Aerobic biodegradation of [ 14C] 6:2 fluorotelomer alcohol in a flow-through soil incubation system

Abstract

The aerobic biodegradation of [1,2- 14C] 6:2 FTOH [F(CF 2) 6 14CH 2 14CH 2OH] in a flow-through soil incubation system is described. Soil samples dosed with [1,2- 14C] 6:2 FTOH were analyzed by liquid scintillation counting, LC/ARC (liquid chromatography/accurate radioisotope counting), LC/MS/MS, and thermal combustion to account for 6:2 FTOH and its transformation products over 84 d. Half of the [1,2- 14C] 6:2 FTOH disappeared from soil in 1.3 d, undergoing simultaneous microbial degradation and partitioning of volatile transformation product(s) and the 6:2 FTOH precursor into the air phase. The overall 14C (radioactivity) mass balance in live and sterile treatments was 77–87% over 84-d incubation. In the live test system, 36% of total 14C dosed was captured in the airflow (headspace), 25% as soil-bound residues recovered via thermal combustion, and 16% as soil extractable. After 84 d, [ 14C] 5:2 sFTOH [F(CF 2) 5CH(OH) 14CH 3] was the dominant transformation product with 16% molar yield and primarily detected in the airflow. The airflow also contained [1,2- 14C] 6:2 FTOH and 14CO 2 at 14% and 6% of total 14C dosed, respectively. The other significant stable transformation products, all detected in soil, were 5:3 acid [F(CF 2) 5CH 2CH 2COOH, 12%], PFHxA [F(CF 2) 5COOH, 4.5%] and PFPeA [F(CF 2) 4COOH, 4.2%]. Soil-bound residues as well as conjugates between fluorinated transformation products and dissolved soil components were only observed in the live test system and absent in the sterile soil, suggesting that such binding and complexation are microbially or enzymatically driven processes. At day 84, 5:3 acid is postulated to be the major transformation product in soil-bound residues, which may not be available for further biodegradation in soil environment.