HUMAN CELL MUTAGENS IN LOS-ANGELES AIR

The human cell mutagenicity of particulate air pollution samples colle cted in southern California is measured. The human cell mutation assay used in this study tests mutagenic activity at the thymidine kinase l ocus in h1A1v2 cells using a 72-h exposure. Throughout 1993, airborne fine particle samples were taken at a regional background site on San Nicolas Island upwind of Los Angeles and at four urban sites: Long Bea ch, central Los Angeles, Azusa, and Rubidoux. The Long Beach site is i n close proximity to direct emissions from industrialized sources incl uding power plants, petroleum refineries, and the Los Angeles-Long Bea ch harbor complex. Central Los Angeles was chosen because of its dense vehicle traffic, railroad yards, and proximity to the central busines s district Azusa and Rubidoux are photochemical smog receptor sites lo cated generally downwind of the highest density of primary emissions s ources. No systematic seasonal variation of the mutagenic potency (mut agenicity per unit organic aerosol mass) is observed at any of the urb an sites. This suggests that the important human cell mutagens are not dominated by a seasonal emission source such as wood combustion and t hat if the atmospheric transformation products of photochemical air po llution are involved, then these reactions must occur during the winte r as well as during the summer photochemical smog season. No significa nt spatial Variation of annual average mutagenic potency of the aeroso l was observed between three of the four urban sites; while the averag e mutagenic potency of the Long Beach aerosol was slightly higher than elsewhere in the air basin. This similarity of mutagenic potency valu es across widely separated monitoring sites suggests that the mutageni city of the aerosol is due largely to ubiquitous emission sources (e.g .; motor vehicle traffic or stationary source fuel combustion) rather than to proximity to isolated po int sources of unusual mutagenic orga nics. The mutagen concentration per cubic meter of ambient air was com puted by weighting the mutagenic potency values of the aerosol accordi ng to the mass concentration of organics present at each monitoring si te. The human cell mutagen concentration in Las Angeles urban air was found to be 1 order of magnitude greater than at the background site s tudied upwind of the city, showing that the city is indeed a source of human cell mutagens.