Effect of Ionic Strength and Index Cation on the Sorption of Phenanthrene

摘要

Sorption characteristics of phenanthrene were studied in batch equilibrium experiments with 32 Australian soils that varied widely in physicochem-ical properties. Sorption of phenanthrene varied widely among the soils and was generally nonlinear, with the nonlinearity index (n) of the Freundlich isotherm varying from 0.62 to 1.01. Simple regression analyses revealed that total organic carbon (TOC) accounts for about 68 % of the variation in the partition coefficient (K'_f) for sorption among the soils at an equilibrium concentration (C_e) of 0.05 mg/L. The organic carbon normalized distribution coefficient (K_(OC)), varied considerably between soils with ＞70 % of the variance of logK_(OC) being accounted for by logTOC, clay and log dissolved organic carbon (DOC). These results show that the phenanthrene C_e is influenced by both TOC as well as the DOC in soil suspensions. The effects of ionic strength (IS) and index cation were investigated using four contrasting soils. Results show that with an increase in IS from 0.03 to 0.15 M sorption of phenanthrene generally increased in CaCl_2 background solutions, whereas the effect was less significant and variable in NaCl background solutions. Sorption of phenanthrene was slightly higher at low IS (0.03 M) with Na~+ as index cation compared with that of Ca~(2+), whereas an opposite trend was observed at higher IS (0.15 M). For two soils high in TOC, the flocculation of endogenous DOC in the presence of Ca~(2+) reduced the influence of background electrolyte and resulted in a more linear sorption isotherm as well as higher sorption capacity. This trend was more significant with Ca~(2+) relative to Na~(2+).