Name Your Poison

The tender scene is a familiar one: a mother cradles her firstborn in her arms as she nurses. But at the same time she’s nourishing the baby she’s also unwittingly transmitting dozens of toxics, the legacy of her own decades on earth. And the infant already has a chemical inheritance from its time in the womb: In one recent study, the umbilical cord blood of 10 newborns was found to contain an average of 200 contaminants, including a range of pesticides, flame retardants, and other pollutants.

We all carry a body burden from the chemical swirl of our environment. But when does that burden grow too heavy? Which chemicals can be tolerated safely, and which trigger the development of cancerous cells?

To help clarify the chemical risks for breast cancer, Silent Spring Institute has compiled the most comprehensive review to date of scientific research on environmental factors that may increase risk of the disease. The study findings—entitled “Environmental Factors in Breast Cancer”—appear in the June 15, 2007 issue of the American Cancer Society’s journal Cancer.

The state-of-the-science review—commissioned by Susan G. Komen for the Cure and conducted by Silent Spring Institute in collaboration with researchers from Harvard University, Roswell Park Cancer Institute, and the University of Southern California—involved the collection and assessment of scientific studies on potential links between specific environmental factors and breast cancer.

The research team synthesized data from national and international sources and identified 216 chemicals that cause mammary tumors in animals. They then used that information to create a searchable online database featuring detailed information on the carcinogens. The Mammary Carcinogens Review Database offers summary assessments of the carcinogenic potential of each chemical, data on mutagenicity, opportunities for exposure in the general population and for women at work, and other characteristics of chemical use, sources, and regulation.

The database reveals that among those 216 compounds identified as causing breast tumors in animals, 73 have been present in consumer products or as contaminants in food, 35 are air pollutants, and 25 have been associated with occupational exposures affecting more than 5,000 women a year. Twenty-nine of the compounds are produced in the United States in large quantities, often exceeding one million pounds a year. The database includes references to 900 studies.

The researchers note that these data are reflected in neither regulatory policies designed to limit chemical exposures nor guidelines designed to alert physicians or public health agents to potential links between chemical exposures and health effects.

The researchers believe the information will prove valuable to regulators who are considering options for limiting human exposure, manufacturers who are planning to reformulate products and re-engineer processes to avoid suspect chemicals, and epidemiologists who are seeking to identify new chemicals, exposure scenarios, and exposed populations for breast cancer studies.

The Silent Spring Institute project also examined lifestyle influences on breast cancer, such as physical activity and diet. The result of this portion of the research—the Environment and Breast Cancer Epidemiology Reviews Database—is composed of critical reviews of approximately 450 primary epidemiologic research articles on breast cancer and diet, environmental pollutants, physical activity, and body size. This database, which includes articles published through June 2006, will be updated periodically.

The researchers sought to determine points of consensus within the scientific community on the relationship between environmental factors and breast cancer and to identify areas needing additional investigation or improved research methods. They are hoping that such information will help guide public policy and allow funding organizations to determine how best to target research funds.

The authors noted a considerable disparity between the attention paid to dietary factors and that paid to environmental pollutants. The diet literature search identified nearly 1,500 relevant articles published since 1950, for example. In contrast, although the environmental pollutants of interest were first synthesized in the 1940s and put into widespread use in the 1950s, interest in these chemicals among breast cancer researchers dates only to the 1990s.

“The overwhelming majority of chemicals identified as animal mammary carcinogens or endocrine-disrupting compounds have never been included in an epidemiologic study of breast cancer,” says Julia Brody, executive director of Silent Spring Institute. “Just as alarming, most chemicals that Americans are exposed to have never been included in an animal cancer bioassay.”

The review of epidemiology related to environmental pollutants shows that research in this area is still relatively sparse. Results in recent years, however, have begun to show evidence of increased risk associated with exposure to polychlorinated byphenols (PCBs)—banned chemicals previously used in electrical equipment and other products—in genetically susceptible women and to polycyclic aromatic hydrocarbons (PAHs), which are ubiquitous air pollutants from vehicle exhaust and other sources of combustion byproducts. Results of studies of organic solvents and dioxins suggest possible associations with breast cancer and support additional research on those compounds.

“The many studies of dietary factors have allowed us a greater opportunity to evaluate consistency across studies before placing confidence in results,” Brody says. “In contrast, conclusions from the environmental pollutants epidemiology rest on fewer studies. Additional support comes from animal studies that identify PAHs and some organic solvents as animal mammary carcinogens and PCBs and dioxins as endocrine disruptors. These studies provide evidence of biological mechanisms that may link these chemicals to breast cancer.”

The databases, available at, are expected to be of particular interest to researchers, health care workers, and policy makers, as well as to members of the public.

“While it’s disturbing to learn that so many chemicals may be linked to breast cancer,” Brody says, “we must remember that we have a great opportunity to save thousands of lives by identifying those links, limiting exposure, and finding safer alternatives. It’s critical that we integrate this information into policies that govern chemical exposures.”