Iodine has one stable isotope and one comsogenic/anthropogenic isotope. ¹²⁹I, the cosmogenic isotope, can be used to date groundwaters from 3 million to 80 milllion years old and trace groundwater flow.

• Cost of Analysis
  
• Origin
  
• Measurement Techniques
  
• Hydrological Applications
  
• References and Further Reading
• Internet Resources

Cost of Analysis (return to top)

Accelerator Mass Spectrometry (AMS):
$200 for batch processing plus $175 to $350 for analysis (depending on precision required).

(See, for example, the Purdue Rare Isotope Measurement Laboratory (PRIME Lab) for more information)

(See our AMS page for more information about the technique)

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Anthropogenic sources
Anthropogenic sources are responsible for the majority of ¹²⁹I in the atmosphere, particularly the chemical reprocessing of irradiated fuel from nuclear power reactors. Anthropogenic ¹²⁹I is mainly a fission product of ²³⁵U and ²³⁹Pu. The isotopic ratio increased in some parts of the world in the 1960's due to above ground nuclear testing. The ¹²⁹I/I ratio in the atmosphere increased to ~10^-7, and has been as high as 10^-4.

Release of ¹²⁹I also has occurred by accident. In April 1986, Chernobyl Reactor 4 in the Ukraine experienced a series of explosions that destroyed the reactor core. Radioactive xenon, iodine, cesium, krypton, and tellurium were released into the environment for nine days.

Measurement Techniques (return to top)

Initially, ¹²⁹I/I ratios were measured by ß^- decay counting, neutron activation to ¹³⁰I, and negative-ion mass spectrometry (Delmore 1982). Now they are typically measured with accelerated mass spectrometry, which provides higher precision with a smaller sample size. Nevertheless, because of the normally low concentration of ¹²⁹I, 5 to 10 liters of water, and 300 to 500 grams of ice are normally required for this analysis.

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1. The estimate of the initial atmospheric ratio is uncertain due to shifts in production rates over time. A possible solution that has been suggested is to measure the ratio in marine sediments, coral, peat and organic soils.

2. Sources of ¹²⁹I and stable iodine are different. The transformation and equilibration rates from these sources to waters need to be estimated.

3. Old groundwater in contact with uranium-bearing minerals may result in ¹²⁹I from spontaneous fission of ²³⁸U. The rate of release is dependent on the contact area and porosity.

4. The release of stable iodine from sediments or fluid inclusions must be estimated.

5. The amount of ¹²⁹I released by volcanic emissions is not known and cannot be separated from the overall atmospheric production of ¹²⁹I.

6. ¹²⁹I is a potentially useful tracer of groundwater contamination from nuclear facilities. However, studies indicate that it may bind with organic compounds, limiting its use. For more information see I. Clark's "Partitioning of ¹²⁹I in the Environment"

References and Further Reading (return to top)

• Clark, I., and P. Fritz, Environmental Isotopes in Hydrogeology, Lewis Publishers, Boca Raton, 1997.
  
  
• Delmore, J.E., Isotopic analysis of iodine using negative surface ionization, Int. J. Mass Spectrometry and Ion Phys. 43: 273-281, 1982.
  
  
• Fabryka-Martin, J., Iodine-129 as a groundwater tracer, in Radioactive tracers in Hydrogeology, edited by P.G. Cook and A.L. Herczeg, 504-510, Kluwer Academic Publishers, Boston, 2000.
  
  
• Fontes, J.C., and J.N. Andrews, Accelerator mass spectrometry in hydrology, Nucl. Instrum. Phys. Res. B92, 367-375, 1994.
  
  
• Kocher, D.C., A dynamic model of the global iodine cycle and estimation of dose to the world population from releases of iodine-129 to the environment, Environ. Int. 5, 15-31, 1981.
  
  
• Martin, J.K., S.N. Fabryka, and D. Davis, Applications of ¹²⁹I and ³⁶Cl in hydrology, Nucl. Instrum. Meth. Phys. Res. B29, 361-371, 1987.
  
  
• Paul, M., D. Fink, G. Hollos, A. Kaufman, W. Kutschera, and M. Magaritz, Measurement of ¹²⁹I in the environment after the Chernobyl reactor accident, Nucl. Instrum. Meth. Phys. Res. B29, 341-345, 1987.
  

Internet Resources (return to top)

USGS Periodic Table - Iodine

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