Web Release Date: June 6,
Widespread Natural Perchlorate in Unsaturated Zones of the Southwest United States
Department of Civil and Environmental Engineering, Texas Tech University, Lubbock, Texas 79409-1023, The Institute of Environmental and Human Health, Texas Tech University, Lubbock, Texas 79409-1163, U.S. Geological Survey, Tucson, Arizona 85719, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, Bureau of Economic Geology, University of Texas at Austin, Austin, Texas, 78713-8924, U.S. Geological Survey, Menlo Park, California 94025, and U.S. Geological Survey, Lakewood, Colorado 80225
Received for review December 1, 2006
Revised manuscript received March 29, 2007
Accepted May 1, 2007
Abstract:
A substantial reservoir (up to 1 kg ha-1) of natural perchlorate is present in diverse unsaturated zones of the arid and semi-arid southwestern United States. The perchlorate co-occurs with meteoric chloride that has accumulated in these soils throughout the Holocene [0 to 10-15 ka (thousand years ago)] and possibly longer periods. Previously, natural perchlorate widely believed to be limited to the Atacama Desert, now appears widespread in steppe-to-desert ecoregions. The perchlorate reservoir becomes sufficiently large to affect groundwater when recharge from irrigation or climate change flushes accumulated salts from the unsaturated zone. This new source may help explain increasing reports of perchlorate in dry region agricultural products and should be considered when evaluating overall source contributions.
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