An azide-based sampler for monitoring abiotic reduction of chlorinated solvent contaminants in groundwater

There is significant interest in monitoring abiotic decomposition of chlorinated solvents at contaminated sites due to large uncertainties regarding the rates of abiotic attenuation of trichloroethylene (TCE) and perchloroethylene (PCE) under field conditions. In this study, an innovative passive sampling tool was developed to quantify acetylene, a characteristic product of abiotic reduction of TCE or PCE, in groundwater. The sampling mechanism is based on the highly specific and facile click reaction between acetylene and an azide compound to form a biologically and chemically stable triazole product. In preliminary investigations using static solutions of acetylene, a strong linear relationship was observed between the quantity of azide formed and the concentration of aqueous acetylene. The product yield was stable within a solution pH range of 5-9 and in the presence of common groundwater salts or gaseous hydrocarbon molecules. Based on these results, a prototypical acetylene passive sampler was constructed, which featured a piece of PDMS membrane embedded with an azide compound and Cu(0) catalyst to form a reactive phase for acetylene capture. The sampler was evaluated in microcosm reactors containing TCE and an abiotic reductant (viz., sulfur-treated iron powder). Acetylene produced during abiotic dechlorination of TCE was effectively captured by the sampler, and the quantity of the product recovered from the sampler correlates with the amount of TCE converted. The specificity and sensitivity of the proposed acetylene sampler proffers a new diagnostic tool for monitoring abiotic degradation of chlorinated ethenes at complex contamination sites.