Detecting a new PCB in Chicago air levels: the concentration of PCB11 was as much as 15% of measured PCBs in the air. The concentrations also varied by season (and temperature), following a typical trend of PCB levels found in ambient air in urban and remote settings. TIM SCHON
Although banned some 30 years ago, PCB compounds are being discovered in urban ambient air. Non-Aroclor PCB (3,3′-dichlorobiphenyl), or PCB11, discovered in a recent study published in ES&T (2008, 42 [21], 7873-7877), is considered an “inadvertent PCB,” says Keri Hornbuckle of the University of Iowa, a coauthor of the new study. PCB11 was not one of the congeners manufactured by Monsanto Chemical Co., and it has been regularly reported as nondetectable in Monsanto’s mixtures, Hornbuckle says. “I think it is a tremendous finding,” says Bob Herrick of the department of environmental health at Harvard University. “Most people have never seen anything published about this congener,” he adds. “The paper shows evidence of something that we didn’t see [before],” says Ann Casey, senior chemist with Northeast Analytical, Inc. PCBs are a set of 209 congeners. Of that total, about 150 were sold by Monsanto as components of Aroclors. As much as 1400 million pounds of PCBs was produced as Aroclor mixtures from 1930 to 1970, says Casey. She estimates that 1233 million pounds of the Aroclor PCBs was used in the U.S. before they were banned in 1977. Hornbuckle and her colleagues collected air samples in Chicago from November 2006 to November 2007 by using vehiclemounted, high-volume air samplers at more than 45 sites throughout the city. The group measured 209 PCB congeners in the air, with a range in total PCB concentration from 75 to 5500 picograms per cubic meter. “PCB11 is one of the PCB congeners we observed most often in the Chicago air sample set, and [it is] among the most concentrated,” the authors write. They discovered fairly significant
Hornbuckle checks an air sampler perched on top of a medical clinic van on a street in Chicago.
What makes this congener inadvertent is that it appears to have been created by weathering, volatilization, or dechlorination and may not be related to Aroclor mixtures, Hornbuckle says. She and her colleagues aren’t sure what the source is, but they theorize that the PCB11 is coming from yellow paint pigments. Previous studies have reported this same congener in water or sediment concentrations collected downstream of industrial wastewater effluent and in the waste from paint and pigment production plants. Yet it is hard to link the high concentrations found in Chicago to proximity to paint factories, because there are more than 50
4 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / January 1, 2009
such plants in and near the city, Hornbuckle says. The finding was made possible with gas chromatography-mass spectrometry (GC/MS/MS), an analytical tool that allowed the scientists to quantify the PCB homologues. Aroclors are commonly measured in air. Indeed, the U.S. National Institute for Occupational Safety and Health set a standard of 1000 nanograms per cubic meter of Aroclor 1254 to protect workers, Casey notes. Yet Hornbuckle’s measurements are in picograms per cubic meter. GC/MS/MS has a great reputation as a detection tool, but “it has not caught on in PCB research,” Casey notes. “I think Keri’s paper will bring this into the forefront.” The paper also makes it clear that researchers must move beyond the Aroclor PCBs when studying ambient air samples, the researchers say. “What it points out is that you have to look at all 209 congeners and not just at the Aroclor mixture,” says Lisa (Totten) Rodenburg, of the department of environmental sciences and Center for Environmental Prediction at Rutgers University. PCB11 “may have always been there, but we didn’t have the sensitivity to see it,” Rodenburg adds. —CATHERINE M. COONEY
10.1021/es803101e
2009 American Chemical Society
Published on Web 11/12/2008
