Bioaccumulation of Triclocarban in Lumbriculus variegatus

摘要

The antimicrobial triclocarban (TCC) has been detected in streams and municipal biosolids throughout the United States. In addition, TCC and potential TCC transformation products have been detected at high levels (ppm range) in sediments near major United States cities. Previous work has suggested that TCC is relatively stable in these environments, thereby raising concerns about the potential for bioaccumulation in sediment-dwelling organisms. Bioaccumulation of TCC from sediments was assessed using the freshwater oligochaete, Lumbriculus variegatus. Worms were exposed to TCC in sediment spiked to 22.4 ppm to simulate the upper bound of environmental concentrations. Uptake from laboratory-spiked sediment was examined over 56 days for TCC and 4,4′dichlorocarbanilide (DCC), a chemical impurity in and potential transformation product of TCC. The clearance of TCC from worms placed in clean sediment was also examined over 21 d after an initial 35-d exposure to TCC in laboratory-spiked sediment. Concentrations of TCC and DCC were monitored in the worms, sediment, and the overlying water using liquid chromatography tandem mass spectrometry. Experimental data were fitted using a standard biodynamic model to generate uptake and elimination rate constants for TCC in L. variegatus. These rate constants were used to estimate steady-state lipid and organic-carbon normalized biota-sediment accumulation factors (BSAFs) for TCC and DCC of 2.2 ± 0.2 and 0.3 ± 0.1 goc/glip, respectively. Alternatively, directly-measured BSAFs for TCC and DCC after 56 days of exposure were 1.6 ± 0.6 and 0.5 ± 0.2 goc/glip, respectively. Loss of TCC from pre-exposed worms followed first-order kinetics, and the fitted elimination rate-constant was identical to that determined from the uptake portion of the present study. Overall, study observations indicate that TCC bioaccumulates from sediments in a manner that is consistent with the traditional hydrophobic organic contaminant paradigm.