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Published April 1996 | Published
Journal Article Open

Seasonal and Spatial Variation of the Bacterial Mutagenicity of Fine Organic Aerosol in Southern California

Abstract

The bacterial mutagenicity of a set of 1993 urban particulate air pollution samples is examined using the Salmonella typhimurium TM677 forward mutation assay. Ambient fine particulate samples were collected for 24 hr every sixth day throughout 1993 at four urban sites, including Long Beach, central Los Angeles, Azusa, and Rubidoux, California, and at an upwind background site on San Nicolas Island. Long Beach and central Los Angeles are congested urban areas where air quality is dominated by fresh emissions from air pollution sources; Azusa and Rubidoux are located farther downwind and receive transported air pollutants plus increased quantities of the products of atmospheric chemical reactions. Fine aerosol samples from Long Beach and Los Angeles show a pronounced seasonal variation in bacterial mutagenicity per cubic meter of ambient air, with maximum in the winter and a minimum in the summer. The downwind smog receptor site at Rubidoux shows peak mutagenicity (with postmitochondrial supernatant but no peak without postmitochondrial supernatant) during the September-October periods when direct transport from upwind sources can be expected. At most sites the mutagenicity per microgram of organic carbon from the aerosol is not obviously higher during the summer photochemical smog period than during the colder months. Significant spatial variation in bacterial mutagenicity is observed: mutagenicity per cubic meter of ambient air, on average, is more than an order of magnitude lower at San Nicolas Island than within the urban area. The highest mutagenicity values per microgram of organics supplied to the assay are found at the most congested urban sites at central Los Angeles and Long Beach. The highest annual average values of mutagenicity per cubic meter of air sampled occur at central Los Angeles. These findings stress the importance of proximity to sources of direct emissions of bacterial mutagens and imply that if important mutagen-forming atmospheric reactions occur, they likely occur in the winter and spring seasons as well as the photochemically more active summer and early fall periods.

Additional Information

© 1996 Environmental Health Perspectives. Received 14 September 1995; accepted 5 December 1995. We thank Henny Smith, Xia He, Clo Butcher, Rich Lee, and John Durant at MIT; Matt Fraser and Lynn Salmon at Caltech; Bill Bope at the South Coast Air Quality Management District; and Jay Rosenthal and Ken Fesperman of the U.S. Navy for assistance with the bioassays and atmospheric monitoring experiments. This research has been supported by the U.S. Environmental Protection Agency under grant RS 19714-01-0 and by center grant P30-ES02109 and program grant P01-ES07168 from the National Institute of Environmental Health Sciences. This paper has not been reviewed by U.S. EPA for publication, and the contents do not necessarily reflect EPA views or policy. Mention of trade names or commercial products does not constitute EPA endorsement or recommendation for use.

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August 20, 2023
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October 20, 2023