Interaction of Perfluorooctanoate and Perfluorohexanoate with Moringa oleifera Seed Protein

Per- and polyfluoroalkyl substances (PFAS) are persistent and potentially toxic pollutants found widely in the environment; however, there is a lack of understanding how these materials interact with many interfaces that are important for remediation. The association of perfluorooctanoate (PFOA) and perfluorohexanoate (PFHxA) with Moringa oleifera seed protein was investigated using neutron reflectometry. The seed protein is known to associate with many materials and adsorbs irreversibly to silica surfaces, and it was shown that it was not removed by rinsing with water. PFHxA and PFOA were found to adsorb to the previously bound protein, forming mixed layers of protein, surfactant, and water that expanded to incorporate the extra material. On rinsing with water, PFOA was removed from the layer, leaving the protein bound to the silica surface. An almost three-times larger volume fraction of PFOA than PFHxA was observed in the protein layer. At the critical micelle concentration, the layer consisted of 1.8 mg m^-2 PFOA and 1.3 mg m^-2 of protein. Comparison of the relative amounts of each surfactant and protein suggests that hydrophobic interactions play a significant role in the coadsorption. The results indicate that the seed protein could be used to adsorb PFAS reversibly as a step toward remediation of contamination. This quantification of association with an albumin-like protein is important for understanding of transport both in human bodies and in the environment.