Title: Rhizodegradation of Sulfamethazine and Tetracycline and the Associated Impacts on Soil Microbial Activities Authors
Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2009
Publication Date: June 1, 2009
Citation: Lin, C., Goyne, K.W., Kremer, R.J., Lerch, R.N., Garrett, H.E. 2009. Rhizodegradation of Sulfamethazine and Tetracycline and the Associated Impacts on Soil Microbial Activities. In: Gold, M.A., Hall, M.M., editors. Agroforestry Comes of Age: Putting Science into Practice. Proceedings of North American Agroforestry Conference, May 31-June 3, 2009, Columbia, Missouri. p. 349-358. Interpretive Summary: Antibiotics are commonly used to control infection and improve weight gain of animals in confined animal feed operations (CAFOs). In recent years, contamination of soil and water with these antibiotics has emerged as a concern. When manure from treated animals is applied to soils during grazing, applied to fields as fertilizer, or disposed of in lagoons, the opportunity for antibiotics to contaminate the environment exists. The primary concern associated with soil or water contamination by antibiotics is the development of antibiotic-resistant bacteria. This study investigated the degradation of two antibiotics commonly used in animal production, sulfamethazine (SLF) and tetracycline (TC), in soils collected from the root zone of different grass and tree species. The plant species included: 1) switchgrass, 2) eastern gammagrass, 3) orchardgrass, and 4) hybrid poplar. All plant treatments were grown in pots containing Mexico silt loam soil. Pots containing soil without plants were used as controls. Plants were grown to maturity, and the root zone soils were collected. SLF or TC were then applied to the soils and incubated in the dark for five weeks. In addition, the activity of three soil enzymes was also measured to see if degradation was related to the activity of the enzymes. The hybrid poplar treatment showed the greatest ability to degrade SLF. The higher SLF degradation rates in the poplar root zone were associated with higher enzymatic activities than the other treatments. When comparing the soil enzymatic activities between the antibiotic treatments, two of the three enzyme activities were lower in TC-treated soils than in SLF-treated soils. The hybrid poplar could be incorporated into buffer designs to mitigate the impacts of these two antibiotics in the environment. This work will benefit conservationists, landowners, and regulatory agencies by demonstrating which plant species should be included in vegetative buffers designed to enhance the degradation of these antibiotics in the environment.
Technical Abstract: The use of sulfamethazine (SLF) and tetracycline (TC) to maintain animal health in the swine, poultry or cattle feedlot operations results in significant application of these veterinary pharmaceuticals to the landscape during grazing or manure disposal operations. Drinking water sources contaminated by these veterinary antibiotics have raised public health concern in the US. Recent studies have demonstrated the benefits of using multi-species vegetated buffers to reduce the transport of the veterinary antibiotics. However, the fates of these antibiotics in vegetative buffers and their impact on the rhizosphere microbial activities have not been well documented. A growth chamber study was conducted to investigate the rhizodegradation of 3H-sulfamethazine and 3H-tetracycline and the relationship of degradation with soil enzyme activities in the rhizosphere of five selected plant species. The plant species included: 1) switchgrass, 2) eastern gammagrass, 3) orchardgrass, and 4) hybrid poplar. All plant treatments were grown in pots containing Mexico silt loam. Pots containing soil without plants were used as controls. Plants were grown to maturity (~3 months), and the rhizosphere soils were collected. Radio-labelled SLF or TC was then applied to the rhizosphere soils and incubated in the dark for five weeks. Among the plant species, hybrid poplar showed the highest capability for promoting degradation of SLF in the rhizosphere. The significantly higher SLF degradation rates in the poplar rhizosphere may have been associated with its high enzymatic activities. When comparing the soil enzymatic activities between the antibiotic treatments, fluorescein diacetate hydrolytic and glucosaminidase enzyme activities were significantly lower in TC treated soils than in SLF treated soils. The Beta-glucosidase activities were similar between the two antibiotics treatments. The hybrid poplar showing high rhizodegradation potential could be incorporated into buffer designs to mitigate the impacts of these two antibiotics in the environment.