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Table 8 Toxicity of TEA and its degradation products. 2. The final formulation consists of DEG as the FPD, with a basic additive package consist- Compound 96hr LD50 P. promelas ing of Tergitol L-64 surfactant, TEA corro- 1 Triethanolamine 11,800 mg/l sion inhibitor, and Carbopol EZ-4 thickener. 2 Diethanolamine 1,370 mg/l 3. Toxicity identification techniques used on 3 Ethanolamine 2,070 mg/l currently used formulations were successful 4 Acetaldehyde 36.8 mg/l in helping to improve the toxicity profile of alternative fluids. 4. The physical properties of the alternative Type IV formulations were affected by interactions surfactant should be the same as those for DEG. The between the surfactants and thickeners. degradation mechanism for the propylene oxide por- 5. Numerous potential alternative components tion of the surfactant's molecular structure is less were identified. certain. An examination of the aquatic toxicities for 6. The techniques used in identifying a less- possible degradation products indicates that they are toxic Type IV formulation have potential fairly toxic to rainbow trout. It is also possible that applicability to developing Type I formula- these products are toxic to bacteria, which could tions with reduced toxicity. partly account for reports of poor biodegradation. 7. There is no current evidence to suggest that the alternative FPD or thickener present sig- Triethanolamine nificant concerns relative to degradation path- ways and degradation products. Byproducts Triethanolamine is the proposed corrosion in- of the alternative surfactant and corrosion hibitor. It would typically be used in formulations at inhibitor may have greater aquatic toxicity less than 2% by weight. Degradation byproducts are than the parent products, but further inves- readily biodegraded and are not expected to persist in tigation is needed for their full evaluation. the environment. However, data on the aquatic toxic- DEG is preferred because of its lower freez- ity of TEA and its degradation products to P. prome- ing point and the resulting reduced risk of las indicate that the aquatic toxicity of the degradation residue formation. products is significantly higher than that of TEA (Table 8). Oxygen Demand Carbopol EZ-4 1. Theoretical oxygen demand is a good screen- Carbopol is the proposed thickener. It is a lightly ing criterion for oxygen demand of FPDs. The cross-linked poly(acrylic acid) polymer. Studies in COD results for FPDs compared well with the- the literature reported that Carbopol does not bio- oretical oxygen demand. degrade, but also showed it does not pass through 2. Conventional BOD tests produced unreliable municipal wastewater treatment facilities into receiv- results for some FPDs. The success of BOD ing waters because it adsorbs onto biomass and is testing was highly variable and dependent on removed with the biosolids during treatment. how well microorganisms acclimated to FPDs. 3. COD was the most useful metric in down- CONCLUSIONS selecting FPDs for oxygen demand. The reliance on COD was necessary because of General Conclusions the uncertainties encountered with BOD tests. 4. FPDs are the predominant source of oxygen 1. An alternative Type IV formulation was iden- demand in all deicer formulations. The rela- tified with significantly reduced toxicity com- tive concentrations of all other components pared to products in current use. The final are so small that any contribution to oxygen candidate formulation has aquatic toxicity val- demand is insignificant. ues that are greater by an order of magnitude 5. No candidate FPD was found with potential or more (less toxic) than the least toxic com- for improvement of environmental character- mercial Type IV products tested. istics compared to the least toxic Type I fluids 10
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and pavement deicer formulations in cur- each of the categories of FPD, surfac- rent use. tants, corrosion inhibitors, and thickeners. 6. DEG and glycerol were identified as promis- Identified candidates included 7 FPDs, ing alternative FPDs for Type IV fluid for- 11 surfactants, 9 corrosion inhibitors, and mulations. 6 thickeners. 7. Parameters such as molecular weight, freezing 2. Empirical observations are necessary to under- point depression, application rates, and trans- stand which components are responsible for port phenomena must be considered to gain a the toxicity of final formulations. comprehensive understanding of the poten- tial impact of PDMs on dissolved oxygen in Pavement Deicers receiving waters. 1. There was significant synergistic interaction be- Aquatic Toxicity tween sodium formate and tripotassium citrate that cannot be readily explained. Resolution of 1. Screening-level toxicity testing identified these counterintuitive results was beyond the potentially viable alternative components in scope of this investigation. 11
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