Modelling biocide leaching from facades.

Area of Science:

• Environmental Chemistry
• Environmental Science
• Aquatic Toxicology

Background:

• Biocides applied to building facades leach into aquatic environments during rainfall.
• Limited understanding exists regarding total biocide losses from urban settlements due to reliance on laboratory wash-off studies.

Purpose of the Study:

• To develop a simplified model simulating biocide losses from facades under various rainfall and application scenarios.
• To elucidate the mechanisms governing biocide wash-off dynamics from building exteriors.

Main Methods:

• A four-box model was developed, incorporating diffusion from storage stocks to mobile stocks and subsequent wash-off.
• The model was calibrated using an existing experimental dataset from a laboratory wash-off experiment.
• Model performance was validated against measured wash-off data across multiple cycles.

Main Results:

• The model accurately reproduced experimental data for single and peak wash-off events.
• Simulations indicated that approximately 70% of applied biocides remain on facades even after prolonged simulated rainfall (1100 mm/year).
• Diuron losses were quantified, revealing substantial retention on facade surfaces.

Conclusions:

• Biocide losses from urban facades are significant and cannot be neglected.
• Accurate estimation of losses requires understanding rainfall-runoff dynamics and facade biocide decay rates.
• The developed model enhances comprehension of laboratory wash-off dynamics and allows for realistic outdoor loss simulations.