The role of microorganisms in the degradation of fluorinated xenobiotics in the environment
Fluorine is a key element in numerous everyday products including pharmaceuticals, agrochemicals and industrial chemicals. Consequently, anthropogenic organofluorine compounds are widely distributed in the environment where microorganisms may biotransform them. Early biodegradation studies employed simple fluorinated aliphatic (e.g. fluoroacetate) and aromatic (e.g. fluorobenzoate) species. These experiments demonstrated that such model compounds could be mineralised with the elimination of fluoride ion. However, fluorinated xenobiotics are likely to contain multiple fluorine atoms, often in recalcitrant groups such as trifluoromethyl, which makes complete biodegradation much less likely and may yield potentially dangerous fluorinated metabolites. The biological impacts of these fluorinated xenobiotics, and their biotransformation products, are important in a ‘one health’ context, so are a focus of contemporary research. In this paper, the recent literature on the microbial degradation of fluorinated xenobiotics will be reviewed and how our improved understanding might impact on fluorochemical production and regulation will be discussed.
Fluorine’s unique physicochemical properties with respect to its atomic size (comparable to hydrogen and hydroxy), electronegativity (3.98 on the Pauling scale) and strength of its bond with carbon make the element particularly useful in the design and manufacture of pharmaceuticals and agrochemicals. The presence of fluorine in these molecules can enhance biological activity and impede metabolism compared with the non-fluorinated analogues. Fluorine is also present in numerous industrial chemicals, notably CFCs/HCFCs and, in particular, per- and poly-fluorinated alkyl substances (PFAS). In the latter most or all of the hydrogen atoms in a hydrocarbon chain are replaced with fluorine, causing the molecules to pack together resulting in a product that can repel oil and water. These compounds have wide-spread use as non-stick coatings, such as Teflon, and in fire-fighting foams. Recently, the contamination of watercourses with PFA ...