Jensen Finds PCBs in Animal Tissues Summary

  • Last updated on November 10, 2022

Swedish chemist Sören Jensen announced that PCBs were present in human and wildlife tissue samples and showed that PCBs could therefore be a serious environmental pollutant.

Summary of Event

In December, 1966, New Scientist magazine published a short statement about a new chemical hazard in the environment. That chemical was polychlorinated biphenyl (PCB), and the author of the statement was Sören Jensen, a Swedish chemist from the University of Stockholm. He had been measuring pesticide residues in animal tissue for the Institute for Analytical Chemistry. Jensen found that PCBs were making some unidentified signals that interfered with his analysis. His conclusion was that PCBs were entering the food chain. Ecology Pollution;Sweden Polychlorinated biphenyls PCBs Hazardous materials [kw]Jensen Finds PCBs in Animal Tissues (Dec., 1966) [kw]PCBs in Animal Tissues, Jensen Finds (Dec., 1966) [kw]Animal Tissues, Jensen Finds PCBs in (Dec., 1966) Pollution;Sweden Polychlorinated biphenyls PCBs Hazardous materials [g]Europe;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] [g]Sweden;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] [c]Environmental issues;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] [c]Biology;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] [c]Chemistry;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] [c]Science and technology;Dec., 1966: Jensen Finds PCBs in Animal Tissues[09040] Jensen, Søren Lovelock, James Tiedje, James M.

Jensen’s news alerted other scientists to the fact that some of the curious signals they saw in tissue samples might also be attributable to PCBs. In 1967, scientists at the University of California at Berkeley also reported finding PCBs in bird tissue. Soon, scientists found PCBs in rainwater in England, in brown seals off the coast of Scotland, in white-tailed eagles in Sweden, in Baltic sea cod, in mussels from the Netherlands, in Adélie penguin eggs in Antarctica, in brown pelican eggs in Panama, in Arctic terns, in Florida shrimp, in river water in Japan, in the Great Lakes, and in human hair and fat. For chemists, industrialists, and environmentalists, this was alarming news. All evidence pointed to a global spread of PCBs.

PCBs were first made in 1881 and became readily available in the 1920’s. On a PCB, chlorine atoms substitute for one or more of the hydrogen atoms on a biphenyl structure. A biphenyl is a pair of benzene rings joined by a single carbon to carbon bond. Benzene itself has the chemical formula C6H6. A related chemical, polybrominated biphenyl (PBB) uses bromine instead of chlorine. Many different kinds of PCBs form during manufacture, since each ring on the biphenyl structure can have up to five chlorine atoms. Theoretically, it is possible to make 209 different kinds, or congeners, of PCBs. In practice, most PCBs are mixtures of seventy or more of these different congeners.

Monsanto Chemical Company Monsanto Chemical Company made PCBs in the United States and sold them with the trade name of Aroclor Aroclor . The trade names of PCBs in Europe and Japan were Phenoclor Phenoclor or Clophen Clophen . Usually the Aroclors were liquids or resins and were identified by four-digit codes. The last two digits in the code indicated the percentage of chlorine by weight in the total mix; the higher the final two digits, the greater the number of chlorines in the PCB. Aroclor 1254 contained 54 percent chlorine by weight, for example.

The properties that made PCBs so attractive were high boiling points, low water solubility, and high dielectric, or nonconducting, constants. These physical properties meant that PCBs were hard to burn, resisted acids and bases, and were mostly inert. Many industrial and manufacturing applications soon used PCBs in adhesives, ballasts for fluorescent fixtures, capacitors, carbonless copy paper, coolant insulation in transformers, high-pressure hydraulic fluids, machine-tool cutting oils, specialized lubricants and gasket sealers, plasticizers in wire and cable coatings, vinyl films, and protective coatings for wood, metal, and concrete. Some varnishes and epoxy paints contained PCBs. Braided cotton and asbestos in electric wire insulation were also impregnated with PCBs. Some companies even briefly entertained the idea of impregnating clothing with a related compound, PBB, to make the clothing fireproof.

The properties that made PCBs so useful to the industry also made them potentially long-lasting and widespread pollutants. PCBs were not suspected of being an environmental problem, however, because PCBs were mostly inert, not deliberately spread, and not very toxic. It was difficult to show chronic PCB toxicity, the physiological effects of long-term exposure, and the Environmental Protection Agency (EPA) did not list PCBs as cancer-causing chemicals Carcinogens until long after they were in use. In addition, PCBs were hard to detect with the analytical instruments available before the early 1960’s.

The first breakthrough in detecting chemicals like PCBs came in 1952, when scientists Tony James James, Tony and Archer Martin Martin, Archer developed the gas chromatograph Gas chromatograph Chromatographs at the National Institute for Medical Research (NIMR) in London. In a gas chromatograph, chemicals in a mixed sample pass through a porous solid at different rates based on their chemical properties and size. The appropriate detector produces a signal proportional to how much of each compound comes through. Comparing how long it takes known chemicals to flow through the gas chromatograph with unknown compounds flowing under the same conditions helps identify and quantify the unknowns. A commercial gas chromatograph was made in London by late 1954.

The early gas chromatographs let scientists separate chemicals, but their detectors were not very sensitive. Sandy Lipsky Lipsky, Sandy of Yale University in Connecticut and James Lovelock from the National Institute for Medical Research in London invented the electron capture detector Electron capture detector (ECD) in 1960. This invention would cause a revolution in environmental science, because the electron capture detector was the first device to be specifically sensitive to organic pollutants and could be used to show that organic pollutants were contaminating the environment.

In 1961, gas and gas liquid chromatographs with electron capture detectors were first used to look at chlorinated chemicals such as insecticides. Scientists in the United States and Great Britain were using the chromatographs to look for pesticide residues in food. What they found surprised them. They soon discovered that dichloro-diphenyl-trichloroethane Dichloro-diphenyl-trichloroethane[Dichlorodiphenyl trichloroethane] (DDT) and other organic pesticides had worldwide distribution.

PCBs appeared as interfering signals in the detection of other chlorinated compounds, such as DDT. Analysts usually ignored these signals, however, because the signals did not match the pesticides they were trying to detect. In 1965, however, scientists began taking a closer look at these interfering signals. It turned out they were chlorinated compounds.

Jensen, in Sweden, was measuring the concentration of long-lasting pesticides in fish, birds, water, sediment, and other environmental samples when he looked at these unidentified signals and identified them as PCBs. He based his reports on tissue samples from fish and fly spawn, and dead eagles collected from different parts of Sweden. Jensen even examined his family’s hair and observed that his wife, his five-month-old daughter, and his own hair contained PCBs.

Jensen was curious to known when PCBs first started entering the environment, so he obtained some eagle feathers from birds preserved in the Swedish Museum of Natural History. The eagles represented a continuous record from 1880 to 1966. Jensen found that PCBs were first detectable in an eagle from 1944.


Between 1930 and 1975, more than 570 million kilograms of PCBs were made in the United States alone. By 1975, 345 million kilograms were still in use, perhaps 25 million kilograms were incinerated, and about 25 million kilograms of PCBs were buried in landfills. That left approximately 70 million kilograms circulating somewhere in the environment, and Jensen’s results indicated that they were starting to contaminate the food chain by 1944. Scientists and environmentalists alike worried that PCBs might ultimately become a greater environmental problem than DDT, because PCBs lasted longer.

Fish-eating bird populations began to decline and thin-shelled eggs began to increase after World War II. This coincided with the time when chlorinated chemicals came into use. In birds, PCBs cause thin-shelled eggs, as does DDT. These chemicals inhibit enzymes involved in calcium movement in healthy birds. The hormone estrogen controls the calcium level in breeding female birds. DDT and PCBs stimulate enzymes that make estrogen more soluble and more readily excreted. When estrogen is low, calcium reserves are low, and little calcium is available for eggshell formation. PCBs and DDT accumulate in birds because fatty tissues in organisms readily absorb these chemicals and do not readily lose them. Predatory birds and fish begin to acquire the accumulated PCBs of their prey in a process called biomagnification.

Although PCB concentrations were highest around industrial or urban areas, the global spread of PCBs seemed odd. PCBs were appearing in areas where they ought not to appear because of their low solubility: in newly developed real-estate lakes, in isolated geological research stations, and in Arctic animals. They were also showing up in remote wilderness areas. Burning wastes that contained PCBs led to their release into the atmosphere. Once there, the PCBs spread everywhere. By 1970, Monsanto began to limit PCB shipments to companies that could not dispose of them without releasing them to the environment.

Once scientists realized PCBs were contaminating the environment, they began to search for ways to destroy them. The more they looked, the more they found that PCBs in anaerobic (oxygen-free) sediments appeared to be breaking down. In 1982, James Tiedje and others reported that chlorine disappeared from chemicals like PCBs in anaerobic conditions. Further studies showed that some important and hazardous chemicals, such as highly chlorinated PCBs, hexachlorobenzene (HCB), tetrachloroethene (PCE), and pentachloro phenol (PCP), needed anaerobic conditions to break down.

In the late 1980’s, John Brown Brown, John and colleagues at the General Electric Research and Development facility in Schenectady, New York, began looking at sediment from sites in the upper Hudson River. These sites contained up to 268,000 kilograms of PCBs. In some spots, PCBs exceeded 50 milligrams per kilogram (ppm). The PCBs had come from a capacitor-manufacturing operation at Hudson Falls and Fort Edward, New York, that had operated between 1952 and 1971.

Brown reported that highly chlorinated PCBs changed to lower chlorinated PCBs in anaerobic sediments. He suggested that PCBs in the environment could break down by a two-step process. Chlorine removal in anaerobic aquatic sediments followed by breakdown in aerobic environments would eventually cause total PCB destruction. More important, chlorine removal detoxified carcinogenic PCB congeners known to persist in humans.

This discovery presented an interesting dilemma for environmentalists. Was it better to leave known deposits of chemicals undisturbed in environments where they slowly decomposed and slowly entered food systems or to remove them and risk suddenly increasing the levels of contamination around a site by disturbing it?

Several events ultimately led to a halt in PCB and PBB production. The most notorious was in 1974, when 30,000 or more cattle and other farm animals were quarantined and destroyed because they were contaminated with PBBs. The contamination occurred during the summer of 1973, when Michigan Chemical Corporation Michigan Chemical Corporation of St. Louis, Michigan, accidentally included 10 to 20 bags of Firemaster, a PBB-containing flame retardant, with a truckload of Nutrimaster, a magnesium oxide mix used to lower the acidity of cattle feed.

Michigan Chemical Corporation delivered the chemicals to a feed mill operated by Farm Services Bureau Incorporated in Battle Creek, Michigan, where they were mixed with feed that was distributed around the state. Farmers first began noticing toxicity in their farm animals beginning in late 1973. Contaminated milk and eggs exposed several thousand farm families to PBBs. This became one of the most widespread and expensive ($75 million to $100 million of damage) of all chemical contaminations.

PCBs and other chlorinated chemicals were widely distributed in the environment, and it is virtually impossible to find samples that do not contain some trace amounts of them. Even foods grown in chemical-free fields can receive trace amounts of PCBs from atmospheric deposition of incinerator exhausts. Analytical techniques are more advanced than knowledge about the environmental effects of trace amounts of chemicals.

Lovelock’s electron capture detector is so sensitive that it can measure trivial pesticide concentrations. This causes a dilemma. With such low detection limits, nearly all edible things would be rejected if the concentration of chemicals were truly required to be zero. If the “dose is the poison,” the ongoing problem with pesticides in the environment continues to be the question of what that dose should be. Pollution;Sweden Polychlorinated biphenyls PCBs Hazardous materials

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Carter, Luther. “Michigan’s PBB Incident: Chemical Mix-up Leads to Disaster.” Science 192 (April 16, 1976): 240-243. Eye-opening account of what can happen through a careless use of toxic chemicals and how difficult it is for society to determine the definition of safe.
  • citation-type="booksimple"

    xlink:type="simple">Gustafson, Carl. “PCBs: Prevalent and Persistent.” Environmental Science and Technology 4 (October, 1970): 214-220. A short review article that concisely describes what PCBs are, why they were made, and how they contribute to environmental problems. Somewhat technical. Summarizes the conditions that led to PCBs being observed as global environmental pollutants.
  • citation-type="booksimple"

    xlink:type="simple">Lovelock, James. “The Electron Capture Detector and Green Politics.” LC-GC: The Magazine of Separation Science 8 (November, 1990): 854-860. Lovelock explains how the technology to detect contaminants like DDT and PCB in nature affected the environmental movement and the social and political response to other potential environmental pollutants such as chlorofluorocarbons (CFCs). Easy to read, balanced, personal essay.
  • citation-type="booksimple"

    xlink:type="simple">_______. Gaia: A New Look at Life on Earth. New York: Oxford University Press, 1987. Worth reading for Lovelock’s style. Lovelock invented the detector that greatly influenced environmentalism. Describes how looking for environmental pollutants led to a new way of looking at how the environment works.
  • citation-type="booksimple"

    xlink:type="simple">Maugh, Thomas. “DDT: An Unrecognized Source of Polychlorinated Biphenyls.” Science 180 (May, 1973): 578-579. Technical article that raises the question of what happened to all the DDT that was sprayed in the United States and attempts to link the question to the ubiquity of PCBs in the environment.
  • citation-type="booksimple"

    xlink:type="simple">National Research Council Committee on the Assessment of Polychlorinated Biphenyls in the Environment. Polychlorinated Biphenyls on the Environment. Washington, D.C.: National Academy of Sciences, 1979. Published after the ban on PCBs went into effect in 1977. Generally easy to read but slightly technical presentation that summarizes the environmental presence of PCBs.
  • citation-type="booksimple"

    xlink:type="simple">“Report of a New Chemical Hazard.” New Scientist 32 (December, 1966): 612. This news brief was the first announcement of Sören Jensen’s research findings in a widely distributed English language journal.
  • citation-type="booksimple"

    xlink:type="simple">Riva-Murray, Karen, Robin A. Brightbill, and Michael D. Bilger. “Trends in Concentrations of Polychlorinated Biphenyls in Fish Tissue from Selected Sites in the Delaware River Basin in New Jersey, New York, and Pennsylvania, 1969-1998.” Denver, Colo.: U.S. Department of the Interior, U.S. Geological Survey, 2003. Government paper documenting the presence of PCBs in fish in the Delaware River Basin over the last three decades of the twentieth century. Bibliographic references.

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