Compound‐specific carbon isotope analysis for mechanistic characterization of debromination of decabrominated diphenyl ether

RATIONALE: Decabrominated diphenyl ether (BDE-209) is a notorious persistent organic pollutant widely found in the environment. Developing a compound-specific isotope analysis (CSIA) method is much needed in order to trace its transport and degradation processes and to evaluate the effectiveness of the remediation of BDE-209 in the environment. However, the conventional CSIA method, i.e., gas chromatography-combustion oven-isotope ratio mass spectrometry (GC/C-IRMS), is not appropriate for BDE-209 because of its high thermal instability and incomplete combustion. METHODS: We developed a high-performance liquid chromatography (HPLC) method for the separation and purification of BDE-209 that prevents its thermal reactivity as occurred in prior GC-based method. The delta(13) C value of the purified BDE-209 was determined by offline elemental analyzer-isotope ratio mass spectrometry (EA/IRMS). This two-step method was applied to determine the delta(13) C values of BDE-209 in two commercial samples and to characterize carbon isotope fractionation associated with the debromination of BDE-209 via nanoscale zero valent iron (nZVI). RESULTS: The mean values of daily delta(13) C analyses of six replicates of a BDE-209 standard varied from -27.66 per thousand to -27.92 per thousand, with a standard deviation ranging from 0.07 per thousand to 0.16 per thousand, indicating a good reproducibility of EA/IRMS. The EA/IRMS analysis of the purified BDE-209 standard indicated no obvious isotope fractionation during the sample purification. The impurity content in commercial BDE-209 samples may contribute additional variation of the delta(13) C values of BDE-209. The delta(13) C values of BDE-209 gradually changed from -27.47 +/- 0.37 per thousand to -24.59 +/- 0.19 per thousand when 74% of BDE-209 standard was degraded within 36 hours. The estimated carbon isotope enrichment factor (epsilonc ) was -1.72 +/- 0.18 per thousand. CONCLUSIONS: The two-step method based on HPLC and EA/IRMS avoids the thermal instability of BDE-209 in traditional CSIA method. It offers a novel approach for elucidating the degradation mechanisms of BDE-209 in the environment and for source identification in contaminated sites.