HR: 1340h
AN: H33E-1697    [Abstracts]
TI: Perchlorate in the Hydrologic Cycle - An Overview of Sources and Occurrence
AU: * Stonestrom, D A
EM: dastones@usgs.gov
AF: USGS, 345 Middlefield Rd (MS-421), Menlo Park, CA 94025, United States
AU: Jackson, W
EM: andrew.jackson@ttu.edu
AF: Texas Tech University, Mail Stop 41023, Lubbock, TX 79409, United States
AU: Mayer, K
EM: mayer.kevin@epa.gov
AF: USEPA, 75 Hawthorne Street, San Francisco, CA 94105, United States
AU: Orris, G J
EM: greta@usgs.gov
AF: USGS, 520 N. Park Avenue, Tucson, AZ 85719, United States
AB: Perchlorate (ClO₄^-) in water and food is of concern due to deleterious health affects associated with hypothyroidism. The presence of widespread perchlorate in 0-to-28 ka-old pristine ground water of the Middle Rio Grande Basin (Plummer et al., 2006, ES&T, DOI:10.1021/es051739h), in ground water >1 mile from agricultural activities in the Southern High Plains (Rajagapolan et al., 2006, ES&T, DOI:10.1021/es052155i), and in unsaturated zones throughout the arid and semiarid southwestern United States (Rao et al., 2007, ES&T, DOI:10.1021/es062853i) clearly indicates that perchlorate is a non-exotic component of the hydrologic cycle, at least in dry environments. The natural system has been greatly perturbed in places by human activities. Most anthropogenic inputs are associated with the manufacture and use of explosives and rocket fuel, providing concentrated sources of excess perchlorate to the hydrologic cycle. Perchlorate-containing fertilizers and irrigation provide dispersed sources within and down-gradient from agricultural areas. Natural sources include photochemically mediated reactions involving ozone at the land surface and in the lower atmosphere. A growing body of work indicates that a small, but persistent, meteoric source acting over thousands of years can explain observed accumulations of unsaturated-zone perchlorate in arid regions. In addition to meteoric sources, oxyanions produced during volcanogenic processes can include appreciable amounts of natural perchlorate. Terrestrial plants take up perchlorate in soil water, with some species of xerophytic succulents concentrating the anion to high levels. Similarly, perchlorate in marine plants indicates that perchlorate is part of marine biochemical cycles. Perchlorate-bearing marine sediments of late Tertiary age suggest that perchlorate has been part of global geochemical cycles for millions of years and, furthermore, can be preserved in the subsurface despite the nearly ubiquitous presence of perchlorate-reducing bacteria in natural environments. New methods involving various combinations of ion chromatography, mass spectroscopy, and molecular biology are providing improved tools for understanding perchlorate in natural and perturbed systems. With large-scale sampling underway, a better understanding of the sources, sinks, and transformations of perchlorate in the hydrologic cycle is starting to emerge.
DE: 1030 Geochemical cycles (0330)
DE: 1831 Groundwater quality
DE: 1834 Human impacts
DE: 1875 Vadose zone
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2007 Fall Meeting