Influence of Soil Properties and Test Conditions on Sorption and Desorption of Testosterone

Abstract

In this study, batch sorption and desorption experiments were conducted for testosterone using four agricultural soils and five clay minerals. Significant differences in sorption behavior were observed between abiotic and biotic systems. The Freundlich sorption coefficient Kf (µg per g)/(µg per mL) ranged from 8.53 to 74.46 for soils and from 35.28 to 1243 for clays. The maximum sorption capacity (µg per g) of soils ranged from 25.25 to 440.61 for soils and 168.46 to 499.84 for clays. Correlation of sorption model parameters with soil properties indicated that both clay content and soil organic matter are important variables in predicting testosterone sorption behavior. Observed testosterone desorption from agricultural soils ranged from approximately 14 to 100 percent after 3 desorption cycles, and the desorption percentage decreased as the initial testosterone concentration decreased. Temperature, ionic strength, the water/soil ratio and soil depth were determined to influence sorption and desorption of testosterone. Desorption significantly increase with the soil depth and with the increase in the water to soil ratio. Temperature had an inverse effect on the sorption capacity of the soils tested. Thermodynamic calculations showed that the enthalpy change of the soils tested were the range of 12.9-20.7 kJ per mol, indicating weak interaction between testosterone and soil. Our results suggest that additional studies on how soil particles with different size fractions affect hormones fate and transport are needed in order to determine the potential risk of testosterone leaching or runoff.