Polychlorinated biphenyls (PCBs)

Monsanto was the dominant US manufacturer of PCBs (sold under the brand name Aroclor) from the 1930s until 1979, producing over 1.25 billion pounds [1]. PCBs were the perfect industrial fluid: chemically stable, fire-resistant, and electrically non-conductive, making them ideal for electrical transformers and capacitors. They were also used in hydraulic fluids, plasticizers, carbonless copy paper, and surface coatings. Internal Monsanto documents, revealed in litigation, showed the company knew PCBs were toxic as early as the 1930s and chose to conceal it. The 1968 Yusho disease outbreak in Japan — where rice oil contaminated with PCBs poisoned 1,800 people, causing chloracne, dark skin discoloration, neurological damage, and elevated cancer rates — provided stark proof of human harm [2]. PCBs were banned in 1979 under TSCA, but the contamination legacy is permanent: PCBs in river sediment, ocean sediment, and the tissues of long-lived fish species cannot be cleaned up. General Electric spent decades fighting EPA cleanup requirements for PCB-contaminated Hudson River sediments [3].

Eating contaminated fish is the most significant ongoing exposure pathway for most Americans [1]. Sport-caught fish from PCB-contaminated rivers and lakes — particularly the Hudson, Fox River, Lake Michigan tributaries, and many industrial waterways — carry PCB levels that trigger consumption advisories. Farmed salmon was found to have significantly higher PCB levels than wild salmon in a landmark 2004 study, leading to recommendations to limit consumption. Dietary exposure also occurs through meat, dairy, and other animal fats, as PCBs concentrate in fatty tissues [2]. Legacy electrical equipment in buildings — old fluorescent light ballasts, capacitors, and transformers built before 1979 — can leak PCBs, particularly when damaged or aging. School buildings and older commercial properties often contain PCB-laden caulking and paint [3].

PCBs are classified as probable human carcinogens (Group 2A by IARC), with the strongest evidence for non-Hodgkin lymphoma and melanoma [1]. But the cancer evidence is almost secondary to PCBs' endocrine disrupting effects: they mimic and block thyroid hormones, disrupting the thyroid signaling that is essential for fetal brain development. Children born to mothers with elevated PCB levels show reduced IQ, impaired memory, slower processing speed, and smaller head circumference in multiple cohort studies [2]. PCBs suppress the immune system, affect reproductive hormones, and accumulate in breast tissue. Because they are highly fat-soluble and resist breakdown, they build up in your body over a lifetime and transfer to your fetus and infant through the placenta and breast milk [3].

Frequent consumers of sport-caught fish from contaminated waterways — particularly near old industrial sites — face ongoing PCB accumulation [1]. People who live near or work in buildings with PCB-containing caulking, electrical equipment, or fluorescent light ballasts face inhalation and skin exposure. Workers in electrical utility maintenance, hazardous waste remediation, and old capacitor manufacturing have occupational exposures [2]. Pregnant women and their fetuses, nursing infants, and children are at the highest risk from PCBs' thyroid-disrupting effects on brain development. Indigenous communities that subsist on locally caught fish are among the most heavily exposed populations in the US [3].

Follow your state fish consumption advisories — these are typically posted by your state's health or environmental department and list specific fish and specific waterbodies with recommendations [1]. Choose wild-caught Alaskan salmon, sardines, and anchovies over farmed salmon and Great Lakes fish. Trim fat from fish and meat, and avoid frying in the cooking liquid — PCBs concentrate in fat [2]. If you work in a building with pre-1979 electrical equipment, report aging or leaking transformers and capacitors to your facilities manager. Before renovating a pre-1979 commercial or school building, test caulk and paint materials for PCBs — remediation is required under EPA rules for concentrations above 50 ppm [3]. Breast milk testing is available for women with high fish consumption or occupational exposures who want to understand their body burden.