The journal Epidemiology has just published new evidence that drinking hexavalent chromium — also called chromium 6 — increases risk of stomach cancer. The study is important for public health purposes, since many drinking water sources are chromium contaminated (including the water in the community in the movie Erin Brockovich).
This new study is also the latest piece of a very ugly scandal that illustrates how polluters manufacture doubt to impede regulation. And this scandal is but one of several in which chromium polluters have manipulated epidemiologic studies to sow uncertainty – see our case study on chromium 6 at DefendingScience.org.
Pump Handle readers may recall our reporting on the controversy around a study of stomach cancer in Chinese villages where there were high levels of chromium in the drinking water. After an initial study reported elevated rates of stomach cancer, product defense consultants working for US chromium polluters reanalyzed the study, and the increased risk disappeared. The consultants re-analyzed the data and arranged for it to be published in the Journal of Occupational and Environmental Medicine (JOEM) without their names on it, hiding any connection to the product defense firm (Chemrisk) or the polluters who paid for the re-analysis. After the controversy was reported in the Wall Street Journal, the editor of JOEM retracted the study.
Now, James J. Beaumont and a group of scientists employed by the state of California have published a new analysis of cancer rates among the Chinese villagers with highest exposures, in which they found an association between chromium 6 exposure and stomach cancer. Beaumont and his colleagues are careful to put many caveats on their conclusion, but the results are of tremendous importance.
Chromium 6 is a powerful lung carcinogen, shown in many studies of workers who breathe the chemical. It also causes cancer in animals given chromium 6-contaminated water, and there is evidence that drinking it causes cancer in humans. Although chromium 6 contaminates the drinking water of many communities, it is difficult to study the effects of the relatively low-level environmental exposures that are common throughout the country (according to Beaumont and his colleagues, chromium 6 was detected in about one-third of 7000 drinking water sources surveyed in California).
As a result, studies on humans who drink heavily contaminated water would be of great use in measuring the risk of cancer associated with this pollutant. And the Chinese villages in question may provide the best opportunity – possibly the only opportunity — to do that.
Allan H. Smith, a very distinguished epidemiologist at the School of Public Health, University of California Berkeley (and one of the world’s experts in the effects of arsenic contaminated drinking water, so he knows the methodological issue well), penned a commentary in the same issue of Epidemiology. He writes that these villages are “perhaps the only place in the world where the effects of ingestion of hexavalent chromium could be studied with adequate power.”
In his commentary, Smith reviews the limitations of the study, but puts them into a very useful perspective:
epidemiology is often at its best when functioning as an opportunistic observational science. Better to conduct shoddy studies of high exposures than high-quality studies of low exposures. It is a bit like the man who searched for his lost wallet under a lamppost. When asked where he lost it, he points to an area in the dark—but, he says, “the light is better over here.” Epidemiologic studies are too often conducted where it is easy to do them, rather than where the real evidence may be found. The excuse is that the high exposures occur where studies are difficult to conduct. Indeed, the future of environmental epidemiology lies in the developing world, where studies are usually difficult to do.
I commend Beaumont and his colleagues for struggling with an epidemiologic analysis with poor data. If there are human risks from hexavalent chromium in water, such risks are more likely to be found where exposures are high than by insisting on high-quality studies of populations where exposures are much lower.
Does the Beaumont reanalysis prove that ingestion of chromium causes cancer in humans? Of course not. Does it provide evidence that is consistent with there being increased risks? I suggest it does. Perhaps the greatest weakness of the evidence is the very short latency from exposure to increased mortality risks. Even if the exposures started as early as 1960, the latency for the period 1970–1978 reported here involves just 10 to 18 years, which (as noted by the authors) is very short for solid tumors. One would hope for and urge further follow-up of this exposed population in China, including both mortality studies and perhaps also case-control studies of stomach cancer. There may be no other population in the world that can provide such valuable information concerning ingestion of hexavalent chromium in water and human cancer.
The public health community should be grateful to Beaumont and his colleagues for undertaking this difficult study. Its now time for environmental regulators to revisit the standards for chromium 6 in drinking water.