Identification of dissipation pathways for pharmaceuticals in soils - a modelling approach

Area of Science:

• Environmental Chemistry
• Soil Science
• Mathematical Modeling

Background:

• Pollutant concentrations in soil decrease over time, but the mechanisms (transformation vs. extractability changes) are often unclear.
• Understanding pollutant dissipation is vital for assessing environmental risks and soil remediation strategies.

Purpose of the Study:

• To develop a mathematical model differentiating pollutant dissipation pathways in soils.
• To quantify concentration differences between aqueous soil extracts and soil solution.
• To investigate the roles of transformation, mineralization, and non-extractable residue formation.

Main Methods:

• Developed a model incorporating kinetic sorption (Freundlich), 1st-order kinetics for transformation/mineralization, and intraparticle diffusion.
• Model assumes uniform spherical soil particles.
• Applied the model to 19 published datasets involving eight pharmaceuticals and three soils.

Main Results:

• Intraparticle diffusion accounted for approximately two-thirds of simulated mass fluxes.
• Reversible formation of non-extractable residues appears to be a major dissipation factor.
• Irreversible transformation and mineralization cannot be ruled out.
• Differences between extract and soil solution concentrations were generally small, except for positively charged pollutants.

Conclusions:

• The model effectively disentangles various pollutant dissipation pathways in soils.
• Intraparticle diffusion and reversible non-extractable residue formation are significant dissipation mechanisms.
• The model aids in designing experiments to determine the long-term fate of soil pollutants.