Advanced Oxidation Kinetics of Aqueous Trialkyl Phosphate Flame Retardants and Plasticizers

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• 作者：Michael J. Watts ; Karl G. Linden
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：April 15, 2009
• 年：2009
• 卷：43
• 期：8
• 页码：2937-2942
• 全文大小：162K
• 年卷期：v.43,no.8(April 15, 2009)
• ISSN：1520-5851

文摘

Trialkyl phosphate esters are a class of anthropogenic organics commonly found in surface waters of Europe and North America, due to their frequent application as flame retardants, plasticizers, and solvents. Four trialkyl phosphate esters were evaluated to determine second-order rates of reaction with ultraviolet- and ozone-generated •OH in water. Tris(2-butoxyethyl) phosphate (TBEP) was fastest to react with •OH (k_OH,TBEP = 1.03 × 10¹⁰ M⁻¹ s⁻¹), followed sequentially by tributyl phosphate (TBP), tris(2-chloroethyl) phosphate (TCEP), and tris(2-chloroisopropyl) phosphate (TCPP) (k_OH,TBP = 6.40 × 10⁹, k_OH,TCEP = 5.60 × 10⁸, and k_OH,TCPP = 1.98 × 10⁸ M⁻¹ s⁻¹). A two-stage process was used to test the validity of the determined k_OH for TBEP and the fastest reacting halogenated alkyl phosphate, TCEP. First, •OH oxidation of TCEP and TBEP, in competition with nitrobenzene was measured in ozonated hydrogen peroxide solutions. Applying multiple regression analysis, it was determined that the UV/H₂O₂ and O₃/H₂O₂ data sets were statistically identical for each compound. The subsequent validated k_OH were used to predict TCEP and TBEP photodegradation in neutral pH, model surface water after chemical oxidant addition and UV irradiation (up to 1000 mJ/cm²). The insignificant difference between the predicted TBEP and TCEP photodegradation and a best-fit of the first-order exponential decay function to the observed TBEP and TCEP concentrations with increasing UV fluence was further evidence of the validity of the determined k_OH. TBEP oxidation rates were similar in the surface waters tested. Substantial TCEP oxidation in the model surface water required a significant increase in initial H₂O₂.