Sorption and desorption of fluorene on five tropical soils from different climes

The main processes controlling soil-polycyclic aromatic hydrocarbon interaction is sorption-desorption as influenced by the soil physicochemical conditions. Sorption-desorption phenomena can influence translocation, persistence and bioavailability. Hence, laboratory batch experiments were undertaken to investigate the sorption characteristics of fluorene on five tropical soils from varying tropical agro-ecological zones having different physicochemical properties. Fluorene concentrations used for the study ranged from 20 to 100 μg/L, and results showed that fluorene sorption equilibria were attained usually within 24 h. Increase in pH had a negative effect on fluorene sorption. Fluorene sorption was concentration dependent and exothermic. The sorbed fluorene molecules were distributed between surface adsorption sites and phases in soil. Sorption was controlled by weak hydrophobic forces, such as the π-π interactions and Van der Waal's forces. Desorption hysteresis were most pronounced in soils with high organic matter contents than lower ones. The sorption was characterized as multiple reaction phenomena composed of several linear and non-linear isotherms. The physicochemical conditions of the soil must be understood in order to predict the fate and bioavailability of fluorene in soil.