Title: Dissipation of Sulfamethazine and Tetracycline in the Root Zone of Grass and Tree Species Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2010
Publication Date: May 20, 2010
Citation: Lin, C., Goyne, K.W., Kremer, R.J., Lerch, R.N., Garrett, H.E. 2010. Dissipation of Sulfamethazine and Tetracycline in the Root Zone of Grass and Tree Species. Journal of Environmental Quality. 39:1269-1278. Interpretive Summary: Antibiotics are used by farmers to treat and prevent illness in livestock. Many antibiotics do not degrade within the animal and are often passed through the animal as the intact compounds. Antibiotics can then be introduced into the environment through land application of animal manures. Release of antibiotics into the environment is of concern because they can be detrimental to soil microorganisms involved in ecological processes including decomposition and nutrient cycling, decrease water quality, and increase spread of antibiotic-resistant bacteria. Certain land management practices, including maintaining permanent vegetative buffer areas across the landscape, may be useful to mitigate the accumulation and spread of antibiotics in soils and in water dissipated from the soil in the form of surface runoff after rainfall events. Our objective was to determine the potential degradation of two antibiotics typically used in livestock production, sulfamethazine and tetracycline, in the root zones (rhizospheres) of various plants often used in buffers. We examined the fate of the antibiotics applied to soils planted to prairie grasses (switchgrass and eastern gammagrass), a cool-season pasture grass (orchardgrass), and young poplar trees. Tetracycline dissipated rapidly under all vegetative treatments possibly indicating the relative instability of this antibiotic in the soil environment. Sulfamethazine, however, was more persistent in soils and degraded most rapidly in the rhizosphere of the poplar saplings. The degradation rate was highly correlated with high microbial activity in the poplar rhizosphere suggesting that this plant species supports an aggressive microbial community for breaking down sulfamethazine. Thus, use of poplar trees in vegetative buffers adjacent to fields receiving livestock manure applications could help alleviate the dispersion of similar antibiotics in the environment. This information has important implications for scientists, land managers, extension personnel, and farmers because it helps to identify an effective land management strategy useful for limiting environmental effects of antibiotics that may be present in field-applied livestock manures. Furthermore, the best plant species for inclusion in the vegetative buffers to degrade those antibiotics are identified.
Technical Abstract: The use of veterinary antibiotics (VAs) to maintain animal health and increase growth promotion in confined animal feeding operations (CAFOs) results in significant application of VAs to agroecosystems during manure disposal operations. The detection of VAs in drinking water resources has raised public health concerns, and land managers are seeking techniques to reduce VA loss from the landscape. Studies have demonstrated the benefits of using multi-species vegetated buffer strips to reduce agrichemical transport from agroecosystems. However, the fate of VAs in vegetative buffers and the effect of antibiotics on rhizosphere microbial activities have not been well documented. A growth chamber study was conducted to investigate rhizodegradation of two commonly administered VAs, sulfamethazine (SMZ) and tetracycline (TC), and the relationship between VA degradation and soil enzyme activities in the rhizosphere of selected plant species. Switchgrass, eastern gammagrass, orchardgrass, and a hybrid poplar tree were grown in pots containing a Mexico silt loam/sand mixture for 3 months, followed by plant removal and collection of rhizosphere soils. Radio-labeled (3H) SMZ or TC was applied to the soils and incubated in the dark for five weeks. Among the plant species studied, hybrid poplar showed enhanced capability for promoting SMZ degradation in the rhizosphere. The increased rate of SMZ degradation in the poplar rhizosphere was positively correlated with enzymatic activity. Correlation coefficients (r) between the estimated SMZ half-life and enzymatic activities range from -0.81 to -0.98 (p = 0.004 to 0.095). Comparison of soil enzymatic activities between the antibiotic treatments revealed that fluorescein diacetate hydrolytic and glucosaminidase enzyme activities were significantly lower in TC treated soils than in SMZ treated soils. The beta-glucosidase activities were similar between the two antibiotic treatments. Enhanced SMZ degradation in the hybrid poplar rhizosphere soil suggests that incorporation of this plant species in vegetative buffer strips could help mitigate deleterious effects of SMZ in the environment.