Polychlorinated biphenyls (PCBs) are a group of synthetic aromatic compounds with the general formula C₁₂H_10-xCl_x that were historically used by industry because of their excellent dielectric properties and their resistance to heat and chemical degradation. PCBs were commonly used as additives in paints and asphaltic-based adhesives that were subsequently applied to Department of Defense (DoD) structures. Prior to 1979, PCBs were extensively used in industrial paints, caulking material, and adhesives, as their properties enhanced structural integrity, reduced flammability, and boosted antifungal properties. Numerous DoD facilities have older metal structures upon which paints containing PCB were applied. These painted structures may present risks to human health or the environment because of inhalation or ingestion concerns, as the paint degrades and becomes brittle and can become airborne or impact soil, surface water, or groundwater. To date, no reliable methods are available that allow for the removal of PCBs from painted structures and equipment without damaging the coating or the structures and equipment. 

The overall objective of this project was to refine and deploy a safe, cost-effective, in situ treatment method for the removal and destruction of PCBs found on DoD structures. This overall project objective was addressed by the following specific objectives:

• Determine the protocol for formulating bimetallic treatment system (BTS) for site specific conditions to enhance applicability to various PCB-containing materials found across numerous DoD facilities while maximizing safety and efficacy with the ultimate goal of reducing PCB concentrations to less than 50 mg/kg. 

• Demonstrate the effectiveness of BTS on a wide range of actual contaminated structures at three DoD facilities. Evaluate the relationships between dose applied, repeated applications, and reaction kinetics with the intention of specifically identifying the factors influencing treatment and limiting reaction rates for a specific media (e.g., different painted structures). Evaluate environmental condition effects (temperature and humidity, weathering) and impact of BTS on material appearance and adhesion.

Research and development work at the National Aeronautics and Space Administration Kennedy Space Center (NASA-KSC) and University of Central Florida (UCF) has led to the development of a BTS consisting of elemental magnesium (Mg) coated with a small amount of palladium (Pd) that is utilized in conjunction with a solvent solution capable of donating hydrogen atoms. BTS as a treatment technology has two functions: (1) to extract the PCBs from weathered coating materials and other PCB-containing materials such as insulation, rubber gaskets, and asphaltic compounds and (2) to degrade the extracted PCBs. The chemical reductant and catalyst system has been optimized for use in BTS and typically consists of 0.1% Pd on zero-valent or metallic Mg. It is hypothesized that the interaction of the bimetallic Mg/Pd system with a solvent containing available hydrogen moieties (i.e., alcohols) results in the generation of atomic hydrogen at particular sites on the metal surface. The bound atomic hydrogen is available for reaction with PCB molecules in solution yielding a reductive dehalogenation reaction.

The BTS technology demonstrations were conducted at two DoD facilities: (1) the Vertical Integration Building (VIB) at the Cape Canaveral Air Force Station (CCAFS), FL; and (2) the Badger Army Ammunition Plant (Badger), Sauk County, WI. Primary and secondary performance objectives were developed that were evaluated using either qualitative or quantitative performance criteria to determine success. These performance criteria included:

Distribution and adherence of the BTS. One of the qualitative performance objectives was that the BTS applicator was able to evenly distribute the paste on the surface to be treated. The metric was evaluated by assessing the adherence of the BTS to an object in a 0.25- to 0.5-inch layer over the time period of exposure to treated surfaces. BTS was applied using a spray applicator and hand trowel application method. This objective was met although the spray application did not work well in the cold weather implementation.

Adherence of sealants. The metric was evaluated by assessing the adherence of the sealant to the BTS, the ability to apply the sealant evenly over the surface of the paste, and its ability to dry to a non-tacky, nonporous layer that reduced volatilization of BTS solvent. Two sealants were tested: (1) a vinyl polymer (VP) truck bed liner and (2) a silicone-based roof sealant (Sil). This objective was met using both sealants.

Ease of implementation. The ease of use of this technology was evaluated based on experience in the field. This objective was met with respect to both the ease of handling and applying both the paste and sealant on the various surfaces and locations that were treated.

Reduction in PCB concentrations in treated paint to less than 50 mg/kg. A key performance objective was the reduction of PCB concentrations in the treated material to less than 50 mg/kg. This objective was partially met. One application of paste was effective in achieving this target after only one week of treatment in all cases where the starting concentration in the paint was less than approximately 500 mg/kg, especially if the surface being treated was metal and not concrete. In cases where the starting concentrations in the paint were greater than 500 mg/kg, significant reductions (93%) in PCB concentrations were achieved, but more than one application of paste is necessary to reduce concentrations below 50 mg/kg.

Reduction in PCB concentrations in BTS paste to less than 50 mg/kg. The reduction of PCB concentrations in the paste to less than 50 mg/kg was another key performance objective. This objective was partially met. For the active paste (metal in the paste), if the starting paint concentrations were below roughly 2500 mg/kg, then the concentrations in the paste were less than 50 mg/kg. If the pretreatment paint concentrations were very high (>20,000 mg/kg), then the active metal paste was not able to degrade all the PCBs in the paste to below 50 mg/kg, although degradation did occur in the paste. Even when Mg/Pd and additional ethanol was added in the laboratory to the active paste that had been exposed to the very high starting concentrations, it was not possible to get the concentrations in the paste to below 50 mg/kg after 21 days. For the nonmetal paste, which was activated in the lab after removal from the field by the addition of ethanol and the active metal (Mg and acid or Mg/Pd), the concentrations were reduced to below 50 mg/kg for all samples using the acidified ethanol and Mg and/or ethanol and the Mg/Pd.

Studies conducted at UCF after the project was initiated have shown that the Pd catalyst can be removed from the BTS paste and a small amount of acid added to make a paste that is less expensive and more reactive. The addition of a small amount of acetic acid to the ethanol significantly increased the rate of PCB degradation. These studies also showed that acidified ethanol with Mg particles was as effective or in some cases more effective than the Mg/Pd particles in non-acidified ethanol at degrading PCBs.