Formatted Title
The Forensic Utility of iPCBs from Polychlorinated Terphenyls: Demonstration of Enhanced PCB Source Identification and Separation
Background/Objectives
Polychlorinated terphenyls (PCTs) manufactured by Monsanto contained PCBs as inadvertent byproducts. The presence of these iPCBs in PCT Aroclors caused Monsanto to withdraw PCT-containing products (mostly Aroclor 5000 and 5400 series) from the market in 1972. To date, published analysis of PCBs in PCT Aroclors has been limited to GC/ECD analytical methods such as Method 8082. For forensic purposes, the state-of-the-art PCB analytical method is congener-specific analysis by HRGC/HRMS. In this study we report PCB and PCT results for two PCT Aroclors (5432 and 5442) by three methods, including PCB congeners by HRGC/HRMS Method 1668A.
Approach/Activities
PCT Aroclor samplers were analyzed for: (1) PCBs by GC/ECD Method 8082; (2) PCTs by modified Method 8082; and (3) PCB congeners Method 1668A. Findings included:- Method 8082 chromatograms for PCT Aroclors showed a bimodal pattern. PCBs eluted within the lower chlorinated Aroclor range (1242 or lighter). PCTs eluted later, within the 1254/1260 range.
- Congener-specific PCB data showed significant concentrations of PCBs in PCT Aroclors: ΣPCB=47,500 mg/Kg in Aroclor 5432 (4.7% PCB); SPCB =900 mg/Kg in Aroclor 5442 (0.1% PCB).
- The PCB congener profile in Aroclor 5432 was very similar to PCB Aroclor 1242 (cos-θ=0.96). A notable difference was for PCB-15, which is higher in the 5432 profile.
- The congener profile of Aroclor 5442 was dominated by PCB-1 (45.2%) and was similar to Aroclor 1221 (cos-θ=0.93). A notable difference between the two was the presence of higher chlorinated PCB congeners in Aroclor 5442. These congeners accounted for less than 15% of PCBs, but within penta-octa chlorination range the 5442 profile was very similar to Aroclor 1260 (cos-θ=0.96).
- PCB-11 and PCB-209 were reported either as non-detect or at low concentrations with “q” or “J” lab qualifiers. Each of these two congeners accounted for < 0.05% of total PCBs in both samples.
Results/Lessons Learned
Total PCB concentrations in Aroclors 5432 and 5442 (0.1 and 4.7% respectively) are entirely consistent with the 0.05-5% range previously reported as the typical range in commercial PCT products (USEPA, 1984). The iPCBs in PCT Aroclors are decidedly “inadvertent” if not “non-Aroclor” PCBs. In analysis of PCBs by GC/ECD methods (i.e., Method 8082) PCTs elute within the retention window of higher chlorinated PCB Aroclors. Thus, the presence of Aroclors 5432 or 5432 in samples may result in false positive reporting of Aroclors 1254 or 1260.
The PCB congener profiles in Aroclors 5432 and 5442 were similar to Aroclors 1242 and 1221, respectively. Furthermore, the penta- through deca-biphenyl content of the 5442 sample closely matched three Aroclor 1260 profiles. This similarity is understandable, given that Monsanto produced PCT and PCB Aroclors by generally similar methods: chlorination and distillation of polyphenyl feedstock. The high similarity is such that if the profiles were observed in the field, one might reasonably (but incorrectly) infer PCB Aroclor sources. If contribution from PCT products is not considered, source identification efforts based on congener profiles are likely to reach erroneous conclusions.
Notably, the level of 4,4’ dichlorobiphenyl (4-4’ diCB or PCB-15) was 3.4% of total PCBs in Aroclor 5432, and <2.5% in Aroclor 1242. Internal Monsanto documents indicate that PCB-15 caused crystallization in lower chlorinated PCB Aroclor products, and production processes included steps designed to keep PCB-15 levels below certain thresholds. For Aroclor 1242 the threshold was 2.5%. Additional work is ongoing, but an implication is that the presence of PCB-15 above 2.5% may be a reliable indicator of Aroclor 5432.