2005 Progress Report: Anaerobic Microbial Reductive Debromination of Polybrominated Diphenyl EthersEPA Grant Number: R830251
Title: Anaerobic Microbial Reductive Debromination of Polybrominated Diphenyl Ethers
Investigators: Nies, Loring , Ahn, Mi Youn , Filley, Timothy , Tokarz, John A.
Current Investigators: Nies, Loring , Ahn, Mi Youn , Filley, Timothy
Institution: Purdue University
EPA Project Officer: Lasat, Mitch
Project Period: August 12, 2002 through August 13, 2004 (Extended to September 1, 2006)
Project Period Covered by this Report: August 12, 2004 through August 13, 2005
Project Amount: $230,795
RFA: Futures Research in Natural Sciences (2001) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Ecological Indicators/Assessment/Restoration , Hazardous Waste/Remediation
The overall objective of this research project is to determine the extent to which decabromodiphenyl ether (BDE-209) will undergo reductive debromination in anaerobic sediments. Based on data regarding the environmental occurrence of polybrominated diphenyl ethers (PBDEs), as well as knowledge about the reductive dehalogenation of polychlorinated biphenyls, polybrominated biphenyls, and polychlorinated dibenzo-dioxins, we postulate that BDE-209 will undergo reductive debromination producing less brominated, more bioavailable and toxic PBDE congeners. To obtain the most complete picture possible of the anaerobic fate of PBDEs, we will conduct sediment microcosm studies and parallel abiotic biomimetic dehalogenation studies on the highly brominated BDE-209, the lesser brominated 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47), and 2,2’,4,4’,5-pentabromodiphenyl ether (BDE-99). BDE-47 and BDE-99 are two PBDE congeners that are being detected in the biosphere in increasing concentrations.
To determine whether reductive debromination of BDE-209 in natural anaerobic sediments could be responsible for some portion of the flux of lesser brominated penta- and tetra-PBDEs into the biosphere, parallel experiments were conducted involving a cosolvent enhanced abiotic biomimetic reducing system and standard anaerobic sediment microcosms. In the biomimetic system, reductive debromination occurred at rates proportional to bromine substitution level with a BDE-209 half-life of 18 seconds (Figure 1) and a BDE-47 half-life of almost 60 days. In sediment microcosms after approximately 3.5 years of anaerobic incubation at room temperature (22 °C), the mole fraction of BDE-209 decreased by more than 12 percent, with a corresponding increase in nona-, octa-, hepta-, and hexa-PBDEs (Figure 2). The calculated laboratory half-life of BDE-209 was well over a decade and in good agreement with the predicted value obtained from the biomimetic experiment. Nine new PBDE congeners appeared in sediment microcosms as products of reductive debromination, but the terminal debromination products of BDE-209 are currently unknown. We can conclude with certainty that BDE-209 can undergo sequential anaerobic reductive dehalogenation to less brominated congeners. It is important to determine if this transformation is a significant source of lesser brominated PBDEs to the environment.
Figure 1. Reductive Debromination of BDE-209 in a Cosolvent Enhanced Biomimetic System. Starting Material (A) and Reactive at 24 Hours (B).
Figure 2. Mole Fraction Distribution of BDE-209 after 3.5 Years Incubation in Anaerobic Sediment Microcosms. All congeners are shown in panel A, and only congeners less than 10 percent Mole Fraction are shown in panel B.
The photodebromination of BDE-209 that adsorbed onto six different solid matrices was investigated in sunlight and by irradiation with 350 ± 50 nm lamps (4 lamps at 24 watts each). After 14 days of lamp irradiation, BDE-209 degraded with a half-life of 36 and 44 days, respectively, on montmorillonite or kaolinite, with much slower degradation occurring when sorbed on pond sediment (t1/2=150 days). In late summer and fall sunlight (40.5 °N, elevation 600 ft), the half-lives of BDE-209 that sorbed on montmorillonite and kaolinite were 261 and 408 days, respectively. Under both irradiation schemes, no significant loss occurred when sorbed to aluminum hydroxide, iron oxide (ferrihydrite), or manganese dioxide (birnessite). Upon exposure to both lamp and solar light, and in the presence of montmorillonite and kaolinite, numerous lesser brominated congeners (tri- to nona-bromodiphenyl ethers) were produced. Nearly identical product distribution was evident on montmorillonite and kaolinite. Dark control experiments for each mineral showed no disappearance of BDE-209 or appearance of degradation products (Figure 3). These results suggest that photodegradation of BDE-209 on mineral aerosols during long-range atmospheric transportation may be an important fate process for BDE-209 in the environment.
Figure 3. GC-ECD Chromatograms of Concentrated Dark Control (A) and Sunlight Irradiated Kaolinite (B) and Montmorillonite (C) Samples at 56 Days. The retention time of BDE-209 is 88.7 min (off-scale), and the nonabromodiphenylethers within the dark control are present in the stock material. Selected peaks are identified.
We will complete two manuscripts for publication and schedule a meeting with our Project Officer to discuss our findings.