Natural perchlorate has a unique oxygen isotope signature

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Perchlorate is known to be a minor component of the hyperarid Atacama Desert salts, and its origin has long been a subject of speculation. Here we report the first measurement of the triple-oxygen isotope ratios ( 18O/16O and 17O/16O) for both man-made perchlorate from commercial sources and natural perchlorate extracted from Atacama soils. We found that the δ18O values (i.e., normalized 18O/16O ratios) of man-made perchlorate were at -18.4 ± 1.2%, whereas natural perchlorate has a variable δ18O value, ranging from -4.5% to -24.8%. The δ18O and δ17O values followed the bulk Earth's oxygen isotope fractionation line for man-made perchlorate, but all Atacama perchlorates deviated from this line, with a distinctly large and positive 17O anomaly ranging from +4.2% to +9.6%. These findings provide a tool for the identification and forensics of perchlorate contamination in the environment. Additionally, they confirm an early speculation that the oxidation of volatile chlorine by O3 and the formation of HClO4 can be a sink (albeit a minor one) for atmospheric chlorine.

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Environmental Science and Technology

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