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Staff Accomplishments

Clever chemistry corrals radioactive iodine

June 2006
Researchers from Pacific Northwest National Laboratory developed new methods to coax radioactive iodine from soil and groundwater, allowing scientists and regulators to measure this troublesome radionuclide. Both methods provide greater accuracy and less cost when hunting for iodine. Radioactive iodine is a byproduct of nuclear weapons development and natural processes. It remains radioactive for millions of years, moves easily in soil and groundwater, and at high levels can damage the thyroid. Several nuclear weapons and chemical manufacturing sites in the United States are contaminated with radioactive iodine. Pulling iodine from soil and waste samples The team successfully used the new fusion extraction method to liberate all of the radioactive iodine from soil samples at the Hanford Site, where plutonium was produced during World War II and the Cold War. By carefully measuring the radioactive iodine, researchers can accurately tell where and how much iodine is under the surface. The research team also used this method to accurately determine the iodine concentration in Hanford tank waste and in a glass sample that represents the tank waste's final treated form. In the fusion extraction method, PNNL's scientists first fuse the sample with a combination of potassium nitrate and potassium hydroxide. Next, they dissolve the sample in a solution of sulfuric acid and sodium bisulfite. The solution now contains all of the radioactive iodine from the sample, which can be measured (after precipitation of the iodine) using standard radioactive measurement equipment. "This simple and cost-effective technique can be applied to solid samples of varying matrixes with little or no adaptation," said project manager Chris Brown, a research scientist at PNNL. Simple, easy groundwater tests In the past, analyzing iodine in groundwater was a slow process that required liters of groundwater to be withdrawn from the soil. Then, laboratory technicians precipitated the iodine to a solid and measured the radioactivity. With this new method, scientists can analyze samples as small as one teaspoon. First, they inject the sample into a commercially available Perkin Elmer inductively coupled plasma mass spectrometer (ICP-MS) containing a dynamic reaction cell. This instrument measures minute amounts of iodine, less than 1 picocurie, as well as a range of metals. Next, the researchers mix in oxygen. Historically, xenon has been a problem when analyzing groundwater for iodine via ICP-MS. PNNL scientists use oxygen to remove the xenon interference, unlocking the ability to more effectively measure iodine. "This approach is a low-cost, high-throughput technique for the quantitative analysis of iodine-129 in groundwater samples at very low concentrations, below the current maximum contaminant level set by the Environmental Protection Agency," said Brown. The ICP-MS method can also be used on the solutions produced from PNNL's fusion method, without requiring separation and pre-concentration steps. "Combining the two methods increases productivity significantly and minimizes the potential for error," said PNNL's Terry Walton, Environmental Solutions lead. What's next? With the iodine tests successfully completed and several scientific journal articles published on the techniques, Brown and his research team are developing new ICP-MS analytical methods to measure ruthenium isotopes and technetium in groundwater and soil samples from the Hanford Site. Contacts: Walter Weimer, Process and Measurement Technology Product Line Manager or Terry Walton, Environmental Solutions Lead.

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