Environmental and Occupational Toxicants and Cancer

By Richard Clapp, DSc MPH

This essay is in response to: What are we learning about the relationship between environmental toxicants and cancer? How should our regulatory system respond to this information?

We’ve known for decades that the environment, defined broadly to include general exposures like air and water pollution, occupational exposures and personal exposures such as tobacco smoke and various components of diet, cause the great majority of cancers. This broad definition was narrowed dramatically in a seminal article published in 1981 by two British epidemiologists, Richard Doll and Richard Peto. They produced a table that attributed percentages of U.S. cancer deaths to factors like tobacco, alcohol, diet, reproductive and sexual behavior and two separate categories called “occupation” and “pollution.” The percentages attributed to these latter two factors were 4% and 2%, respectively. Since the publication of this article, the governmental and non-governmental cancer establishment and the spokespeople for the industries that create carcinogenic materials and exposures have combined to downplay their importance and oppose attempts to reduce their use. Instead, the vast majority of attention and resources has been focused on finding cures for various types of cancer, or at least extending the life of people who have already been diagnosed with the disease.

In the thirty years since publication of the Doll and Peto analysis, a vast literature on the causes of cancer has been published and the number of toxicants or conditions of exposure known or suspected to cause cancer in humans has increased many times. For example, as of April 2011 the International Agency for Research on Cancer currently identifies 107 agents or exposures known to cause cancer in humans, another 59 that are probably carcinogenic to humans, and 266 more that are possibly carcinogenic to humans. Of the 107 agents in the first group, over one quarter cause cancer in occupational settings.

The epidemiologic literature about environmental and occupational causes of cancer has been summarized in review articles by my colleagues at Boston University and the University of Massachusetts – Lowell, among others (see here). Likewise, much more has been learned about the “daunting complexity” of the carcinogenic process, both from animal studies and from the frustratingly slow progress in finding effective treatments for many types of cancer. The often-stated goal of devising individually targeted therapies to cure cancer or render some types a manageable chronic disease remains elusive. For cancer of the bronchus and lung, the progress that has been made in reducing incidence and mortality has come about from primary prevention. This is mostly because of reduction in use of tobacco, but also to reduction of workplace exposure to asbestos, some specific chemicals and radiation.

As a result of this accumulated knowledge and on-going public concern about environmental toxicants, the President’s Cancer Panel addressed this topic in their 2008-2009 report, released in May 2010. The Panel, which reports directly to the President, reviewed scientific evidence and invited testimony from a variety of organizations and individuals over a two-year period. The report, “Reducing Environmental Cancer Risk, What We Can Do Now,” is a remarkable document. While avoiding attribution of a specific percentage of the total cancer burden to environmental and occupational exposures, the letter to the President said “the true burden of environmentally induced cancer has been grossly underestimated.” The report further pointed out that “industry has exploited regulatory weaknesses, such as government’s reactionary (rather than precautionary) approach to regulation.”

The first recommendation the authors of the report make is that “a precautionary, prevention-oriented approach should replace current reactionary approaches to environmental contaminants in which human harm must be proven before action is taken to reduce or eliminate exposure.” This recommendation also explicitly supports chemicals policy reform, such as envisioned by Sen. Frank Lautenberg in the “Safe Chemicals Act of 2011” (S. 847). Health care professionals should build support for this and similar state-level legislation in order to reduce the burden on environmental and occupational toxicants on the public health.

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