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This Research Results Digest summarizes the key Characterization of Components results, findings, and conclusions of ACRP Project in Commercial Deicer Products 02-01. The complete two-volume project final re- A wide range of chemicals potentially used in port is available as ACRP Web-Only Document 3,1 deicers was identified in the literature, including Formulations for Aircraft and Airfield Deicing and 25 freezing-point depressants (FPDs), 21 surfac- Anti-Icing: Aquatic Toxicity and Biochemical Oxygen tants, 11 corrosion inhibitors, 13 thickening agents, Demand, and ACRP Web-Only Document 8,2 Final 6 defoamers, 9 pH modifiers, 5 dyes, 4 oils, and Report: Alternative Aircraft Anti-Icing Formulations 4 antioxidants and antimicrobial agents. Not all of with Reduced Aquatic Toxicity and Biochemical Oxy- these component categories are present in all deicers; gen Demand. In this digest and the project final re- thickeners, for example, are found only in aircraft port, the term "deicer" is used to refer generally to anti-icing products. aircraft deicing fluids (ADFs), aircraft anti-icing flu- Toxicity data were available for less than one ids (AAFs), and airfield pavement-deicing materials third of these chemicals, and the available data were (PDMs), which may be in liquid or solid form. not always comparable among different chemicals or relevant to deicing situations. Therefore, the con- LITERATURE AND DATA REVIEW clusion was reached that further testing would be needed to define the toxicity of individual candidate An extensive library of policy documents, patent deicer components. literature, professional literature, project reports, and Deicer manufacturers are constantly consider- other data was compiled and reviewed as well as a ing modifications to their products to improve per- collection of deicer manufacturer literature. This formance, environmental characteristics, and cost. extensive review helped to define the current state of Nearly all Type I ADFs now meet SAE specifications public (non-proprietary) knowledge regarding deicers. for toxicity; BOD characteristics of PDMs have been improved; four manufacturers introduced new Type Federal Aviation Administration IV formulations in the 20072008 winter season; and and SAE International Policies one manufacturer introduced a new Type I formula- Regarding Toxicity and Biochemical tion for the 20082009 winter season, with the asser- Oxygen Demand in Deicers tion that these new formulations would be more environmentally friendly than previously available SAE International (formerly the Society of products. Automotive Engineers) develops and issues stan- dards for aircraft and airfield pavement deicers. The Federal Aviation Administration (FAA) recom- Characteristics of Deicers mends these standards in Advisory Circulars. SAE in the Environment International provides the only numerical limits The primary environmental concerns with deicers related to environmental characteristics through are high organic content, resulting in high BOD, and its Aerospace Material Specification (AMS) 1424, aquatic toxicity. Some fate and transport characteris- which requires Type I fluids to have 50% lethal tics of deicers are understood, but many others have concentrations (LC50) greater than or equal to not been extensively studied. Most research on the 4,000 mg/l for several organisms.3 No guidance is fate and transport of deicers has focused on FPDs and, provided for the BOD content of deicers. to a lesser extent, on benzotriazole-derived corrosion inhibitors and alkylphenol ethoxylate (APE) surfac- 1 tants. The components with environmental charac- Available at http://184.108.40.206/Main/Public/Blurbs/155 teristics that are not well understood include dyes, 765.aspx or at the TRB website (www.trb.org) by searching thickeners, pH modifiers, defoamers, other corrosion "ACRP Web-Only Document 3" 2 Available at http://www.trb.org/Publications/Blurbs/163310. inhibitors and surfactants, and even the FPD used in aspx or at the TRB website (www.trb.org) by searching "ACRP pavement deicers. Web-Only Document 8" FPD degradation rates are dependent on envi- 3 LC50 is the highest concentration at which 50% of the tested or- ronmental factors such as medium, temperature, ganisms do not survive the test period. travel time, and established bacterial communities in soils and receiving waters. Benzotriazoles and APE 2
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have been studied at a small number of airports, but cific literature. Triazoles are unlikely to completely the bulk of research on APE has been in waste- biodegrade in typical biological treatment systems. water treatment and not in situations where these In sufficient concentration, they have been shown surfactants are released directly to receiving waters to inhibit degradation of other organic compounds, without being treated. Benzotriazoles stay mostly in thereby decreasing treatment effectiveness of spent solution but have been detected in soils near deicing deicers. Recent research indicates that the effective- activities. Benzotriazoles have proven to degrade ness of different treatment strategies varies, with slowly or not at all in the environment. Of several conventional activated sludge the least effective, different pathways, some APE degradation products membrane bioreactors more effective, and ozonation are more toxic than their parent compounds, express resulting in complete mineralization of benzotriazole endocrine disruption potential, and have potential and 4- and 5-methyl-1H-benzotriazole. for sorption to sediment particles and persistence in benthic sediments. Operational and Infrastructure Assessing the aquatic toxicity of deicers is a com- Considerations plicated issue owing to several different factors. First, toxicity in ADFs and AAFs is due primarily to pro- Potential impacts on aircraft operations and infra- prietary additives, and the chemical identities of most structure were identified in the literature. PDMs based of these additives are treated by the manufacturers as on potassium formate and potassium acetate have confidential business information. Second, different been identified as potential contributors to corrosion formulations have different degrees of toxicity, so dif- of cadmium-plated electrical connectors in the ferent effluents with similar glycol concentrations Boeing 737 New Generation aircraft and to acceler- may have very different levels of toxicity. Third, ated catalytic oxidation of carbon composite brake different ADF and AAF formulations have different components. In both cases, potassium-based PDMs concentrations of glycol, again posing complications were in widespread use prior to material changes in to interpreting chemical analysis from effluent sam- the newer aircraft involved. Changes to components ples. Last, the fate and transport characteristics of and maintenance procedures, including Boeing's rec- additives are not necessarily the same as those of ommended practice to eliminate cadmium corrosion glycol, so glycol concentration and glycol surrogates through the use of corrosion-inhibiting compound such as chemical oxygen demand (COD) and BOD (CIC) on electrical connectors, have eliminated or cannot be used as reliable indicators of additive con- minimized the corrosion reactions. SAE G-12 and air- craft manufacturers have specific task groups work- tent in effluents. ing on these important issues. Conclusions from the literature indicate that Increased failure rates of airfield electrical com- research is necessary to better understand toxicity in ponents were also thought to be linked to potassium ADF and AAF formulations and deicer runoff; acetate PDMs. It was subsequently found that poorly however, available data indicate that the most likely maintained systems allowed PDM entry. Corrective sources of toxicity in PDMs are the FPDs. actions and improved products and components have greatly reduced or eliminated the problems. Characteristics of Deicers in Wastewater Reports of pavement deterioration, including Treatment Systems degradation and disintegration, softening and strip- ping effects, and scaling and surface cracking were The most commonly used FPDs (propylene gly- determined to be a result of alkali-silica reactivity col, ethylene glycol, acetates, and formates) are read- linked to pavement deicers based on potassium ily biodegradable under both aerobic and anaerobic acetate. Subsequent investigation determined that methanogenic conditions. Because of the ease by other factors, especially construction methods and which FPDs can be biodegraded, their primary materials, can be used to mitigate these issues. impact on biological treatment systems is increased Residues from Type II and Type IV fluids may organic load. form on aerodynamically quiet areas on aircraft, and Available literature indicates that nonylphenol if not removed by deicing or anti-icing, the residue ethoxylates (NPEs) may be degraded through bio- may absorb rainwater (rehydrate) and subsequently logical treatment, but reported details on degradation freeze, restricting the movement of unpowered flight and byproduct generation vary depending on the spe- control surfaces. 3