An understanding of the various factors and processes that influence the fate and effects of pollutant mixtures in wastewater-irrigated soils is largely still missing even though wastewater becomes more and more prominent for irrigation in agriculture due to population growth and climate change, especially in countries with water shortage. The implementation of wastewater treatment in long-established irrigation systems with untreated wastewater might mobilize pollutants that have formerly been accumulated in soils, leading to concentrations that (co-)select for antimicrobial resistance, with release and concentrations of antibiotics as well as selection of antibiotic resistance depending on soil type. To test these hypothesis, this subproject (SP 7) of the research unit “Pollutant – Antibiotic Resistance – Pathogen Interactions in a Changing Wastewater Irrigation System” will combine mathematical models with data from observations in the laboratory and in the field (Mexico City – Valle Mezquital) to quantify processes and analyze different scenarios that simulate consequences of selected environmental or laboratory conditions of interest (so-called in silico experiments) on the fate of antibiotics and quaternary alkylammonium disinfectants and their effects on the selection and spread of antimicrobial resistance. The chemical fate of pollutants in soils as well as the selection and spread of antimicrobial resistance have been described by process-based mathematical models. For the description of microbial population dynamics and spread of resistant bacteria model approaches range from ordinary differential equations (ODEs) to stochastic approaches and to individual based or agentbased models. Thus, in close cooperation with all involved subprojects of the research unit we will: i) develop a conceptual and a mathematical model that combines pollutant fate in wastewater irrigated soils with bacterial dynamics and spread of resistance genes, which enables us to ii) couple pollutant concentrations, release from soil and fate to the selection of resistant bacteria and horizontal gene transfer (HGT) in wastewater and soils; iii) consider heterogeneity and plant uptake into the overall evaluation of interactions between pollutants and bacteria; and iv) integrate the process understanding across the different spatial scales. In this way, the outcomes of this sub-project will specifically contribute to elucidating and quantifying processes and parameters that drive the pollutant fate and spread of bacterial resistance in agricultural soils that face a shift from irrigation with untreated to irrigation with treated wastewater.