Predicting soil-water partition coefficients for Hg(II) from soil properties

Area of Science:

• Environmental Chemistry
• Soil Science
• Geochemistry

Background:

• Understanding metal adsorption in soils is crucial for environmental risk assessment.
• Mercury (Hg(II)) is a toxic heavy metal with significant environmental implications.
• Soil properties, such as pH, organic matter, and metal oxides, influence metal adsorption.

Purpose of the Study:

• To evaluate the metal adsorption characteristics of Hg(II) in Taiwan soils.
• To investigate the influence of pH on Hg(II) adsorption.
• To elucidate the mechanisms governing Hg(II) adsorption using a partition coefficient model.

Main Methods:

• Characterization of physical and chemical properties of fifteen Taiwan soil samples.
• Evaluation of Hg(II) adsorption across a range of pH values.
• Application and testing of a partition coefficient model to relate adsorption to soil components (organic matter, metal oxides).

Main Results:

• Hg(II) adsorption increased with pH from 2.5 to 5.5, then decreased significantly above pH 5.5.
• Soils with higher organic matter content showed greater Hg(II) adsorption below pH 5.5.
• Normalization of partition coefficients (Kd) for organic matter content (Kom) improved the correlation with pH below 5.5, indicating organic matter as the primary adsorption site.

Conclusions:

• Soil organic matter is the principal surficial adsorption site for Hg(II) at pH less than 5.5.
• The partition coefficient model's success was limited by pH variations and dissolved organic matter complexation at higher pH.
• Diffusion through organic matter coatings is not a significant factor in Hg partitioning within the studied timeframe.