HR: 1340h
AN: H43D-0402    [Abstracts]
TI: Stable Cl And O Isotope Ratios Of Anthropogenic And Natural Perchlorates
AU: * Beloso, A
EM: abelos1@uic.edu
AF: University of Illinois at Chicago, Earth and Environmental Sciences, MC-186, 845 W. Taylor St., Chicago, IL 60607 United States
AU: Sturchio, N C
EM: sturchio@uic.edu
AF: University of Illinois at Chicago, Earth and Environmental Sciences, MC-186, 845 W. Taylor St., Chicago, IL 60607 United States
AU: B\H{o}hlke, J
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 431 National Center, Reston, VA 20192 United States
AU: Gu, B
EM: gub1@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37381 United States
AU: Horita, J
EM: horitaj@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37381 United States
AU: Brown, G
EM: browngm1@ornl.gov
AF: Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37381 United States
AU: Hatzinger, P
EM: Paul.Hatzinger@shawgrp.com
AF: Shaw Environmental, Inc, 17 Princes Road, Lawrenceville, NJ 08648 United States
AB: Perchlorate (ClO$_{4}$$^{-}$) in aqueous systems, even in low concentrations, is recognized to have potential human health risks. The drinking and irrigation water supplies of millions of people in the U.S. have recently been found to be contaminated with perchlorate, and this problem continues to become even more widespread. Perchlorate, as a highly soluble and relatively inert anion, tends to persist over long time periods and its removal by conventional water treatment technologies is difficult and expensive. Many known sources of perchlorate contamination are anthropogenic, resulting from its extensive use as an oxidizer component in solid propellants for missiles, rockets, and fireworks. However, certain fertilizers derived from Chilean nitrate evaporate deposits are known to contain a low percentage of perchlorate ($<$0.5%) that may contaminate groundwater. New isotopic evidence provides insights on the possible natural sources of perchlorate in surface and ground waters. Stable isotope ratios of Cl and O can now be used to determine whether the source of perchlorates in a given area is natural or anthropogenic. Microbial perchlorate reduction has a large ($\sim$15 per mil) kinetic isotope effect, and this may be used to identify whether natural attenuation of perchlorate is occurring. Anthropogenic perchlorate salts in milligram amounts are readily analyzed for $^{37}$Cl and $^{18}$O isotopes. Extracting an isotopically measurable amount of perchlorate from natural waters, which are usually within ppb range of concentrations, is a challenge. But with the use of a new class of highly-selective bifunctional anion exchange resins, recovery of trace amounts of perchlorate for accurate isotopic analysis has been demonstrated. Isotopic characterization is being conducted on anthropogenic perchlorate reagents, natural perchlorate-bearing salt deposits, and perchlorate-bearing groundwaters. Significant and consistent isotopic differences in both the Cl and O isotope ratios between anthropogenic and natural perchlorate sources have been identified. Anthropogenic perchlorate has \delta$^{37}$Cl values between -3.1 and +1.3, and \delta$^{18}$O values between -24.7 and -16.1. In contrast, naturally-occurring perchlorate analyzed thus far has \delta$^{37}$Cl values between -14.5 and -11.8, and \delta$^{18}$O values between -9.3 and -4.2, as well as a significant $^{17}$O excess not seen in anthropogenic perchlorate. These distinct isotopic characteristics may indicate an atmospheric origin for natural perchlorate. Perchlorate extracted from groundwater samples can be clearly identified in terms of source. Stable isotope forensics will provide a powerful tool for understanding perchlorate occurrences and contamination in the environment.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting