Spectroscopic studies of ternary interactions in an oocyst-surfactant-hematite system

摘要

Prior studies have indicated that the subsurface transport of Cryptosporidium parvum is diminished in sediments containing iron oxides, but the molecular mechanisms are poorly known, as are the impacts thereon of natural organic matter (NOM). Using in-situ attenuated total reflectance (ATR)-FTIR spectroscopy, we examined the molecular mechanisms of viable Cryptosporidium parvum oocyst adhesion at the hematite (alpha-Fe_2O_3)-water interface over a wide range in solution chemistry. The anionic surfactant sodium dodecylsulfate (SDS) was used as a surrogate for NOM to examine the impacts of surfactant-type components on oocyst adhesion mechanisms. Results indicate that, in the absence of SDS, oocyst surface carboxylate groups form inner-sphere complexes with hematite Fe metal centres at low pH and outer-sphere complexes at high pH. Such direct chemical bonding is likely one mechanism whereby Fe oxides diminish oocyst transport. The presence of SDS significantly diminishes Fe-carboxylate complexation in the oocyst-SDS-hematite ternary system. Results suggest that the sulfate groups (OSO_3) of SDS compete effectively for alpha-Fe_2O_3 surface sites, and this is likely the primary mechanism for decreasing Fe-carboxylate complexation. Sorptive competition with NOM may, therefore, increase the mobility of C. parvum oocysts in soils.