It is difficult to prove with 100% conviction that PCBs (or any other chemicals) cause cancer, for the following reasons.   (Nevertheless, the Precautionary Principle must be used to prevent risky exposures.)

• Overall cancer rates have increased dramatically in the U.S. over the last 50 years. Now, each of us has nearly a 50% chance of developing cancer. This makes it difficult to detect increased rates of cancer from one cause. In Northeast Wisconsin, researchers would need to look at a large population of local fish-eaters, measure their body levels of PCBs, and look for increased rates of cancer among those with higher PCB exposure. We need a full-scale epidemiological study like this before local effects can be shown. Such studies have not been done in Northeast Wisconsin. People are sick or dying of cancer all around us, but on an individual level it’s very difficult to claim a single cause.

 
• On the local level, it can be misleading to look at an map of cancer rates in Northeast Wisconsin (see cartoon below), to compare our region with other areas, because so many factors must be weeded out to detect a true cancer-causing effect. Many people move in and out of the area, some neighborhoods are dominated by older citizens, some areas are low-income or high-income, etc. Many people don’t eat local fish, come in contact with the water or sediment, or breathe concentrated PCB vapors near the water or sediment. A true epidemiological study is needed of only those people with PCB exposures, especially through fish-eating.

 
• It’s unethical and illegal to conduct controlled chemical experiments on humans, so researchers resort to studying accidental human exposures or occupational exposures when they want human data. These studies are usually rare, expensive, and involve too few people to be absolutely conclusive. Sometimes, it’s hard to quantify the PCB exposure or to know how long the exposure occurred. It’s also impossible to repeat the "experiment" to prove that the results are reproducible. 

 
• Though some studies may not find an association between PCBs and cancer, or though scientists may declare certain studies "inconclusive," this is not the same as proving PCBs don’t cause cancer. Particularly when several studies do show links between PCBs and cancer.

• Scientists suspect that the types of PCBs which accumulate in fish tend to be the more carcinogenic forms of PCBs, but none of the cancer studies cited above involved fish-eaters. Such studies have not been done yet.

• All of us are exposed to thousands of chemicals in our lives, so it’s difficult to sort out all the confounding variables to determine a true effect. Results also have to be adjusted to take into account age, level of chemical exposure, bad diet, smoking, and drinking habits, and other occupational chemical exposures.

• In a controlled animal experiment, some of the animals are "clean" for purposes of comparison. But in real life, ALL humans carry some PCBs in our bodies, so we have no true "clean" population to compare PCB exposed people with. We can only compare effects at relative levels of PCB contamination.

• Many cancers take a long time to develop, perhaps 10 or 20 years after exposure to the chemical. This lag time can complicate studies. It’s also possible that the children of fish-eaters may be at more risk of cancer, due to chemically triggered PCB effects during development of the baby in the womb. Such an effect may not appear for decades, long after exposure occurred.

• Preliminary research shows that certain PCBs tend to PROMOTE cancer, once the cancer has been initiated by another cause --- so the cancer may require a mixture of chemicals including PCBs.  For example, PCBs may increase the cancer effect of smoking.  Research shows that PCBs stimulate the production of important liver enzymes, which activates key metabolic processes, which enhances the cancer-causing activity of carcinogens contained in tobacco.  A commercial mixture of PCBs, called Aroclor 1254, is used routinely by laboratories to induce liver enzymes in order to test the cancer-causing ability of other chemicals.   Commercial labs currently sell pre-made enzyme mixtures induced by Aroclor 1254, for use in medical research.  (See In Vitro Technologies website.)

• Research shows some PCBs promote tumors, and some inhibit tumors --- so it matters how much of each is present in the study mixture. Many older PCB studies made no distinction between the 209 types (congeners) of PCBs being analyzed.

• PCBs are proven to damage the immune system, which may influence the body's susceptibility to cancer over time due to other causes.

• Most animal and human cancer studies don’t examine the combined cancer risk of PCBs, furans and dioxins all present at the same time, despite the fact that PCBs are rarely found without the other two. PCBs were generally contaminated with furans (up to 10 ppm), and sometimes dioxins, during the manufacturing process at Monsanto, or at Monsanto licensed producers. Some researchers believe that as PCBs aged they partly degraded into furans as well. A Canadian scientific journal published research revealing that post-consumer waste paper processed in paper recycling plants was the source of "high levels of dioxin and furan" in the effluent from mills (mills which did not use any chlorine-based bleaching). In addition, the high heat in some paper industry processes along the Fox River may have converted some of the PCBs to furans. The burning of waste oils containing PCBs could also convert them to both furans and dioxins. The conversion temperature from PCBs to furans is 270 degrees C. This means the Japanese Yusho rice-oil poisoning incident, which showed increases in liver and lung cancer, is significant because both PCBs and furans were present. Industry representatives claim that ALL the Yusho cancer risk was due to furans not PCBs; however, Fox River PCBs are contaminated with furans, so it doesn't matter which chemical caused cancer. We have both here, plus dioxins. Dioxins are a "known human carcinogen." (See PCBs, Dioxins and Furans --- They Travel Together.)

• Animal studies with pure PCBs are unrealistic and probably miss normal effects of PCBs combined with furans and dioxins. In 1970, Monsanto’s R.E Keller noted in an internal memo that specially prepared PCBs samples sent to a lab for animal toxicity testing were free of troublesome dibenzofurans [furans] "which might bias the results." As an aside, he added they were free from dioxin contamination as well. According to attorney Paul Merrell, "The implication is that the PCBs they tested did not contain the toxic material, but that it was common in their product. It’s evidence of a cover-up." (It turns out that "pure" PCBs also cause cancer in animals, so the difference may be a matter of degree.)  (See The History of PCBs)

• The numerous animal studies which prove that PCBs cause cancer must be taken seriously. Though we may consider ourselves superior to rats and mice, our bodies operate in similar fashion on the biochemical level.

• Lab animals are much shorter-lived than humans, so cancer tests with these animals may miss greater long-term cancer risks, or certain rare forms of human cancer. Even so, all commercial mixtures of PCBs have been shown to cause cancer in animals, with some PCB types more potent than others.

• In 1978, a leading toxicity testing laboratory, Industrial Bio-Test Laboratories, Inc., was closed after disclosures that thousands of its tests of "high use" pesticides, drugs, food additives, soaps, and cosmetics were faked or improperly conducted. In 1970, IBT Labs was hired by Monsanto to test PCBs. One of IBT’s top executives was Dr. Paul Wright, a Monsanto toxicologist who took a job at IBT Labs in part to supervise the PCB tests. Afterwards, he returned to Monsanto. Wright was eventually convicted of multiple counts of fraud in one of the longest criminal trials in U.S. history --- with his legal fees paid by Monsanto. Internal memos show that in at least two instances the lab’s conclusion that PCBs were "slightly tumorigenic" was changed to "non-carcinogenic" at Monsanto’s request. Courtroom testimony indicates that IBT Labs was aware that PCBs caused extremely high numbers of tumors in test rats, but IBT Labs certified PCBs as non-carcinogenic.  (See The History of PCBs)

This cartoon illustrates the misleading use of simplistic cancer 
statistics by Fox River paper industry lobbyists.

(to see more Lyle Lahey political cartoons, click here)

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