Incorporation of trifluoroacetate, a hydrofluorocarbon decomposition byproduct, by freshwater benthic microbial communities

Abstract

Concentrations of trifluoroacetate (TFA) in the environment are expected to increase because it is an atmospheric degradation product of CFC replacement compounds that will receive widespread use. TFA possesses high water solubility and its movement in the biosphere will be closely linked with the hydrologic cycle. Surface waters and sediment pore waters will receive loadings directly through precipitation and runoff and indirectly via soil-and ground-water inputs. Studies were conducted to assess whether TFA could be metabolized under aerobic conditions by microbial communities in freshwater surface sediments. Sediment samples were collected to a depth of 2–3 mm from flowing-water mesocosms in which organisms were pre-exposed to 30 μg TFA/l over a 2.5 year period and from control mesocosms that received no TFA. The sediment-associated microbial communities were tested for ability to incorporate of 2-[ 14C]TFA (added at 43 μg/l) in time course experiments. The communities pre-exposed to TFA in the mesocosms showed a low, but statistically significant, level of radiolabel incorporation. The cell-specific rate of incorporation for communities sampled from the TFA mesocosms increased nearly 20-fold during the 2.5 year experiment, from 1.15×10 −13 to 2.22×10 −12 μg·cell −1·day −1. Communities from the control mesocosm never showed statistically significant incorporation. Communities pre-exposed to TFA for ∼1.5 years also incorporated [ 14C]TFA when exposed to concentrations as low as 2 μg/l. Our results indicate a low level of incorporation of the xenobiotic TFA by natural microbial communities and thus their potential to serve as a point for TFA to enter into the food web.