In 1991, Congress enacted legislation that required each state to use a minimum amount of crumb-rubber modified (CRM) hot-mix asphalt in road paving operations. However, because of concerns over the lack of information on the environmental and human health effects caused by CRM asphalts, Congress passed a temporary moratorium and directed that these effects be evaluated. In 1995, Congress eliminated the requirement to use CRM asphalts but continued the requirement to conduct research. Because asphalt emissions may contain mutagenic compounds (e.g., polycyclic aromatic hydrocarbons), their mutagenic potential was investigated using a spiral Salmonella mutagenicity assay. Asphalt emissions were collected above open ports of heated asphalt storage tanks, at seven hot-mix plants in six states. At each site, asphalt emissions from the same asphalt formulation, with or without crumb-rubber, were collected on 37-mm polytetrafluoroethylene filters at 28.3 L/min over approximately 8 to 10 hrs. Asphalt samples were extracted with methylene chloride, evaporated to dryness for total mass determination, and dosing solutions were prepared in dimethyl sulfoxide. The spiral Salmonella mutagenicity assay was conducted using tester strains TA98 and TA100, with and without 10% S9 metabolic activation. Because of dispersion problems (sample formed beads on the plate) with samples from the first three sites, the remaining samples were extracted using hexane and half of the extract was fractionated into aliphatic compounds, polycyclic aromatic compounds, and polar compounds using NIOSH Method 5800. These fractions and the remaining extract were dried for total mass determination. As before, dosing solutions were prepared, and the spiral Salmonella assay was conducted. Test doses ranged from 13 to 900 u/mL equivalents per plate. None of the asphalt emissions or fractions were found to be mutagenic at the doses tested.
The Toxicologist. Society of Toxicology 43nd Annual Meeting and ToxExpo, March 21-25, 2004, Baltimore, Maryland