One more reason to eat organic: Conventionally grown vegetables may be more likely to serve up a dose of antibiotics along with their nutritional properties.
When nonorganic farmers and ranchers give antibiotics to their animals—a widespread practice to ensure health and stimulate growth—small traces of the drug are excreted. When that manure is applied to crops, the vegetables retain the antibiotics in their tissues, according to a University of Minnesota study published in the Oct. 12 online edition of the Journal of Environmental Quality .
The U of M study examined corn, green onion and cabbage for levels of two commonly used antibiotics. All three crops absorbed chlortetracycline but not tylosin. The amount of antibiotics in the plants was small, but increased according to the concentration present in the manure.
"This study points out the potential human health risk associated with consumption of fresh vegetables grown in soil amended with antibiotic-laden manures," the study's authors wrote. "The risks may be higher for people who are allergic to antibiotics and there is also the possibility of enhanced antimicrobial resistance as a result of human consumption of these vegetables."
The U.S. Food and Drug Administration this summer banned the use of Baytril, which belongs to a different class of antibiotics than those in the study. The European Union in 1998 banned many human antibiotics from being used in animals, except for therapeutic purposes. The bans came amid concerns that foodborne illness was resistant to treatment when humans ate meat from animals treated with antibiotics.
While organic agriculture has drawn fire in the past for its reliance on manure as a fertilizing agent, the practice is widespread in conventional agriculture as well.
"Manure use is very tightly regulated in organic agriculture and is completely unregulated in conventional agriculture," said Mark Lipson, policy program director at the Organic Farming Research Foundation in Santa Cruz, Calif. "The National Organic Rule is really quite strict on the use of uncomposted manure. It cannot be applied to a crop within 120 days of harvest," Lipson said. Because of that, he said, "The use of manure in organic agriculture is much less risky than in conventional."
Lipson also cited several flaws in the U of M study's design: "They tested the crops after only six weeks after planting and application of manure," not the 120 days that organic farming would require. And, he said, "they were doing it greenhouse pots, so it wasn't a real field." The amount of manure used was "not outlandish, but it's a heavy application," he said. "This study is not that relevant to drawing any conclusions about organic agriculture."
In addition, relatively few organic farmers use uncomposted, or raw, manure, the type used in the study. In OFRF's Third Biennial National Organic Farmers' Survey, published in 1999, 22 percent of organic farmers said they used uncomposted manure frequently or regularly; nineteen percent said they used it occasionally. "The number has almost surely gone down," Lipson said, since the survey was conducted before implementation of the National Organic Rule. In addition, he said, some organic growers are almost certainly using organic manure—compost derived from animals raised organically—so the issue of antibiotics in manure would be nonexistent for them.
"The real issue is the use of antibiotics," Lipson said. "The alternatives for managing healthy livestock systems are only just beginning to get serious scientific research. Organic growers are figuring out how to get by but they have very, very little help from the scientific community in doing that. … If organic research … got a fraction of a fair share of resources that are spent on agricultural research and livestock management, we'd be able to help wean conventional livestock manufacturers off of these materials."