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Reforming the Toxic Substances Control Act
Reforming Chemical Safety

Legislation to reform the Toxic Substances Control Act have renewed hope that public health will shape chemical regulation.



Janet Gray, Ph.D.
Janet Gray, Ph.D.

As author of our 2008 and 2010 State of the Evidence reports, Dr. Gray drives the science behind all our work.

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Dieldrin and Aldrin

CATEGORY*: Endocrine disruptor

FOUND IN: Fully banned in the U.S. in 1987, persists in the environment even where it's not used.

THE GIST: Similar to DDT, Dieldrin and Aldrin are pesticides that were widely used from the 1950s through the 1970s, but banned because of their health effects. Regardless, these chemicals are present in human systems and continue to create health problems, including breast cancer. The EPA banned the chemical, except for termite control, in 1975, and fully banned it in 1987.

State of the Evidence on Dieldrin and Aldrin

From the 1950s until 1970, the pesticides dieldrin and aldrin (which breaks down to dieldrin, the active ingredient) were widely used on crops, including corn and cotton. Because of concerns about damage to the environment and, potentially, to human health, the U.S. Environmental Protection Agency in 1975 banned all uses of aldrin and dieldrin except for termite control; the EPA banned these pesticides altogether in 1987 (ATSDR, 2010). Thus, most of the human body burden of this chemical comes either from past exposures or from lingering environmental contamination. NHANES data examining levels in blood serum found dieldrin in 87.2 percent of people in the United States age 12 and older but was not able to detect aldrin in any of the people tested (Patterson, 2009).


Since dieldrin and aldrin are already banned in the United States, there is little we can do besides ensure that similar chemicals are not allowed on the market in the future.

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One body burden study showed a clear relationship between breast cancer incidence and dieldrin exposure. Conducted by the Copenhagen Center for Prospective Studies in collaboration with the Centers for Disease Control and Prevention, the study examined a rare bank of blood samples taken from women before development of breast cancer (Hoyer, 1998). During the late 1970s and early 1980s, blood samples were taken from approximately 7,500 Danish women ranging in age from 30 to 75. In 2000, researchers looking at blood samples of 240 women from the original study who were later diagnosed with breast cancer, detected common pesticides in most of the samples. They found dieldrin, which has exhibited estrogenic activity during in vitro tests, in 78 percent of the women who were later diagnosed with breast cancer. Women who had the highest levels of dieldrin long before cancer developed had more than double the risk of breast cancer compared to women with the lowest levels. This study also showed that exposure to dieldrin correlated with the aggressiveness of breast cancer: Higher levels of dieldrin were associated with higher rates of breast cancer mortality (Hoyer, 2000).

Like many other pesticides found in the environment, dieldrin has been shown to be an endocrine disruptor, both by stimulating estrogen-regulated systems and by interfering with androgen-regulated pathways. Addition of dieldrin to human breast cancer (MCF-7) cells in vitro stimulated their growth and proliferation (Andersen, 2002; Soto, 1994). The exposure of normal (non-cancerous) human breast epithelial cells to mixtures of pesticides, including dieldrin and aldrin, at levels found in the environment, led to greater actuation of cellular processes linked to cancer than exposures to any of the chemicals individually (Valeron, 2009). Another cell culture study demonstrated that environmentally relevant mixtures of pesticides that include dieldrin, aldrin and several other organochlorine compounds, increased proliferation in estrogen-receptor-positive human breast cancer cells (MCF-7) by causing cells to enter the active phases of cell division (Aube, 2011).

Exposing mice prenatally and just after birth to environmentally relevant doses of dieldrin increased the number and size of mammary tumors. These effects may be the result of changes in the cellular expression of the growth factor BDNF and cell-signal receptor Trks. Both of these were elevated in tumors from the dieldrin-treated animals (Cameron, 2009).

*For chemicals that have been shown to be carcinogens, we provide classifications from two authoritative bodies: the International Agency for Research on Cancer (IARC, an international body) and the National Toxicology Program (NTP, a division of the U.S. Department of Health and Human Services). We have categorized endocrine-disrupting compounds where the body of peer-reviewed research indicates a strong foundation for doing so.