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 (GC) combustion isotope ratio mass spectrometry, 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 methods. The delta C-13 value of the purified BDE-209 was determined using offline elemental analyzer isotope ratio mass spectrometry (EA/IRMS). This two-step method was applied to determine the delta C-13 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. Results The mean values of daily delta C-13 analyses of six replicates of a BDE-209 standard varied from -27.66 parts per thousand to -27.92 parts per thousand, with a standard deviation ranging from 0.07 parts per thousand to 0.16 parts 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 C-13 values of BDE-209. The delta C-13 values of BDE-209 gradually changed from -27.47 +/- 0.37 parts per thousand to -24.59 +/- 0.19 parts per thousand when 74% of the BDE-209 standard was degraded within 36 h. The estimated carbon isotope enrichment factor was -1.72 +/- 0.18 parts per thousand. Conclusions The two-step method based on HPLC and EA/IRMS avoids the thermal instability of BDE-209 in the 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.