US finds corn absorbing antibiotics from livestock

US farmers frequently feed their livestock antibiotics to prevent infections and diseases, but residues can be absorbed by corn crops that are fertilised with livestock manure.

Minnesota researchers planted corn in manure-treated soil in 2005 to evaluate the environmental impacts of feeding antibiotics to livestock. Six weeks later, the crops were analysed and found to have absorbed chlortetracycline, a drug widely used to treat livestock diseases.

In another 2007 study, corn was planted in soil treated with liquid hog manure and the crop also accumulated concentrations of a common antibiotic named Sulfamethazine.

Levels of antibiotics absorbed by the corn crops increased as the amounts rose in soil.

About 90 percent of the drugs administered to animals are excreted as either urine or manure, which is then mostly used as an important input for 9.2 million hectares of US farmland, said Holly Dolliver from the Minnesota research team.

The studies highlight a flaw in the organic labelling system, and it was not until recently that the USDA closed a loophole in organic milk regulations by requiring farmers to put their cows out to pasture. Before that, many cows were placed in large feedlots.