Project at a Glance

Title: Executive Summary to Identification of particulate mutagens in Southern California's atmosphere.

Principal Investigator / Author(s): Pitts, James N., Jr.

Contractor: University of California Statewide Air Pollution Research Center

Contract Number: A1-155-32

Research Program Area: Health & Exposure

Topic Areas: Health Effects of Air Pollution


We report results from a one-year element of our CARB / UC-supported research program to obtain laboratory and field data on the atmospheric levels sources and sinks and mutagenicities of compounds present in respirable ambient particles collected at selected sites across California's South Coast Air Basin. These data are essential inputs into risk assessment evaluations and development of cost-effective strategies if these are deemed necessary, for the protection of public health. In field studies designed to investigate the levels of ambient mutagen to which populations are exposed, and their diurnal variations, we found average three-hour mutagen densities (revertants m-3 air sampled) on Salmonella strain TA98 (-59) at a West Los Angeles (WLA) site ranged from a minimum of 32 revertants m-3 between midnight and 0300 hour to a maximum of 150 revertants m-3 between 0600 and 0900 hour. The mutagenicity profiles were comparable to those we found earlier at "an East Los Angeles (ELA) site and were generally higher than those reported from other major urban air sheds throughout the world. Additionally, offshore (east to west) air flows which drain the air basin between midnight and 0600 were shown to result in elevated mutagen density levels at the western edge of the Los Angeles Basin (e.g., ~72 revertants m-3 at 0300-0600 hr). During the period from 1200 to 2400 on March 9t 1983t concurrent measurements of particulate mutagen densities at sites upwind and downwind of the San Diego Freeway (1-405) took place under wind conditions favorable for demonstrating that the incremental burden of direct mutagens in respirable POM attributable to freeway traffic reached 50 rev m-3. Finally, diminished response on the nitroreductase-deficient strain TA98NR vs. TA98 suggested that nitroarenes contributed significantly to the direct mutagenicity of ambient POM collected at the WLA sites. As with our ELA study, over a 24-hour period highs and lows in mutagen densities occurred over short time intervals (several hours) probably because of changes in emissions, mixing heights and wind speeds. These short-term peak mutagen densities clearly can be much higher than 24- or 12-hour averages typically reported in the literature. In our initial study of the feasibility of determining changes in mutagenic POM during west-to-east transport across the basin, we found no significant difference in specific activity (rev mg-l extract) between the POM collected in Redlands and that collected later in the day at Whitewater, a site farther downwind and approximately 60 km to the east of Redlands. [See the full report for the second page of this abstract.]

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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