Biomedical subjects

J Samuel Arey

Publications and source records attributed to J Samuel Arey.

6 recordsLinked to original sources

PubMed2006

Methyl tertiary hexyl ether and methyl tertiary octyl ether as gasoline oxygenates: assessing risks from atmospheric dispersion and deposition.

Methyl tertiary hexyl ether (MtHxE) and methyl tertiary octyl ether (MtOcE) are currently being developed as replacement oxygenates for methyl tertiary butyl ether (MtBE) in gasoline. As was the case with MtBE, the introduction of these ethers into fuel supplies guarantees their introduction into the environment as well. In this study, a screening-level risk assessment was performed by comparing predicted environmental concentrations (PEC) of these ethers to concentrations that might cause adverse effects to humans or ecosystems. A simple box model that has successfully estimated urban air concentrations of MtBE was adapted to predict atmospheric concentrations of MtHxE and MtOcE. Expected atmospheric concentrations of these ethers were also estimated using the European Union System for the Evaluation of Substances (EUSES) multimedia fate model, which simultaneously calculates PECs in the various environmental compartments of air, water, soil, and sediment. Because little or no data are available on the physicochemical, environmental, and toxicological properties of MtHxE and MtOcE, estimation methods were used in conjunction with EUSES to predict both the PECs and the concentrations at which these ethers might pose a threat. The results suggest that these ethers would contaminate the air of a moderately sized U.S. city (Boston, MA) at levels similar to those found previously for MtBE. The risk assessment module in EUSES predicted risk characterization ratios of 10(-3) and 10(-2) for MtHxE and MtOcE, respectively, in Boston, and 10(-2) and 10(-1) in very large urban centers, suggesting that these ethers pose only a minimal threat to ecosystems at the anticipated environmental concentrations. The assessment also indicates that these compounds are possible human carcinogens and that they may be present in urban air at concentrations that pose an unacceptable cancer risk. Therefore, testing of the toxicological properties of these compounds is recommended before they replace MtBE in gasoline.

Animals↗

PubMed2005

Using comprehensive two-dimensional gas chromatography retention indices to estimate environmental partitioning properties for a complete set of diesel fuel hydrocarbons.

Comprehensive two-dimensional gas chromatography (GCxGC) provides nearly complete composition data for some complex mixtures such as petroleum hydrocarbons. However, the potential wealth of physical property information contained in the corresponding two-dimensional chromatograms is largely untapped. We developed a simple but robust method to estimate GCxGC retention indices for diesel-range hydrocarbons. By exploiting n-alkanes as reference solutes in both dimensions, calculated retention indices were insensitive to uncertainty in the enthalpy of gas-stationary-phase transfer for a suite of representative diesel components. We used the resulting two-dimensional retention indices to estimate the liquid vapor pressures, aqueous solubilities, air-water partition coefficients, octanol-water partition coefficients, and vaporization enthalpies of a nearly complete set of diesel fuel hydrocarbons. Partitioning properties were typically estimated within a factor of 2; this is not as accurate as some previous estimation or measurement methods. However, these relationships may allow powerful and incisive analysis of phase-transfer processes affecting petroleum hydrocarbon mixtures in the environment. For example, GCxGC retention data might be used to quantitatively deconvolve the effects of water washing and evaporation on environmentally released diesel fuels.

Journal Article↗

PubMed2005

The electrostatic origin of Abraham's solute polarity parameter.

A computational method was developed which relates the empirical linear solvation energy relationship (LSER) solute polarity parameter, S (formerly denoted ), to two more fundamental quantities: a polarizability term and a computed solvent-accessible-surface electrostatic term. Electrostatics computations were conducted explicitly or with dielectric field polarizable continuum models (PCM, SCIPCM, IPCM), employing a density functional theory (B3LYP/6-311G(2df,2p)) or efficient Hartree-Fock (HF/MIDI!) method for 90 polar and nonpolar organic solutes. Electrostatic parameters calculated at electron isodensity solute surfaces were found to produce significantly better correlations with empirical S values than the same electrostatic parameters deduced from a fixed Bondi atomic radii based surface. The best-fit expression was found employing SCIPCM/IPCM at the 0.0004 e(-)/bohr(3) solvent-accessible-surface: S(fit)() = 0.46E - 0.091SigmaV(s)()(2), with squared correlation coefficient = 0.96 and standard deviation = 0.10, where E is a measured solute excess polarizability scale and SigmaV(s)()(2) is a quantum-calculated solute electrostatic descriptor in kcal A/mol. The resulting model is more accurate than previously developed estimation approaches and relies on only two fitted coefficients; it has the potential advantage of applicability to any solute composed of C, H, N, O, S, F, Cl, and Br. Finally, this investigation offers quantitative insight into the relative contributions of solute polarity and solute polarizability to the empirical LSER polarity parameter, S.

Journal Article↗

PubMed2005

Estimating partition coefficients for fuel-water systems: developing linear solvation energy relationships using linear solvent strength theory to handle mixtures.

In many environmental transport problems, organic solutes partition between immiscible phases that consist of liquid mixtures. To estimate the corresponding partition coefficients, we evaluated the efficacy of combining linear solvation energy relationships (LSERs) developed for pure 1:1 systems via application of linear solvent strength theory. In this way, existing LSERs could be extended to treat solute partitioning from gasoline, diesel fuel, and similar mixtures into contacting aqueous mixtures. Unlike other approaches, this method allowed prediction of liquid-liquid partition coefficients in a variety of fuel-water systems for a broad range of dilute solutes. When applied to 37 polar and nonpolar solutes partitioning between an aqueous mixture and 12 different fuel-like mixtures (many including oxygenates), the root-mean-squared error was a factor of approximately 2.5 in the partition coefficient. This was considerably more accurate than application of Raoult's law for the same set of systems. Regulators and scientists could use this method to estimate fuel-water partition coefficients of novel additives in future fuel formulations and thereby provide key inputs for environmental transport assessments of these compounds.

Energy Transfer↗

PubMed2005

A physical-chemical screening model for anticipating widespread contamination of community water supply wells by gasoline constituents.

Continuing modifications of fuels like gasoline should include evaluations of the proposed constituents for their potential to damage environmental resources such as subsurface water supplies. Consequently, we developed a screening model to estimate well water concentrations and transport times for gasoline components migrating from underground fuel tank (UFT) releases to typical at-risk community water supply wells. Representative fuel release volumes and hydrogeologic characteristics were used to parameterize the transport calculation. Subsurface degradation processes were neglected in the model in order to make risk-conservative assessments. The model was tailored to individual compounds based on their abundances in gasoline, gasoline-water partition coefficients (Kgw), and organic matter-water partition coefficients (Kom). Transport calculations were conducted for 20 polar and 4 nonpolar compounds found in gasoline, including methyl tert-butyl ether (MTBE) and other ether oxygenates, ethanol, methanol, and some aromatic hydrocarbons. With no calibration, the screening model successfully captured the reported magnitude of MTBE contamination of at-risk community supply wells. Such screening indicates that other oxygenates would cause similar widespread problems unless they were biodegradable. Stochastic analysis of field parameter variability concluded that community supply well contamination estimates had order-of-magnitude reliability. This indicated that such pre-manufacturing analyses may reasonably anticipate widespread environmental problems and/or inspire focused investigations into chemical properties (e.g., biodegradability) before industrial adoption of new fuel formulations.

Carcinogens, Environmental↗

PubMed2003

Emission and fate assessment of methyl tertiary butyl ether in the Boston area airshed using a simple multimedia box model: comparison with urban air measurements.

Expected urban air concentrations of the gasoline additive methyl tertiary butyl ether (MTBE) were calculated using volatile emissions estimates and screening transport models, and these predictions were compared with Boston, MA, area urban air measurements. The total volatile flux of MTBE into the Boston primary metropolitan statistical area (PMSA) airshed was calculated based on estimated automobile nontailpipe emissions and the Universal Quasi-Chemical Functional-Group Activity Coefficient computed abundance of MTBE in gasoline vapor. The fate of MTBE in the Boston PMSA was assessed using both the European Union System for the Evaluation of Substances, which is a steady-state multimedia box model, and a simple airshed box model. Both models were parameterized based on the meteorological conditions observed during air sampling in the Boston area. Measured average urban air concentrations of 0.1 and 1 microg/m3 MTBE during February and September of 2000, respectively, were comparable to corresponding model predictions of 0.3 and 1 microg/m3 and could be essentially explained from estimated temperature-dependent volatile emissions rates, observed average wind speed (the airshed flushing rate), and reaction with ambient tropospheric hydroxyl radical (*OH), within model uncertainty. These findings support the proposition that one can estimate gasoline component source fluxes and use simple multimedia models to screen the potential impact of future proposed gasoline additives on urban airsheds.

Air Pollutants↗