Sorption of benzothiazoles onto sandy aquifer material under equilibrium and non-equilibrium conditions

In this study, the sorption behaviour of 1,3-benzothiazole (BT) and 2-(methylthio)benzothiazole (MTBT, 2-methylsulphanyl-1,3-benzothiazole) on Danube geosorbent under equilibrium and non-equilibrium conditions was investigated. All sorption isotherms fitted well with the Freundlich model (R-2: 0.932-0.993). The results showed that the organic matter of the Danube geosorbent has a higher sorption affinity for the more hydrophobic MTBT compared to BT. However, sorption-desorption experiments showed that MTBT was more easily desorbed than BT molecules, which indicates the importance of absorption relative to adsorption in the overall sorption mechanism of MTBT. In general, molecules of BT and MTBT were more easily desorbed in the lower concentration range, which resulted in an increase in the hysteresis indices with increasing concentration. Column experiments revealed that the retention of the investigated compounds on the aquifer material followed the hydrophobicity of the compound. BT showed a lower retention, in accordance with its lower sorption affinity obtained in the static experiments, while MTBT showed a,greater sorption affinity, and thus had a longer retention time on the column. Thus during transport, BT represent a greater risk for groundwaters than MTBT. These results improved the understanding of the sorption and desorption processes of benzothiazoles, which represent one of the most important factors that influence the behaviour of organic compounds in the environment.