SORPTION AND TRANSPORT OF A COMMON ANTI-BACTERIAL AGENT, TRICLOSAN, IN SOILS

Pharmaceutical and active ingredients in personal care products are some of the most ubiquitous compounds found in surface water across the world. Triclosan (5-chloro-2-(2,4-dichlorophenoxy) phenol), used as an antibacterial agent in many hand soaps and toothpastes, is commonly detected in surface waters and has been linked to endocrine-disrupting activity in mammals and aquatic life. After it is released into surface water as wastewater effluent, little is known about the transport and fate of triclosan in the environment. Because it is relatively nonpolar (log K_ow = 4.76), triclosan tends to accumulate in organic carbon-rich soils, sediments, and very importantly, in tissues of organisms that come in contact with it. The main goal of this study is to quantify how strongly triclosan sorbs to soils and sediments as a function of soil composition. A, E, and B horizon soils collected from a pristine forested watershed near Charleston, SC, were used for this study. Soils were homogenized and characterized for various soil properties including organic carbon (f_oc = 4-9%) and clay mineral content (4-9%). Soil-aqueous suspensions were spiked with varying concentrations of triclosan and allowed to equilibrate over a period of 72 h. Following the equilibration period, the aqueous phase was separated from the soil suspension, filtered, and analyzed using a GC/MS. The resulting sorption isotherms were fitted with Freundlich isotherms with distribution coefficients (K_f) that ranged from 0.060-0.342. A strong linear correlation between K_f and f_oc was found, indicating that triclosan preferentially sorbed to soils that contained higher organic carbon. Data from sorption isotherms will be used to model transport of triclosan in soil columns with reactive transport codes based on advection-dispersion equation and incorporating different sorption models. This will be followed up by actual column experiments and the model fits will be compared with actual data. It is expected that this study will help us gain a better understanding of geochemical fate of triclosan in the environment. Coastal marshes and estuarine zones, which are rich in organic matter, could potentially act as sinks for triclosan as well as other organic contaminants with similar chemical properties.