Findings of the Cape Cod Breast Cancer and Environment Study
When the Massachusetts Department of Public Health first reported breast cancer incidence rates by town in 1993, the towns of Cape Cod showed up with consistently higher incidence than the statewide rate. Silent Spring Institute began the Cape Cod Breast Cancer and Environment Study to find out why. Researchers at Boston University, Tufts and Harvard universities, and elsewhere joined the team.
What did we do?
- The Cape Cod Study began with a scoping process to gather input from community members, researchers, healthcare providers, and policymakers about the best hypotheses to pursue.
- Silent Spring Institute built an innovative geographic information system (GIS) to map breast cancer incidence, demographic data, and environmental data about pesticide exposure and drinking water quality.
- The study evaluated Massachusetts Cancer Registry data for 1982-1995.
- We worked with other researchers to mine earlier studies – the Upper Cape Cancer Incidence Study and the Collaborative Breast Cancer Study—for new insights about breast cancer on Cape Cod.
- We conducted a case-control study of 2100 Cape Cod women, including women diagnosed with breast cancer in 1988-1995.
- We developed new methods and data resources to use the GIS to estimate individual women’s historical exposures to pesticides and drinking water contamination.
- We tested air, dust, and women’s urine from 120 homes.
- We tested wastewater, groundwater, and drinking water for endocrine disruptors to assess potential exposure to estrogenic compounds from septic systems.
- We developed the Massachusetts Health and Environment Information System (MassHEIS) to make our data available to others.
What did we find?
- Three separate data sets show that breast cancer incidence has been higher on Cape Cod over many years since the beginning of the state cancer registry.
- Women who have lived longer on Cape Cod have higher breast cancer risk, after controlling for established breast cancer risk factors and mammography use, lending support to the hypothesis that a regional factor, perhaps an environmental factor, is at work.
- We found evidence of increasing infiltration of wastewater from septic systems into drinking water supplies, and we measured low levels of endocrine disrupting compounds in drinking water wells. These results provide evidence that drinking water is a pathway for exposure. We did not find an association between nitrate (a marker for wastewater contamination) and breast cancer risk. This result might mean that drinking water contamination at the levels found on Cape Cod in the past is not associated with breast cancer risk; however, it might alternatively mean that nitrate is not an accurate indicator specifically for exposure to estrogen mimics.
- We found weak evidence of an association between breast cancer risk and living near cranberry bogs during the years when organochlorine pesticides, such as DDT, were applied (1948- mid 1970s). This finding was not statistically significant, but it is consistent with another study on Cape Cod by researcher Ann Ashengrau at Boston University and with a new study in California that found higher risk among women exposed to DDT when they were young.
- The Household Exposure Study on Cape Cod found an average of about 20 endocrine disruptors per home. Levels of some pesticides were higher on Cape Cod than in other regions of the US. For 30 of the 89 compounds we tested, this was the first study to measure concentrations indoors.
- The Cape Cod Study has produced 21 peer-reviewed scientific articles to date.
- We continue to analyze Household Exposure Study data for insights into sources of exposure, and we are comparing Cape Cod samples with homes we tested in California. These ongoing studies will provide insight about how to reduce exposures and whether there are unusual exposures on the Cape that could contribute to breast cancer risk.
- We are pursuing new studies of endocrine disruptors in groundwater and drinking water to help Cape Cod plan for safe drinking water supplies.
- We are working to develop better exposure measures for future breast cancer studies.
Frequently Asked Questions:
What was the purpose of the original study?
Current regulation and research focuses on a very short list of chemicals and does not reflect the chemicals to which we are most commonly exposed. One of our goals was to expand the universe of chemicals that get regulatory attention. The Household Exposure Study was designed to learn about exposure to endocrine disrupting compounds (EDCs)—chemicals that can mimic or interfere with hormones—and mammary carcinogens. We tested 120 homes for 89 chemicals. These chemicals are commonly found in household products such as some pesticides, detergents, plastics, furniture, building materials, and cosmetics. This is the most comprehensive study to date of EDCs in homes. For 30 of the target chemicals, ours were the first measurements reported from indoor environments.
Who were the study’s participants?
The homes were selected from the 2,100 women who participated in the Cape Cod Breast Cancer and Environment Study. Half of the women in the larger study were chosen because they were diagnosed with breast cancer between 1988 and 1995; the other half were a comparison group comparable in age. Homes were tested during the period of 1999–2001.
What types of chemicals did you find and where do they come from?
We found many different types of chemicals that are used in plastics, detergents, furniture, carpets, electronic equipment, pesticides, and cosmetics. Click here for information on the major chemical classes and potential sources. We expected to find many of these compounds in homes, as they are in widely used pesticides, detergents, plastics, and furniture, as well as personal care products such as cosmetics and hair products.
How do such chemicals get into my body?
Chemicals can enter your body when you breathe, eat, and drink, and through your skin. Chemicals can also be passed from mothers to infants through the placenta and breast milk.
Which chemicals did you find at the highest concentrations?
We found phthalates and alkylphenols at the highest concentrations in both dust and air.
How many different chemicals did you find in a typical house?
The number of chemicals detected in a home ranged from 13 to 28 for indoor air and from 6 to 42 for dust. The average number of chemicals per home was 19 for air and 26 for dust.
Are levels on Cape Cod higher than levels elsewhere?
Some comparison data from other locations are available for some pesticides, polybrominated biphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and phthalates. The indoor air concentrations we measured on Cape Cod were generally similar to levels reported elsewhere. In house dust, we observed some regional differences. PBDEs on Cape Cod were about ten times higher than levels reported in two studies in Europe, where these compounds are not used as much. PAHs were lower than on Long Island but higher than in other regions of the United States. For pesticides, levels of DDT, carbaryl, chlordane, methoxychlor, propoxur, and pentachlorophenol appeared higher on Cape Cod than in other regions; levels of diazinon and permethrin were lower; and the level of chlorpyrifos was about the same. Comparisons must be interpreted with caution because sample collection methods differ among studies.
Did detected levels exceed government standards?
There are no regulatory standards for contaminants in indoor air and house dust. The U.S. Environmental Protection Agency has issued health-based exposure guidelines for about half of the compounds in our study. Where these guidelines exist, levels we measured are often below the guidelines. For 15 compounds, though—including bis(2-ethylhexyl) phthalate (from plastics) and some pesticides and PCBs that are currently banned—we measured levels in some samples that exceeded the guidelines. These chemicals are still found in and around homes worldwide, sometimes at levels exceeding health guidelines, because they break down very slowly.
What are the public health implications of these findings?
This study demonstrates that chemicals from common consumer products affect indoor air quality and are found in house dust, providing an ongoing opportunity for exposure. However, not enough is known about the potential health effects of these exposures to determine whether they pose significant health risks. By studying these compounds and how women may be exposed, we will learn which exposures are most important. In this way we hope to identify ways to reduce health risks by reducing exposure, and to prioritize chemicals with high exposures for more rigorous health effects testing.
Did you look for all the endocrine disrupting chemicals?
No comprehensive list of endocrine disrupting chemicals exists, and most of the 87,000 chemicals in use have not been tested to determine whether they affect hormone systems. We tested for chemicals that scientists have reported to be endocrine disruptors. We prioritized chemicals that have consumer uses or are produced in large quantities.
What additional analyses of these data are under way?
We are analyzing data on urinary levels of phthalates and pesticides in relation to air and dust measurements in order to understand major pathways of exposure. We are also analyzing the relationship between individuals’ self-reported pesticide and product use data and measured air, dust, and urine levels. Finally, we are identifying commonly occurring mixtures of chemicals.
Why are you retesting some of those homes?
Silent Spring Institute and Massachusetts Department of Public Health (MDPH) selected for retesting those homes that had unusually high levels of a contaminant that exceeded a federal health guideline or homes with higher-than-expected levels of a contaminant for which the federal government has not set a health guideline. All of the homes that contained 2,3-dibromo-1-propanol, a breakdown product the flame retardant tris (2,3-dibromopropyl) phosphate, were selected for retesting, because this chemical is a potent carcinogen that was banned in the 1970s. With further testing, we hope to determine where and why it is still present in some homes, so residents can remove the source of the pollutant.
Did you find higher levels of chemicals in any particular cluster of homes?
We are still analyzing data to identify factors that may be shared among homes that had elevated levels of similar chemicals. We will make this information public when the data analysis is complete. So far we have identified a few homes with high levels of PCBs that likely come from a floor finish used in the 1950s and 1960s.
Why didn’t you retest all the homes?
Testing and retesting is expensive, so we limited our retests to those homes most at risk. Testing costs about $5,000 per home. Women in the study can refer to the results for their own home to see how it ranks compared with other homes and with federal health guidelines. The results sent to each woman show the federal health guidelines for comparison (though federal guidelines have not yet been developed for all the chemicals) and how each home ranks in comparison with others in the study. The chemicals in the study were identified because they are endocrine disruptors or mammary carcinogens, so many people will want to reduce exposures as a precaution. The testing and retesting is designed to help us develop guidelines to reduce contamination in any home, not just the homes we are testing.
Why spend money on this research when no one knows the relationship between these contaminant levels and breast cancer?
Understanding exposure is a critical first step toward evaluating health effects, including breast cancer risk. The Massachusetts Breast Cancer Coalition founded Silent Spring Institute specifically to do this kind of research, because most breast cancer studies are focused on diagnosis and treatment and not placing an emphasis on science that can lead to prevention. The science needed to make a link between chemical pollutants and breast cancer is complex. This study answers questions about which chemical exposures are most common, which chemicals are found at the highest concentrations, and whether women are likely exposed by breathing or ingestion. Scientists have to be able to answer these questions about exposure before we can make the link from exposure to breast cancer or other health effects. This study also gives us information we can use now to reduce exposures as a precaution.
How safe is it for my family to be around these chemicals?
Researchers haven’t resolved the questions of what level of exposure to certain chemicals is safe, or how these chemicals work in combination to affect our health. Many of the chemicals have caused health problems in animal studies, and for some, there is evidence of health harm to humans. Air and dust are sources of everyday exposure. We are also exposed from water and food. Based on what is currently known, many people decide to take steps to reduce the levels of these potentially harmful chemicals in homes by reducing chemical use and encouraging manufacturers and government officials to take steps to reduce exposure and test chemicals more thoroughly.
The levels of chemicals found in my home seem too low to cause me any harm. I have heard that there’s no link between low exposures to these chemicals and cancer. You may hear different assessments from different sources, because there isn’t enough evidence yet for scientists to agree on whether some of these chemicals at low levels are linked to disease. For about 30 of the chemicals in this study, the Silent Spring Institute measurements are the first ever reported from indoor environments. For 28 of the chemicals, there is no health-based federal guideline for evaluating health risk associated with exposures. When you hear “there is no evidence of harm” from these chemicals, it is often the case that there is no evidence because no one has studied the health effects yet. Sometimes there is strong evidence from animal studies, but none from tests with humans as it is unethical to test toxic chemicals on people. Also, keep in mind that we don’t know very much about the cumulative effects of multiple chemicals since most are tested alone. That’s important because people are exposed to chemicals in combinations, not individually. We found 26 target chemicals per home, on average. We selected these chemicals for testing based on laboratory studies that show they can affect the hormone system or cause mammary tumors in animals. Many of them mimic estrogen, resulting in the growth of human breast cancer cells in laboratory studies. Scientists have not yet investigated a link between most of these chemicals and breast cancer in women, and the few previous studies have yielded conflicting results. But, given that we do know that natural estrogen and pharmaceutical hormones, like hormone replacement therapy, cause breast cancer, the hypothesis that estrogen mimics from other sources increase breast cancer risk is strong enough that many of us would want to reduce exposure as a precaution. Finally, there are lab studies that show low levels of exposure to some of these chemicals cause health effects other than cancer, such as reproductive disorders, learning disabilities and immune system disorders. Again, the science isn’t yet complete, but until we know more we can limit exposure to toxic chemicals as a wise strategy to reduce risk.
Are these findings just relevant for Cape Cod? Is Cape Cod more contaminated than other areas?
This research is important and relevant to women and families everywhere, not just on Cape Cod. The chemicals we tested for come from common products and are also in air pollution, so we would expect to find them across the United States. The scientific journal that published the study results placed this as their cover story, indicating that the scientific community considers these findings to be relevant internationally. At the same time, some of the results do have particular significance for Cape Cod. For a few of the chemicals, we can compare Cape Cod results to other places. For the pesticides DDT, chlordane, carbaryl, methoxychlor, pentachlorophenol and propoxur, the levels found in Cape Cod homes were higher than in studies done in Long Island, Seattle, Detroit, Los Angeles, Iowa, or Arizona. Cape Cod homes did not have the highest levels of chemicals such as PAH, PCBs, or the pesticides diazinon, chlorpyrifos and permethrin. These regional differences could be due to differences in product use or air pollution.
How can I reduce the levels of chemicals in my home?
To reduce chemical levels in your home, choose less toxic alternatives when shopping for common household products. Research on indoor air pollution identifies some steps to reduce exposure:
- Reduce or eliminate pesticides.
- Avoid tracking pollutants into your home by placing a rug at each entry; remove outdoor shoes there.
- Improve indoor air quality by opening windows.
- Choose a vacuum cleaner that contains the dust from the floor, rather than spreading it. Consumer Reports lists the best ones.
- Don’t smoke indoors.
- Vent your gas stove, broiler, grill, or fireplace.
- Avoid using wood-burning fireplaces and stoves.
- Choose fuel-efficient vehicles, because auto exhaust contains mammary carcinogens.
- Choose fragrance-free cleaning products and cosmetics and try to avoid cosmetics and personal care products with phthalates and parabens. For details about which products contain these chemicals, visit the Campaign for Safe Cosmetics website.
- Don’t store gas-powered engines, gasoline, or solvents in your basement or an attached garage. If you must, open the space to the outdoor air, ventilate, and consider storing hazards in an airtight box.
- Use glues, paints, solvents, and fingernail polish outside or in a well-ventilated area.
- Shop for electronics and furniture that don’t contain the flame retardant PBDEs.
We must all work together to get hazardous chemicals removed from consumer products, and to reduce air and water pollution. A good way to do this is to become involved with the MA Breast Cancer Coalition and the Alliance for a Healthy Tomorrow. These groups have programs underway to get manufacturers and governments to choose safer alternatives for ingredients in cleaning products, cosmetics, and other common products and to require more rigorous testing of health effects. Similar organizations exist in other regions of the country.