PCBs, polychlorinated biphenyls, are a group of related chemicals that were used for a variety of applications up until the 1970s. In the 1960s the development of improved gas chromatography methods allowed environmental scientists to become aware of the environmental persistence and global distribution of PCBs in the environment. Since that time there have been hundreds of studies conducted to better understand the environmental transport and fate of PCBs.
However, it has been only over the past 20 years or so that studies have focused on learning more about PCBs that were incorporated into building products and their fate in the indoor environment. Much of what has been learned is surprising and counter-intuitive.
For example, while it is generally true that PCBs have low volatility and low water solubility, it turns out that even at room temperature they are volatile enough to permit them to migrate in and around buildings at concentrations high enough to have regulatory implications. This migration may take place slowly, over the course of several decades, but in some instances, it has happened in as little as a year. With today’s sensitive instrumentation, chemists are able to track the movements of even tiny concentrations of PCBs as they migrate.
This post is a primer on the three primary categories of building materials which contain PCBs and how their PCBs can move inside of buildings.
As the name suggests, primary sources are building materials that were either deliberately or accidentally manufactured with PCBs as an ingredient prior to their installation in a building. The most common primary sources are:
- Various surface coatings; and
- Fluorescent light ballasts (FLBs).
FLBs are different from the other materials on this list because they use PCBs in an “enclosed” manner. This is defined as use in a manner that will ensure no exposure of human beings or the environment to PCBs. However, with continuous use FLBs are known to deteriorate, sometimes resulting in the release of PCBs. Only FLBs manufactured before the PCB ban (1979) should contain PCBs and by now (2017) any of these older PCB containing FLBs should have been replaced with non-PCB ballasts since even the youngest PCB FLBs are almost 40-years old. FLBs are considered to have had a functional life span of only 10-15 years. The type of PCBs used in US-made FLBs were almost exclusively Aroclors 1242 and 1016.
The other primary PCB sources on the above list are considered to be “open” PCB uses because, unlike FLBs, the PCBs were not contained in an enclosure. In most of these cases PCBs were added to the materials to improve the performance of the products by contributing: fire resistance, plasticity, adhesiveness, extended useful life and other desirable properties. For PCBs to impart these properties they were generally included at concentrations ranging from 2% to about 25%; this is equivalent to 20,000 parts per million (ppm) to 250,000 ppm. The most common PCBs found in US-made building materials are Aroclor 1254 followed by Aroclor 1248, 1260 and 1262.
PCBs can sometimes be present in primary sources by accident rather than by design. The presence of Aroclor PCBs in primary sources at concentrations less than 1,000 ppm (equal to 0.1%), or non-Aroclor PCBs at any concentration, may indicate an accidental PCB use.
Under the federal PCB regulations primary sources of are referred to as PCB Bulk Products and they are regulated when their PCB concentration is 50 ppm or greater.
Secondary Sinks and Secondary Sources
When a PCB primary source is in direct contact with a porous building material, the PCBs in the primary source can often migrate from the primary source into the porous material. Porous building materials known to adsorb PCBs in this way include concrete, brick and wood. When this migration occurs, the now PCB containing porous materials are referred to as secondary PCB sinks. Secondary sinks often have PCB concentrations in the range of 10-1,000 ppm.
While the federal regulations apply to primary sources when their concentration is 50 ppm or greater, requirements for secondary sinks are stricter. They are categorized as PCB Remediation Wastes and are regulated when their PCB concentration is 1 ppm or greater.
In some situations, the PCBs in secondary sinks can be remobilized and either migrate directly into other porous materials or they can volatilize into the air. When this occurs, these secondary sinks may be referred to as secondary sources. In practice one hears the terms secondary sinks and secondary sources being used interchangeably.
Tertiary Sinks and Sources
Tertiary sinks arise when PCBs from primary or secondary sources volatilize into the air and then condense onto other materials in a building. The significance of volatilization as a PCB migration pathway was underappreciated until recent times because the relatively low volatility of PCBs suggested that the volatilization rate was too low to be meaningful. However, laboratory testing and numerous real-world examples have demonstrated that volatilization of PCBs from primary and secondary sources with redeposition on other materials can be significant in some settings. Tertiary sinks often have PCB concentrations between 1-100 ppm.
Some authors prefer to use the term secondary sinks to describe both secondary and tertiary sinks. Personally, I prefer to use ‘tertiary sinks’ to identify materials affected by indirect contact (through the air) and ‘secondary sinks’ to identify materials affected by direct contact to primary sources. However, I acknowledge that it is not always evident whether a material is a secondary or tertiary sink.
Why Understanding PCB Sources and Sinks Matters
Understanding the ways that PCBs move around in buildings is important if your goal is to reduce potential exposures inside of buildings. It is a frequent occurrence in PCB building remediation for primary sources to be removed only to find that indoor air concentrations have not been reduced to the extent expected. Or for air concentrations to fall immediately after remediation, only to return to previous levels with the passage of time. This is often due to an insufficient appreciation for the influence and action of secondary and tertiary sinks.
If you have a particular PCB in building condition that needs a fresh set of eyes to review it, consider reaching out us for another opinion.