Effects of water soluble perfluorinated pollutants on phospholipids in model soil decomposer membranes

Water soluble perfluorinated compounds (PFCs) as perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA) and their shorter chain homologues are persistent organic pollutants widely distributed in the environment. PFCs accumulate in soils and sediments and because of their toxicity endanger the decomposer organisms. PFCs are toxic to a wide spectrum of soil bacteria and their biocide activity was related with their membrane activity; however, the exact mechanism of PFCs - bacterial membrane interactions is unknown. Therefore, to shed light on these questions we applied phospholipid Langmuir monolayers as simplified models of bacterial membranes and studied their interactions with selected environmentally relevant PFCs. The mechanical properties of the monolayers were characterized by surface pressure-mean molecular area isotherms and the analysis of compression modulus. The effects of PFC on the texture of the model membranes were studied with Brewster angle microscopy, whereas their influence on molecular packing in the 2D crystal lattice was searched by the Grazing Incidence X-ray diffraction technique. The effects of PFCs on the phospholipid polar heargroup conformation were studied by PM-IRRAS spectroscopy, whereas the effectivenes of the incorporation of PFCs into the model membrane was monitored in penetration tests. It turned out that the membranes rich in phosphatidylethanolamine typical to Gram negative bacteria are much PFCs susceptible than the cardiolipin rich membranes imitating Gram positive species. Moreover, the studies indicated that the switch from eight-carbon atom perfluorinated chains to shorter chain homologues is not necessarily environmentally benign as perfluorobutane sulfonate caused also significant structural changes in the model membranes.