Environmental Health News reports that vegetables fertilized with livestock manure absorb small amounts of the drugs routinely given to American farm animals to increase growth and reduce infection. Even organic produce isn’t necessarily safe, since there are no regulations in place regarding antibiotics in manure used as fertilizer.
Steve Roach, a public health program director for Food Animal Concerns Trust, told EHN that “‘the clearest public health implication from treating livestock with antibiotics is the development of resistant bacteria that reduces the effectiveness of human medicine.”
Root veggies are probably the most risky, because they absorb the bulk of their nutrients from the soil, and we eat the root—as opposed to the leaves—of the plants. Crops destined for processing, like corn, are pretty safe; and composting manure before spreading it on the fields can help reduce the levels of antibiotics. But if you want to be sure your vegetables are free of antibiotics, you might try buying from a veganic farm.