ATMOSPHERIC CONCENTRATIONS OF PCDDS/PCDFS IN SOUTHERN CALIFORNIA

A comprehensive air toxics measurements program designed to establish baseline concentrations of atmospheric polychlorinated dioxins and dibenzofurans (PCDDs/PCDFs) in the South Coast Air Basin has been completed. The program utilized state-of-the-art air sampling and laboratory analysis techniques (HRGC/HRMS) to quantify the fifteen 2,3,7,8-substituted PCDDs/PCDFs congeners of primary toxicological significance. This study, which included nine discrete sampling sessions between December 1987 and March 1989, provides the first systematic assessment of ambient PCDDs/PCDFs concentrations in the state of California. The highest PCDDs/PCDFs concentrations noted during this study occurred in December 1987. This period was dominated by off-shore air flows, suggesting a regional air mass and transport phenomena. Concentrations of the PCDDs/PCDFs were diminished markedly in subsequent sampling sessions where air flow patterns were primarily of on-shore or of coastal origin. Ambient PCDDs/PCDFs concentrations, expressed as toxic equivalents, were highest during the December 1987 sampling period. The El Toro monitoring site, located approximately 40 miles southeast of Los Angeles, consistently showed the lowest measured ambient PCDDs/PCDFs concentrations and toxic equivalents values. In the majority of the sessions and samples examined the PCDDs/PCDFs congener profiles strongly suggest combustion source influences. Typical of combustion source profiles, 1,2,3,4,6,7,8-HpCDD was the predominant 2,3,7,8-substituted species and most prevalent PCDD after OCDD. The congener of highest toxicological significance, 2,3,7,8-TCDD, was reported below the 10-20 fg/m3 detection limit for most of the ambient air samples selected for analysis.