Cape Cod Breast Cancer and the Environment Atlas

land use

The Cape Cod Breast Cancer and the Environment Atlas is an online resource that provides researchers and residents alike with information on a range of critical issues related to the disproportionately high rates of breast cancer on Cape Cod.

Silent Spring Institute researchers compiled the information as part of their work with the Cape Cod Breast Cancer and Environment Study. To understand the possible environmental triggers of breast cancer, the researchers developed a geographic information system (GIS). This mapping database integrates health outcomes with historical environmental data, allowing the researchers to assemble clues across geographies and across decades. By mapping data in the GIS, researchers have been able to look for patterns and regional differences in breast cancer incidence and environmental features. The resultant atlas includes maps that depict such key factors as breast cancer incidence, drinking water safety, pesticide use, and land use.


Between 1982 and 1994, eleven of the fifteen towns on Cape Cod had breast cancer incidence rates at least 15 percent higher than those found in the rest of Massachusetts. Elevated incidence was statistically significant in eight of those towns.

The Cape Cod Breast Cancer and Environment Atlas provides maps of Cape Cod breast cancer incidence by towns from 1982 to 1999, by census tracts from 1982 to 1994, and from census block groups from 1982 to 1994. Also available are graphs of breast cancer mortality and incidence.

For index, maps, and graphs click here.


Approximately 80 percent of Cape Cod residents receive their drinking water from 18 publicly or privately owned municipal water supplies, which draw on one surface water source and approximately 130 groundwater wells. The Massachusetts Department of Environmental Protection regulates Cape public water supplies to ensure they meet health standards. Yet several factors in the Cape Cod environment suggest that water may be an important pathway of exposure to contaminants from residential and commercial development:

  • The aquifer that underlies the entire land surface of the Cape supplies almost all of the drinking water for Cape residents;
  • The high permeability of Cape Cod’s typically sandy, acidic soil leaves the groundwater aquifer vulnerable to contamination;
  • Multiple potential groundwater contamination sources exist, including wastewater from septic tanks, pesticide applications, and known chemical spills and leaks; and
  • The Cape Cod Commission and the U.S. Geological Survey have documented wastewater contamination of drinking water.

Many compounds commonly found in wastewater are known to mimic estrogen or affect hormone systems in some way. These compounds may be important for breast cancer research. To help tease out any possible connections, Silent Spring Institute researchers have prepared maps that show public water distribution systems and residential land use for most Cape Cod towns.

These maps depict water distribution systems as they existed in the late 1980s or early 1990s. Note that residents of several Cape towns rely on both private wells and public supplies for their drinking water; residences not located near distribution pipes rely on private drinking water wells. Maps for the towns of Eastham and Wellfleet are not included in this atlas because these towns have no public water distribution system; residents of both towns use private drinking water wells.

For maps click here.

Public Wells and Zones of Contribution

Much of the work of the Cape Cod Commission, the Massachusetts Department of Environmental Protection, local governments, and individual water suppliers has focused on protecting water quality in public water supplies and on determining potential locations for new wells. To identify potential threats to the water supply, these organizations have mapped the zones of contribution (ZOCs) for the supply wells.

A ZOC is the land area above the aquifer that contributes water to a well under the most severe pumping and recharge conditions that can be realistically anticipated. A clear understanding of the ZOCs allows officials to restrict land use in those zones, if necessary, to protect water quality in the wells.

Silent Spring Institute researchers have looked closely at ZOCs for possible sources of contamination by chemicals that may be linked to breast cancer. Because of the potential for contamination, public water supplies are regularly monitored to ensure they meet existing health standards. ZOCs are shown for all public wells for which state regulations have required delineation.

It should be noted that maps for the towns of Eastham and Wellfleet are not included because those towns have no public water distribution system; the residents of those towns rely on private drinking water wells instead.

For maps click here.

Click here to read more about Silent Spring Institute's “Water Research.”


Laboratory tests in animals have linked some pesticides with tumors or effects on reproductive organs. Some pesticides have also been shown to be endocrine disruptors, including some that mimic estrogen in animal and cell studies. Human studies of links between pesticides and breast cancer are difficult, as we do not have good measures of women’s exposures to pesticides years ago; but in 2007, researchers reported on a study that found higher breast cancer risk among women who had higher levels of DDT in stored blood samples that were drawn when DDT was still in use and the women were in their twenties. Women who were under 14 years old when DDT came into use were at higher risk for breast cancer later on, the study showed.

Historically, pesticides have been widely used on Cape Cod, especially for mosquito control, and in the decades before it was banned, DDT was used in sprayings throughout the Cape. These maps show areas of large-scale pesticide application between 1956 and 1990, as well as areas of pesticide applications to agriculture and wetlands on Cape Cod in 1951. These old maps retain their relevance; even though much of this land has been developed since 1951, the pesticides used back then tend to degrade very slowly, and previously applied pesticides likely persist today.

Silent Spring Institute researchers have added to the maps the locations of cranberry bogs and golf courses from multiple sources, representing both current and historical land use. Numbers coded in green indicate the years in which a portion of the town was sprayed, and the italicized numbers indicate the years in which an entire town was sprayed. For all other years shown, the area sprayed is unknown.

For maps click here.

Large-Scale Insect Control Data by Town

See table here.


Land use data can be useful in estimating possible environmental exposures, both current and historical. Researchers can look at current land use, for example, to identify the environmental impact on a drinking water well’s zone of contribution. Or they can study historical land use to gauge a population’s possible exposure to pesticides over time.

Silent Spring Institute researchers have developed a number of maps that reveal the rapid development that took place on Cape Cod between 1951 and 1990. When compared with the 1951 map, the 1990 map of Cape Cod shows a dramatic increase in residential areas (yellow), as well as a marked disappearance of forest (light green) and agricultural land (dark blue).

The researchers used aerial photographs provided by the University of Massachusetts to reconstruct this land use information. These data are available in GIS format through the Massachusetts Executive Office of Environmental Affairs and MassGIS.

For maps click here.


U.S. census data can help researchers assess the social characteristics that may affect women’s health. Silent Spring Institute researchers have used the 1990 U.S. census to incorporate into the Cape Cod Breast Cancer and Environment Atlas data on population change, the population-to-housing ratio, and indicators of socioeconomic status.

Population Change

Rapid population growth on Cape Cod has led to the development of forest or agricultural land for residential use. During the 1980s the towns of Mashpee, Sandwich, and Brewster experienced the greatest relative increase in population. Click here for map.

Population-to-Housing Ratio

When determining an area’s ratio of permanent residents to total housing units, those with smaller ratios have more seasonal housing and a permanent year-round population that is comparatively small. Areas with seasonal units are concentrated along the coasts. Click here for map.

Indicators of Socioeconomic Status

U.S. census data are especially relevant to breast cancer, as studies have shown a link between breast cancer incidence and a higher socioeconomic status, which is usually measured by such criteria as education, occupation, and income. Although neither wealth nor level of education causes breast cancer, researchers believe that women with a higher socioeconomic status may share environmental exposures or lifestyle factors that increase their risk.

To help illuminate the link between socioeconomic status and breast cancer risk, Silent Spring Institute researchers have created several maps to approximate socioeconomic status. Because income does not accurately reflect the standard of living of the large retired population on Cape Cod, the researchers used property values and education level, such as the completion of high school or college, to assess socioeconomic status. Click here for median housing value map.

Three maps show educational attainment track populations aged 25 or older. The colors are keyed to percentages of this population having a high school diploma, a bachelor’s degree, or a bachelor’s degree or higher.