Quaternary ammonium compounds (QACs) are surface-active, antimicrobial, high production volume (HPV) chemicals with a broad application in agriculture. This review provides a comprehensive overview of (1) predicted and measured concentrations of QACs in soils including their analysis, (2) sequestration mechanisms in soils based on their physicochemical properties and chemical structure, and (3) implications of concentrations and fate of QACs in soils for the proliferation of antibiotic resistance in the environment. Predicted environmental concentrations (PEC) for QACs that are applied to soils with manure are in the order of 3.5 mg kg -1 . Based on literature data, the median PEC of QAC in sewage sludge amended soils is 25 lg kg -1 . The positively charged QACs are mainly sorbed to clay minerals. We propose that QACs might be sequestered in the interlayer regions of layered silicates in clayrich soils, reducing their acute toxicity, while increasing their persistence. The release of sequestered QACs from soil can still potentially maintain concentration levels that are sufficient to develop antibiotic resistance in the environment.

The use of urea as nitrogen (N) fertilizer in agriculture needs to consider environmental, economic and resource conservation aspects because of low N‐use efficiency (NUE). Polymer‐coated urea (PCU) offers an effective way to improve the NUE of urea and to reduce its environmental trade‐offs. However, we lack information on the impact of climate and soil properties on N release from PCU. Therefore, this study was performed to quantify the effects of soil texture, moisture and temperature on the release kinetics of N from PCU. We designed a test system for soil incubation experiments and investigated three fertilizers with different release patterns, five topsoils, three moisture levels and two temperatures over 48 days. We analysed the concentrations of inorganic N ( and ) in the soil and estimated N release rates using the unified Richards model. Soil texture did not change the N release patterns, but release rates varied significantly among the investigated soils. Changes in soil moisture for a given soil had no effect on N release from PCU and urea when fertilizers were incorporated into the soil at conditions supportive of crop growth. Lowering soil temperatures, however, decreased N release rates from PCU by 16%–49% but only in silt loam and not in sandy loam. We conclude that PCU improves the N residence time in soil, but predictions on N release from PCU must be adapted to the prevailing environmental conditions and cannot be generalized across differently textured soils.

River deltas are frequently facing salinity intrusion, thus challenging agricultural production in these areas. One adaption strategy to increasing salinity is shrimp production, which however, heavily relies on antibiotic usage. This study was performed to evaluate the effect of increasing salinity on the dissipation rates of antibiotics in tropical flooded soil systems. For this purpose, paddy top soil from a coastal Vietnamese delta was spiked with selected frequently used antibiotics (sulfadiazine, sulfamethazine, sulfamethoxazole, trimethoprim) and incubated with flood water of different salt concentrations (0, 10, 20 g L −1). Antibiotic concentrations were monitored in water and soil phases over a period of 112 days using liquid chromatography and tandem mass spectrometry. We found that sulfamethazine was the most persistent antibiotic in the flooded soil system (DT 50 = 77 days), followed by sulfadiazine (DT 50 = 53 days), trimethoprim (DT 50 = 3 days) and sulfamethoxazole (DT 50 = 1 days). With the exception of sulfamethoxazole, the apparent distribution coefficient increased significantly (p < 0.05) for all antibiotics in course of the incubation, which indicates an accumulation of antibiotics in soil. On a whole system basis, including soil and water into the assessment, there was no overall salinity effect on the dissipation rates of antibiotics, suggesting that common e-fate models remain valid under varying salinity. Salinity intrusion is a natural phenomenon in coastal ecosystems that becomes particularly relevant in delta regions 1,2. However, synergistic effects with anthropogenic drivers like groundwater overuse, hydro-dam construction, and sea level rise currently exacerbate salinization of deltaic soil and freshwater resources and restrict freshwater related agriculture 2,3. In the Mekong Delta of Vietnam, for instance, salinization has already become a major threat 4. About 1.8 million ha of land are affected by increasing salinity 5 , and the El Niño dry season 2015-2016 damaged up to 240,000 ha of paddy rice fields 6. One approach to adapt to this changing environment is by shifting the freshwater land use systems, like paddy rice, to brackish or saltwater compatible agriculture, such as shrimp production 7. Intensive shrimp production, however, frequently goes along with heavy use of antibiotics 8 , which disseminate in the environment. Accordingly, in shrimp ponds, single substances have already been detected in concentrations of up to 0.82 g kg −1 in pond mud and 2.39 mg L −1 in pond water 9 , thus posing risks for the selection and spread of antibiotic resistances 10. The final fate of antibiotics likely depends on soil order and temperature 11,12 , as well as several physicochemical soil properties affecting sorption rates and dissipation 13,14. Several studies dealt with dissipation rates of antibiotics in soil under field (e.g. 11,15) or laboratory conditions (e.g. 16-18). While field studies reflect natural conditions best, laboratory studies allow to determine the influence of a sin...