HR: 1340h
AN: H33E-1690    [Abstracts]
TI: Enriched Perchlorate and Relationship with Other Major Anions in Atmospherically Derived Deposits of Nitrate of the Mojave Desert
AU: * Jackson, W A
EM: andrew.jackson@ttu.edu
AF: Texas Tech University, MS 41023, Lubbock, TX 79409, United States
AU: Anderson, T A
EM: todd.anderson@TIEHH.ttu.edu
AF: Texas Tech University, MS 41023, Lubbock, TX 79409, United States
AU: Orris, G J
EM: greta@espri.arizona.edu
AF: U.S. Geological Survey, 520 N. Park Ave., Suite 355, Tucson, Az 85719, United States
AU: Böhlke, J K
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 431 National Center 12201 Sunrise Valley Drive, Reston, VA 20192, United States
AU: Rajagopalan, S
EM: srinath.rajagopalan@ttu.edu
AF: Texas Tech University, MS 41023, Lubbock, TX 79409, United States
AB: Perchlorate has been known to be present in salt deposits from the Atacama Desert for over a century. Its presence is typically associated with NO₃^-, although relatively few samples from the Atacama have been evaluated. Perchlorate in the Atacama nitrate deposits has a substantial Δ¹⁷O anomaly strongly suggesting an atmospheric origin, or at least a production mechanism involving O₃ (e.g. surface oxidation). Reports of natural ClO₄^- in North America have been increasing recently. These reports indicate that ClO₄^- is widely distributed in groundwater and in unsaturated surface soils. However, most reported occurrences have been at low concentrations. Because of the association of ClO₄^- with NO₃^- in the Atacama deposits, previously identified NO₃^- deposits with atmospheric components in North America were investigated for the occurrence of ClO₄^-. These nitrate deposits are located in the Death Valley region of the Mojave Dessert and have been previously characterized with respect to chemical composition and isotopic ratios of N, O, and S. Perchlorate concentrations varied but, in general, were significantly higher (1 mg/kg) than in most other reported occurrences. Although the Mojave deposits were enriched in ClO₄^-, the relative molar ratios of NO₃^- or Cl^- to ClO₄^- were significantly higher (10⁵-10⁶ and 10⁴ for Cl^-/ClO₄^- and NO₃^-/ClO₄^- respectively) than those of the Atacama deposits (1-10² and 10¹-10² for Cl^-/ClO₄^- and NO₃^-/ClO₄^-, respectively ) even for samples highly enriched in NO₃^- (1~5% of soil by weight). NO₃^-/Cl^- molar ratios are roughly similar between the deposits (0.83 and 0.2-0.8 for Atacama and Death Valley, respectively) if similar grades of NO₃^-ores (1-20%) are compared. Molar ratios of Cl^-/ClO₄^- and NO₃^-/ClO₄^- in the Mojave deposits are similar to those reported for both groundwater and unsaturated zone samples in the U.S. attributed to natural sources. Possible reasons for the large discrepancies in molar ratios between the Chilean and North American samples include differences in post depositional segregation or degradation, or differences in production mechanisms and/or extent of ClO₄^- production relative to other atmospherically deposited species.
DE: 1065 Major and trace element geochemistry
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
DE: 1838 Infiltration
SC: Hydrology [H]
MN: 2007 Fall Meeting