Improved Prediction of Octanol−Water Partition Coefficients from Liquid−Solute Water Solubilities and Molar Volumes

A volume-fraction-based solvent−water partition model for dilute solutes, in which the partition coefficient shows a dependence on solute molar volume ( ), is adapted to predict the octanol−water partition coefficient (Kow) from the liquid or supercooled-liquid solute water solubility (Sw), or vice versa. The established correlation is tested for a wide range of industrial compounds and pesticides (e.g., halogenated aliphatic hydrocarbons, alkylbenzenes, halogenated benzenes, ethers, esters, PAHs, PCBs, organochlorines, organophosphates, carbamates, and amides-ureas-triazines), which comprise a total of 215 test compounds spanning about 10 orders of magnitude in Sw and 8.5 orders of magnitude in Kow. Except for phenols and alcohols, which require special considerations of the Kow data, the correlation predicts the Kow within 0.1 log units for most compounds, much independent of the compound type or the magnitude in Kow. With reliable Sw and data for compounds of interest, the correlation provides an effective means for either predicting the unavailable log Kow values or verifying the reliability of the reported log Kow data

Fast and Slow Rates of Naphthalene Sorption to Biochars Produced at Different Temperatures

This study investigated the sorption kinetics of a model solute (naphthalene) with a series of biochars prepared from a pine wood at 150–700 °C (referred as PW100–PW700) to probe the effect of the degree of carbonization of a biochar. The samples were characterized by the elemental compositions, thermal gravimetric analyses, Fourier transform IR spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller-N₂ surface areas (SA), and pore size distributions. Naphthalene exhibited a fast rate of sorption to PW150 owning a high oxygen content and a small SA, due supposedly to the solute partition into a swollen well-hydrated uncarbonized organic matter of PW150. The partial removal of polar-group contents in PW250/PW350, which increased the compactness of the partition medium, decreased the diffusion of the solute into the partition phase to result in a slow sorption rate. With PW500 and PW700 displaying low oxygen contents and high SA, the solute sorption rates were fast, attributed to the near exhaustion of a partition phase in the sample and to the fast solute adsorption on the carbonized biochar component. The results illustrate that the sorption rate of a solute with biochars is controlled largely by the solute’s diffusivity in the biochar’s partition phase, in which the medium compactness affects directly the solute diffusivity

Relation of Organic Contaminant Equilibrium Sorption and Kinetic Uptake in Plants

Plant uptake is one of the environmental processes that influence contaminant fate. Understanding the magnitude and rate of plant uptake is critical to assessing potential crop contamination and the development of phytoremediation technologies. We determined (1) the partition-dominated equilibrium sorption of lindane (LDN) and hexachlorobenzene (HCB) by roots and shoots of wheat seedlings, (2) the kinetic uptake of LDN and HCB by roots and shoots of wheat seedlings, (3) the kinetic uptake of HCB, tetrachloroethylene (PCE), and trichloroethylene (TCE) by roots and shoots of ryegrass seedlings, and (4) the lipid, carbohydrate, and water contents of the plants. Although the determined sorption and the plant composition together suggest the predominant role of plant lipids for the sorption of LDN and HCB, the predicted partition with lipids of LDN and HCB using the octanol−water partition coefficients is notably lower than the measured sorption, due presumably to underestimation of the plant lipid contents and to the fact that octanol is less effective as a partition medium than plant lipids. The equilibrium sorption or the estimated partition can be viewed as the kinetic uptake limits. The uptakes of LDN, PCE, and TCE from water at fixed concentrations increased with exposure time in approach to steady states. The uptake of HCB did not reach a plateau within the tested time because of its exceptionally high partition coefficient. In all of the cases, the observed uptakes were lower than their respective limits, due presumably to contaminant dissipation in and limited water transpiration by the plants

Turbulence Effects on Volatilization Rates of Liquids and Solutes

Volatilization rates of neat liquids (benzene, toluene, fluorobenzene, bromobenzene, ethylbenzene, m-xylene, o-xylene, o-dichlorobenzene, and 1-methylnaphthalene) and of solutes (phenol, m-cresol, benzene, toluene, ethylbenzene, o-xylene, and ethylene dibromide) from dilute water solutions have been measured in the laboratory over a wide range of air speeds and water-stirring rates. The overall transfer coefficients (KL) for individual solutes are independent of whether they are in single- or multi-solute solutions. The gas−film transfer coefficients (kG) for solutes in the two-film model, which have hitherto been estimated by extrapolation from reference coefficients, can now be determined directly from the volatilization rates of neat liquids through a new algorithm. The associated liquid−film transfer coefficients (kL) can then be obtained from measured KL and kG values and solute Henry law constants (H). This approach provides a novel means for checking the precision of any kL and kG estimation methods for ultimate prediction of KL. The improved kG estimation enables accurate KL predictions for low-volatility (i.e., low-H) solutes where KL and kGH are essentially equal. In addition, the prediction of KL values for high-volatility (i.e., high-H) solutes, where KL ≅ kL, is also improved by using appropriate reference kL values

Resolution of Adsorption and Partition Components of Organic Compounds on Black Carbons

Black carbons (BCs) may sequester non-ionic organic compounds by adsorption and/or partition to varying extents. Up to now, no experimental method has been developed to accurately resolve the combined adsorption and partition capacity of a compound on a BC. In this study, a unique “adsorptive displacement method” is introduced to reliably resolve the adsorption and partition components for a solute–BC system. It estimates the solute adsorption on a BC by the use of an adsorptive displacer to displace the adsorbed target solute into the solution phase. The method is validated by tests with uses of activated carbon as the model carbonaceous adsorbent, soil organic matter as the model carbonaceous partition phase, <i>o</i>-xylene and 1,2,3-trichlorobenzene as the reference solutes, and <i>p</i>-nitrophenol as the adsorptive displacer. Thereafter, the adsorption–partition resolution was completed for the two solutes on selected model BCs: four biochars and two National Institute of Standards and Technology (NIST) standard soots (SRM-2975 and SRM-1650b). The adsorption and partition components resolved for selected solutes with given BCs and their dependences upon solute properties enable one to cross-check the sorption data of other solutes on the same BCs. The resolved components also provide a theoretical basis for exploring the potential modes and extents of different solute uptakes by given BCs in natural systems