Selenium speciation in acidic environmental samples: application to acid rain-soil interaction at Mount Etna volcano

Area of Science:

• Environmental Chemistry
• Geochemistry
• Analytical Chemistry

Background:

• Elemental mobility is significantly influenced by speciation.
• Trace selenium (Se) speciation analysis in acidic aqueous samples is difficult due to analyte adsorption on precipitates.
• Precipitate formation occurs during pH adaptation required for chromatographic separation.

Purpose of the Study:

• To develop a robust selenium speciation method for acidic environments, particularly for acid rain-soil interaction studies.
• To overcome challenges of analyte adsorption on precipitates in acidic samples.
• To investigate selenium speciation in volcanic soil and acid rain samples from Etna volcano.

Main Methods:

• Thermodynamic calculations to determine optimal pH (<4) for preventing Al and Fe precipitation.
• Development of a low pH eluent (20mM ammonium citrate, pH 3) matching natural sample pH.
• Separation of selenate and selenite in acidic media using (78)Se detection with a limit of quantification (LOQ) of 0.2 μg L(-1) in under 10 minutes.

Main Results:

• Successful separation of selenate and selenite in various acidic matrices (spiked water, rain, soil leachates).
• Application to Etna volcano samples showed dominance of selenate over selenite in leachates near volcanic craters.
• Identified potential competitive behavior between sulfate in acid rain and selenium mobilization.

Conclusions:

• A novel, rapid selenium speciation method was developed for acidic, Al/Fe-rich environments.
• The method effectively analyzes selenium in acid rain and soil interaction scenarios.
• Sulfate competition may be a critical factor influencing selenium cycling in volcanic acid rain environments.