Polar fuel constituents: compound identification and equilibrium partitioning between nonaqueous phase liquids and water.
Groundwater contamination by fuel constituents from nonaqueous phase liquids (NAPLs) on top of the groundwater table is a widespread problem. While leaching of classical fuel constituents such as benzene, toluene, ethylbenzene, and xylenes (BTEX) from NAPLs into groundwater has been studied extensively, little is known about the identity and partitioning of polar fuel components. Our work shows that gasoline commonly contains appreciable amounts of aniline, phenol, and their alkyl-substituted homologues as well as a suite of other polar compounds. To assess the potential for leaching of such compounds from NAPLs into groundwater we measured the equilibrium fuel/water partitioning coefficients, Kfw, of some representative constituents in batch systems. Kfw values for the investigated phenols, anilines, benzotriazoles, and S-heterocycles ranged from 0.2 to 1700. These values are up to 3 orders of magnitude lower than the Kfw of benzene. The NAPL--water partitioning of anilines and phenols strongly depends on the compounds' structure as well as on pH and the gasoline composition (e.g., MTBE content). Linear free energy relationships (LFERs) using Kow or Cwsat failed to predict measured Kfw values of polar solutes. In contrast, a polyparameter approach taking into account molecular interactions (van der Waals forces, hydrogen bonds) between solutes and major gasoline components allows precise a-priori predictions of Kfw values of both polar and BTEX fuel constituents without any fit parameters. Since most of the polar fuel constituents studied here are extracted from NAPLs by groundwater much more efficiently than BTEX, such compounds could form contaminant plumes threatening receiving wells before detectable concentrations of BTEX are present.
Schmidt
Torsten C
TC
Swiss Federal Institute for Environmental Science and Technology (EAWAG), Swiss Federal Institute of Technology, Zurich (ETHZ), P.O. Box 611, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland. torsten.schmidt@uni-tuebingen.de
Kleinert
Peter
P
Stengel
Caroline
C
Goss
Kai-Uwe
KU
Haderlein
Stefan B
SB
D002274:Carcinogens, Environmental / Q000032:analysis* / Q000737:chemistry*; D005742:Gasoline / Q000032:analysis*; D006838:Hydrocarbons / Q000032:analysis* / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D012995:Solubility
D002274:Carcinogens, Environmental; D005742:Gasoline; D006838:Hydrocarbons; D012989:Soil Pollutants