Perchlorate reconnaissance sampling in streams and groundwater in the Central and Southwestern U.S.
Experimentally determined holding times for environmental samples containing low levels of perchlorate
Sarah J. Stetson1,2, Richard B. Wanty1, and Stephen J. Kalkhoff3
1 U.S. Geological Survey, MS 973, Denver Federal Center, Denver, CO 80225
2 Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401
3 U.S. Geological Survey, PO Box 1230, Iowa City, IA 52244
Perchlorate ion (ClO4-) is an environmental contaminant of growing concern due to its potential negative human health effects, impact on aquatic and land animals, and widespread occurrence throughout the United States. The stability of perchlorate ion in common matrix water samples has not been thoroughly examined, and scientifically defensible holding times before analysis of perchlorate ion-bearing environmental samples and standards are unknown. In this study the long-term stability of perchlorate ion in deionized water, tap water, ground water, and surface water matrices was examined. Sample sets containing 1000, 100, 1.0, 0.5 and 0 mg/L perchlorate ion in deionized water and local tap water were formulated. A ground water and surface water with known perchlorate contamination were collected and filtered. The deionized and tap water samples were analyzed by ion chromatography for perchlorate ion concentration against freshly prepared standards every 24 hours for the first seven days, biweekly for the next four weeks, and periodically after that for a total of 30 weeks for the two low concentrations and a total of 34 weeks for the high concentrations. These samples were found to be stable for the duration of the study, allowing for holding times of at least 210 days. The perchlorate contaminated ground and surface water samples were also analyzed by ion chromatography and perchlorate ion is stable in them for at least 40 days. Ongoing studies are being conducted to determine the long term stability of perchlorate ion in these common environmental matrice.