William J. Doucette

Generator column determination of octanol/water partition coefficients for selected polychlorinated biphenyl congeners.

A generator column technique has been used to directly determine log K/sub ow/ values for 15 PCB congeners and biphenyl. The method circumvents many of the experimental difficulties encountered with the traditional shake-flask system. Log K/sub ow/ values generated by this procedure are compared with data obtained from the shake-flask method, two chromatographic estimation techniques, and the computational method of Hansch and Leo. Log K/sub ow/ values reported for the higher chlorinated congeners, including octa- and decachlorobiphenyl, are some of the highest ever measured directly.

Use of molecular connectivity indices to estimate soil sorption coefficients for organic chemicals

A correlation model is presented which relates log Koc to molecular connectivity indices (MCI) for a variety of organic compounds. Linear relationships are greatly improved when MCI indices relating to non-dispersive intermolecular interactions are included in the regression model.

Quantitative structure‐activity relationships for predicting soil‐sediment sorption coefficients for organic chemicals

Sorption coefficients are used to describe the equilibrium distribution of a chemical between a soil or sediment and the aqueous phase that it is in contact with. Although sorption coefficients for a particular organic chemical vary greatly from soil to soil, the observation has been made that sorption generally increases as the organic carbon content of the soil and the hydrophobicity of the chemical increases. This general observation resulted in the acceptance of organic carbon normalized sorption coefficients (KOC) as unique properties or constants of organic chemicals. In turn, KOC values have been estimated by quantitative structure-activity relationships (QSARs) developed by correlation with a variety of physical or chemical properties and structural descriptors related to the hydrophobicity of the chemical such as octanol-water partition coefficients, aqueous solubilities, molecularconnectivity indices, molecular weight, molecular surface area, and reverse-phase high-performance liquid chromatography retention times. The selection and application of the most appropriate QSAR for predicting KOC depend on several factors, including the availability of required input, the appropriateness of model to chemical of interest, and the methodology for calculating the necessary topological or structural information. A review of the existing QSARs for predicting KOC and the limitations of using the KOC approach to estimate sorption coefficients will be presented.

Estimation of octanol/water partition coefficients: Evaluation of six methods for highly hydrophobic aromatic hydrocarbons

Abstract Six methods for estimating log K ow were evaluated using a set of experimental values for 64 aromatic compounds. All log K ow values used in this evaluation were experimentally measured using a generator-column technique. This provided an accurate, self-consistent set of compounds having log K ow values ranging from 2.13 to 8.58. The estimation methods examined included two group contribution methods and four correlative methods utilizing molecular weight, HPLC retention time, molecular connectivity index, and total molecular surface area.

Assessing the aerobic biodegradability of 14 hydrocarbons in two soils using a simple microcosm/respiration method.

The aerobic biodegradability of 14 hydrocarbons in two soils was determined using a simple microcosm/respirometric method based on oxygen consumption. Biodegradability was assessed indirectly by measuring the depletion of oxygen over time in the headspace of microcosms containing soil and test chemicals. The microcosms consisted of small glass vials fitted with valves that allowed headspace gas samples to be collected, essentially resulting in a sealed system. Respiration data from control microcosms were obtained from identically treated microcosms with no test chemical. Control data were necessarily included in all calculations of percent of theoretical oxygen demand (%ThOD) for any given test chemical. Two experiments were performed to verify this simple biodegradation test method. First, an experiment was performed in which disappearance of n-tetradecane from the microcosms was measured directly by standard soil extraction and analytical techniques while simultaneously performing this simple respirometric method based on %ThOD with the same test chemical. Second, the method was compared to a well-established radiochemical technique using 14C-phenanthrene. Results of both comparisons showed that the method is both accurate and reliable. The consistent manner with which the data were produced in two different soils show that the method is also very reproducible. The method described here provides a simple and inexpensive method for determining the aerobic biodegradability of organic compounds in soils.

Prediction of aqueous diffusion coefficients for organic compounds at 25°C

Abstract Correlations for the prediction of aqueous diffusion coefficients from molecular connectivity indices (MCIs) were developed using data for 108 organic compounds at 25°C. A good correlation between MCIs and aqueous diffusion coefficients was observed for the entire data set. Some correlations improved when the compounds were divided into specific chemical classes. Aqueous diffusion coefficients predicted using MCIs were compared statistically (r 2 and mean percent difference) to values calculated using molar volume and alkyl chain length estimation methods. Based on mean percent difference, the MCI-based estimation methods were as good as or better than the molar volume and alkyl chain length methods.

Plant Uptake of Xenobiotics

Plant uptake of organic chemicals is an important process when considering the risks associated with land contamination, the role of vegetation in the global cycling of persistent organic pollutants, the potential for contamination of the food chain and the design of pesticides. There have been some significant advances in our understanding of the processes of plant uptake of organic chemicals in recent years; most notably there is now a better understanding of the air to plant transfer pathway, which may be significant for a number of chemicals. This chapter identifies the key processes involved in the plant uptake of organic chemicals and also identifies other important factors in the uptake process e.g., plant lipid content, growth dilution and plant metabolism.

Solubility of polychlorinated biphenyls in binary water/organic solvent systems

Abstract Solubilities of four polychlorinated biphenyls (PCBs), 4-chlorobiphenyl, 2,4,6-trichlorobiphenyl, 2,3,4,5-tetrachlorobiphenyl and 2,2′,4,4′,6,6′-hexachlorobiphenyl, were determined in pure water and in several water/organic solvent (methanol, butanol, octanol, benzyl alcohol and benzene) systems using a generator column technique. A batch equilibrium method was also used to ensure that result from the two techniques were comparable. The presence of methanol and butanol in water enhanced the solubility of all four PCB congeners, the degree of the enhancement increasing with both cosolvent concentration and hydrophobicity of the PCB solutes. Dissolved octanol and benzene, at a concentration near saturation in water, reduced the solubility of the PCBs, with a larger reduction observed for the more hydrophobic PCB congeners. The effects of dissolved benzyl alcohol on the aqueous solubility of the four PCB congeners varied with the benzyl alcohol concentration and the individual PCB congener.

Estimation of aqueous solubility, octanol/water partition coefficient, and henry's law constant for polychlorinated biphenyls using unifac

Abstract The ability of the UNIFAC group-contribution model to accurately predict aqueous solubility (S), 1-octanol/water partition coefficient (Kow) and Henrys law constant (HLC) for polychlorinated biphenyls (PCBs) was evaluated by comparing experimental values of S, Kow and HLC with those estimated using UNIFAC-derived activity coefficients. Five different sets of interaction parameters tables were evaluated along with two previously published regression equations designed to correct for systematic errors. The best estimates of S, Kow and HLC were obtained using vapor-liquid equilibrium (VLE)-based parameter table published in 1982 by Gmehling et al., with modified values for aromatic chlorine and water interaction parameters.

Mineralization and plant uptake of 14C-labeled nonylphenol, nonylphenol tetraethoxylate, and nonylphenol nonylethoxylate in biosolids/soil systems planted with crested wheatgrass.

Microcosm experiments (duration, 150 d) were conducted to evaluate the mineralization and plant uptake of [14C]nonylphenol (NP), [14C]nonylphenol tetraethoxylate (NPE4), and [14C]nonylphenol nonylethoxylate (NPE9) in a soil/biosolids (99.5:0.5 w/w) environment planted with crested wheatgrass (Agropyron cristatum). Three initial nominal concentrations (6, 24, and 47 mg/kg dry wt) each of NP, NPE4, and NPE9 were examined along with unplanted and unplanted poisoned controls. Phenol (22 mg/kg) also was evaluated as a more degradable reference compound. The biosolids were obtained from a municipal treatment plant, and the loamy sand soil was freshly collected. Mineralization ranged from 7% for NP to 53% for phenol, and no enhancement was observed in the planted systems. For NP, NPE4, and NPE9, 14C foliar tissues concentrations were proportional to exposure concentrations but were 10-fold lower than the root concentrations and two- to threefold lower than the soil concentrations. Bioconcentration factors (BCFs) based on 14C measurements ranged from 0.31 (mg compound/kg dry plant/ mg compound/kg dry soil) for systems spiked with NP to 0.52 for systems spiked with NPE9. Results of the NP analysis (initial concentration, 47 mg/ kg) showed a 90% decrease in the soil concentration and an average BCF of 1.0. The lower BCF calculated from the 14C analysis likely resulted from the presence of NP transformation products in the soil that are less available or are translocated by the plants but quantified by the combustion/liquid scintillation counting procedure.