Modeling the fate of organic micropollutants in agricultural soils: Laboratory parameterization and field-scale implications

Organic micropollutants (OMP) increasingly enter agricultural soils through irrigation with reclaimed water, raising concerns about their mobility and persistence in soils and their potential to contaminate groundwater. This study investigates the fate of ten OMP in an arable loamy-sand topsoil using a combined experimental and modeling approach. Abiotic/biotic kinetic and isotherm batch experiments were performed to derive process-relevant parameters for sorption and biodegradation. An inverse modeling approach was employed to simultaneously fit the parameters for the different processes to all three data types (i.e., abiotic kinetic, biotic kinetic data, equilibrium data), allowing robust parameter estimation across varying levels of model complexity. The model incorporated equilibrium and kinetic sorption (linear and Freundlich isotherms; one- and two-site kinetic models), first-order biodegradation, and explicitly accounted for vaporization losses due to aerated vessels, extending traditional batch modeling frameworks. Four OMP (adamantan-1-amine, carbamazepine, diclofenac, and sulfamethoxazole) exhibited biphasic sorption behavior, which was best described by a two-site kinetic model. Three OMP (acesulfame, saccharin, and valsartanate) showed negligible sorption but, following lag phases between 4 and 9 days, indicated microbial adaptation. After adaption, rapid biodegradation with half-lives of 0.4, 0.9, and 3.3 days, occurred. The remaining compounds (diatrizoate, trifluoromethanesulfonate, primidone) showed neither sorption nor degradation. The necessity of applying the relatively complex modeling approaches - required to describe the lab experiments - to field conditions was investigated using Hydrus-1D simulations under realistic soil and climate scenarios. The simulations revealed that sorption kinetics and microbial adaptation phases had minimal impacts on OMP transport simulations at field-scale under matrix-dominated flow, despite their importance for laboratory-scale interpretation. The results suggest that simplified equilibrium and immediate-degradation assumptions may be sufficient for risk assessment regarding to OMP in homogeneous soils with predominantly uniform flow conditions. Overall, this study presents a comprehensive framework for bridging laboratory observations with field-scale modeling, offering new insights into OMP fate and guiding efficient parameterization strategies for environmental risk assessment for the management of reclaimed water.