Release and dissipation of antibiotics and disinfectants in different soil types as influenced by irrigation water quality

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The reuse of wastewater for irrigation of agricultural land is an efficient and widespread practice for dealing with water shortages and for increasing food production with a long tradition in many areas of the world. Irrigation with untreated wastewater in the past resulted in an accumulation of chemical pollutants like pharmaceutical residues and disinfectants in soils. Investments in infrastructure for reaching the Sustainable Development Goal 6 “Clean Water and Sanitation” cause a shift from irrigation with untreated wastewater to irrigation with treated wastewater. We hypothesize that this shift will transiently i) trigger the release of legacy pollutants from soil back into soil water, ii) lead to environmental concentrations of antibiotics and disinfectants that are large enough to promote the selection of antibiotic resistance, with iii) release and concentrations of antibiotics depending on soil type. SP 2 will test these hypotheses with the three soil types Leptosol, Phaeozem and Vertisol for highly used antibiotic agents of different structure and mode of action (sulfamethoxazole, trimethoprim, ciprofloxacin, clindamycin, erythromycin, azithromycin) and quaternary alkylammonium compound disinfectants (alkyltrimtethylammonium, dialkyldimethylammonium and benzylalkylammonium compound) in the Research Units three joint experiments and 2 satellite experiments. The analysis of time series of concentrations in soil extracts with water (all target compounds), pressurized liquid extraction (antibiotics) and ultrasonic extraction (quaternary ammonium compounds) by means of mathematical models will deliver information on the sorption/desorption kinetics and distribution of the target pollutants in the ternary system stationary soil solid phase – solution phase – suspended colloids (in collaboration with SP 1 and SP 7). The kinetics of pollutant (de)sorption and the amounts of desorbable target pollutants will be assessed additionally by means of artificial sinks (diffusive gradients in thin films) and isotope exchange experiments. Integration of the results of SP 2 into the Research Units fate and effects model (SP 7) and relating them to the results of SPs 3-6 will show the relevance of antibiotics and quaternary ammonium compounds introduced with wastewater and released from soil for the selection and spread of antibiotic resistance. In this way, SP 2 contributes to a mechanistic understanding of interactions between pollutants, antibiotic resistance and pathogens in changing wastewater irrigation systems.