Critical Limits for Hg(II) in soils, derived from chronic toxicity data.

Area of Science:

• Environmental Chemistry
• Soil Science
• Ecotoxicology

Background:

• Chronic toxicity data for mercury(II) (Hg(II)) in soils is crucial for ecological risk assessment.
• Existing critical limits for Hg(II) in European soils may not adequately account for soil properties.

Purpose of the Study:

• To assemble and evaluate chronic toxicity data for Hg(II) in soils.
• To derive new critical limits for Hg(II) in soils based on species sensitivity distributions.
• To develop a critical limit function incorporating soil properties like pH.

Main Methods:

• Compiled 52 chronic toxicity end-points for plants, invertebrates, and microbes.
• Derived critical limits from the 5th percentiles of species sensitivity distributions.
• Applied the WHAM/Model VI chemical speciation model to estimate Hg(2+) concentrations in soil solution.

Main Results:

• Derived soil organic matter-based critical limits of 0.13 µg/g soil and 3.3 µg/g soil organic matter.
• The derived soil organic matter limit (3.3 µg/g) exceeds the current European critical limit (0.5 µg/g).
• Developed a critical limit function (CLF) relating Hg(2+) activity to pH: log [Hg(2+)](crit) = -2.15 pH - 17.10.

Conclusions:

• Soil organic matter-based limits and the CLF provide a more accurate assessment of Hg(II) toxicity across different soil types.
• These refined limits account for soil properties, leading to a better understanding of mercury's toxic threat.
• Predicted ranges of up to 100-fold in mercury content corresponding to the critical limit for different soils.