Simulation of the effect of soil organic matter on carbamazepine transport.

Carbamazepine, one of the most frequently detected pharmaceuticals in the environment, is a representa-tive pollutant in the category of pharmaceuticals and personal care products. It can easily enter soil and groundwater through recycled water irrigation and sludge application. However, the impact of soil organic matter on the transport of carbamazepine remains unknown. We investigated the transport behavior of carbamazepine using indoor saturated soil column experiments, complemented by simulations performed with Comsol Multiphysics. We compared the transport capacity of carbamazepine in high organic matter soil (22.7 g·kg^-1) and low organic matter soil (8.0 g·kg^-1), aiming to analyze the differences in carbamazepine transport and provide a theoretical basis for assessing agricultural soil and groundwater contamination risks associated with recycled water irrigation. The results showed that soil organic matter significantly affected the transport capacity of carbamazepine. In soil with high organic matter, carbamazepine exhibited weaker mobility, with a longer initial breakthrough time (2.86 h). In contrast, in soil with low organic matter, carbamazepine had stronger mobility, a shorter initial breakthrough time (1.67 h). The dynamic transport process of carbamazepine in soil column was simulated by numerical simulation. The results showed that high organic matter soil had a higher adsorption rate (5.54×10^-8 mol·m^-3·s^-1) and adsorption amount (6.85×10^-5 mol·kg^-1 ), likely due to its larger surface area and greater number of adsorption sites. In contrast, low organic matter soil exhibited a lower adsorption rate (3.03×10^-8 mol·m^-3·s^-1) and lower adsorption capacity (5.44×10^-5 mol·kg^-1), leading to faster transport. In summary, soil organic matter plays a crucial role in regulating carbamazepine transport. The transport and diffusion risk of carbamazepine is higher in low organic matter soils. Furthermore, numerical simulations using Comsol Multiphysics could effectively complement traditional experimental data, providing a valuable tool for predicting the environmental fate of carbamazepine in natural soils.