Chemical Fractionation of Particulate Extracts from Diesel Vehicle Exhaust: Distribution of Ligands for the Dioxin Receptor

Diesel vehicle emission particulates were collected using a cyclone sampler. A solvent extract made from the particulate material was fractionated on the basis of polarity into five fractions (I-V). Fractions I and II were further subfractionated (I-1 and -2, II-1 to II-7). The amounts of 28 polycyclic aromatic compounds present in the extract and its fractions were measured. The ability of each fraction to compete with 2,3,7,8- tetrachloro[1,6-³H]dibenzo-p-dioxin (dioxin) for its receptor was determined. The majority of dioxin receptor binding activity was seen in the primary fractions II and III. These fractions contain those polycyclic aromatic compounds of a size and polarity expected of good dioxin receptor ligands. With respect to the subfractions of fraction II, greater than 90% of the polycyclic aromatics occurred in subfractions II-1 to II-4 while the greatest dioxin receptor binding activity was seen in II-5 and II-6. Although these latter fractions contain polycyclic hydrocarbons that would be expected to be good dioxin receptor ligands, it is not known if the amounts of known ligands present would be sufficient to account for the observed receptor binding.