Solvent Suitability for HFPO-DA ("GenX" Parent Acid) in Toxicological Studies

Per- and polyfluorinated alkyl substances (PFAS) are of significant interest because of their prevalence and environmental persistence. Further, for many PFAS, including fluorinated ethers, such as hexafluoropropylene oxide dimer acid (HFPO-DA, or the parent acid of "GenX"), toxicological data are sparse. In general, in vitro testing frequently uses dimethyl sulfoxide (DMSO) as a carrier solvent due to its low toxicity, solubility across vast chemical space, and permeation across biological barriers. For PFAS, laboratory practice has assumed that the materials are stable across a wide range of solvents, pHs, and temperatures. In this study, HFPO-DA stability was evaluated with DMSO and other commonly used solvents to determine each solvent's suitability for use in toxicity assays. The formation of HFPO-DA's degradation product, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether (Fluoroether E-1), was monitored by headspace gas chromatography-mass spectrometry (GC-MS) over time. These experiments revealed degradation of HFPO-DA to Fluoroether E-1 in DMSO and other aprotic, polar solvents, with half-lives on the order of hours (1 h, 1.25 h, and 5.2 h for DMSO, acetone, and acetonitrile, respectively). This rapid degradation suggests the need for caution when performing or using data from toxicity assessments on HFPO-DA and closely related PFAS compounds.