|Lerch, Robert - Bob|
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2013
Publication Date: 5/1/2013
Citation: Chu, B., Anderson, S.H., Goyne, K.W., Lin, C., Lerch, R.N. 2013. Sulfamethazine transport in agroforestry and cropland soils. Vadose Zone Journal. DOI:10.2136/vzj2012.0124. Interpretive Summary: Veterinary antibiotics (VAs) are commonly used in livestock feed to prevent disease and enhance weight gain. These VAs can be introduced into the soil environment when animal manures are land applied as crop fertilizer or for waste disposal. Environmental concerns associated with VA contamination of soil include toxic effects to bacteria and potential development of antibiotic resistance genes. Some VAs, such as sulfamethazine (SMZ), are mobile in the soil environment and may leach to groundwater or be transported by surface runoff to streams or lakes where their presence may be toxic to existing bacteria or contaminate drinking water supplies. Determining the fate of VAs in the soil environment is important to understanding their potential environmental impacts and for assessing the effectiveness of practices that can mitigate their off-site transport. Vegetative buffers are one example of a practice that has been shown to reduce VA loss in surface runoff and may reduce leaching. The objectives of this research were to investigate the effect of two soils with different vegetative management on the sorption and leaching of the SMZ. Sorption is the term used to describe the binding of a compound to the soil by chemical and physical processes, and leaching refers to the downward movement of water and chemicals through the soil. Soils represented agroforestry (AGF) or cropland (Crop) management practices. The results showed that SMZ was bound more tightly to the AGF soil than the Crop soil. The greater organic matter content and lower soil pH of the AGF soil were the most important factors affecting SMZ binding. Because of its greater binding to the AGF soil, SMZ leaching through a 5 inch long soil column was also less than that of the Crop soil. Results of the column leaching study were used to develop models to predict the extent of SMZ leaching and the binding mechanisms of SMZ to soil. Model predictions were shown to be in good agreement with our observed results for binding and leaching of SMZ. The results provided further evidence that SMZ is quite mobile in soils and a threat to contaminate groundwater. The greater binding intensity of SMZ to the AGF soil compared to Crop soil supports the use of vegetative buffers to mitigate VA loss from manure-treated fields. This research will benefit land management agencies and growers by providing evidence to support the use of vegetative buffers as a best management practice for mitigating VA transport.
Technical Abstract: Knowledge of veterinary antibiotic transport and persistence is critical to understanding environmental risks associated with these potential contaminants. To understand mobility of sulfamethazine (SMZ) and sorption processes involved during SMZ transport in soil, column leaching experiments were performed with repacked soil columns containing silt loam soils collected from cropland and agroforestry (AGF) buffer systems. Bromide was applied as a non-reactive tracer. Sulfamethazine with or without 150 mg/L OC manure-derived dissolved organic matter (DOM), was added as a pulse and leaching of the compounds was monitored for 21 days. Breakthrough curves of SMZ and Br- were constructed for each column. Bromide breakthrough curves were fitted with an equilibrium model using the CXTFIT software, whereas SMZ breakthrough curves were fitted with the HYDRUS-1D software using multi-site models with linear or Freundlich sorption components. Results indicated that the three-site model containing two reversible sites and one irreversible site coupled with the Freundlich sorption component (3S2R-Freu-irrev model) best described SMZ transport through the columns with model efficiencies of 0.998, 0.994, and 0.991 for AGF, AGF + DOM and cropland soils, respectively. Fitted sorption parameters such as the linear sorption coefficient (Kd), Freundlich sorption coefficient (Kf), and Freundlich linearity parameter (N) were in the same range of those obtained from equilibrium sorption experiments. Data from equilibrium sorption experiments and column transport experiments suggested that the AGF soil had a larger capacity to retain SMZ than the cropland soil, and DOM had little effect on SMZ sorption or leaching. The results provided further evidence that SMZ is quite mobile in soils and a threat to contaminate groundwater. The greater SMZ sorption intensity to the AGF soil compared to cropland soil supports the use of vegetative buffers to mitigate VA loss from agroecosystems.