Testing for PCB Congeners & Aroclors

PCB congeners are chlorine-substituted biphenyl compounds. Individual congeners are identified by the number and position of the chlorine atoms around the biphenyl rings. There are 209 possible PCB congeners, ranging from the mono-substituted 2-chlorobiphenyl to the fully-substituted decachlorobiphenyl.

PCBs were first isolated in the 1880s from coal tar extracts, and commercial production of PCBs began in the 1920s. The compounds were in widespread use throughout most of the 20th century in the design of industrial transformers and capacitors. However, the toxic effects of PCB exposure were observed as early as 1933. In the 1970s, PCB production was banned in the United States and regulations concerning the presence of PCBs in the environment were promulgated.

PCBs were typically synthesized by chlorinating biphenyl with chlorine gas. Varying the conditions of this chlorination process produced different mixtures of congeners with different physical properties. These mixtures were sold as products called Aroclors.

Aroclors are inconsistent PCB mixtures, while PCB congeners are specific PCB compounds. The number appearing after the Aroclor name refers to the amount of chlorine (the percent by weight) present in the product, not the specific PCB congener composition. For instance, in any two manufacturing batches of Aroclor 1254, the amount of chlorine present in each batch is the same, but the mixture of PCB congeners making up those batches may be different. So each Aroclor product, designated by a specific number, represents a mixture of PCB congeners inconsistent between different manufacturing batches of that Aroclor product.

EPA Method 8082 is the most common analytical method used for the analysis of PCB Aroclors. This method uses a capillary column gas chromatography with electron capture detection (GC/ECD). The Aroclors are identified by characteristic peak patterns. Improvements can be made to this method to allow some individual or homologue congener identification with much lower detection limits. Typical reporting limits range from 0.011 mg/Kg in soils to a range roughly ten times lower (1.7 µg/Kg) by using advanced analytical techniques. In waters, typical reporting limits are 0.0004 – 0.02 µg/L and low level limits are 0.001 µg/L.

Learn about increasing the sensitivity of EPA Method 8082...

Common Concerns for Aroclor Testing:

• PCBs have been present in the environment for many decades, possibly changing the congener profile over time due to degradation and weathering
• Often there are many interfering compounds in a sample masking the identifying chromatogram peak pattern
• A significant amount of PCBs may be present in a sample, yet the chromatogram doesn't show a peak pattern consistent with any Aroclor standard available
• Recent data has shown that 12 individual PCB congeners are more toxic than the others.
• It is possible a sample with a significant amount of PCB congeners present is not as much of an ecological risk as a sample with fewer but more toxic PCB congeners present

As a result, there has been an increased interest in the analysis for individual PCB congeners rather than the analysis for PCB Aroclors.

EPA Method 1668 is used to analyze individual PCB congeners by high resolution gas chromatography with high resolution mass spectrometry (HRGC/HRMS) using isotope dilution. This method was originally developed by the EPA to determine the concentrations of the 12 toxic PCB congeners as designated by the World Health Organization (WHO). In 1999, the EPA released Revision A of the method, which expanded its scope to include all 209 PCB congeners. However, approximately 30 percent of the PCB congeners co-elute and are reported either as pairs, triplets, or even quadruplets. Method 1668A is applicable to aqueous, solid, multiphase and tissue matrices. It is used under many different regulatory programs including CWA and RCRA.

See the advantages of method 1668A...