-point depressants (FPDs), 21 surfac- tants, 11 corrosion inhibitors, 13 thickening agents, 6 defoamers, 9 pH modifiers, 5 dyes, 4 oils, and 4 antioxidants and antimicrobial agents. Not all of these component categories are present in all deicers; thickeners, for example, are found only in aircraft anti-icing products. Toxicity data were available for less than one third of these chemicals, and the available data were not always comparable among different chemicals or relevant to deicing situations. Therefore, the con- clusion was reached that further testing would be needed to define the toxicity of individual candidate deicer components. Deicer manufacturers are constantly consider- ing modifications to their products to improve per- formance, environmental characteristics, and cost. Nearly all Type I ADFs now meet SAE specifications for toxicity; BOD characteristics of PDMs have been improved; four manufacturers introduced new Type IV formulations in the 2007–2008 winter season; and one manufacturer introduced a new Type I formula- tion for the 2008–2009 winter season, with the asser- tion that these new formulations would be more environmentally friendly than previously available products. Characteristics of Deicers in the Environment The primary environmental concerns with deicers are high organic content, resulting in high BOD, and aquatic toxicity. Some fate and transport characteris- tics of deicers are understood, but many others have not been extensively studied. Most research on the fate and transport of deicers has focused on FPDs and, to a lesser extent, on benzotriazole-derived corrosion inhibitors and alkylphenol ethoxylate (APE) surfac- tants. The components with environmental charac- teristics that are not well understood include dyes, thickeners, pH modifiers, defoamers, other corrosion inhibitors and surfactants, and even the FPD used in pavement deicers. FPD degradation rates are dependent on envi- ronmental factors such as medium, temperature, travel time, and established bacterial communities in soils and receiving waters. Benzotriazoles and APE 2 1Available at http://144.171.11.107/Main/Public/Blurbs/155 765.aspx or at the TRB website (www.trb.org) by searching “ACRP Web-Only Document 3” 2Available at http://www.trb.org/Publications/Blurbs/163310. aspx or at the TRB website (www.trb.org) by searching “ACRP Web-Only Document 8” 3LC50 is the highest concentration at which 50% of the tested or- ganisms do not survive the test period.

have been studied at a small number of airports, but the bulk of research on APE has been in waste- water treatment and not in situations where these surfactants are released directly to receiving waters without being treated. Benzotriazoles stay mostly in solution but have been detected in soils near deicing activities. Benzotriazoles have proven to degrade slowly or not at all in the environment. Of several different pathways, some APE degradation products are more toxic than their parent compounds, express endocrine disruption potential, and have potential for sorption to sediment particles and persistence in benthic sediments. Assessing the aquatic toxicity of deicers is a com- plicated issue owing to several different factors. First, toxicity in ADFs and AAFs is due primarily to pro- prietary additives, and the chemical identities of most of these additives are treated by the manufacturers as confidential business information. Second, different formulations have different degrees of toxicity, so dif- ferent effluents with similar glycol concentrations may have very different levels of toxicity. Third, different ADF and AAF formulations have different concentrations of glycol, again posing complications to interpreting chemical analysis from effluent sam- ples. Last, the fate and transport characteristics of additives are not necessarily the same as those of glycol, so glycol concentration and glycol surrogates such as chemical oxygen demand (COD) and BOD cannot be used as reliable indicators of additive con- tent in effluents. Conclusions from the literature indicate that research is necessary to better understand toxicity in ADF and AAF formulations and deicer runoff; however, available data indicate that the most likely sources of toxicity in PDMs are the FPDs. Characteristics of Deicers in Wastewater Treatment Systems The most commonly used FPDs (propylene gly- col, ethylene glycol, acetates, and formates) are read- ily biodegradable under both aerobic and anaerobic methanogenic conditions. Because of the ease by which FPDs can be biodegraded, their primary impact on biological treatment systems is increased organic load. Available literature indicates that nonylphenol ethoxylates (NPEs) may be degraded through bio- logical treatment, but reported details on degradation and byproduct generation vary depending on the spe- cific literature. Triazoles are unlikely to completely biodegrade in typical biological treatment systems. In sufficient concentration, they have been shown to inhibit degradation of other organic compounds, thereby decreasing treatment effectiveness of spent deicers. Recent research indicates that the effective- ness of different treatment strategies varies, with conventional activated sludge the least effective, membrane bioreactors more effective, and ozonation resulting in complete mineralization of benzotriazole and 4- and 5-methyl-1H-benzotriazole. Operational and Infrastructure Considerations Potential impacts on aircraft operations and infra- structure were identified in the literature. PDMs based on potassium formate and potassium acetate have been identified as potential contributors to corrosion of cadmium-plated electrical connectors in the Boeing 737 New Generation aircraft and to acceler- ated catalytic oxidation of carbon composite brake components. In both cases, potassium-based PDMs were in widespread use prior to material changes in the newer aircraft involved. Changes to components and maintenance procedures, including Boeing’s rec- ommended practice to eliminate cadmium corrosion through the use of corrosion-inhibiting compound (CIC) on electrical connectors, have eliminated or minimized the corrosion reactions. SAE G-12 and air- craft manufacturers have specific task groups work- ing on these important issues. Increased failure rates of airfield electrical com- ponents were also thought to be linked to potassium acetate PDMs. It was subsequently found that poorly maintained systems allowed PDM entry. Corrective actions and improved products and components have greatly reduced or eliminated the problems. Reports of pavement deterioration, including degradation and disintegration, softening and strip- ping effects, and scaling and surface cracking were determined to be a result of alkali-silica reactivity linked to pavement deicers based on potassium acetate. Subsequent investigation determined that other factors, especially construction methods and materials, can be used to mitigate these issues. Residues from Type II and Type IV fluids may form on aerodynamically quiet areas on aircraft, and if not removed by deicing or anti-icing, the residue may absorb rainwater (rehydrate) and subsequently freeze, restricting the movement of unpowered flight control surfaces. 3

Deicer Products under Development During the past two decades there have been a number of efforts to develop more environmentally friendly deicers. Some of these new products are en- tering the market, while others are not yet available commercially. Octagon Process, Inc., introduced a Type I ADF based on propylene glycol and glycerol that is described as having lower 5-day BOD (BOD5) and aquatic toxicity compared to many previous Type I formulations. Battelle recently released an ADF–AAF and a PDM, both based on glycerol as the primary FPD. Battelle is also working on alter- native PDM formulations that are less damaging to aircraft components and less expensive than current products. Foster-Miller has previously developed two Type I fluids and one Type II fluid, with the objective of producing environmentally advantaged formu- lations that consider BOD and toxicity. METSS Corporation has developed two Type I fluids using agriculturally based products intended to further reduce toxicity and BOD. While some of these for- mulations have been certified according to SAE standards, problems involving residue formation, foaming, and unfavorable thickening after applica- tion have been encountered during field testing. The prospects for near-term commercial availability of these products are unclear. Methodological Issues The literature review identified a number of methodological issues. Biochemical Oxygen Demand. BOD5 testing and extended-length BOD testing pose unique challenges in samples containing deicers. Issues include deter- mining proper dilutions to characterize BOD accu- rately, properly acclimating microorganisms, and the possibility of seeds with insufficient microorganism densities. Analysis of Additives. There are no standard tech- niques for determining concentration of deicer addi- tives such as benzotriazoles and APE. Techniques are currently in flux, necessitating regular review of literature to evaluate the most current methods. Aquatic Toxicity. The results of acute deicer toxicity testing at low temperature were not dramatically dif- ferent from those at standard temperatures, with the freshwater crustacean C. dubia slightly less sensitive to deicers at lower temperatures and fathead minnows (P. promelas) slightly more sensitive to deicers at lower temperatures. One complication when con- ducting toxicity tests with samples containing deicer is low dissolved oxygen resulting from high BOD. A successful method for improving dissolved oxygen levels during fathead minnow tests is to reduce the number of fish per replicate and reduce the sample volume. Representativeness of Laboratory Analyses. Results of BOD and toxicity tests performed in a laboratory under controlled light and temperature conditions provide valuable ecological information, but such conditions do not mimic environmental conditions, especially during deicer application events. TOXICITY CHARACTERIZATION Baseline toxicity tests were conducted on seven Type I formulations, four Type IV formulations, and three PDMs. One group of five Type I products re- sulted in LC50 averaging about 10,000 mg/l, whereas two products showed LC50 near 30,000 mg/l. Type IV deicer products consistently demonstrated much greater toxicity than the Type I products, with LC50 near 2,500 mg/l and lower. Toxicity results were sim- ilar for marine and freshwater species. Toxicity in fractionated Type I and Type IV deicers was associated with the presence of poly- ethoxylated nonionic surfactants, including both APE surfactants and aliphatic alcohol ethoxylate surfac- tants. Relatively high concentrations of triazole-based corrosion inhibitors in one Type IV deicer triggered toxicity in toxicity identification and evaluation (TIE) assays. Toxicity in pavement deicers is associated pri- marily with the FPD. BIOCHEMICAL OXYGEN DEMAND AND CHEMICAL OXYGEN DEMAND BOD and COD were characterized in seven deicer formulations, including ethylene glycol and propylene glycol formulations of Type I ADF, ethyl- ene glycol and propylene glycol formulations of Type IV AAF, a liquid PDM based on potassium acetate, and solid PDMs based on sodium acetate and sodium formate. Expanded testing was conducted on one for- mulation of propylene glycol Type I ADF, one propy- lene glycol Type IV AAF, and one potassium acetate PDM to determine decay rates over a 40-day period 4

at 20°C and 5°C in marine water and freshwater. BOD5 and COD results are presented in Table 1. Biodegradability was examined by comparing BOD and COD results. The degradation percentage was between 40% and 82% for six of the formula- tions. Decay rates in the 40-day test indicate that degradation occurred more rapidly in the first 15 days than during the rest of the test period. At least 78% degradation occurred for the six formulations over the 40-day test period. Results from sodium formate PDM testing are not included owing to apparent toxicity of this formulation to organisms in the BOD seed. Freshwater and marine water test results were comparable in the 40-day tests conducted at 20°C. Results of the 40-day freshwater tests at 5°C indicate lower degradation than those at 20°C with 23–55% degradation for ethylene glycol products, 61–77% degradation for propylene glycol products, and 86–94% for acetate-based products. Results of the 5°C marine tests indicated that degradation was sig- nificantly less in low temperatures with less than 10% degradation for the propylene glycol ADF and AAF and 69% degradation for the potassium acetate PDM. EVALUATION OF ALTERNATIVE ADF COMPONENTS AND FORMULATIONS The primary objective of this phase of the research was to identify and characterize alternative deicer formulations with reduced aquatic toxicity and BOD that would be operationally and commercially viable. ACRP also stressed the need to present the research findings in a format useful to chemical manufac- turers in producing more environmentally friendly deicing formulations and to airport operators in eval- uating alternatives to meet environmental compli- ance requirements. Research Approach A tiered approach was taken to achieve this objective. Pure candidates and simple mixtures with water were tested in tier 1. Candidates that survived tier 1 testing were subjected to tier 2 tests involving more complex mixtures. In tier 1, 1. Candidate FPDs, thickeners, surfactants, and corrosion inhibitors were identified with im- proved environmental qualities compared to components of commercial aircraft deicers and anti-icers. 2. Laboratory analysis of the candidate compo- nents were conducted for BOD and aquatic toxicity. 3. Candidate components were down-selected to identify a subset for use in building candi- date formulations. In tier 2, 1. A series of testing and down-selecting of pro- gressively more complex mixtures was con- ducted to arrive at a final formulation that is equivalent to, or better than, commercial for- mulations in current use in terms of deicing per- formance and environmental characteristics. 5 Table 1 Summary of BOD5 and COD results for tested deicers. Values as Neat Values as Primary Source Formulation of Oxygen Demand % COD BOD5 Primary COD BOD5 Formulation FPD (mg/kg) (mg/kg) Source (mg/kg) (mg/kg) Ethylene glycol Type I 92 1,180,000 492,000 EG 1,280,000 535,000 Ethylene glycol Type IV 64 826,000 331,000 EG 1,290,000 517,000 Propylene glycol Type I 88 1,420,000 990,000 PG 1,610,000 1,130,000 Propylene glycol Type IV 50 842,000 539,000 PG 1,680,000 1,080,000 Potassium acetate (liquid) 50 315,000 247,000 Acetate 1,050,000 821,000 Sodium acetate (solid) 96 700,000 571,000 Acetate 1,010,000 826,000 Sodium formate (solid) 98 242,000 —a Formate 373,000 —a a BOD test results for sodium formate deicer were not considered reliable estimates of potential BOD exertion in environmental situations due to apparent toxicity of the formulation to BOD seed organisms.

2. Candidate anti-caking agents were identified and tested in solid FPD formulations to eval- uate performance. 3. The environmental characteristics of the final formulations were determined. Tables 2 through 4 summarize the tiered testing. The results of the tier 2 tests yielded a final selec- tion of components for complete Type IV formu- lation development. Tests needed to certify the down-selected formulations, including deicing and anti-icing performance and aircraft materials compat- ibility, were not undertaken as part of this research. Tier 1 Results A combination of molecular modeling, database searches, and literature searches were used to identify candidates for each of four major functional cate- gories of deicer components. The following numbers of candidates were identified for further experimental evaluation based on their performance characteristics related to their function in deicer formulations and their contributions to BOD and toxicity: • FPD: 27 candidates (5 aircraft, 12 runway, and 10 for both aircraft and airfield pavement). • Thickeners: 6 candidates. • Surfactants: 19 candidates. • Corrosion Inhibitors: 14 candidates. Two candidate anti-caking additives were also identified for use in sodium formate runway deicers, and one candidate defoamer was identified for use in deicing formulations. Upon review of the tier 1 results, there did not ap- pear to be substantial potential to improve BOD and aquatic toxicity in Type I fluids, nor did there appear to be potential to improve upon BOD in PDMs as compared to the products in current use with the most favorable environmental characteristics. For this rea- son, ACRP directed the research team to focus the tier 2 testing on Type IV aircraft anti-icing formula- tions and anti-caking additives for sodium formate runway deicers. Tier 2 Results Type IV Aircraft Anti-Icing Formulations Table 5 lists the FPDs, surfactants, thickeners, and corrosion inhibitors that were evaluated during tier 2 testing of Type IV aircraft anti-icing formula- tions. Based on the results of tier 1 testing, the FPDs that were selected showed improvements in COD, BOD, aquatic toxicity, or all three over propylene gly- 6 Table 2 Number of components and deicer formulations tested in tiers 1 and 2. Deicer Component Tier No. FPD Surfactant/Antifoam Corrosion Inhibitor Thickener Deicer Formulations 1 26 19 14 6 — 2 2 3 2 3 Type IV AAF 1a Runway PDM aEvaluated with two anti-caking materials. Table 3 Tier 1 deicing and anti-icing formulation tests. Key Area Test/Evaluation Deicing performance Freezing point depression, viscosity, contact angle Environmental impact Biological oxygen demand, aquatic toxicity Safety properties Flash point Cost Supplier cost estimates Table 4 Tier 2 tests for Type IV and runway PDM. Key Area Test/Evaluation Type IV AAF Deicing Surface tension (contact angle), performance viscosity, foaming Environmental Biological oxygen demand, impact aquatic toxicity Materials Total immersion and sandwich compatibility corrosion testing (aluminum clad and anodized aluminum) Runway Deicer Deicing performance Water absorption, anti-caking

col. Many surfactants tested in tier 1 had improve- ments in toxicity over currently used surfactants. Surfactants were selected to take advantage of these toxicity improvements as much as possible while reducing the contact angle and surface tension to en- sure that the formulations completely coat the air- craft surfaces. Thickeners were selected based on their aquatic toxicity and their ability to shear in a manner similar to commercial Type IV anti-icing agents. Corrosion inhibitors were down-selected based on aquatic toxicity. Tier 2 experiments involved the testing of pro- gressively more complex mixtures as compared to tier 1: • FPD + water + thickeners; FPD:water = 1:1 by weight. • FPD + water + surfactants; FPD:water = 1:1 by weight. • FPD + water + thickeners + surfactants; FPD: water = 1:1 by weight. • FPD + water + thickeners + surfactants + corro- sion inhibitors; FPD:water = 1:1 by weight. FPD Selection Diethylene glycol (DEG) and glycerol were con- sidered to be equally promising FPD candidates through the first three stages of the tier 2 down- selection process. The properties of the two are very similar: glycerol’s theoretical oxygen demand and aquatic toxicity, as measured by Microtox® testing, are lower than that of DEG, but the aquatic toxicity of DEG toward C. dubia and P. promelas is lower than glycerol’s. Mammalian toxicity is nearly identical for both candidates. What proved to be a differentiator was the freezing point characteristics for mixtures of each candidate with water that suggested the higher freezing point of glycerol solutions could cause oper- ational problems. Specifically, asymmetric evapora- tion of water from applied Type IV formulations may result in concentrated FPD solutions on aircraft sur- faces. In the case of glycerol, this could result in for- mation of residues. For example, at –20°C a 90 wt% glycerol solution would partially freeze into a slurry or highly viscous solution whereas a 90 wt% DEG solution would still be completely liquid. Concentra- tion of FPD in this manner could potentially result in the accumulation of highly viscous glycerol residues on the aircraft surface. For this reason, DEG was selected as the preferred FPD for the final formulation. Additive Selection Additives in the final formulation include Tergi- tol L-64 as the surfactant, triethanolamine (TEA) as the corrosion inhibitor, and Carbopol EZ-4 as the thickener. These additives were chosen by consider- ation of performance, aquatic toxicity, and cost. Toxicity Results Results from the stepwise toxicity testing show how toxicity changed as each additional component was included in the formulation (Table 6). These results were compared to theoretical results calcu- lated from the toxicity of the individual components and their concentrations in the mixtures, and assum- ing no synergistic or antagonistic toxicity inter- actions. In most cases, it was valid to assume that individual component toxicity could be used to deter- mine formulation toxicity. In the instances where this was not true, toxicity evaluation was more com- plicated, requiring empirical observations to under- stand which components were responsible for final formulation toxicity. Addition of the anti-foaming agent to the first formulation indicated a synergistic interaction for all three organisms (the formulation was more toxic than the theoretical value). Simi- larly, synergistic interactions in the Microtox and fathead minnow tests were observed from addition of TEA in the final formulation. In addition, dif- ferent interactions were observed depending on the FPD. Of particular interest was the difference be- tween addition of the thickener to DEG as opposed 7 Table 5 Candidate components of Type IV aircraft anti-icing fluids evaluated in tier 2. FPD Surfactants Thickeners Corrosion Inhibitors Glycerol Tergitol L-64 Kalzan HP TEA Diethylene glycol (DEG) Tergitol TMN-10 K1A96 Mazon RI 325 Triton CG-110 with Carbopol EZ-4 with 10% Ridafoam NS 221 triethanolamine (TEA)

to for glycerol. In the DEG formulation, results were similar to theoretical values, but a synergistic inter- action for toxicity was present in this step for the glycerol formulation. This indicated that synergistic interactions for the same component were different depending on the composition of the rest of the formulation. In this case, it was only a difference in FPD that caused a difference in the synergistic interaction. Results of definitive aquatic toxicity tests on the final formulation indicate that acute and chronic tox- icity endpoints were one to three orders of magni- tude greater (i.e., the toxicity was lower) than results previously published for formulations in current use (Table 7). Acute toxicity endpoints ranged from 219 to 13,800 mg/l in tests with currently used for- mulations, with each of the four tested products hav- ing one or more of the three endpoints at least as low as 528 mg/l. The lowest of the acute toxicity end- points in the final DEG formulation in this research was 32,700 mg/l. Chronic toxicity endpoints ranged from 79.4 to 1,350 mg/l in tests with currently used formulations, with each of the four tested products having one or more of the three endpoints at least as low as 130 mg/l. The lowest of the chronic toxicity endpoints in the final DEG formulation from this research was 8,970 mg/l (Table 7). 8 Table 6 Comparison of theoretical values with measured test results for stepwise Type IV anti-icing formulation construction. Theoretical Values Test Results Percent of Fathead Fathead Component Microtox C. dubia minnow Microtox C. dubia minnow Added to EC 50a LCb50 LC50 EC50 LC50 LC50 Added Component Mixture (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) DEG formulation Water 50 — — — — — — DEG 50 130,000 110,000 110,000 130,000 110,000 110,000 Carbopol EZ4 with TEAc 0.0763 130,000 66,000 110,000 140,000 71,000 120,000 (thickener) Tergitol L-64 (surfactant) 0.25 130,000 66,000 110,000 110,000 57,000 140,000 Ridafoam 0.025 12,000 66,000 110,000 25,000 25,000 59,000 (anti-foaming agent) TEA (corrosion inhibitor, 0.2 110,000 66,000 110,000 43,000 53,000 89,000 does not include Ridafoam)— final formulation Glycerol formulation Water 50 — — — — — — Glycerol 50 260,000 70,000 92,000 260,000 70,000 92,000 Carbopol EZ4 with TEA 0.0552 260,000 70,000 92,000 43,000 66,000 71,000 (thickener) Tergitol L-64 260,000 70,000 92,000 18,000 75,000 63,000 (surfactant) Ridafoam 12,000 91,000 480,000 18,000 53,000 63,000 (anti-foaming agent) Screening toxicity results are only approximations. Screening toxicity procedures include fewer replicates, non-renewal of test solutions, shorter exposure duration for Pimephales promelas, and other procedural variances from definitive toxicity tests. Compounds are organized by least toxic to most toxic endpoint, determined by the most sensitive species. a The Microtox EC50 is the statistically determined concentration that would result in a 50% reduction in light emission compared to a labora- tory control. b The LC50 is the statistically determined concentration that would cause death in 50% of the population exposed. c TEA is triethanolamine.

In currently used formulations, surfactants were identified as the component with the greatest influence on toxicity. In the final formulation developed from this research, toxicity results indicated that the chosen surfactant had little or no influence on toxicity. Biochemical Oxygen Demand Results The concentration of COD in the final formula- tion was 752 g/kg with a relative standard deviation of 0.96%. These results are consistent with tier 1 test- ing results on neat DEG (COD = 1,500 g/kg), con- sidering that the final formulation contains 50% DEG. The concentration of BOD5 could not be de- termined. Difficulties with seed acclimation to DEG encountered in tier 1 testing remained in tests with the final formulation. Runway Deicers The effectiveness of potassium carbonate and tripotassium citrate to prevent the caking of sodium formate granules was experimentally tested. The pro- cedure involved drying the components and mixtures of the components in a desiccator, weighing the individual components and mixtures, and placing sets of sample dishes in an environmental chamber at constant temperature (30oC) and humidity (50%) for different periods of time. The percentage of powder passing through a sieve was the metric used to eval- uate additive effectiveness. No satisfactory anti-caking solution was found for sodium formate. The experimental results indi- cated that mixtures containing the anti-caking addi- tives and sodium formate absorbed more moisture than the samples of sodium formate alone. Tests of the individual components found that aluminum sample dishes containing the potassium carbonate were corroded and partially dissolved after two days in the environmental chamber, which eliminated this candidate additive from further testing. Further experiments with sodium formate and mixtures of sodium formate and tripotassium citrate were con- tinued. The results showed that although tripotas- sium citrate picked up a negligible amount of water, the mixtures of tripotassium citrate and sodium for- mate picked up more water than the sodium formate by itself, indicating that the tripotassium citrate pro- duced a synergistic water absorption effect. No ready explanation for these observations is available, and further testing was discontinued. Degradation Pathways for Down-Selected Deicer Components Possible degradation pathways and degradation products for the down-selected components of the final Type IV formulation were examined to evaluate the potential for significant environmental effects. Diethylene Glycol Diethylene glycol is the proposed FPD. Its mix- ture with water constitutes more than 90% of the weight of the final deicing or anti-icing product. An evaluation of potential biodegradation pathways indicated that intermediate biodegradation products are fairly reactive and are thus are not expected to persist in the environment. Tergitol L-64 Tergitol L-64 is a nonionic ethylene oxide/ propylene oxide copolymeric surfactant marketed as readily biodegradable. The degradation pathways and products for the ethylene oxide portion of the 9 Table 7 Results from definitive aquatic toxicity testing of final Type IV DEG formulation (95% confidence interval). Acute Toxicity Chronic Toxicity Microtox C. dubia P. promelas C. dubia P. promelas S. capricorutum EC50a (mg/l) LC50b (mg/l) LC50 (mg/l) IC25c (mg/l) IC25 (mg/l) IC25 (mg/l) 54,900 32,700 126,000 8,970 60,200 42,100 (53,700–56,100) (28,600–37,400) (116,000–136,000) (4,730–13,800) (56,600–62,500) (40,100-44,000) a The Microtox EC50 is the statistically determined concentration that would result in a 50% reduction in light emission compared to a labora- tory control. bThe LC50 is the statistically determined concentration that would cause death in 50% of the population exposed. c The IC25 is the statistically determined concentration that would cause a 25% inhibition in growth (Fathead minnow) or reproduction (C. dubia).

surfactant should be the same as those for DEG. The degradation mechanism for the propylene oxide por- tion of the surfactant’s molecular structure is less certain. An examination of the aquatic toxicities for possible degradation products indicates that they are fairly toxic to rainbow trout. It is also possible that these products are toxic to bacteria, which could partly account for reports of poor biodegradation. Triethanolamine Triethanolamine is the proposed corrosion in- hibitor. It would typically be used in formulations at less than 2% by weight. Degradation byproducts are readily biodegraded and are not expected to persist in the environment. However, data on the aquatic toxic- ity of TEA and its degradation products to P. prome- las indicate that the aquatic toxicity of the degradation products is significantly higher than that of TEA (Table 8). Carbopol EZ-4 Carbopol is the proposed thickener. It is a lightly cross-linked poly(acrylic acid) polymer. Studies in the literature reported that Carbopol does not bio- degrade, but also showed it does not pass through municipal wastewater treatment facilities into receiv- ing waters because it adsorbs onto biomass and is removed with the biosolids during treatment. CONCLUSIONS General Conclusions 1. An alternative Type IV formulation was iden- tified with significantly reduced toxicity com- pared to products in current use. The final candidate formulation has aquatic toxicity val- ues that are greater by an order of magnitude or more (less toxic) than the least toxic com- mercial Type IV products tested. 2. The final formulation consists of DEG as the FPD, with a basic additive package consist- ing of Tergitol L-64 surfactant, TEA corro- sion inhibitor, and Carbopol EZ-4 thickener. 3. Toxicity identification techniques used on currently used formulations were successful in helping to improve the toxicity profile of alternative fluids. 4. The physical properties of the alternative Type IV formulations were affected by interactions between the surfactants and thickeners. 5. Numerous potential alternative components were identified. 6. The techniques used in identifying a less- toxic Type IV formulation have potential applicability to developing Type I formula- tions with reduced toxicity. 7. There is no current evidence to suggest that the alternative FPD or thickener present sig- nificant concerns relative to degradation path- ways and degradation products. Byproducts of the alternative surfactant and corrosion inhibitor may have greater aquatic toxicity than the parent products, but further inves- tigation is needed for their full evaluation. DEG is preferred because of its lower freez- ing point and the resulting reduced risk of residue formation. Oxygen Demand 1. Theoretical oxygen demand is a good screen- ing criterion for oxygen demand of FPDs. The COD results for FPDs compared well with the- oretical oxygen demand. 2. Conventional BOD tests produced unreliable results for some FPDs. The success of BOD testing was highly variable and dependent on how well microorganisms acclimated to FPDs. 3. COD was the most useful metric in down- selecting FPDs for oxygen demand. The reliance on COD was necessary because of the uncertainties encountered with BOD tests. 4. FPDs are the predominant source of oxygen demand in all deicer formulations. The rela- tive concentrations of all other components are so small that any contribution to oxygen demand is insignificant. 5. No candidate FPD was found with potential for improvement of environmental character- istics compared to the least toxic Type I fluids 10 Table 8 Toxicity of TEA and its degradation products. Compound 96hr LD50 P. promelas 1 Triethanolamine 11,800 mg/l 2 Diethanolamine 1,370 mg/l 3 Ethanolamine 2,070 mg/l 4 Acetaldehyde 36.8 mg/l

and pavement deicer formulations in cur- rent use. 6. DEG and glycerol were identified as promis- ing alternative FPDs for Type IV fluid for- mulations. 7. Parameters such as molecular weight, freezing point depression, application rates, and trans- port phenomena must be considered to gain a comprehensive understanding of the poten- tial impact of PDMs on dissolved oxygen in receiving waters. Aquatic Toxicity 1. Screening-level toxicity testing identified potentially viable alternative components in each of the categories of FPD, surfac- tants, corrosion inhibitors, and thickeners. Identified candidates included 7 FPDs, 11 surfactants, 9 corrosion inhibitors, and 6 thickeners. 2. Empirical observations are necessary to under- stand which components are responsible for the toxicity of final formulations. Pavement Deicers 1. There was significant synergistic interaction be- tween sodium formate and tripotassium citrate that cannot be readily explained. Resolution of these counterintuitive results was beyond the scope of this investigation. 11

Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP). Persons wanting to pursue the project subject matter in greater depth should contact the CRP Staff, Transportation Research Board of the National Academies, 500 Fifth Street, NW, Washington, DC 20001. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. Subscriber Categories: Materials ISBN 978-0-309-11832-3 9 780309 118323 9 0 0 0 0

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TRB’s Airport Cooperative Research Program (ACRP) Research Results Digest 9: Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics explores the aquatic toxicity and biological oxygen demand state of the art, components, and promising alternative formulations of deicing and anti-icing products. The report also examines the performance; efficiency; material compatibility; and environmental, operational, and safety impacts of alternative formulations and components as well as the fate and transport of deicing and anti-icing formulation components and their degradation products.

A full report on this issue was published by TRB as ACRP Web-Only Document 8.

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