T8 PM Measurement/ Estimation of Environmentally Relevant Physico-Chemical Properties|
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 337-338
367 (ZEP-1117-860495) Techniques for Determining UV Exposure in Coastal Waters: Case Study in South Florida.
Start time: 1:50 PM
Zepp, R1, Shank, C2, Fisher, W3, Miller, W4, Fichot, C4, Bartels, E5, Stabenau, E6, Moran, M4, Lee, R4, 1 US EPA, NERL, Ecosystems Research Division, Athens, GA, USA2 US EPA, National Research Council Associate, Athens, GA, USA3 US EPA, NHEERL, Gulf Ecology Division, Gulf Breeze, FL, USA4 University of Georgia. Dept. of Marine Sciences, Athens, GA, USA5 Mote Marine Laboratory, Summerland Key, FL, USA6 NOAA, Atlantic Oceanogrphic Marine Laboratory, Miami, FL, USA
The photosynthesis of coral reefs is inhibited by solar ultraviolet (UV) radiation and UV in combination with unusually high sea surface temperatures is believed to play an important role in coral bleaching. Although exposure to solar UV is an important determinant of corals condition, little is known about its variability in coastal regions where corals live. In this presentation we use a new technique based on remotely sensed ocean color to estimate UV attenuation in coastal areas. This technique is applied in a case study of the coral reefs in the South Florida region to estimate fluctuations in underwater solar spectral UV irradiance as a function of location and season. We demonstrate that colored dissolved organic matter (CDOM) controls the penetration of UV radiation in most locations in the Florida Keys and that microbial processing of seagrass and mangrove detritus are major sources of the CDOM. Suspended particles also play an important role in attenuating UV-A (315 to 400 nm), especially in the shallowest areas. UV-induced photoreactions coupled with microbial degradation are the primary loss pathways for the CDOM. Relationships between visible reflectance, UV attenuation, and absorption by colored dissolved organic matter (CDOM) in the ocean water are used along with SeaWiFS images of normalized water-leaving radiance to calculate the CDOM absorption and UV attenuation for the water over the coral reefs. Using this approach we used the satellite observations to compute diffuse attenuation coefficients in the UV region that were within 25% of the observed coefficients. (This abstract of a proposed presentation has been approved by the US EPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.)
368 (ESC-1117-137742) Liposome-water partitioning of hydrophobic copper-organic complexes and their components.
Start time: 2:10 PM
Kaiser, S1, Schwarzenbach, R1, 2, Escher, B1, 1 EAWAG, Duebendorf, Switzerland2 ETH, Zürich, Switzerland
This study is part of a project that develops concepts and methods to evaluate bioavailability and toxic effects of complexes of copper and hydrophobic ionogenic organic compounds. A first step in understanding bioavailability and passive uptake of these complexes is to investigate their partitioning into biological membranes. We used liposomes as model systems and studied the uptake of copper in the presence of hydrophobic ligands (oxines) as a function of concentration, pH and type of ligand. Our goal was to determine the influence of the mentioned factors on the uptake of hydrophobic copper complexes and to compare the partitioning of these complexes with that of its components. In the first step we investigated the ligand alone. The results showed higher liposome-water-partitioning coefficients (Klipw) for neutral oxine species than for their ionic species. The uptake of the latter is decreased due to their charge. However, Klipw of oxine anions were generally higher than those of the cations. This observation can be rationalized by the delocalisation of the negative charge of the anion over the aromatic ring system while the positive charge of the cation is localized at the nitrogen atom. It was also remarkable that the Klipw of all oxines were dependent on their hydrophobicity, expressed by Kow of the neutral species, and that there existed parallel regression lines between logKlipw of the three different species and logKow of the neutral species. In the second step we looked at Cu2+ and the copper-oxine complexes. The experiments with copper showed no detectable uptake of copper in liposomes. For the copper-oxine complexes we observed a dependency of their Klipw from their molecule size and the hydrophobicity of their ligands. In conclusion, partitioning of charged ligands and copper complexes is significant and by less than three orders of magnitude smaller than partitioning of the neutral species of the ligand. Hence we postulate that all species play a role and need to be considered in bioaccumulation and toxicity studies.
369 (LIU-1117-821025) Determining Aqueous Solubility of Fluorotelomer Alcohols Using the Log-linear Cosolvency Model.
Start time: 2:30 PM
Liu, J1, Lee, L1, 1 Agronomy Department, Purdue University, West Lafayette, IN, USA
Fluorotelomer alcohols, characterized by 4 to 14 even numbered perfluorinated carbon atoms attached to a -CH2CH2OH group, are a key class of compounds in understanding the global contamination of alkyl polyfluorinated compounds. However, the high level of perfluorination imparts to this group of compounds strikingly different properties than observed for its hydrogen and halogen analogues. Therefore, experimentally determined values of polyfluorinated compound properties such as solubility are needed to improve the predictive capability of current Quantitative Structure Activity Relationships (QSARs) and environmental fate and effects models. Accurate measurement of aqueous solubility of polyfluorinated compounds is greatly limited by their low solubilities, high volatility, sorption affinity for glassware and fluoropolymeric materials, thus a cosolvency approach was employed in this study to reduce possible bias of direct aqueous measurement. The log-linear cosolvency model assumes a log-linear relationship between solubility and volume fraction cosolvent (fc) allowing estimation of aqueous solubility by extrapolation. Solubilities of 6:2, 8:2, and 10:2 fluorotelomer alcohols, the major components in commercial telomer alcohol mixtures, were determined directly in aqueous solution at 22°C and estimated by extrapolation from data measured in acetone/water and methanol/water solutions. LC-ESI-MS/MS was employed to directly analyze the fluorotelomer alcohols in aqueous and cosolvent solutions without a pre-concentration step. For the 8:2 fluorotelomer alcohol, aqueous solubilities of 0.194 mg/L and 0.224 mg/L were estimated by direct measurement and the log-linear cosolvency approach, respectively. Solubility data for the 6:2 and 10:2 fluorotelomer alcohols are currently being collected. Solubilities for the three alcohols will be correlated with each other and compared to literatures values for alky hydrocarbon alcohols using a QSAR approach.
370 (JAN-1117-832108) Henrys Law constants of toxaphene congeners and estimates of gas exchange in Lake Superior.
Start time: 2:50 PM
Jantunen, L1, Bidleman, T1, Audette, C1, 1 Environment Canada, Meteorological Service of Canada, Egbert, ON, Canada
Toxaphene is an abundant organochlorine pesticide in the North American Great Lakes ecosystem and the Henrys Law constant (HLC, Pa m3 mol-1) is a critical property for describing its partitioning between air and water. The HLC of the technical toxaphene mixture has been determined, but not for single congeners. The HLCs of twelve toxaphene congeners (hepta- to nonachlorobornanes) were determined by the gas stripping method over a temperature range of 5-30C, the same technique previously used to determine the HLC of total toxaphene. Past estimates of gas exchange in Lake Superior for total toxaphene predicted volatilization from the water to the air, but gas exchange of individual congeners has not been reported. During the summer of 2005, parallel air and water samples were collected in Lake Superior from aboard the CCGS Limnos. In these samples, concentrations of total toxaphene and the twelve congeners were determined. Using the air and water concentrations and the temperature dependant HLCs, the fugacity ratios and net fluxes were estimated.
Start time: 3:10 PM
371 (MAC-1117-797533) Estimating the Temperature Dependence of Liquid Vapor Pressure of Nonpolar Substances Using Trouton's Rule.
Start time: 3:50 PM
MacLeod, Matt1, Scheringer, Martin, Hungerbühler, Konrad1, 1 Swiss Federal Institute of Technology, Zurich, Switzerland
The fate of persistent chemicals in the environment is determined to a large extent by their physico-chemical properties. Variability in environmental temperatures can strongly influence these properties, and thus partitioning between air, water and soils, overall persistence and potential for long-range transport. Therefore, the temperature dependence of vapor pressure (quantified by the enthalpy of vaporization, HVAP) is an important factor in the overall fate of chemicals in the environment. We demonstrate that HVAP of liquids and sub-cooled liquids at an arbitrary system temperature can be reliably estimated for nonpolar substances from vapor pressure (PL) using Trouton's rule and assuming that HVAP is linearly dependent on temperature between the boiling temperature and the temperature of interest. Our relationship successfully describes HVAP and PL data at 298 K for nonpolar chemicals with subcooled liquid vapor pressures ranging over 15 orders of magnitude. The uncertainty associated with estimating HVAP from PL is low, and is likely acceptable for most practical applications. We apply the relationship based on Trouton's rule to assess the accuracy of a popular method for determining HVAP and PL from relative retention times on a gas chromatographic column compared to a reference substance. Recently reported HVAP and PL data for polybrominated diphenyl ethers and polychlorinated napthalenes appear to be biased by errors associated with extrapolating temperature dependent vapor pressure data for the reference compound from the solid state to the subcooled liquid state, and ignoring temperature dependence of the associated enthalpy and entropy changes. To reduce uncertainties and avoid bias, substances with a complete set of temperature dependent thermodynamic properties should be selected as reference compounds for gas chromatographic estimation of HVAP and PL, and determination of thermodynamic properties for commonly used reference substances such as p,p'-DDT should be a high research priority.
372 (MAC-1117-798159) A least-squares adjustment procedure to improve accuracy of physico-chemical properties of organic compounds.
Start time: 4:10 PM
Schenker, Urs1, MacLeod, Matt1, Scheringer, Martin1, Hungerbühler, Konrad1, 1 Swiss Federal Institute of Technology, Zurich, Switzerland
Partitioning properties (vapor pressure, water solubility, octanol solubility, the partition coefficients between air, water, and octanol, and their temperature dependencies) are used to describe the behavior of organic contaminants in environmental fate and exposure models. If such quantities are measured, random measurement errors will appear and systematic errors are possible, leading to datasets that are not internally consistent. Beyer et al. (Environ. Toxicol. Chem., 2002; p. 941-953) have suggested an adjustment procedure that calculates a set of internally consistent property data which, they claim, is minimally divergent from the measured quantities. We show that their adjustment procedure does not actually minimize the adjustments applied to the measured quantities, and that the adjusted values differ unnecessarily from the measured quantities. We suggest a new adjustment procedure that is based on the theory of least squares and show that the adjusted values calculated with the new method are always closer to the measured quantities than the values calculated with the Beyer method. The requirement of the least-squares theory (normal distribution of measurement errors) allows us to identify bias and systematic measurement errors if series of property data are reported. Such a bias is evident in properties of a recently reported PCB dataset (Li et al.; J. Phys. Chem. Ref. Data, 2003; p. 1545-1590). We discuss possible reasons for this bias and suggest new values for the physico-chemical properties of the PCB congeners. The new least-squares adjustment procedure also incorporates a more rigorous approach of dealing with measurement uncertainties: variances of the measured quantities can be propagated through the adjustment procedure, and variances (and confidence intervals) of the adjusted quantities can be indicated. Such information improves accuracy of model input data and helps to perform uncertainty analyses (such as Monte-Carlo simulations) of environmental fate and exposure models.
373 (LOD-1117-846240) Interpretations of detailed phase distribution measurements and their implication for fate and risk assessment.
Start time: 4:30 PM
Lodge, K1, Danso, D1, Egyepong, E1, 1 University of Minnesota Duluth, Duluth, Minnesota, USA
The measurement of physical-chemical properties is beset by many difficulties; a detailed description of those associated with basic laboratory and reporting procedures for the water solubilities and octanol-water distribution coefficients of DDT and DDE have been given by Pontolillo & Eganhouse (USGS, Water-Resources Investigations Report 01-4201, 2001). These difficulties make the selection of "reliable" data difficult. However, we believe that there may also be physical phenomena present in the system under test that make the use of single phase-distribution coefficient inappropriate as an accurate descriptor of the system. That is, the coefficient depends upon the concentration of the chemical because of association in the phases. For ionizing compounds, this is not new; for example, these phenomena were reviewed by Leo & coworkers (Chem Rev. 71(6), p525-616, 1971). However, we are investigating the possibility that association may be significant for non-ionizing compounds, such as benzene, toluene, ethylbenzene and p-xylene distributed between water and octanol, and water and air. We were led to study these "simple" systems after having measured octanol-water distribution coefficients for a series of acylate esters as a function of concentration. These data can be interpreted in terms of association in the octanol phase (Edelbach & Lodge, Phys. Chem. Chem. Phys., 2, p.1763-1771, 2000). Later attempts to measure the octanol-water distribution coefficients for dioxin and p,p'-DDT brought us to a "back-to-basics" approach (Lodge et al., unpublished work, 1995). Detailed measurements of octanol-water distribution coefficients for toluene may be interpreted in terms of association in both the aqueous and octanol phases; supporting evidence is also found in our data for p-xylene and ethylbenzene. We will describe a new method for the measurement of fugacities of these compounds in the air-water system. These data may also be interpreted by invoking association in the aqueous phase.
374 (ROT-1117-726142) Beyond Kow and vapor pressure.
Start time: 4:50 PM
Roth, C.1, 2, 3, Goss, K.-U.2, 3, Niederer, C.2, 3, Arp, H.-P.2, 3, Schwarzenbach, R.2, 3, 1 Harvard University, Boston, MA, USA2 Swiss Federal Institute for Environmental Science and Technology (EAWAG), Duebendorf, Switzerland3 Swiss Federal Institute of Technology (ETHZ), Zurich, Switzerland
Sorption of pollutants in various phase systems plays a key role for the transport and transformation in the environment. Many sorption processes between two specific phases have been examined, but only for a few compound classes. Results have often been evaluated with one-parameter linear free energy relationships (LFER) based on one compound descriptor, usually vapor pressure, water solubility, the octanol-water or the octanol-air partitioning coefficient. For many compounds, the experimental determination of these descriptors is error-prone and gives highly variable results. These LFERs also remain limited to the one compound class for which they were developed. Poly-parameter LFERs can overcome these shortcomings because they specifically consider the various types of interactions that govern each partition process: i.e. van-der-Waals and electron-donor/acceptor interactions. A comparison of both approaches shows that the poly-parameter LFERs have three important advantages: 1) for many compounds the required descriptors can be determined easier and with better precision, 2) the pp-LFERs successfully describe sorption for polar and non-polar compound classes alike and extrapolation to compound classes that have not been part of the calibration data set is much more reliable, 3) provides a method to describe and understand the variability of sorption properties in various compartments. The talk will illustrate these points with a large amount of experimental data, including a range of environmental compartments such as mineral and salt surfaces as well as various organic sorbents.
375 (ARE-1118-178860) Estimating partition coefficients for fuel-water mixture systems.
Start time: 5:10 PM
Arey, Jeremy1, Gschwend, Philip2, 1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, United States2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
In many environmental transport problems, organic solutes partition between two immiscible phases that are each liquid mixtures. Examples include solute partitioning from gasoline, diesel fuel, and similar mixtures into contacting aqueous mixtures. To estimate the corresponding partition coefficients, we utilized linear solvation energy relationships (LSERs) developed for pure liquid-liquid systems, and we extended these to handle mixtures using either linear solvent strength theory or the solvent compartment model. These methods allowed prediction of liquid-liquid partition coefficients in a variety of fuel-water systems for a chemically diverse set of dilute solutes. When applied to 37 polar and nonpolar solutes partitioning between an aqueous mixture and several fuel-like mixtures (many including oxygenates), the root-mean-squared errors were a factor of 2 to 3 in the partition coefficient using these approaches. This was considerably more accurate than application of Raoult's law for the same set of systems. Regulators and scientists can use these methods to estimate fuel-water partition coefficients of novel additives in future fuel formulations and thus provide key inputs for "pre-manufacture" environmental assessments of these compounds.