Response of microorganisms from natural and constructed wetlands to veterinary drugs

In the last years, contamination of freshwater systems by chemical compounds has been increasing along with human development, being many of these chemicals emerging environmental pollutants. These compounds can be a potential threat to public health and the environment but remain without regulations. Pharmaceuticals (including veterinary antibiotics), polar pesticides, veterinary products, among others, are examples of emerging pollutants. Veterinary antibiotics have been widely used in livestock industry in an intensive and uncontrolled way leading to its detection in wastewater, freshwater and groundwater. Conventional methods of wastewater treatment are generally not capable or equipped to remove these compounds therefore, they are released without efficient treatment. Consequently, veterinary antibiotics or their active compounds can enter directly in the water system through effluent discharges. In addition, veterinary antibiotics can reach the environment indirectly through manure’s lixiviation used as organic fertilizer. Despite of being found at low concentrations, they can cause toxic effects in organisms and promote antibiotic resistance. Natural wetlands, like salt marshes present in estuarine areas, are characterized by the presence of water and adapted vegetation in saturated conditions and unique soils that differ from upland soils. Furthermore, wetland has a high rate of biological activity having the potential to transform several common pollutants, some presented in wastewater treatment plants, in harmless byproducts or essential nutrients that can be used for additional biological productivity. Constructed wetlands (CWs) are being considered a potential technology to remove pharmaceuticals from wastewater effluents, but their ability to improve water quality depends greatly on their microbial communities. They are designed to mimic natural wetlands, being based on the interactions among soil/sediment, plant and microorganisms to remove contaminants from effluent. The aim of this study was to understand the response of microbial communities from natural and constructed wetlands to veterinary antibiotics. For that, two different experiments were performed using the salt marsh plant Phragmites australis, which is commonly found in Portuguese estuarine areas and has been widely used for wastewater treatment in CW in America and Europe. In one of the experiments, microbial community dynamics associated with veterinary antibiotics (enrofloxacin and tetracycline) removal from livestock wastewater was evaluated in CWs microcosms, in terms of abundance, diversity and community structure. Results point to CWs applicability for veterinary antibiotics removal from FCUP Response of microorganisms from natural and constructed wetlands to veterinary drugs viii livestock wastewaters, showing that CWs microbial communities were able to adapt without significant changes in their diversity or depuration capacity. On the other experiment, the response of a salt marsh plant-microorganisms association to a contamination with a veterinary antibiotic (enrofloxacin) under different nutritional conditions was evaluated using natural estuarine water and sediments. Results showed that the presence of veterinary antibiotics in estuarine areas can affect their microbial community structure and that salt marsh plants and associated microorganism present a potential for antibiotic removal that is highly dependent on their nutritional status. This study emphasizes the potential salt marsh plant-microorganisms association for the removal of veterinary antibiotics contamination from both natural and constructed wetlands, showing promising results for its application in the remediation of the environmental impact of these contaminants.