Determination of the Rates and Mechanism of the OH-initiated Oxidation of Brominated Diphenyl Ethers in the AtmosphereEPA Grant Number: F5B20303
Title: Determination of the Rates and Mechanism of the OH-initiated Oxidation of Brominated Diphenyl Ethers in the Atmosphere
Investigators: Raff, Jonathan D.
Institution: Indiana University
EPA Project Officer: Packard, Benjamin H
Project Period: July 21, 2005 through September 30, 2006
Project Amount: $89,172
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Brominated diphenylethers (BDEs) are flame retardants produced in large quantities (70,000 metric tons) and added to polymers used to fabricate materials for electronics, textiles, construction, and other applications. It is now clear that BDEs are migrating from the products in which they are used and enter the environment and people. Their volatility and persistence make them susceptible to atmospheric transport and their structural resemblance to polychlorinated diphenyls (PCBs) and dibenzo-p-dioxins (PCDDs), has raised concern that they may be mutagens and endocrine disruptors. Despite recent measures to limit their use, there is still concern over the present levels of BDEs in the environment, which in many cases rival those of PCBs. At the moment, little is understood about how long these chemicals will remain in the environment, and only recently has work started to address our understanding of their major sinks or transformation processes. These studies have focused almost solely on photolysis as a degradation for pathway for BDE degradation in water or other solvents. Extensive atmospheric chemistry research has established that chemical reactions with OH radicals (OH) are the dominant loss processes for most organic compounds in the atmosphere. Surprisingly, gas-phase OH reaction rate constants have not yet been determined for BDEs. This research will attempt to address this deficiency.
The specific goals of this research are to:
- Measure the rate constants for the BDE-OH reaction in the gas-phase as a function of temperature;
- identify and quantify the products that arise from the reaction of OH with BDEs;
- attempt to establish a link between laboratory scale studies and real atmospheric reactions by verifying the presence of BDE-OH reaction products in air samples.
The OH reaction rate constants for BDE congeners with 1-4 bromines will be measured with an instrument featuring a small-volume (190 mL) quartz reaction chamber housed in a GC oven (to control temperature) and coupled to a mass spectrometer. A typical experiment will proceed as follows: A BDE congener and a reference compound having similar OH reactivity are injected into a reaction cell containing an OH-radical source (hydrogen peroxide or methyl nitrite) and an atmosphere of helium or air. Hydroxyl radicals will be generated by irradiation of the reaction mixture and the mass spectrometer (operating in selected ion monitoring mode) will measures the decay of unique m/z values of the reactants. Rate constants will be determined using the relative rate method. Experiments will be conducted over a temperature range of 253-373 K to ensure adequate PBDE vapor pressure and increase instrument sensitivity. Room temperature rate constants will be obtained by extrapolation from the high temperature measurements. Products studies will be conducted by solvent extracting the reaction chamber and subsequent analysis using GC/MS. Air samples from the Integrated Atmospheric Deposition Network (IADN) will be analyzed via GC/MS to search for evidence of PBDE reaction products in the atmosphere.
Reactions with OH radical should be a significant loss process for BDE congeners as they are for PCBs (polychlorinated biphenyls). The OH rate constants measured in this research will be used with air-particle partition coefficients to model the congener profiles of BDE in air and sediment samples. We expect these results to contribute to a more complete mass balance of BDEs in the environment. In addition, these results will help us determine if atmospheric degradation of BDEs is a source of polybrominated dioxins and dibenzofurans to the environment.