A recent study found that antimicrobials used on two California dairies can be recovered from surface soil and manure lagoons, but that groundwater contamination was limited.
Thomas Harter, PhD, a faculty member with the Department of Land, Air, and Water Resources at the University of California-Davis, said the researchers detected all 13 antimicrobials used on two free-stall dairies in the dairies' surface soil and lagoons, and they found low concentrations of two sulfonamides and lincomycin in the first 20 feet of groundwater below the dairies. The groundwater concentrations were typically an order of magnitude less than those seen in manure lagoons, and affected groundwater was primarily in the immediate vicinity of the manure lagoons or near irrigation valves on manure-irrigated fields.
University information indicates many of the antimicrobials, while frequently found in corrals and manure flush lanes, degraded within the first foot of soil.
The researchers selected sites in the San Joaquin Valley that have sandy loam soil, high levels of irrigation, and groundwater located in a sandy aquifer between 10 and 30 feet below the surface. Dr. Harter said the sites were chosen on the basis of their high risk of groundwater contamination.
The research by UC-Davis and U.S. Geological Survey Water Science Center employees was funded with $568,000 from the CALFED Bay-Delta Authority Drinking Water Program and $65,000 from the California Department of Food and Agriculture. The study results were published online Aug. 10 by the journal Environmental Science & Technology; the text is available at http://pubs.acs.org/doi/full/10.1021/es100834s.