The application of reporter gene assays for the determination of the toxic potency of diffuse air pollution.

Diffuse air pollution consists of a mixture of numerous compounds. It is emitted by many distributed sources and is omnipresent due to atmospheric transport. Risk assessment of the complex mixture of air pollutants on the basis of the toxicity of the individual compounds is not yet possible because the chemical identity and/or toxicity of the constituencies of a substantial fraction is unknown. In addition, no adequate procedures are available to integrate toxicity data of such complex mixtures, so that an individual risk assessment of the constituents of air pollution disregards possible combination effects. In the present study, an approach has been developed to assess the toxic potency by using in vitro bio-assay techniques. Genotoxicity was assessed in the umu-assay, a reporter gene assay using a strain of Salmonella typhimurium stably transfected with a plasmid (pSK1002) carrying the SOS-gene umuC fused to the reporter gene lacZ. Arylhydrocarbon-receptor activation was assessed in the DR-CALUX-assay, using a stably transfected H4IIE hepatoma cell line containing a plasmid for the luciferase gene under transcriptional control of dioxin-responsive elements. Samples of airborne particulate matter (APM) were collected with a high volume sampler next to a highway and in a natural conservation area. Both assays proved to be applicable to quantify genotoxicity and the presence of polycyclic aromatic hydrocarbons (PAHs) in small extracts from air-filter samples. Results indicate that PAHs from traffic exhausts seem to be largely responsible for an increased genotoxic activity of APM collected down-wind from the highway (western wind). APM collected at eastern wind directions seems to have a different composition of compounds, with a higher genotoxic activity that is less related to highway-emitted PAH-like compounds. At northern wind directions, APM is relatively less genotoxic and contains less PAHs than at other wind directions. Dioxin-like compounds contribute negligibly to the Ah-receptor agonistic potency of APM. Airborne pollutants with genotoxic and/or PAH-like characteristics form an undesired mutagenic risk, which will be evaluated in further in vivo studies.