Sorption of Neutral Organic Compounds in Mixtures to Mineral Surfaces and Humic Acid-Mineral Complexes

Abstract

The sorption of 12 neutral organic compounds (NOCs) contained in mixtures to both hydrophilic mineral surfaces [uncoated, iron (hydr)oxide-coated, and aluminum (hydr)oxide-coated sands] and humic acid-mineral complexes with different fractions of organic carbon, foc (=0.051, 0.119, and 0.221%) was evaluated using batch equilibrium sorption tests. The 12 compounds included six nonpolar NOCs (1,2,4-trichlorobenzene; 1,4-dichlorobenzene; chlorobenzene; m-xylene; toluene; and benzene) and six polar NOCs (2,4-dimethyl phenol; p-cresol; phenol; 2-hexanone; 2-butanone; and acetone). For sorption of the nonpolar NOCs, mixture effects (e.g., competitive or cooperative effects) were not statistically significant (95% confidence level) regardless of changes in mixture composition or type of sorbent. In contrast, mixture effects for some of the polar NOCs (2,4-dimethyl phenol; p-cresol; phenol; and 2-hexanone) were statistically significant and depended on both the mixture compositions (concentration and polarity of the NOC) and the type of sorbent (availability of hydrophilic interaction sites). These results suggest that direct experimental measurement of sorption coefficients for polar NOCs contained in mixtures may be required to reduce errors in predicting the fate and transport of the polar NOCs and the risk posed to potential receptors.