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Fate and Ecological Effects of Livestock Antibiotics in Soils
Department of Plant and Soil Sciences
Millions of pounds of antibiotics are used each year to prevent disease and promote animal growth in livestock industries, a large fraction of which are excreted in manure, and enter rivers and streams from surface runoff from manure-amended lands. The primary concerns are that contamination will increase the spread of antibiotic resistant bacteria and suppress bacterially-mediated processes in soils (e.g. nutrient cycling). Once antibiotics are deposited to soils, they can be removed from the bioavailable pool through sorption and microbial degradation, depending on temperature, water content, soil mineralogy, solution composition, pH, organic matter, nutrients, and oxygen.
The first objective of this project is to develop an accurate and sensitive technique for determining antibiotic concentrations in manure and soil samples.
The second major objective of this research proposal is to determine the effect of landscape position on changes in antibiotic levels and ARB numbers after application of manure and antibiotics to agricultural fields.
2009 Project Description
Numerous studies were conducted to determine whether three common livestock antibiotics had significant effects on biotransformations of nitrogen and microbial communities in soils using the phospholipid fatty acid analysis approach. Results from experiments were presented at the southern region American Society of Agronomy meeting in Atlanta, GA in Feb 2009.
This project resulted in a change in knowledge about the effects of livestock antibiotic dissemination to the soil environment. Specifically, it was discovered that antibiotics, at levels used in feed, found in manure, and added to soils, did not have significant effects on soil bacterial population composition or processes. This was primarily due to rapid and strong sorption of antiobiotics to soil surfaces, which reduced the antibiotic concentration in the bioavailable pool. In the absence of sorption, the antibiotics had adverse effects on microbial populations.
Therefore, results from this study indicated that there is little risk in the practice of applying manure to soils on the soil microbial community in soils with moderate amounts of clay minerals, due to high sorption in these soils. However, it is possible that antibiotics could have adverse affects in other soils.