Development of a synthetic PCB mixture resembling the average polychlorinated biphenyl profile in Chicago air

Abstract

Studies of environmental and toxic effects of polychlorinated biphenyls (PCBs) are ideally performed with PCB mixtures reflecting the composition of environmental PCB profiles to mimic actual effects and to account for complex interactions among individual PCB congeners. Unfortunately, only a few laboratory studies employing synthetic PCB mixtures have been reported, in part because of the challenges associated with the preparation of complex PCB mixtures containing many individual PCB congeners. The objective of this study was to develop a PCB mixture that resembles the average PCB profile recorded from 1996 to 2002 at a satellite station of the Integrated Atmospheric Deposition Network located at the Illinois Institute of Technology (IIT) in Chicago, Illinois, using commercial PCB mixtures. Initial simulations, using published Aroclor profiles, showed that a mixture containing 65% Aroclor 1242 and 35% Aroclor 1254 was a good approximation of the target profile. A synthetic Chicago air mixture (CAM) was prepared by mixing the respective Aroclors in this ratio, followed by GC/MS/MS analysis. Comparison of the PCB profile of the synthetic mixture with the target profile suggests that the synthetic PCB mixture is a good approximation of the average IIT Chicago air profiles (similarity coefficient cos θ = 0.82; average relative percent difference = 84%). The synthetic CAM was also a reasonable approximation of the average of 184 PCB profiles analyzed in 2007 at 37 sites throughout Chicago as part of the University of Iowa Superfund Basic Research Program (isbrp), with a cos θ of 0.70 and an average relative percent difference of 118%. While the CAM and the two Chicago air profiles contained primarily di- to pentachlorobiphenyls, higher chlorinated congeners, including congeners with seven or eight chlorine atoms, were underrepresented in the synthetic CAM. The calculated TCDD toxic equivalency quotients of the synthetic CAM (2.7 ng/mg PCB) and the IIT Chicago air profile (1.6 ng/mg PCB) were comparable, but lower by two orders of magnitude than the isbrp Chicago air profile (865 ng/mg PCB) due to surprisingly high PCB 126 levels in Chicago air. In contrast, the calculated neurotoxic equivalency quotients of the CAM (0.33 mg/mg PCB) and the two Chicago air profiles (0.44 and 0.30 mg/mg PCB, respectively) were similar. This study demonstrates the challenges and methods of creating and characterizing synthetic, environmental mixtures of PCBs.

Figure 1

Representative GC/MS/MS chromatograms for the synthetic Chicago air mixture (CAM) consisting of 65% Aroclor 1242 and 35% Aroclor 1254 showing the homologue composition. The analysis was done in the monitored reaction mode. A detailed description of the gas chromatographic separation is provided under Materials and Methods.

Figure 2

Comparison to the synthetic CAM with the average PCB profile in Chicago air. (A) Average PCB IIT Chicago air profile; (B) PCB profile of the synthetic CAM consisting of 65% Aroclor 1242 and 35% Aroclor 1254; (C) difference in percentage of the PCB congener profiles (synthetic CAM minus the IIT Chicago air profile).

Figure 3

Comparison of the average 2007 PCB profile in Chicago air with the synthetic CAM. (A) Average PCB isbrp Chicago air profile; (B) PCB profile of the synthetic CAM consisting of 65% Aroclor 1242 and 35% Aroclor 1254; (C) difference in percentage of the PCB congener profiles of both mixtures (synthetic CAM minus the isbrp Chicago air profile). The labels on the x-axis show only every other PCB congeners.

Figure 4

Homologue composition of (A) Aroclor 1242, (B) Aroclor 1254, (C) the synthetic CAM, (D) the average IIT Chicago air profile and (E) the average isbrp Chicago air profile.

Figure 5

Relative contribution of dioxin-like PCB congeners to the TCCD Toxic Equivalency Quotient (TEQ) of A) Aroclor 1242, (B) Aroclor 1254, (C) the synthetic CAM, (D) the average IIT Chicago air profile and (E) the average isbrp Chicago air profile. TEQ values were calculated from the PCB congener profiles using the 2005 WHO TCDD toxic equivalent factors (TEF) (Van den Berg et al., 2006). PCB 105 was not included in the TEQ calculation for the IIT Chicago air profile because it co-eluted with PCBs 153 and 132.

Figure 6

Relative contribution of PCB congeners with a Neurotoxic Equivalency Factor (NEF) to the Neurotoxic Equivalency Quotient (NEQ) of A) Aroclor 1242, (B) Aroclor 1254, (C) the synthetic CAM, (D) the average IIT Chicago air profile and (E) the average isbrp Chicago air profile. The NEQ for each mixture was calculated from the PCB congener profiles using the neurotoxic equivalence factors proposed by Simon et al. (Simon et al., 2007).

Figure 7

Weight percentage of chiral PCB congeners in (A) Aroclor 1242, (B) Aroclor 1254, (C) the synthetic CAM, (D) the average IIT Chicago air profile and (E) the average isbrp Chicago air profile. Only major chiral PCB congeners are shown.