An Epidemiologist's Nightmare

Chinese pollution. Photo by Robert Gagnon via Flickr I'll say it again: You can sympathize with the people who drank the water and abhor the polluters and still not be persuaded that there was a cancer outbreak. That sums up the message of my recent posts on Erin Brockovich and the article I wrote for Slate on the Toms River cancer cluster. It could apply just as easily to the case in Woburn, Massachusetts, which was made famous by Jonathan Harr's book, A Civil Action. Woburn and Toms River are the only two places in the United States where epidemiologists have found an association -- a very murky one -- between pollution and cancer in some of the residents. Both incidents involved childhood leukemia, and the number of excess cases finally attributed to toxic effluents was about half a dozen in each town, occurring over a period of 10 or more years. For no known reason boys were affected in Woburn and girls in Toms River. Both may have been statistical flukes. As far as cancer clusters go, Hinkley, California, the town in Erin Brockovich, is not even considered a contender. I find all of this as surprising as anyone. As I was researching my book, The Cancer Chronicles, I was struck again and again by how many of the perceptions we share about cancer are wrong. To find levels of pollution high enough to cause a noticeable rise in cancer, epidemiologists have had to look to China, where lax environmental standards and the rush to industrialization surpass anything still happening in the developed world. A recent story in the New York Times describes the catastrophe. The Chinese government itself puts the economic toll for just one year at $230 billion. But money is a pale measure. If there is any salvation to come from the harm, it is the emergence of China as a testbed for cancer epidemiology. With large numbers of people exposed for years to high levels of industrial waste, researchers might get a better sense of the link to cancer -- as they did with radiation by studying the sad aftermath of Hiroshima and Nagasaki. Yet even in these extreme situations, the evidence can be frustratingly ambiguous. It was in Liaoning Province that chromium 6 contamination was so high -- 200 times the EPA limit -- that the drinking water turned yellow. According to a commentary in the journal Epidemiology, there has been only one other place in the world with comparable levels: León, Mexico. Both involved people living near factories that produce chromium compounds. In Mexico there weren't enough residents exposed to the water to provide plausible statistics. But in villages near the Chinese plant, researchers found an elevated rate of lung and stomach cancer. The report was published in 1987 in the Chinese Journal of Preventive Medicine (I have not been able to find a copy, in Chinese or English). But 10 years later the numbers were reanalyzed and no increased cancer was found. On the surface the revised conclusion seemed legitimate. The earlier study compared the villages near the factory with the overall population. This time the control group consisted of other nearby villages without chromium-tainted water. That sounds like a more direct and meaningful comparison. But whatever merits the science may have had were obscured when a conflict of interest was discovered: the epidemiologist leading the study, Dennis Paustenbach, had been working at the behest of Pacific Gas and Electric, the Hinkley polluter, through his consulting firm, ChemRisk Inc. There are other twists to the tale, which was laid out in a 2006 account in the International Journal of Occupational and Environmental Health: "Corporate Corruption of Science -- The Case of Chromium (VI)." The Paustenbach paper was later retracted but that left the question hanging: though conducted under suspicious circumstances, was the science itself right or wrong? A third and independent study did find signs of an increase in stomach cancer. But the matter is still unresolved. In the commentary in Epidemiology, Allan H. Smith of the School of Public Health at Berkeley welcomed the new findings. But he noted that they had their own problems, suffering from "serious limitations" caused by poor demographic records.