The Cancer Chronicles: Erin Brockovich and Mother Jones

By George Johnson | June 5, 2013 10:10 pm

Erin Brockovich in 2012. Wikimedia Commons.

When toxicologists prepare to test a chemical on lab animals to see if it is carcinogenic, they are faced with a dilemma. Suppose you have reason to suspect that a chemical, at the low concentrations found in air, food, or water, might cause one case of cancer for every 10,000 people who are exposed. You’re not going to get funding to test every substance on tens of thousands of mice — at a potential cost of tens of millions of dollars. To force the issue, scientists administer far larger dosages to a far smaller number of creatures and see if they can induce a tumor.

That is the approach — prevalent throughout the profession — taken by researchers for the National Toxicology Program in 2009 to study whether chromium 6, the pollutant involved in the Erin Brockovich case, is capable of causing cancer when ingested in drinking water.

I hadn’t intended to write about the Brockovich story again. (For more background please see the list of my earlier posts below.) But the Center for Public Integrity — first in a report on PBS Newshour and now in an article for Mother Jones — is pursuing the matter with such ardor that I’ve decided to take a closer look.

I’ll start with the toxicology. That will be followed sometime soon (I’m juggling this with many other things) by a consideration of the epidemiological studies that found cancer rates in Hinkley to be no higher than those of the general population — the research the Center for Public Integrity is trying its hardest to undermine. I’ll be feeling my way as I go along, and intelligent feedback is appreciated.

In the NTP study, doses as high as 516 parts per million of chromium 6 — more than 5,000 times greater than the standard set by the Environmental Protection Agency and 25 million times greater than California’s “public health goal”— were added to the drinking water given to 100 lab rats and 100 lab mice. Two years later some of them had developed malignant tumors in their mouths and digestive tracts.

Mice are mice and people are people, but how does that compare to the levels experienced by the citizens of Hinkley? The best information seems to be in an old report on the website of the California Water Resources Control Board. In 1988, when the pollution was discovered, the maximum concentration of chromium 6 measured directly below the PG&E compressor station — the source of the contamination — was 3.7 parts per million. The highest level  in a private well near the site was 0.7 ppm. That is less than one-tenth of one percent of what the lab animals were getting. Was that enough, spread over many more years, to cause cancer in people? Given the state of the science, no one can honestly claim to know.

Making this even harder to judge is the fact that mice and rats are far more tumor-prone than people. Perhaps because of their shorter lifespans, they have evolved weaker cellular safeguards against genetic damage. It takes fewer mutations to start a cancer.

In addition to the toxicology, you have to consider the chemistry of chromium. When it is ingested, chromium 6 is almost immediately converted into chromium 3, which is not just harmless but necessary to human health. I know I’m repeating myself from earlier posts, but this is a crucial part of the story: Toxicologists have come to agree that chronic exposure to air laden with chromium 6 particles has caused lung cancer in industrial workers. But they have genuine questions about its effect in drinking water, even at the relatively high doses encountered in Hinkley.

The epidemiology is even murkier — not just in Hinkley but anywhere scientists have tried to establish a correlation between aqueous chromium and human cancer. Given all of these uncertainties, the self-assured tone of articles like the one in Mother Jones are reason to be wary.

To be continued.

Previous posts:

Erin Brockovich

The Brockovich Story, Part 2

The Psychology of Cancer Clusters

An Epidemiologist’s Nightmare


  • Jersey Swamp

    Your argument seems to be with the application of standard
    toxicology and epidemiology to a public health issue. It may take more than feeling your way as you
    go along to understand this. You may
    want to crack open a text on public health practice. You’ll find that the linear no threshold dose
    response model for assessing the potency of carcinogens (giving test animals a range of doses of a
    carcinogen) and accounting for
    interspecies differences are routine
    practices. All your writing in the so
    called “cancer chronicles” seems to be
    toward the goal of proving that there is no environmental cause for

    • George Johnson

      Thanks for your comment. I did say in the post that the toxicology I describe is routine practice.

      There are plenty of environmental factors involved with carcinogenesis. They just often aren’t the ones that people suspect. That is just one of many themes in my book. It keeps coming up on the blog lately because the issue is so often in the news.

    • utah

      Mr. Swamp presents an outdated approach to evaluating cancer dose response relationships. While linear
      no-threshold modeling has been the default approach for decades, federal and
      state regulatory agencies are recognizing that this does not reflect reality
      for all carcinogens. Per the 2005 USEPA Cancer Guidelines, thresholds should be
      considered where the weight of the evidence on mode of action demonstrate such.

      Thus, there is now a recognition that public health policy decisions should be
      based on a consideration of the best science (an explicit platform position of
      the 2008 Obama administration), not just blindly applying the most conservative
      one-size-fits-all assumptions about chemical dose response relationships and


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Fire in the Mind

Whether a subtle new pattern shows up in an experiment on the Higgs boson, an epidemiological report about a suspected cancer cluster, or a double-blind trial purporting to demonstrate ESP, it can be maddeningly difficult to distinguish between what we see and what we think we see. "Fire in the Mind" takes a look at the big questions behind today’s science news.

About George Johnson

George Johnson writes about science for the New York Times, National Geographic Magazine, Slate, and other publications. His nine books include The Cancer Chronicles: Unlocking Medicine's Deepest Mystery (August 2013), The Ten Most Beautiful Experiments, A Shortcut Through Time, and Fire in the Mind. He is a winner of the AAAS Science Journalism Award and has twice been a finalist for the Royal Society science book prize. Co-founder and director of the Santa Fe Science Writing Workshop, he can be found on the Web at Twitter @byGeorgeJohnson.


See More


@byGeorgeJohson onTwitter

Collapse bottom bar