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 Donald L. Macalady2

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

Perchlorate, a component in rocket fuels, fireworks, and some fertilizers, has been detected in many water supplies throughout the country. Because of its presence in drinking waters such as Lake Mead, the Colorado River, and various drinking water supplies, perchlorate has become a significant public health concern. It has been placed on the US EPA’s Contaminant Candidate List, the list of potentially harmful drinking water contaminants for which more data is needed. Reliable, sensitive methods for detecting perchlorate in drinking water, food, and tobacco are presently under development. However, the stability of perchlorate in water samples has not been thoroughly examined, so that scientifically defensible holding times of perchlorate-bearing samples and standards is unknown. In this study the long-term stability of perchlorate standards in deionized water and in a common water matrix are determined.

Sets of samples containing 1000, 100, 10, 1, 0.5, and 0.1 mg/L perchlorate in deionized water and also in local tap water were formulated. These samples were analyzed for perchlorate concentration against freshly prepared standards every 24 hours for the first seven days, biweekly for the next four weeks, and weekly after that for a total of 25 weeks. They were analyzed using a Dionex ion chromatograph system with an AG16/AS16 columns at a flow rate of 1.25 ml/min, 35 mM KOH eluent, and 500 ml injection loop. The results for this 6-month study will be presented, with a recommendation for maximum holding times of perchlorate samples after collection.