Antibiotics are commonly added to animal feeds as a supplement to promote growth of food animals. Absorption of antibiotics in animal gut is not complete and as a result a substantial amounts of antibiotics are excreted in urine and feces that end up in manure. Manure is used throughout the World not only as a source of plant nutrients but also as a source of organic matter to improve soil quality especially in organic and sustainable agriculture. Greenhouse studies were conducted to see if plants grown in manure-applied soil absorb antibiotics present in manure. The test crops were corn, green onions, and cabbage. All the three crops absorbed chlortetracycline but not tylosin. The concentrations of chlortetracycline in plant tissues were small (2 to 17 ng g-1 fresh weight), but these concentrations increased with increasing amount of antibiotics present in the manure. The study points out to the potential human health risks associated with consumption of fresh vegetable grown on antibiotic laden manures especially to people who are allergic to antibiotics and the possibility of enhanced antimicrobial resistance as a result of human consumption of these vegetables.
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