Thursday, January 24, 2013
It likely comes as a surprise to no one that antibiotics found in soil can pose a threat to human and environmental health. Research has shown that bacteria exposed to low-doses of antibiotics found in livestock manure or wastewater runoff can develop a resistance to the drugs. And the concern that antibiotics currently used to fight diseases could become ineffective has inspired the U.S. Food and Drug Administration (FDA) to call for practices that limit the amount of drugs given to livestock and the World Health Organization to name antibiotic resistance among the top three threats to global health.
New research on the impacts of long-term exposure to antibiotics, though, may come as more of a surprise. A 2012 study out of Canada indicates that continuous amounts of veterinary antibiotics added to agricultural soil may actually lead to less resistance. The reason is the dynamic nature of food chains. A consistent and concentrated supply of antibiotics creates an ideal opportunity for the evolution of microorganisms that convert the drugs into a food source. With these microbes eating up antibiotics each time more is added to the soil, the drugs are degraded before other bacteria are able to build up a resistance.
This observed effect was not universal. Of the three antibiotics tested, only two degraded in the soil more rapidly after their long-term use spurred the growth of new bacteria. And researchers had to increase the concentration of antibiotics applied to the soil mid-study before they were able to detect any amplified biodegradation at all. Additional studies will be needed to determine effects at lower concentrations. But the results of this study echo what others on chemical pollution–like this one on the long-term effects of herbicides and insecticides in farming–have revealed: the environmental risks posed by pharmaceuticals and other contaminants do not necessarily increase at higher concentrations or over longer periods of exposure.
Written by: Anjanette Riley, IISG Science Writer
Topp, E., R. Chapmana, M. Devers-Lamranib, A. Hartmannc, R. Martia, F. Martin-Laurentb, L. Sabourina, A. Scotta, and M. Sumaraha. 2012. Accelerated biodegradation of veterinary antibiotics in agricultural soil following long-term exposure, and isolation of a Sulfamethazine-degrading microbacterium sp.. Journal of Environmental Quality 42(1): 173-178.