Agricultural fields, surface waters and ground water can be contaminated with antibiotics through the application of antibiotic-contaminated swine manure. One of the more common antibiotics used for the swine industry is sulfamethazine (SMZ). The focus of this dissertation is to investigate the fate and transport of SMZ in soils in the presence of manure when applied to the fields. Sorption coefficients of SMZ for five local soils from Iowa with organic carbon (OC) contents ranging from 0.1 % to 3.8 % and solution pHs ranging from 5.5 to 9 were determined using batch sorption experiments. Sorption data fitted well to a linear sorption model but not to a non-linear Freundlich model. The linear sorption coefficients (Kd) were found to decrease with an increase in soil-solution pH. In addition, the K d values were found to increase with an increase in % OC of soil at a given pH. At pH 5.5, Kd values were 0.58 L kg-1 and 3.9 L kg-1 for soils with 0.1 % OC and 3.8 % OC, respectively. Hydrophobic sorption was probably involved for pH < 7.4 due to the unionized form of SMZ while some surface sorption was probably involved for pH > 7.4 due to the ionized form of SMZ. A mechanistic model and a linear regression model incorporating soil properties and fractions of ionized SMZ were developed and found to estimate Kd values of other studies.
Inhibitory effects of SMZ on anaerobic microbial respiration were observed at SMZ concentration of 50 mg kg-1 while inhibition of aerobic microbial respiration was observed at between 50 and 100 mg kg-1. The availability-adjusted first-order model but not simple first-order kinetics was found to fit the data well. Half-lives of SMZ ranged from 1.2 to 6.6 days and 2.3 to 15.1 days under aerobic and anaerobic conditions, respectively. The fate of 14C-SMZ in soil showed that 70 to 91 % of 14C-SMZ was bound to soils. Only 0.1 to 1.5 % of 14C-SMZ was completely mineralized to 14CO2 with the highest mineralization under aerobic conditions. The metabolites accounted for 5 to 10 % of SMZ and were found to be N4-acetylsulfamethazine and desamino sulfamethazine.
Leaching of SMZ from soils and from manure-amended soils were investigated using topsoil mixed with SMZ or with SMZ-contaminated manure to a concentration of 7.25 mg kg-1 soil. The first simulated rainfall event applied to soil cores at 1, 4 and 7 days after the application of SMZ was followed by a second rain event, three days after the first rain event. Concentrations of SMZ in leachate were found to be the highest for first day after rainfall with concentration of 432 ± 167 µg L-1. Concentrations of SMZ in the leachate decreased with longer time duration between application of SMZ and the first rain event. The results showed that manure in the soils did not impact the leaching of SMZ and that colloid-facilitated transport of SMZ was unlikely. This study suggested that SMZ is expected to leach from manure-amended soils or manure even though SMZ may be degraded or bound to the soils.
|Advisor:||Ong, Say Kee, Moorman, Thomas B.|
|Commitee:||Ellis, Timothy G., Gu, Roy, Loynachan, Thomas E.|
|School:||Iowa State University|
|Department:||Civil, Construction, and Environmental Engineering|
|School Location:||United States -- Iowa|
|Source:||DAI-B 70/01, Dissertation Abstracts International|
|Subjects:||Soil sciences, Agricultural engineering, Environmental engineering|
|Keywords:||Degradation, Depth distribution, Fate, Inhibiting, Leaching, Manure, Manure-amended soils, Sorption, Sulfamethazine, Sulfonamide|
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