PCBs (polychlorinated biphenyls) are no longer manufactured, but they are far from gone. Intentional production was banned in the United States in 1979, yet PCBs remain legally in service inside older electrical equipment, persist in building materials installed before 1980, and even show up as unintentional byproducts in modern pigments and dyes. Understanding where PCBs still exist today matters because these chemicals are persistent, accumulate in living tissue, and disrupt hormonal systems even at very low concentrations.
Legacy Electrical Equipment Still in Service
The largest category of intentional PCB use that continues today is older electrical infrastructure. Under federal regulations, PCBs at any concentration may remain in transformers, electromagnets, switches, voltage regulators, circuit breakers, and electrical cable for the remainder of their useful lives. Utilities and building owners are not required to remove this equipment preemptively. They can even rebuild and service it, as long as they follow specific handling rules.
This means that transformers installed decades ago, many of which sit on utility poles or in the basements of commercial buildings, can still contain PCB-laden dielectric fluid. Natural gas pipeline systems are also authorized to operate with PCB concentrations below 50 parts per million, and in some cases higher concentrations are permitted for pipelines not owned by gas sellers or distributors. The Stockholm Convention, an international treaty on persistent pollutants, set a 2025 deadline for disposing of PCB-containing equipment and a 2028 deadline for managing the associated waste, but compliance varies widely by country.
Building Materials From the Mid-20th Century
Buildings constructed or renovated between roughly 1950 and 1979 are likely to contain PCBs embedded in everyday materials. The EPA has identified a long list of products from that era that frequently test positive: caulk around windows and doors, joint sealants, expansion joint material, paints, varnishes, floor tiles, acoustic ceiling tiles, adhesives, insulation (fiberglass, felt, foam, cork), rubber gaskets, asphalt roofing, tar paper, sprayed-on fireproofing, pipe coatings, and PVC applications.
Caulk is one of the most concentrated sources. A review of testing data found PCBs in 48% of caulking samples, with median concentrations in the 1,000 to 10,000 parts per million range. The EPA has documented caulk samples reaching 500,000 ppm, meaning the material was 50% PCBs by weight. These materials don’t just sit inert. PCBs slowly off-gas from caulk, paint, and sealants into indoor air, which is why older schools and office buildings can have measurable PCB vapor concentrations inside them. Research has shown that school indoor air contaminated by PCBs released from building materials and paint may pose health risks to children, teachers, and staff through inhalation alone.
Fluorescent Light Ballasts in Older Buildings
Fluorescent light fixtures manufactured before 1979 used magnetic ballasts that contained PCB fluid as an insulator. These ballasts had a designed lifespan of 10 to 15 years, which means every single one still in operation has far exceeded its intended service life. The EPA specifically flags schools built before 1979 as likely to still contain these components. As the ballasts age, they become increasingly prone to leaking, smoking, or catching fire, releasing PCBs directly into occupied spaces. Replacement is voluntary, and many older buildings, particularly underfunded schools and public facilities, have never upgraded their lighting.
Unintentional Production in Modern Manufacturing
Even though nobody manufactures PCBs on purpose anymore, they are still being created as accidental byproducts in certain chemical processes. The most significant source is the production of organic pigments, specifically azo pigments (used to make orange, red, and yellow colors) and phthalocyanine pigments (used for blues and greens). These pigments end up in paint, ink, textiles, paper, cosmetics, leather, plastics, and even food packaging.
The mechanism is straightforward: manufacturing these pigments requires chlorinated solvents or chemical intermediates, and side reactions during production generate PCB molecules. Phthalocyanine blue pigments, for example, are made using chlorobenzene as a reaction medium, which forms lower-chlorinated PCB congeners as a byproduct. When blue pigments are further processed into green through a step called perchlorination, highly chlorinated PCBs form as well. Azo pigments involve more than 10 common chlorinated starting materials, any of which can generate PCBs through side reactions under basic or high-heat conditions.
Testing has found PCB concentrations ranging from 2 to 200 nanograms per gram in 15 of 33 paint pigments analyzed in one study. Researchers identified a specific PCB variant, known as PCB 11, that appears consistently in these pigments but is largely absent from the old commercial PCB mixtures. This makes PCB 11 a useful marker for distinguishing modern inadvertent production from legacy contamination. These regulations have a notable gap: U.S. law does not require an exemption for PCBs resulting from what the EPA classifies as “excluded manufacturing processes,” which includes unintentional byproduct formation, as long as certain conditions are met.
Accumulation in the Food Chain
Decades of PCB contamination have left a lasting imprint on the global food supply. PCBs are fat-soluble and resist breakdown, so they concentrate as they move up the food chain. Fatty fish are the primary dietary source for most people. Sardines, which carry more body fat than many other fish, show some of the highest concentrations, with PCB levels measured at roughly 4 to 18 nanograms per gram of fish. Anchovy and other small species carry lower but still detectable amounts. Tuna caught in heavily industrialized waters near Japan has been measured at up to 1,100 nanograms per gram on a fat-weight basis.
For most people eating typical amounts of fish, weekly intake remains below the safety threshold set by European food authorities (2 picograms of toxic equivalents per kilogram of body weight per week). But the margin is not enormous, particularly for people who eat fatty fish frequently or who also face PCB exposure from indoor air or contaminated soil.
How PCBs Affect the Body
PCBs are classified as endocrine disruptors, meaning they interfere with hormone signaling. Their molecular structure closely resembles thyroid hormone, which allows them to interact with thyroid hormone receptors. Research has shown that even at extremely low doses, hydroxylated PCBs suppress the ability of thyroid hormone receptors to activate gene transcription. They do this by partially pulling the receptor complex away from the DNA sequences it normally binds to, effectively muting the signal that thyroid hormone is supposed to send.
This is particularly concerning for developing brains. Thyroid hormones play a central role in fetal and childhood brain development, and disruption during critical windows can lead to neurological and cognitive effects. PCBs also accumulate in body fat over a lifetime, meaning exposure is cumulative rather than something the body clears quickly.
How PCB Waste Is Handled
When PCB-containing equipment or materials are removed, disposal is tightly regulated. The four approved methods are high-temperature incineration (burning at temperatures that break down the chemical bonds), combustion in high-efficiency industrial boilers, chemical dechlorination (a process that strips chlorine atoms from the molecules, rendering them less toxic), and landfilling in approved hazardous waste facilities. Equipment and materials contaminated at 50 ppm or above can only be distributed after being decontaminated to meet specific standards. Items below 50 ppm face fewer restrictions but still require proper disposal channels.
The practical challenge is scale. PCBs are embedded in millions of buildings, electrical systems, and industrial sites worldwide. Identifying contaminated materials requires testing, removal requires trained workers and containment protocols, and disposal requires specialized facilities. For many building owners and utilities, the cost and complexity mean PCB-containing materials stay in place until renovation or demolition forces the issue.