Transport of Monensin to Groundwater at a California Dairy.

Animal waste products generated by concentrated animal feeding operations are a major source of antibiotics to the environment. Many antibiotics are administered to livestock to enhance growth or prevent disease, and a large percentage pass chemically unchanged with the waste which is frequently applied to agricultural land as fertilizer. Monensin, an ionophore antibiotic commonly used to increase feed efficiency in livestock, is known to have varied toxicological effects on non-target species but has not been sufficiently studied in soils. The current study examines the transport of monensin in a field soil irrigated with lagoon water from a typical California dairy. This study utilizes a unique opportunity to sample from shallow groundwater monitoring wells installed around a dairy and adjacent to irrigation fields, allowing for the measurement of antibiotics potentially reaching groundwater as a direct result of manure storage or irrigation with lagoon water.