What are PCBs and why are they toxic?
What Are PCBs?
PCBs are a group of man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms. The number of chlorine atoms and their location in a PCB molecule determine many of its physical and chemical properties. PCBs have no known taste or smell, and range in consistency from an oil to a waxy solid.
PCBs belong to a broad family of man-made organic chemicals known as chlorinated hydrocarbons. PCBs were domestically manufactured from 1929 until manufacturing was banned in 1979. They have a range of toxicity and vary in consistency from thin, light-colored liquids to yellow or black waxy solids. Due to their non-flammability, chemical stability, high boiling point and electrical insulating properties, PCBs were used in hundreds of industrial and commercial applications including:
Electrical, heat transfer and hydraulic equipment
Plasticizers in paints, plastics and rubber products
Pigments, dyes and carbonless copy paper
Other industrial applications
In the United States, PCBs were commercially manufactured from 1929 until production was banned in 1979 by the Toxic Substances Control Act (TSCA). However, EPA’s regulations implementing TSCA for PCBs allow some inadvertent generation of PCBs to occur in excluded manufacturing processes, as defined in title 40 of the Code of Federal Regulations (CFR) section 761.3.
Specifically, the PCB regulations allow inadvertently generated PCBs (iPCBs) at defined concentrations, under certain conditions, and with requirements to report to EPA and maintain certain records. Learn more about iPCBs, including the regulatory context, EPA enforcement, iPCBs in the environment, ongoing research conducted by the EPA, and pollution prevention efforts.
Commercial Uses for PCBs
Although no longer commercially produced in the United States, PCBs may be present in products and materials produced before the 1979 PCB ban. Products that may contain PCBs include:
Transformers and capacitors
Electrical equipment including voltage regulators, switches, re-closers, bushings, and electromagnets
Oil used in motors and hydraulic systems
Old electrical devices or appliances containing PCB capacitors
Fluorescent light ballasts
Thermal insulation material including fiberglass, felt, foam, and cork
Adhesives and tapes
Carbonless copy paper
The PCBs used in these products were chemical mixtures made up of a variety of individual chlorinated biphenyl components known as congeners. Most commercial PCB mixtures are known in the United States by their industrial trade names, the most common being Arochlor.
Release and Exposure of PCBs
Today, PCBs can still be released into the environment from:
Poorly maintained hazardous waste sites that contain PCBs
Illegal or improper dumping of PCB wastes
Leaks or releases from electrical transformers containing PCBs
Disposal of PCB-containing consumer products into municipal or other landfills not designed to handle hazardous waste
Burning some wastes in municipal and industrial incinerators
PCBs do not readily break down once in the environment. They can remain for long periods cycling between air, water and soil. PCBs can be carried long distances and have been found in snow and sea water in areas far from where they were released into the environment. As a consequence, they are found all over the world. In general, the lighter the form of PCB, the further it can be transported from the source of contamination.
PCBs can accumulate in the leaves and above-ground parts of plants and food crops. They are also taken up into the bodies of small organisms and fish. As a result, people who ingest fish may be exposed to PCBs that have bioaccumulated in the fish they are ingesting.
The National Center for Health Statistics, a division of the Centers for Disease Control and Prevention, conducts the National Health and Nutrition Examination Surveys (NHANES). NHANES is a series of U.S. national surveys on the health and nutrition status of the noninstitutionalized civilian population, which includes data collection on selected chemicals. Interviews and physical examinations are conducted with approximately 10,000 people in each two-year survey cycle. PCBs are one of the chemicals where data are available from the NHANES surveys.
A PCB congener is any single, unique well-defined chemical compound in the PCB category. The name of a congener specifies the total number of chlorine substituents, and the position of each chlorine. For example: 4,4'-Dichlorobiphenyl is a congener comprising the biphenyl structure with two chlorine substituents - one on each of the #4 carbons of the two rings. In 1980, a numbering system was developed which assigned a sequential number to each of the 209 PCB congeners.
Homologs are subcategories of PCB congeners that have equal numbers of chlorine substituents. For example, the tetrachlorobiphenyls are all PCB congeners with exactly 4 chlorine substituents that can be in any arrangement.
PCB Mixtures and Trade Names
With few exceptions, PCBs were manufactured as a mixture of individual PCB congeners. These mixtures were created by adding progressively more chlorine to batches of biphenyl until a certain target percentage of chlorine by weight was achieved. Commercial mixtures with higher percentages of chlorine contained higher proportions of the more heavily chlorinated congeners, but all congeners could be expected to be present at some level in all mixtures. While PCBs were manufactured and sold under many names, the most common was the Aroclor series.
Individual PCB Congeners
Aroclor is a PCB mixture produced from approximately 1930 to 1979. It is one of the most commonly known trade names for PCB mixtures. There are many types of Aroclors and each has a distinguishing suffix number that indicates the degree of chlorination. The numbering standard for the different Aroclors is as follows:
The first two digits usually refer to the number of carbon atoms in the phenyl rings (for PCBs this is 12)
The second two numbers indicate the percentage of chlorine by mass in the mixture. For example, the name Aroclor 1254 means that the mixture contains approximately 54% chlorine by weight.
Table of Aroclors
PCB Trade Names
PCBs were manufactured and sold under many different names. The names in the following table have been used to refer to PCBs or to products containing PCBs. Please note:
Some of these names may be used for substances or mixtures not containing PCBs.
Many of these names were used with distinguishing suffixes, indicating degree of chlorination, type of formulation, or other properties (e.g., Aroclor 1254; Clophen A60).
Some of these names may be misspellings of the correct names, but are included here for completeness.