Adding manure to vegetable gardens is a time-honored method of fertilizing plants. However, many animals are fed regular doses of antibiotics, and up to 90 percent of those antibiotics can pass into the urine and manure. Some gardeners are concerned that chemicals in the manures we're adding to the soil are ending up on the food we eat. Little research has been done, however, to determine if these antibiotics actually are transferred from soil to plant.
Researchers at the University of Minnesota recently conducted experiments to find out. They grew green onions, corn, and cabbage in plots outdoors and in a greenhouse. They added small amounts of chlortetracycline and tylosin antibiotics to the soil and analyzed the vegetables three to six weeks later at harvest time. No tylosin was found in the plants, but small amounts of chlortetracycline were transferred to the plants.
Although the levels were not considered an immediate hazard, the results pose a concern for people allergic to this antibiotic. Also, scientists are concerned that consuming small doses of antibiotics regularly could lead to developing a resistance to the antibiotics when they are truly needed.
More research is planned on this topic, but for now home gardeners can protect their plants -- and themselves -- by making sure they use only well-composted manure or buying bags of sterilized manures that are more likely to be antibiotic-free.
For more information on this research, go to: Journal of Environmental Quality.