Facilitated transport of hydrophobic organic compounds by cosolvent effects due to oxygenated fuels.

摘要

Oxygenated fuels have led to increased interest in the transport and fate of miscible organic liquids in the environment and the effect of these liquids on the transport and fate of other contaminants. Cosolvent-induced solubilization of hydrophobic organic compounds (HOCs) into water will increase the potential for secondary contamination in an impacted site. The objectives of this research were to study (1) the phase redistribution of hydrophobic organic compounds in aqueous and sediment/soil systems with simulated spills of oxygenated fuels in river and subsurface environments; and (2) the facilitated transport of HOCs by colloids in a sediment/water system where colloids serve as nucleating agents for condensing solutes as the cosolvent fraction is diluted during transport.; The cosolvent effect of oxygenated compounds (methanol, ethanol, and methyl tert-butyl ether (MTBE)) on the solubility and enhanced mobilization of polynuclear aromatic hydrocarbons (PAHs) was examined using laboratory experiments. Coal tar contaminated sediment and soil were used to study the redistribution and facilitated transport of eighteen PAHs when oxygenated fuel spills occur. The results indicated that PAH solubility increased essentially in a log-linear manner with an increased volume fraction of methanol and ethanol. Deviations from a log-linear relationship were observed for MTBE due to its limited aqueous solubility, and the cosolvent effect was seen only at the simulated spill site. A log-linear relationship between the octanol/water partition coefficient and cosolvency power was observed. In column experiments, the elution profile of 18 PAHs suggested that oxygenated compounds from fuel can serve as cosolvents which will enhance the dissolution of PAHs from contaminated soil while the fuel makes contact with the contaminated soil.; The significance of the colloidal phase in the redistribution of PAHs in coal tar contaminated sediment/water system by introduction of oxygenated fuels was also evaluated. Ultrafiltration was employed to differentiate colloids from aqueous phase samples to examine the colloid-facilitated transport of PAHs in simulated fuel-spill systems. A three-phase distribution (sediment-colloidal-aqueous phase) was applied to study the redistribution of PAHs from coal tar contaminated sediment. The results showed that cosolvency was more significant than the role of colloids in the redistribution of PAHs because the cosolvent effect reduces the sorption of PAHs onto colloids.; This study provides a basis to predict the facilitated transport of HOCs from contaminated sediment and soil due to the cosolvent effects of oxygenated fuels. The fuel spill scenarios may assist in the further assessment of the environmental and health effects of spills and leaks of oxygenated fuels.