Contamination of organic raw materials and recycled organic fertilizers with antibiotics

Since the resources for mineral fertilizers are limited and the energy costs have recently risen considerably, there is an increasing interest in closing nutrient cycles and the recycling of nitrogen and phosphorus in secondary raw materials. Nutrient-rich waste materials can be used directly as a fertilizer or after processing. If other valuable ingredients such as organic carbon are in the product after processing, pollutants can be present as well. In the present work, contamination by antibiotics will be discussed. Antibiotics are used in large quantities to treat bacterial infections in humans but also in animals for food production. Resistant or even multi-resistant strains can occur in feces if antibiotics are regularly used in higher quantities. It was the aim of the study to show which recycled organic fertilizers contain a particularly high amount of antibiotics and how this might affect the relative abundance of resistance genes and mobile genetic elements. Sewage sludge and composted sewage sludge, digestate with animal excrements, residues from food production and processed fertilizers such as ash products or struvite were studied. Exemplary, 14 antibiotics out of three classes were analyzed. Especially fluoroquinolones and tetracyclines are present at higher concentrations in fertilizers of animal origin. In processed fertilizers, the concentrations depend not only on the origin but also on the carbon content, since antibiotics can bind to organic matter.