PAH desorption from river floodplain soils using supercritical fluid extraction.

Area of Science:

• Environmental Chemistry
• Soil Science
• Geochemistry

Background:

• River floodplain soils can accumulate polycyclic aromatic hydrocarbons (PAHs) from coal and coal-derived particles.
• Understanding PAH desorption kinetics is crucial for assessing long-term environmental risks.

Purpose of the Study:

• To estimate the desorption rates of PAHs from river floodplain soils containing coal-derived particles.
• To evaluate the influence of soil fractions on PAH desorption kinetics.

Main Methods:

• Sequential supercritical fluid extraction (SFE) was employed to study PAH desorption.
• Analysis focused on original soils, light fractions (density < 2 g cm⁻³), and fine soil fractions (< 63 µm).
• Desorption data were modeled using a two-site kinetic model.

Main Results:

• Desorption rate constants were significantly lower than previously reported 'slow' and 'very slow' rates, indicating very slow and extremely slow desorption.
• Estimated time scales for 99% PAH release ranged from decades (2-4 ring PAHs) to hundreds of years (5-6 ring PAHs).
• Soil fractions exhibited similar desorption behaviors, suggesting a consistent release mechanism.

Conclusions:

• Despite high PAH concentrations from coal sources, the environmental risk is mitigated by extremely slow desorption rates.
• The long time scales for PAH release indicate persistent soil contamination but reduced immediate bioavailability.
• Supercritical fluid extraction provides valuable insights into the long-term fate of PAHs in contaminated soils.