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Antibiotics Discovered in Crops Treated with Manure

January 08, 2009 08:57 AM
by Isabel Cowles
Crops fertilized with manure from livestock treated with antibiotics absorbed trace amounts of the drugs, sparking health concerns about increased antibiotic resistance.

Something Extra in the Vegetables

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Vegetables fertilized with manure are absorbing more than just nutrients, researchers say. While meat and dairy eaters have long been susceptible to ingesting antibiotics via animal products, vegetarians may also be at risk for unwittingly consuming these drugs.

Scientists at the University of Minnesota analyzed corn, green onions, cabbage and corn in 2005 and corn, lettuce and potatoes in 2007; in both studies, they determined that crops fertilized with manure from livestock treated with antibiotics also absorbed the chemicals.

Livestock farmers have typically fed animals antibiotics to promote growth and prevent infection. Holly Dolliver, a member of the Minnesota research group explained that about 90 percent of the antibiotics given to animals are excreted as urine or manure. “A vast majority of that manure is then used as an important input for 9.2 million hectares of (U.S.) agricultural land,” she said.

Although the scientists determined that crops absorbed less than 0.1 percent of antibiotics in the soil, concern remains over the accumulated ingestion of such trace amounts. Even organic produce is at risk of absorbing antibiotics, as organic farmers often use manure for fertilizer. In addition, rain and runoff from fields can introduce antibiotics into water systems.

Livestock who have consistently been given antibiotics have shown resistance to the drugs, which has prompted researchers to question the possible effects on humans. For example, if a person consumes pork with a strain of resistant bacteria and becomes ill, it is theoretically possible that treatment could be much more difficult.

Despite the potential risks, many farmers assert that eliminating antibiotic use in livestock could have damaging effects on food safety. For now, it appears the FDA is in agreement; in 2007, the agency overruled a warning about cattle antibiotic cefquinome and put the highly potent antibiotic on track for approval, despite concern by health groups. 

The levels of antibiotics in fertilizer can be decreased, however, if manure is treated properly. In a 2007 study funded by the USDA Agricultural Experiment Station and the National Science Foundation, researchers at the University of Colorado saw a decrease in manure that was managed by adding leaves and alfalfa, watered and turned.  

Background: Manure becomes fertilizer of choice

Manure has become an increasingly popular fertilizer in recent years. The high cost of fertilizer and a surplus of animal waste have caused many farmers to turn to manure as a source of vital nutrients for their soil.

Environmentalists and political leaders have also advocated for its use: in 2005, agricultural, environmental and political leaders in the Shenandoah Valley worked together to encourage new technologies to store and process poultry and other farm animal manure as well as efforts to effectively transport manure to areas where it was needed.

Reference: Studies on plants and manure

Abstracts and the complete text of the 2005 and 2007 studies of plant absorption of antibiotics by researchers at the University of Minnesota are available at the Journal of Environmental Quality.

An abstract of the report on manure treatment from researchers at the University of Colorado is also available at the Journal of Environmental Quality’s Web site.
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