Bitumen Microfuming

Background: For the majority of its industrial applications, bitumen must be either heated to a temperature at which it is workable, or dissolved (emulsified) in a solvent. The former approach, which is by far the most widely used, results in the production of fumes that contain low levels of polycyclic aromatic compounds (PACs), a class which includes suspect and known carcinogens.

Concerns about possible worker exposure to such compounds have prompted numerous epidemiology and industrial hygiene studies of the asphalt industry. While a great deal has been learned from these studies, the presence of confounding exposures from sources such as ambient air pollution, cigarette smoke, and solvents used for cleaning tools and equipment, have made it difficult to determine what proportion of the measured exposures comes from the fume itself and what from other sources.

Efforts to circumvent this problem have focused on two basic approaches: first, the study of workplace-analogous fumes generated under controlled laboratory conditions, and second, the selective exclusion of confounding field exposures by imposition of temporary work rules and/or the use of appropriate protective equipment.

The strength of the former approach, the one relevant to PetroLabs' microfuming method, is obvious: any PAC-mediated effect of laboratory-generated fumes is, by definition, attributable to compounds derived solely from bitumen. Its weakness is that generation of sufficient fume for biological studies has in the past required heating at higher temperatures for longer times than is typical in workplace operations, both of which factors necessarily affect the representativeness of the fumes so generated.

The PetroLabs method circumvents this drawback by using the Nitration Assay (see link above) to determine the relative aggregate contents of PACs in fumes generated under conditions of time and temperature exactly correspondent to those used in the workplace. This approach is possible because only sub-microgram quantities of fume are needed for the Nitration Assay, as compared, for example, to the hundreds of milligrams required for a typical Modified Ames Test.

Because this level of sensitivity is achieved only by chemical nitration of the fume prior to testing, the mutagenicity measured in the Ames Test is not mediated by the PACs themselves, but by their nitro-derivatives. This, in turn, means that, when used as a stand-alone test, microfuming can only provide relative PAC-contents for fumes generated from the same bitumen under a variety of experimental parameters.

However, if more qualtitative information is required, PetroLabs now offers HPLC and GC-MS analyses (see link above) that can be used to chemically characterize the fumes produced by microfuming, and compare them to those collected in the workplace, in the headspace of bitumen storage silos, or generated in the laboratory using more macro-scale methods.