Sorption and desorption of testosterone at environmentally relevant levels: Effects of aquatic conditions and soil particle size fractions

Sorption and desorption have been found to be critical in the fate and transport of hormones in soils. Previous study indicated that the sorption and desorption properties of soil particles of different size fractions associated with hormones were very different. However, the interaction mechanisms of hormones with these soil particles are still unclear. This study investigated the influence of aquatic conditions [e.g., temperature, hydrogen ion concentration (pH), ionic strength, soil/water ratio, organic matter] on the sorption and desorption of soil particles of three size fractions [i.e., sand (0.425-0.075 mm), silt (0.045-0.002 mm), and clay (0.6-2 μm)] associated with testosterone at environmentally relevant concentrations (i.e., 20-150 ng/L) in batch reactors. The results indicate that lower temperature will facilitate sorption but hinder desorption of testosterone onto/from all of the soil particles. Lower pH and higher organic matter content will favor the sorption of testosterone onto all of the soil particles, especially for clay, but will impede desorption. A higher soil/water ratio would impede desorption of testosterone from all of the soil particles. The main sorption mechanism of trace-level testosterone onto sand is electrostatic attraction, whereas that onto clay is mainly hydrogen bonding and functional groups, and that onto silt is in the middle of sand and clay. The study provides insights on controlling/predicting the behavior/fate of hormones in the soil environment.