Vegetative Treatment Systems to Treat Feedlot Runoff: Fate of Antibiotics and Resistant Microorganisms.

When rain falls on a feedlot it gets mixed with animal manure.  The feedlot runoff contains manure nutrients and microorganisms that could impact environmental and public health.  This includes antibiotic resistant bacteria and pharmaceutical compounds.  It is important to keep this feedlot runoff water from contaminating surface and ground water sources.  Vegetated Treatment Systems (VTS) are a novel method to treat feedlot runoff from rain events as an alternative to conventional manure storage systems.  Feedlot runoff is collected in sediment basins, and distributed to vegetative treatment areas planted with perennial grasses harvested for hay.  We looked at how antibiotic resistant bacteria and pharmaceutical compounds traveled through the VTA.  Bacteria resistant to two specific antibiotics were isolated from the runoff water, but not from soil cores.   The most frequently detected pharmaceutical compound was monensin.  Great variability was observed in the types of antibiotics detected during the two years for which data was collected.  We conclude that while the VTS does not stop the transport of antibiotic resistant bacteria across the VTA surface at the time of runoff application, the system effectively reduces the concentrations of residual manure-associated bacteria over time and are an efficient feedlot runoff treatment system.