Browsing by Author "Lodge, Keith B"

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    Desorption from Contaminated Sediment and the Organic-Carbon Normalized Sediment-Water Partition Coefficient, Koc, for Dioxin
    (University of Minnesota Duluth, 1998-09) Lodge, Keith B; Cook, P.M.
    We use the “solids concentration effect” in an attempt to measure the organic-carbon normalized sediment-water partition coefficient, Koc, for 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) using desorption from contaminated sediment from Lake Ontario. The sediment was collected from Station 208 (Onuska et al., J. Great Lakes Res. 9(2), 169-182, 1983); it contains 470 pg/g dry weight of dioxin and 2.37% of organic carbon. We prepared a series of sediment suspensions of decreasing solids concentration; after various periods of equilibration followed by separation of sediment solids and water by sedimentation, we analyzed the aqueous phase for dioxin and organic carbon. The ranges of solids concentration (Cs,w ), of total aqueous phase dioxin (Clc,w ), and of aqueous phase organic carbon (Coc,w) are 0.06-60 g/L, 2-1000 pg/L, and 0.23-65 mg/L respectively. For the measured partition coefficient, Kmoc , our data fit the functions, log Kmoc = a constant - log Cs,w, and log Kmoc = a constant - log Csorb,w; values of R2 range from 0.61 to 0.92. Csorb,w is related to the organic carbon content of the water by Csorb,w = Coc,w - 0.2 mg / L; the prime indicates that the aqueous organic carbon levels are corrected for blank contributions. The total aqueous phase dioxin concentration only depends strongly on the concentration of organic carbon when Coc,w > 0.2 mg / L. We think this is an example of the phenomenon described by the term “critical micelle concentration”, CMC, which is usually reserved for the description of surfactant solutions, but here we have evidence that it applies to natural organic carbon also. For the system here the CMC is about 0.2 mg/L. By spiking the apparatus with C13-labeled dioxin, we are able to judge the degree to which the system has reached equilibrium or steady state. We establish clearly thereby that the dioxin in the water is at steady state in four experiments. Another feature is the recovery of the settled sediment solids at the end of experiments, and we show that the dioxin concentration, on a dry weight basis, decreases; levels are in the range 230-380 pg/g. This begs the question: What is the organic-carbon normalized dioxin concentration in the sediment at the end of the experiment? With assumptions, mass balance shows that significant quantities of organic carbon are adsorbed on the walls of the apparatus, and it appears that equilibrium is reached when concentrations of dioxin on organic material in the sediment, in the water and on the walls of the apparatus are the same. When doing partitioning experiments at low solids in large apparatus, it is important to recover the settled solids, and determine the level of adsorbed chemical and the organic carbon content. Then, we can complete the mass balance and determine uniquely the quantities of material adsorbed to the walls of the apparatus. Work with less hydrophobic compounds than dioxin shows that Kmoc becomes independent of solids concentration as the solids concentration decreases, whence Koc = Kmoc. We did not reach a sufficiently small concentration of solids; however, we are able to conclude that for dioxin Koc > 7.1; this observation agrees with other partitioning work done with dioxin and its isomers.
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    The Measurement of the 1-Octanol/Water Partition Coefficient (Log P) for Thirteen Acrylates
    (University of Minnesota Duluth, 1992-08-10) Lodge, Keith B; Edelbach, David
    The partition coefficient, which describes the distribution of a chemical between 1-octanol and water, is referred as "P" or "Log P". It finds wide application for the purposes of understanding the fate, distribution and potential toxicity of chemicals. This report describes the measurements of Log P for a set of thirteen acrylates. These were performed for the Speciality Acrylates & Methacrylates (SAM) Panel of the Chemical Manufacturers Association (CMA). The set was chosen by SAM to be representative of several classes of acrylates and agreed upon with EPA as appropriate compounds to test. They exhibit a variety of structural characteristics including branching, straight hydrocarbon chain moieties, hydrocarbon chain moieties containing a hetero atom (oxygen), the alcohol grouping as well as variation in the number acrylate groups per molecule. Since measurements of Log Pare very costly and time consuming, methods have been developed in order to predict values of Log P from molecular structure. In these experiments we compared our measurements with the values predicted by the CLOGP program (MedChem Software Release 3.51, Pomona College, CA); a model that is widely used. The data indicate that the predictions are not accurate for cases where the acrylates: contain the {-CH2-CH2-0-} structural unit (DEGA, PDDA, DEGDA, TREGDA & TTEGDA), contain "significant" branching (PETA, NPGDA & TMPTA), and are predicted to be very hydrophobic (DA, XDA & SA). Measurements of Log Ps for the very hydrophic chemicals are considered to be unreliable. The new experimental design developed here shows that this may be due to the influence of the concentration of octanol in the water in the presence of the acrylate on the measured Log P. Predictions for the structurally "simple" molecules (PA, HMGDA) are in excellent agreement with the measurements.
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    Method for the Determination of Polycyclic Aromatic Hydrocarbons (PAHs) in Sediment
    (University of Minnesota Duluth, 1999-01-04) Lodge, Keith B; Moser, I. M; Kohlbry, S. W
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    Predicting Toxicity and Degradability of Quadricyclane, Fluorocarbon Ethers and their Analogs (1994-1995)
    (University of Minnesota Duluth, 1995) Basak, Subhash C; Lodge, Keith B; Schubauer-Berigan, Joseph
    In a large number of cases, we have to assess the risk of chemicals and predict the toxic potential of molecules in the face of limited experimental data. Structural criteria and functional criteria (if available) are routinely used to estimate the possible hazard posed by a chemical to the environment and ecosystem. Frequently, no biological or relevant physicochemical properties of the chemical species of interest are available to the risk assessor. In the proposed project, we will develop and implement a number of methods of quantifying molecular similarity of chemicals using techniques of computational and mathematical chemistry. Some of the methods are new and will be based on our own research on the theoretical development and implementation of molecular similarity methods. These techniques will be implemented in a user friendly computer environment of the Silicon Graphics workstation. The similarity methods will be used to select analogs of chemicals of interest to the Air Force, viz., QUADRICYCLANE, FLUOROCARBON ETHERS AND THEIR ANALOGS, from databases containing high quality physicochemical data and toxicity endpoints for large number of chemicals. The databases used in the project will come from three sources: a) public domain databases, b) our own in-house databases, and c) databases acquired from commercial vendors. The set of selected analogs, called probe-induced subsets, will be used to: a) develop structure-activity relationships (SAR), and b) carry out ranking of chemicals. Both of these methods will be used to estimate the hazard of the chemicals of interest. A set of chemicals (five to ten) will be chosen for experimental work with the purpose of evaluating and refining computer models. The set will include quadricyclane and fluorocarbon ethers of interest to the Air Force. It will also include a selection of analogs (probe-induced subset) that are readily available, suitable for experimentation, and for which data are lacking. Experiments will be performed to assess the biodegradability and photochemical degradability of the members of the set. Their toxicity will be tested by MicroTox and MutaTox. In cases where significant degradation is observed, the toxicity of the degradation products will also be tested. Direct measurement of the hydrophobicity (octanol-water partition coefficient) will be performed on the members of the set.
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    Predicting Toxicity and Degradability of Quadricyclane, Fluorocarbon Ethers and their Analogs (1996-1997)
    (University of Minnesota Duluth, 1997) Basak, Subhash C; Lodge, Keith B; Schubauer-Berigan, Joseph
    In a large number of cases, we have to assess the risk of chemicals and predict the toxic potential of molecules in the face of limited experimental data. Structural criteria and functional criteria (if available) are routinely used to estimate the possible hazard posed by a chemical to the environment and ecosystem. Frequently, no biological or relevant physicochemical properties of the chemical species of interest are available to the risk assessor. In the proposed project, we will develop and implement a number of methods of quantifying molecular similarity of chemicals using techniques of computational and mathematical chemistry. Some of the methods are new and will be based on our own research on the theoretical development and implementation of molecular similarity methods. These techniques will be implemented in a user friendly computer environment of the Silicon Graphics workstation. The similarity methods will be used to select analogs of chemicals of interest to the Air Force, viz., QUADRICYCLANE, FLUOROCARBON ETHERS AND THEIR ANALOGS, from databases containing high quality physicochemical data and toxicity endpoints for large number of chemicals. The databases used in the project will come from three sources: a) public domain databases, b) our own in-house databases, and c) databases acquired from commercial vendors. The set of selected analogs, called probe-induced subsets, will be used to: a) develop structure-activity relationships (SAR), and b) carry out ranking of chemicals. Both of these methods will be used to estimate the hazard of the chemicals of interest. A set of chemicals (five to ten) will be chosen for experimental work with the purpose of evaluating and refining computer models. The set will include quadricyclane and fluorocarbon ethers of interest to the Air Force. It will also include a selection of analogs (probe-induced subset) that are readily available, suitable for experimentation, and for which data are lacking. Experiments will be performed to assess the biodegradability and photochemical degradability of the members of the set. Their toxicity will be tested by MicroTox and MutaTox. In cases where significant degradation is observed, the toxicity of the degradation products will also be tested. Direct measurement of the hydrophobicity (octanol-water partition coefficient) will be performed on the members of the set.
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