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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #216241

Title: Effect of Organic Carbon and pH on Soil Sorption of Sulfamethazine

item Moorman, Thomas - Tom

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2009
Publication Date: 4/5/2009
Citation: Lertpaitoopan, W., Ong, S., Moorman, T.B. 2009. Effect of Organic Carbon and pH on Soil Sorption of Sulfamethazine. Chemosphere. 76(4):558-564.

Interpretive Summary: Antibiotics used in swine production enter the environment when manure is applied to fields. Subsequent movement of antibiotic in soils is governed by water flow, the degradation of the antibiotic and its binding to soil. Chemicals that are weakly bound to soil are more prone to leaching into tile drainage networks or groundwater. These experiments showed that soil organic carbon and pH control the movement of sulfamethazine in Iowa soils. Soil surface area was also an influence on binding of sulfamethazine. Sulfamethazine binding was weakest in soils with low organic carbon, high pH, and low surface area. We developed regression equation that predicts binding from these soil properties. These general findings may be used by other scientists in predicting binding of sulphonamide antibiotics and thus contribute to our understanding of these chemicals in the environment.

Technical Abstract: Batch sorption of sulfamethazine (SMZ) was conducted using five soils with organic carbon (OC) contents ranging from 0.1% to 3.8% and solution pHs ranging from 5.5 to 9. Initial aqueous SMZ concentrations ranged from 1.1 to 22.2 mg/L. Sorption of SMZ was found to be impacted by both OC and soil solution pH. The Kd’s were found to decrease as the pH increased. Linear partition coefficients, Kd’s, at pH 5.5 were found to be 0.83 ± 0.04 L/kg for soil with 0.1% OC and 3.90 ± 0.38 L/kg for soil with 3.8% OC. At pH 9, the Kd’s were found to be 0.18 ± 0.13 L/kg (soil with 0.1% OC) and 1.11 ± 0.05 L/kg (soil with 3.8% OC). Hydrophobic sorption was probably involved for pH < 7.4 (pKa,1 = 7.4 for SMZ) due to the unionized form of SMZ while surface sorption was probably involved for pH > 7.4 due to the ionized form of SMZ. A linear regression model incorporating the percent of SMZ ionization, percent organic carbon, and soil specific surface area was developed to estimate the Kd’s for soils at different pH and OC content.