Sorption Of Neutral Organic Compounds Research Articles

Predicting the Sorption of Aromatic Acids to Noncarbonized and Carbonized Sorbents.

Approaches based on the octanol-water partition coefficient are commonly used to describe sorption of neutral organic compounds in environmental systems, but they are not suitable for organic acids, which can dissociate to form anions. We here investigate the applicability of an alternative approach based on the pH-dependent distribution ratio (DOW) to describe sorption of aromatic acids to sorbents representing different degrees of carbonization. Sorption isotherms for four structurally similar acids ((2,4-dichlorophenoxy)acetic acid (2,4-D), 4-chloro-2-15 methylphenoxy)acetic acid (MCPA), 4-(2,4-dichlorophenoxy)butanoic16 acid (2,4-DB), and 5-chloro-2-(2,4-dichlorophenoxy)phenol (triclosan)) were measured for 15 sorbents: fresh and carbonized wood shavings, pig manure, sewage sludge, carbon nanotubes, and activated carbon. Dissociation greatly affected the sorption of all acids. Sorption coefficients measured in the high pH range indicated that sorption of the anions ranged over several orders of magnitude and should not be neglected. Sorption trends for all sorbates and carbonized sorbents could be very well described by a single regression equation that included DOW of the sorbate and the specific surface area of the sorbent (R(2) > 0.89).

Performance of chromatographic systems to model soil–water sorption

A systematic approach for evaluating the goodness of chromatographic systems to model the sorption of neutral organic compounds by soil from water is presented in this work. It is based on the examination of the three sources of error that determine the overall variance obtained when soil–water partition coefficients are correlated against chromatographic retention factors: the variance of the soil–water sorption data, the variance of the chromatographic data, and the variance attributed to the dissimilarity between the two systems. These contributions of variance are easily predicted through the characterization of the systems by the solvation parameter model. According to this method, several chromatographic systems besides the reference octanol–water partition system have been selected to test their performance in the emulation of soil–water sorption. The results from the experimental correlations agree with the predicted variances. The high-performance liquid chromatography system based on an immobilized artificial membrane and the micellar electrokinetic chromatography systems of sodium dodecylsulfate and sodium taurocholate provide the most precise correlation models. They have shown to predict well soil–water sorption coefficients of several tested herbicides. Octanol–water partitions and high-performance liquid chromatography measurements using C18 columns are less suited for the estimation of soil–water partition coefficients.

Lumping Analysis for Sorption of Neutral Organic Compounds in Mixtures to Simulated Aquifer Sorbents

The concept of using lumping analysis to reduce the complexity associated with the sorption of 12 neutral organic compounds (NOCs) comprising complex mixtures to simulated aquifer sorbents was evaluated. The sorbates covered a wide range of octanol-water partitioning coefficients, Kow (i.e., � 0:24 ≤ logKow ≤ 4:23), and the sorbents included different types of mineral surfaces and humic acid- mineral complexes with different fractions of organic carbon, f oc (i.e., 0:006% ≤ f oc ≤ 0:221%). Both a priori lumping criteria (i.e., the aqueous activity coefficient at saturation γ sat , and the organic carbon partitioning coefficient, Koc) and experimentally derived lumping criteria (i.e., Freundlich sorption parameters) were evaluated as potential lumping criteria. The results indicated that the sorption behavior of the 12 NOCs contained in mixtures could be approximated reasonably well by lumping them into a fewer number of pseudocompounds (four to six) with similar sorption behaviors based on Freundlich sorption parameters, and that both γ sat and Koc could be used as viable a priori lumping criteria. However, the number and compositions of the pseudocompounds were a complex function of the hydrophobicity (i.e., γ sat and Koc) of the NOCs and varied as a function of the type of mineral surface (e.g., uncoated, α-FeOOH-coated, and Al2O3-coated sands) and the f oc of the sorbent. DOI: 10.1061/(ASCE)EE.1943-7870.0000498. © 2012 American Society of Civil Engineers. CE Database subject headings: Organic carbon; Organic compounds; Organic matter; Pollutants; Soil pollution; Sorption; Subsurface environment. Author keywords: Lumping analysis; Mixtures; Neutral organic compounds; Pseudocompounds; Simulated aquifer sorbent; Sorption.

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

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.

The influence of salting out on the sorption of neutral organic compounds in estuaries

The relative (unsaturated) solubility and sorption of 2,2′,5,5′-tetrachlorobiphenyl have been studied along an estuarine salinity gradient. The aqueous compound was salted out with increasing salinity and an aqueous salting constant of about 0.002 l g −1 was derived. Sorption of the compound to estuarine particles increased with increasing salinity for a range of particle concentrations, but the magnitude of this effect (sorption salting constants of about 0.005–0.01 l g −1) indicated that salting out of the aqueous phase was not solely responsible. It is suggested that the hydrophobicity of sediment organic matter is enhanced by its interaction with seawater ions through a reduction in the charge of the particle surface and, possibly, modification of the structure of the organic matter. Examination of literature data on the sorption of neutral organic compounds to estuarine sediment indicates a general increase in sorption with increasing salinity which can be empirically defined by a salting equation. Although charge reduction of estuarine particles is a general observation, it is not possible to establish the general significance of this effect (or any other form of salting out of sediment organic matter) on the sorption of organic compounds in estuaries because appropriate site- and compound-specific aqueous salting constants are unavailable. Increased sorption at high salinities has obvious implications for the disposal and transport of organic chemicals in estuaries. However, the inverse dependency of sediment–water partitioning on particle concentration is likely to be of at least equal significance in macrotidal environments where sediment resuspension occurs. An empirical model, combining the effects of salinity and particle concentration, is proposed for deriving first-order estimates of the partitioning of neutral organic compounds in estuaries.

Chromatographic models for the sorption of neutral organic compounds by soil from water and air

The solvation parameter model is used to construct models for the estimation of the soil–water and soil–air distribution constants and to characterize the contribution of fundamental intermolecular interactions to the underlying sorption processes. Wet soil is shown to be quite cohesive and polar but relatively non-selective for dipole-type, lone-pair electron and hydrogen-bond interactions. Using a comparison of system constant ratios chromatographic systems employing reversed-phase liquid chromatography on polar bonded phases are shown to provide suitable models for estimating soil–water distribution constants. No suitable gas chromatographic models were found for the soil–air distribution constant but the requirements for such a system are indicated. Models are also provided for adsorption at the air–water interface. Estimation methods based on either the solvation parameter model or chromatographic model reproduce experimental distribution constants for a wide variety of compounds with a similar error (0.2–0.3 log units) to that expected in the experimental data.