Simulation of the biocide distribution in soil using PELMO coupled with COMLEAM

Biocides, applied in building materials as antimicrobial protectants, can be leached out by rain, presenting substantial environmental risks as confirmed by studies on aquatic environments. However, these biocides are consistently released throughout the year in a diluted form, posing unique challenges for the prediction of transport, transformation, and ecotoxicity assessment in soil. To address this challenge, we combined COMLEAM, which predicts leaching from facades into the soil, with the FOCUS PELMO pesticide model to predict biocide distribution in soil. The study predicted the concentration of the commonly used biocides 1,2-benzisothiazol-3(2H)-one (BIT), 2-n-octyl-4-isothiazolinone-3-one, and terbutryn at various soil depths over 600 days, thereby evaluating the influence of different leaching simulations, absorption, and degradation kinetics on the PELMO simulation results. The findings suggest an effective simulation of biocide behavior in soil, with a tendency to overestimate the risk associated with short-acting in-can preservatives like BIT and provide more precise predictions for long-acting film preservatives. Biocide concentrations showed little variance in the upper layers and increased discrepancies at greater depths. This integrated approach provides a cost-effective means for predicting environmental risks and formulating management strategies, especially when paired with experimentally determined soil-specific degradation and absorption values.