Sorption of triclosan onto sediments and its distribution behavior in sediment–water–rhamnolipid systems

Abstract

Triclosan has been commonly used as an antimicrobial and disinfectant agent. Distribution between water and sediment plays a key role in its occurrence, transfer, and fate in the aquatic environment. Sorption of triclosan onto sediments and the effect of the biosurfactant rhamnolipid on distribution were studied in the present work. Batch equilibrium experiments were performed on three different sediments, with a wide triclosan concentration range. S-shaped equations can be used to describe the sorption behavior when triclosan concentration is relative high (50-250 µg · g⁻¹). The Pearl River, China (PR), sediment, which has the largest cumulative volume of pores, appeared to have great capability for continuously capturing triclosan. In the lower concentration range (10-150 µg · g⁻¹) assays, linear and Freundlich equations fitted the sorption isotherm data well. The pH value of sediment appeared to have a significant influence on sorption of low triclosan concentrations. Formation of rhamnolipid micelle remarkably decreased the sediment-water distribution ratio, K(d)*. Evaluation of the distribution efficiency, E, suggested that pores of sediment might have played a role in triclosan distribution, whereas sediment organic matter bound triclosan and reduced solubilization of triclosan. Rhamnolipid appears to be a good sorbent for triclosan. The findings of the present study suggest that, to understand the sorption and distribution of triclosan fully, studies should be carried out over a relatively broad concentration range.