Final Report: Environmental Photochemistry of Polybrominated Diphenylethers

EPA Grant Number: R830398
Title: Environmental Photochemistry of Polybrominated Diphenylethers
Investigators: Jafvert, Chad T. , Filley, Timothy , Hua, Inez
Institution: Purdue University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2003
Project Amount: $234,586
RFA: Futures Research in Natural Sciences (2001) RFA Text |  Recipients Lists
Research Category: Futures , Ecological Indicators/Assessment/Restoration , Land and Waste Management , Hazardous Waste/Remediation

Objective:

The overall objective of this research project was to investigate the photochemical transformation of several polybrominated diphenyl ether (PBDE) congeners under conditions of environmental relevance. Specific objectives include: (1) examining environmental matrix and media influences on photolytic transformation rates and product distributions of decabromodiphenyl ether (BDE209); (2) identifying organic products by gas chromatography/mass spectrometry; (3) conducting experiments of sufficient length to evaluate reaction product mass balances; and (4) testing solar photo-reactivity of major BDE209 products (tetra- through nona-congeners).

Summary/Accomplishments (Outputs/Outcomes):

The results of this research project have been documented in four manuscripts. Three have been published in scientific journals or are in press, and the fourth will be submitted in early 2006. In Bezares-Cruz, et al. (2004), BDE209 and several other PBDE congeners, dissolved in hexane, were irradiated with sunlight at West Lafayette, Indiana, (40° 29’ N, 86° 59.5’ W). In sunlight, BDE209 decayed within minutes with only 30 percent remaining after 5 minutes with an observed first-order rate constant (kobs) for solar photolysis of kobs = 1.86 x 10-3 sec-1 and a wavelength-averaged (300-350 nm) quantum yield of 0.47. Within a solar exposure period of 34 hours, BDE209 transformed to less brominated PBDEs ranging from nona- to tribromodiphenyl ethers. For example, after 6.1 hours of solar irradiation on July 2, 2003, 3 (of 3) nona-, 6 (of 12) octa-, 5 (of 24) hepta-, 11 (of 42) hexa-, 8 (of 46) penta-, 6 (of 42) tetra-, and 3 (of 24) tribromodiphenyl ethers were identified. In total, 43 PBDEs were detected within the 34-hour irradiation period, and the structures of more than 20 specific congeners were identified via matching with the mass spectra of standard compounds. Products-intermediates with identical retention times as standards and similar mass spectra include: BDE209 (parent compound), 208, 207, 206, 197, 196, 183, 154, 153, 138, 100, 99, 85, 77, 71, 49, 47, 37, and 28.

Photodebromination of BDE209 adsorbed onto six different solid matrices was investigated in sunlight and by irradiation with 350 ± 50 nm lamps (4 lamps at 24 watts each; Ahn, et al., 2005). After 14 days of lamp irradiation BDE209 degraded with a half life of 36 and 44 days, respectively, on montmorillonite and kaolinite, with much slower degradation occurring when sorbed on organic carbon-rich natural sediment (τ1/2=150 days). The half-lives of BDE209 sorbed on montmorillonite and kaolinite were 261 and 408 days, respectively. Under both irradiation schemes, no significant loss of BDE209 occurred when sorbed to metal oxides. In the presence of montmorillonite and kaolinite, numerous lesser brominated congeners (tri- to nonabromodiphenyl ethers) were produced. These results suggest that photodegradation of BDE209 on mineral aerosols during long-range atmospheric transport may be an important fate process for BDE209 in the environment.

The dark reaction of BDE209 with birnessite (δ-MnO2) was investigated in water-tetrahydrofuran (water-THF) mixtures (Ahn, et al., submitted 2005). Loss of BDE209 was complete after approximately 10 hours at some water-THF ratios, again with the overall reaction proceeding through consecutive losses of bromine, forming less brominated congeners, including 47 and 99, and bromide ion in solution. The THF influences the reaction in two ways. First, it affects the partitioning of the brominated diphenyl ethers between the solid phase and solution; and second, it can be the hydrogen donor in the reductive debromination reaction. Experiments with deuterated water indicated that water was not the hydrogen donor, and the formation of succinic acid as a reaction product provides evidence that supports this statement. Using catechol, a natural reductant rather than THF, produced similar results, indicating that birnessite-mediated reductive debromination of BDE209 is likely to occur in nature.

The photodecay of BDE209 in aqueous humic acid solutions and in paraffin wax films also was examined (Bezares-Cruz, et al., in preparation). BDE209 (~80 μg/L) was dissolved in an aqueous solution of 82 mg/L Waskish River humic acid (from the International Humic Substance Society), and irradiated with solar light over a 125-day period (July 8-November 3, 2005). Samples were collected periodically until November 3, 2005. Decay of the parent compound required weeks, and by the end of the study period, the products of the reaction proceeded only to several of the octa-BDE congeners. The much slower reactivity compared to reactivity in hexane likely occurs as a result of: (1) the inner-filter effect of the humic acid; (2) the weaker hydrogen donor ability of the humic acid molecules compared to hexane; and (3) the lower reactivity of the brominated diphenyl ethers as a result of association with the humic acids in solution. DBE209 also was prepared in paraffin wax at 56 ppm and irradiates with both solar and lamp (λ = 350 ± 50 nm, 6 24-watt lamps) light. The paraffin wax was 80 to 90 percent weight/weight C20-C30 straight chain hydrocarbons. The paraffin wax was used to mimic organic coatings on exterior surfaces of the built-environment (i.e., windows, walls) where PBDEs can be expected to partition. After irradiation in late fall 2005 at 40.470 N, 86.990 W, samples were extracted with hexane and analyzed using gas chromatography/electron capture detector. Accumulation of nona-, octa-, hepta-, and hexa-BDEs was observed within the first 100 hours of irradiation with both light sources, whereas no decay occurred in dark control samples. The increased reaction rate in the paraffin wax compared to the humic acid solutions likely results from the improved hydrogen donor ability of the paraffin wax and the negligible inner filter effect of the wax at a wavelength of350 nm.

In the past, BDE209 has accounted for approximately 80 percent of the total global production of PBDEs. Although lesser brominated congeners, specifically some of the tetra- and penta- congeners, were manufactured in smaller quantities and have been routinely detected in the natural environment, BDE209 rarely is detected. The results of this research suggest that transformation of BDE209 does occur in the natural environment via photochemical and other abiotic processes, and that many of the congeners that are found in the environmental can be produced from photochemical and abiotic transformation of BDE209. The very low aqueous solubility of BDE209 results in its accumulation in natural organic materials, including aqueous humic substances and organic films. In some cases, this may reduce its ability to react; whereas in other cases, these materials may act as the essential hydrogen donor in the overall reductive dehalogenation reaction. Clearly, absorption of solar light within the wavelength range of approximately 300 to 350 nm leads to direct photoreduction of BDE209, producing as reaction intermediates and products lesser brominated congeners over periods of months to years. These findings help elucidate the fate of BDE209 in the environment.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 16 publications 4 publications in selected types All 4 journal articles
Type Citation Project Document Sources
Journal Article Ahn M-Y, Filley TR, Jafvert CT, Nies L, Hua I, Bezares-Cruz J. Photodegradation of decabromodiphenyl ether adsorbed onto clay minerals, metal oxides, and sediment. Environmental Science & Technology 2006;40(1):215-220. R830398 (Final)
R830251 (Final)
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  • Journal Article Ahn M-Y, Filley TR, Jafvert CT, Nies L, Hua I. Birnessite mediated debromination of decabromodiphenyl ether. Chemosphere 2006;64(11):1801-1807. R830398 (Final)
    R830251 (Final)
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  • Journal Article Bezares-Cruz J, Jafvert CT, Hua I. Solar photodecomposition of decabromodiphenyl ether: products and quantum yield. Environmental Science & Technology 2004;38(15):4149-4156. R830398 (Final)
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  • Supplemental Keywords:

    environmental fate, aquatic, brominated flame retardants, decabromodiphenylether, photochemistry, solar light, environmental chemistry, photolysis, debromination, quantum yield, humic substances,, RFA, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Contaminated Sediments, Environmental Chemistry, Restoration, Resources Management, Environmental Monitoring, Ecology and Ecosystems, Water Pollutants, Aquatic Ecosystem Restoration, Exp. Research/future, Futures, reducitve debromination, biodiversity, reductive debromination, photochemical transformation, contaminated sediment, flame retardants, PBDE, conservation, contaminant uptake, exploratory research, remediation, ecological pollutants, environmental stress, environmental rehabilitation, ecotoxicology, anaerobic biotransformation

    Relevant Websites:

    http://bridge.ecn.purdue.edu/~jafvert/ Exit
    https://engineering.purdue.edu/Engr/ Exit

    Progress and Final Reports:

    Original Abstract
  • 2002