The Cancer Clusters That Weren’t

A recent post in ACSH Dispatch examines an interesting question: How likely is it that some U.S. communities have elevated cancer rates, a.k.a, “cancer clusters,” because of chemical pollution? The answer: not very.

ACSH points to an enlightening article published in Slate by George Johnson, who notes:

Time after time, the clusters have turned out to be statistical illusions—artifacts of chance. … The Erin Brockovich incident, one of the most famous, is among the many that have been debunked. Hexavalent chromium in the water supply of a small California town was blamed for causing cancer, resulting in a $333 million legal settlement and a movie starring Julia Roberts. But an epidemiological study ultimately showed that the cancer rate was no greater than that of the general population. The rate was actually slightly less.

Johnson also discusses the alleged cancer cluster in Toms River, N.J., which is the subject of a new book: Toms River: A Story of Science and Salvation, by Dan Fagin. But contrary to Fagin’s book, Johnson concludes: “… no matter how hard I squinted at the numbers, I found it hard to be convinced that there had been a cancer problem in Toms River.”

It is true that chemicals cause cancers where people are exposed for long periods of time to very high levels. For example, populations in Taiwan whose drinking water was contaminated with extremely high levels of arsenic for many decades experienced elevated rates of skin cancer. Is that a cluster? Surely it is. Does it convey information about the risks to populations exposed to much lower concentrations? Not particularly.

Yet activists focus on relatively low-level exposures to generate headlines and push regulations, and trial lawyers bring cases to extort large settlements because no one can prove their claims wrong — or right. Ironically, there’s evidence that low-level and long-term exposures to chemicals may have benefits, an effect that scientists refer to as hormesis.

Hollywood has sensationalized “cancer cluster” allegations, producing two major motion pictures — A Civil Action and Erin Brockovich — on the alleged effects of chemicals on various communities. In both cases, tort lawyers claimed that drinking water contaminated by industrial facilities caused cancers in nearby areas. Despite the ability of trial lawyers to win such cases, it is nearly impossible to pin down the causes of such clusters. In 1990, the Centers for Disease Control and Prevention reported on 22 years of studies that covered clusters in 29 states and five foreign countries. They could not establish a clear cause for any cluster.

Part of the problem is that clusters occur by mere chance. Raymond R. Neutra of the California Department of Health Services finds that we can expect nearly 5,000 such random cancer clusters to exist in any given decade in the United States (Scientific American 275, no. 3 (1996): 85–86.).

The risks of cancer clusters resulting from low-level exposures to chemicals in the environment are simply too low to detect. But allegations about such clusters are good fodder for trial lawyers looking to make a buck, and they serve the agenda of activists who want to pass regulations on chemicals.