Sorption of perfluorooctane sulfonate (PFOS) on oil and oil-derived black carbon: influence of solution pH and [Ca2+].

Sorption of perfluorooctane sulfonate (PFOS) to oil and oil-derived black carbon (BC) from solutions varying in pH and [Ca(2+)] was investigated. Oil is a strong sorbent for PFOS, together with the independence of oil-water distribution coefficient (K(oil)) on solution parameters (pH values and [Ca(2+)]), suggesting that hydrophobic interactions of the hydrophobic moieties of PFOS with oil played a dominant role. BC sorption for PFOS is not stronger or more nonlinear than other natural organic carbon from solution in the case of 0.5mM [Ca(2+)] and pH 5.05, indicating that specific adsorption sites on BC were probably not fit for PFOS. However, both sorption capacity and nonlinearity of PFOS increased obviously with decreasing solution pH and increasing [Ca(2+)], resulting in the potential importance of BC at environmentally low PFOS level, from solution at high [Ca(2+)] or low pH. The role of BC in PFOS sorption was significantly influenced by environmental conditions and solute aqueous concentrations.