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Forensic Analysis of Obscure Chlorinated Compounds in Sediment Samples for Historic Source Identification
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Identification of individual sources of polychlorinated biphenyls (PCBs) to sediment sites is often complicated due to multiple factors. These include the limitations of the commonly-used USEPA Method 8082 for PCB Aroclor identification; sediment transport processes; ongoing degradation of PCB mixtures that confounds interpretation of congener data, and the widespread former use of mixed Aroclors in industrial products.

As awareness of environmental impacts associated with PCBs increased during the late 1960s, the Monsanto Company reformulated its line of fire-resistant hydraulic fluids (aka Pydrauls). PCB Aroclors (e.g., 1221, 1232, 1242, 1248, 1254, and 1260) were blended with or entirely replaced by polychlorinated terphenyls (PCTs), specifically Aroclors 5432 and 5442. In 1972, production of PCTs ceased due to environmental concerns resulting from the unintended contamination of PCTs by PCBs during the manufacturing process.

While production volumes were not insubstantial, PCTs are "obscure" to the extent that they are rarely analyzed at sediment sites, and scant research is available regarding the toxicity and fate and transport characteristics. This may be due (in part) to the fact that the PCT structure allows for 8,557 congeners. However, PCTs as a class remain useful for PCB source identification and separation, due to their persistence and composition. Geosyntec was retained by a client at a National Priorities List (NPL) sediment site to develop and implement a successful forensic investigation incorporating PCT analysis for PCB source identification and separation.


Existing PCB Aroclor sediment data were used to identify suspected areas of PCB- and PCT-based Pydraul releases from former (late 1960s/early 1970s) operations. These stations were reoccupied to collect sediment cores from elevations corresponding to the Aroclor detections and the historical sediment surface. Sediment cores were analyzed for PCB Aroclors by USEPA Method 8082A; PCT Aroclors by a modified Method 8082, and PCB congeners by USEPA Method 1668. PCB congener data were evaluated using multiple linear regression (MLR) to identify PCB Aroclors not identified by Method 8082A. Historical documents were used to confirm purchase of Pydraul fluids composed of PCBs and PCTs during former operations.


PCT Aroclor 5432 was positively identified in sediment samples collected offshore of former outfalls suspected of discharging to the site. Concentrations ranged as high as 4,000 ug/kg, at depths up to 12 feet below mudline, reflecting the persistence of these highly chlorinated compounds. Samples collected upstream and downstream of the facility were non-detect for Aroclor 5432, isolating the source to former outfalls. These results were integrated with the PCB Aroclor identification and congener analysis to delineate the extent of sediment impacted by the former operations. The results also supported the ability to distinguish PCB Aroclors released by the former operations from the site-wide PCB impacts.

Publication Summary

  • Geosyntec Authors: James Peale, Luke Smith, Brian Webb
  • All Authors: James Peale (Geosyntec Consultants), Luke Smith (Geosyntec Consultants), Brian Webb (Geosyntec Consultants), Marty French (Specialty Analytical)
  • Title: 2023 Battelle Sediments Conference
  • Event or Publication: Event
  • Practice Areas: Sediment assessment and remediation, Contaminated site assessment and clean up
  • Citation: Battelle's International Conference on the Remediation and Management of Contaminated Sediments at the JW Marriott in Austin, Texas, on January 9 through 12, 2023
  • Date: January 9 through 12, 2023
  • Location: JW Marriott in Austin, Texas
  • Publication Type: Poster Presentation