Journal Article: Atmospheric Measurements of CDDs, CDFs, and Coplanar PCBs in Rural and Remote Locations of the U.S. for the Years 1998-2001 from the National Dioxin Air Monitoring Network (NDAMN)
The U.S. EPA established a National Dioxin Air Monitoring Network (NDAMN) to determine background air concentrations of PCDDs, PCDFs, and cp-PCBs in rural and remote areas of the United States. Background is defined as average ambient air concentrations inferred from long-term and multi-year atmospheric measurements at the same locations using identical monitoring and analytical procedures. The rural sites were chosen in order to obtain air concentrations in areas where crops and livestock are grown, and that encompassed a range of geographic locations in terms of latitudinal and longitudinal positions. Remote sites were selected on the basis that they were relatively free of human habitation and >100 km away from human dioxin sources. The locations of sampling sites covered a wide range of climate conditions from tropical sub-humid to sub-Artic climates. The idea behind the sampling configuration was to provide reasonable geographic coverage of the United States limited only by budgetary constraints. Funding was sufficient for the establishment and maintenance of 34 NDAMN stations over a period of 6 years.
Results were reported as the toxic equivalent (TEQ) of the mix of PCDDs/PCDFs (TEQ-DF) and the mix of coplanar PCBs (TEQ-PCB). At the studied rural sites the mean annual TEQ-DF for each of the NDAMN sampling years was 10.43, 11.39, 10.40, and 10.47 femtograms per cubic meter (fg/cu. m) for 1999, 2000, 2001, and 2002, respectively.There was no statistically significant difference in the rural mean TEQ-DF air concentrations across the sampling years (at 0.05 level of significance), although the mean concentration in sampling year 2000 increased 10% relative to the other sampling years. The 95th percent confidence interval of TEQ-DF air concentrations in rural areas of the United States is from 6.4 to 15.4 fg/cu. m, indicating there is a 95% probability that the true mean falls within this range. Mean annual atmospheric concentrations (TEQ-DF) at the remote sites were 1.41, 0.99, 0.7, and 1.07 fg/cu. m in 1999, 2000, 2001, and 2002, respectively. The 95th percent confidence interval of TEQDF air concentrations suggest that the true mean annual atmospheric TEQDF concentration in remote areas of the United States is between 0.1 and 3 fg m-3. The remote sites have average air TEQDF concentrations that are approximately 10 times lower than those of the rural sites. For the rural sites, there was close agreement in the mean annual air concentrations of coplanar PCBs (TEQPCB) among the years 1999, 2000, 2001, and 2002 (i.e., 0.62, 0.69, 0.59, and 0.7 fg/cu. m, respectively).