Adaptation to a quaternary ammonium surfactant in aquatic sediment microcosms

Abstract

Adaptation by natural microbial communities may be operationally defined as an increase in the biodegradation rate of a chemical as a result of exposure to the material. The comparative adaptation of sediment-associated and water microbial communities to the sorptive cationic surfactant dodecyltrimethylammonium chloride (C12-TMAC) was studied in continuous-flow, settled-sediment microcosms. In microcosms initially exposed to an input concentration of 0.1 mg/L C12-TMAC, biodegradation activity in the water column increased 20-fold after approximately 10 to 15 d. As input concentrations of C12-TMAC entering the microcosm were increased, water column biodegradation activity also increased, even though measured water column concentrations remained relatively constant, due to biodegradation and/or adsorption. When C12-TMAC input was reduced to zero, microbial activity returned to control levels. Sediment biodegradative activity was unaffected by input concentrations of C12-TMAC below 0.5 mg/L. When the input concentration was increased to 10 mg/L, biodegradative activity increased by at least 10-fold. Once adaptation had occurred in the sediments, the process was relatively unaffected by reductions in the concentration of C12-TMAC entering the microcosms. Thus, relative to processes in the water column, the presence of sediments can influence both the onset of adaptation and its persistence.