Natural Perchlorate Has a Unique Oxygen Isotope Signature

Huiming Bao*
Department of Geology & Geophysics, E235 Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, Louisiana 70803
Baohua Gu
Environmental Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37381
Environ. Sci. Technol., 2004, 38 (19), pp 5073–5077
DOI: 10.1021/es049516z
Publication Date (Web): August 24, 2004
Copyright © 2004 American Chemical Society
*

 Corresponding author phone:  (225)578-3419 (office), −3413 (lab); e-mail:  bao@lsu.edu.

Abstract

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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History

  • Published In Issue October 01, 2004
  • Received for review March 30, 2004
    Revised manuscript received July 7, 2004
    Accepted July 19, 2004

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