Polychlorinated biphenyls (PCBs) are synthetic organic chemicals widely used in industrial applications due to their non-flammability, chemical stability, and excellent electrical insulating properties. Commercial production began in 1929, leading to their use in electrical equipment (like transformers and capacitors), paints, sealants, and hydraulic fluids. Although banned in the United States in 1979 and internationally by the Stockholm Convention, PCBs remain a significant environmental challenge. They are classified as persistent organic pollutants because they do not easily break down, allowing them to linger in the environment for decades and ensuring widespread human exposure.
Primary Exposure Through the Food Supply
The consumption of contaminated food is the main source of PCB exposure for the general population. This occurs through bioaccumulation, where PCBs are absorbed by organisms faster than they can be metabolized or excreted. Because PCBs are highly lipophilic (fat-loving), they readily dissolve and become stored in the fatty tissues of living things.
As contaminated organisms are consumed by others, PCB concentration increases at each successive level of the food chain, a process known as biomagnification. This results in the highest concentrations being found in animals at the top of the food web, which humans consume. High-risk foods are those with high-fat content, such as meat, dairy products, and especially fatty fish.
Bottom-feeding fish and sportfish caught in contaminated waters (like polluted rivers or lakes) tend to have elevated PCB levels. Ingesting these food sources remains the dominant exposure pathway, even as environmental concentrations decrease. Dietary intake of these fatty animal products accounts for the majority of the total PCB burden in the average person.
Inhalation from Indoor and Outdoor Air
Exposure to PCBs also occurs through breathing contaminated air, particularly indoors. PCBs volatilize (evaporate) from materials containing them, releasing chemical vapors into the surrounding air. Since people spend most of their time indoors, this route of exposure is increasingly recognized and can sometimes rival dietary intake.
Indoor PCB sources primarily stem from older building materials and products installed before the 1979 ban. These include caulking, sealants, paint, and fluorescent light ballasts, which slowly release PCBs into the air and dust. Studies show that PCB concentrations inside buildings, such as older schools, can be significantly higher than in outdoor air.
Outdoor exposure generally occurs at lower concentrations but is present due to the global cycling of these persistent chemicals. Higher concentrations are found near contaminated sites, such as hazardous waste landfills, incinerators, or former manufacturing facilities. In these areas, PCBs enter the air through volatilization from soil and water surfaces or via the combustion of waste.
Dermal Contact and Water Sources
Dermal contact (absorption through the skin) is a route of exposure, though it is generally less significant than ingestion or inhalation for the public. This exposure happens when skin contacts contaminated surfaces, such as soil or sediment near a waste site. Children, who often play on the ground, may face a higher risk through contact with contaminated dust and soil.
Exposure through water is generally minor compared to food sources because PCBs tend to partition out of the water and adsorb to sediments due to their lipophilic nature. However, drinking water can be a source, especially for those relying on private wells near waste sites where PCBs have contaminated the groundwater. Recreational activities, such as swimming in contaminated lakes or rivers, also present a low-level risk through skin contact and accidental ingestion.
Exposure in High Risk and Occupational Settings
Certain populations face significantly higher exposure levels due to their proximity to contamination or the nature of their work. Occupational exposure often involves both inhalation and dermal contact with materials containing concentrated PCBs. This includes workers maintaining or repairing old electrical equipment, such as transformers and capacitors, which historically used PCBs as a dielectric fluid. High exposure also affects hazardous waste cleanup crews involved in the remediation of Superfund sites or other locations with massive PCB contamination.
In these settings, chronic exposure results from the daily handling of contaminated materials, while acute exposure can result from accidental spills or equipment failures. Individuals living adjacent to former manufacturing plants or disposal sites may also experience elevated exposure through contaminated air, soil, and water. Occupational exposure can lead to blood PCB concentrations substantially higher than those found in the general population. People engaged in do-it-yourself renovations on pre-1979 buildings, where they may disturb PCB-containing materials like caulk, also face elevated exposure risks.