An investigation of the biodegradation potential of 8:2 fluorotelomer monomers in environmentally relevant systems
Much of the scientific literature on perfluorinated alkyl chemicals in the last decade has focused on the fate of fluorotelomer alcohols (FTOHs) in soil, sludge and the atmosphere as well as the identification and quantification of acid metabolites. The FTOH degradation metabolite of greatest interest has been perfluorooctanoic acid (PFOA) due to its apparent persistence, subsequent accumulation, and potential toxicity to wildlife and humans. The hydrolysis of fluorotelomer monomers used as surfactants or in the manufacturing of polymers is one of the most likely but unconfirmed source of FTOH and ultimately PFOA in the environment. To probe this hypothesis, and to explore structural factors affecting the microbial hydrolysis rates of two fluorotelomer esters, the biotransformation of 8:2 fluorotelomer acrylate (8:2 FTA), and 8:2 fluorotelomer methacrylate (8:2 FTMA) was monitored in aerobic soils for up to 105 days. At each sampling time, triplicate soil microcosms were sacrificed by sampling the headspace for volatile FTOHs followed by sequential extraction of soil for parent compounds, and transient and terminal degradation products. In microbial-active systems, both 8:2 FTA and 8:2 FTMA were hydrolyzed releasing 8:2 FTOH. Observed half-lives for FTA ranged between 3 and 5 days in three different soils. Furthermore, the observed half-lives for 8:2 FTMA in two different soils were determined to be at least three times (15-d) longer. Maximum FTOH levels between 8 and 11 mol % occurred by day 3 in 8:2 FTA microcosms. Subsequently, fluorotelomer carboxylic acids (FTCAs) and perfluorinated carboxylic acids (PFCAs) metabolites were generated consistent with the known biotransformation pathway of 8:2 FTOH. For 8:2 FTMA, the addition of a methyl group to the acrylate moiety adds sufficient bulk to cause some steric hindrances as well as elicit electronic differences that affect microbially-mediated ester cleavage rates. The subsequent aerobic degradation of 8:2 FTOH released from 8:2 FTMA followed the same pathway as observed for 8:2 FTA but yielded correspondingly lower metabolite concentrations. These biotransformation studies confirm the fluorotelomer esters as indirect sources of PFOA. Additional preliminary studies were conducted to probe the susceptibility of fluorotelomer-based polymers to biodegradation as well as the role of fungal enzymes in the transformation process. A small custom FTA polymer (seven acrylate monomer units) was synthesized and incubated in an aerobic agricultural soil. FTOH generation was observed, but hydrolysis of the fluorotelomer ester side chains could not be clearly delineated from degradation of the 8:2 FTA residuals. Fungi are ubiquitous organisms capable of catalyzing the degradation of lignin and other biopolymers. For assessing the potential for fungi to hydrolyze the ester bond, fluorotelomer monomers were incubated with Trametes versicolor and Pleurotus ostreatus in potato dextrose broth and potato dextrose agar. Results from the analysis of solvent extracts as well as headspace were statistically lacking, thus additional work is needed to validate fungal biodegradation potential. The dissertation work presented provides some of the first evidence of the biodegradation potential of fluorotelomer ester monomers to degrade into 8:2 fluorotelomer alcohol and subsequently perfluorinated acids. Although better experimental designs are needed to more completely understand the fate of fluorinated polymers in the environment, this work with some fluorotelomer monomers is a great starting reference. In addition, since the parent compounds along with primary and subsequent metabolites were all measured, this data set can be used to validate and improve current models used to predict fluorinated polymer biodegradation.
Lee, Purdue University.
Environmental Health|Soil sciences
Off-Campus Purdue Users:
To access this dissertation, please log in to our