Analytical Research: Selenium and Mercury Content of the Great Salt Lake

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Analytical ResearchSelenium and Mercury
Contentof the Great Salt Lake

• Alan Pannier
• Chris Glezos

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Rationale

• Determine the concentration of mercury and
  selenium in the Great Salt Lake
• Gain insight as to how selenium and mercury
  circulate through the ecosystem and the effects
  caused by each.

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Samples
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Origination

• Recent hypothesis show a possibility of the toxic
  mercury found in the Great Salt Lake to be a
  byproduct of Nevada gold mines.
• Kenecott is investigating the possibilities of
  dumping selenium into the Great Salt Lake from
  contaminated ground water throughout the valley.

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Potential Hazards

• Methyl-mercury bioaccumulates, thus causing
  potential for neurological and kidney disease,
  loss of motor control, as well as death.

• Plants as well as birds can accumulate large
  amounts of selenium potentially causing wildlife
  toxicity in the ecosystem.

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Mercury Analysis

• Initial tests have shown that the amount of
  mercury present in the Great Salt Lake is so
  small it is undetectable using our equipment and
  methodology.
• 45 ppt of total mercury or 25 ppt of methyl
  mercury was found to be in the Great Salt Lake.

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Elemental Forms of Selenium

• The three most common types of selenium found in
  nature are
• -Selenate (Se 6)
• -Selenite (Se 4)
• -Organic Selenium
• Each form of selenium is analyzed by a similar
  procedure, however the organic and selenate forms
  must be oxidized and or reduced to its 4 state.

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Procedures

• Analysis is done by means of standard addition.
• The experimental procedure involves a series of
  steps that extracts the selenium from the sample
  into a cyclohexane layer.
• DAN (diaminonapthlene) is very selenium specific
  and is used to extract the selenium from the
  water sample.
• Once the selenium/DAN complex is isolated the
  concentration is analyzed using fluorescence
  spectroscopy.

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• A typical run involves six samples consisting of
  a blank, a control, a water sample, and three
  other spiked water samples.
• The fluorescence counts are then plotted and the
  line extrapolated back to obtain the selenium
  concentration of the analyzed sample.

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Selenite

• DAN (diaminonaphthlene) extracts selenium in the
  4 state, thus extraction of the selenite gave
  the most accurate results
• Upon analysis of both Farmington bay as well as
  the GSL water, extremely low concentrations of
  selenite were found.

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Selenite Graphs
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Selenite Graphs
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Selenate

• The analysis of Selenate involves a reduction
  step using Hydrochloric acid.
• Multiple runs were made with both samples due to
  the difficulty of obtaining consistent results.

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Selenate Graphs
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Selenate Graphs
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Organic Selenium

• Analysis of organic selenium involves an
  oxidation step using hydrogen peroxide as well as
  a reduction step as done with the selenate.
• This process converts all of the Selenium to the
  4 state and, thus gives the concentration of the
  total selenium in the sample.

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Organic Selenium Graphs
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Organic Selenium Graphs
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Results
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Summary

• Artificial salt water was made up in order to
  determine possible interferences in our
  methodology.
• Bioaccumulation of methyl mercury in brine shrimp
  of the Great Salt Lake will be further analyzed.
• Further samples will be taken from various parts
  of the lake to more deeply analyze the content of
  selenium.

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References

• Henetz, Patty. A Poison Wind. Salt Lake Tribune.
  May 1, 2005.
• Naftz, David. Mercury Rising. Friends of the
  Great Salt Lake. Vol. 11 3
• Stowell-Nielson, Amelia. Study of Kennecott
  groundwater sought. Deseret News. June 28, 2004.
• Tamari, Yuzo. Methods of Analysis. Biological,
  Geological, and Water samples.