Antibiotics have been commonly fed to livestock in the United States for about 50 years. A portion is excreted unchanged in the animals' waste. When manure from antibiotic-fed livestock is used as a fertilizer, some of the antibiotic content enters the soil and is taken up by crops. One experiment by University of Minnesota researchers showed that the antibiotic chlortetracycline was taken up by cabbage, green onions and corn grown in manure treated soil. In a second experiment using liquid hog manure, the antibiotic sulfamethazine ended up in corn, lettuce and potatoes.
Tubers or root vegetables will likely accumulate the highest amount of antibiotic, since they are in closer contact with the soil.