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Science for the People

Cadmium Exposure and Breast Cancer

Compiled by Mary Beth Doyle
October/November Issue, 2003

For the first time, there is scientific evidence that exposure to cadmium, a naturally occurring metal, may be a risk factor for developing breast cancer in a woman and her unborn baby. For the general public, exposure to cadmium is primarily through contaminated food and water, breathing contaminated air, and cigarette smoke.

Published in the online version of Nature Medicine, researchers at the Lombardi Cancer Center at Georgetown University studied cadmium and its ability to mimic estrogen’s effects on the body. When exposed to low doses of cadmium, female rats show an increase in mammary gland density and uterine weight, and changes in the endometrial lining, all telltale developments in the early onset of breast cancer.

Additionally, when pregnant rats were exposed to the same low dose, their female offspring experienced earlier onset of puberty and mammary gland development. Early onset of puberty significantly increases a woman’s breast cancer risk.

“We never expected to see this strong a relationship, given how different the cadmium and estrogen compounds are,” said Mary Beth Martin, Ph.D., associate professor of oncology at Georgetown University Medical Center. “What we saw suggests a direct link between low dose cadmium exposure and increased risk for breast cancer.”

Johnson, MD, et al. “Cadmium mimics the in vivo effects of estrogen in the uterus and mammary gland,” Nature Medicine, August 2003.

Low Levels of Lead Impair Intelligence

The Centers for Disease Control has established a “level of concern” for lead at 10 µg/dL in the blood. The assumption is that levels below that cause little or no harm. But a recent study finds that even levels below this “safe” level can have a significant impact on children’s intellectual development. The researchers followed a cohort of children from birth through age 5. They measured the children’s blood lead levels several times during those years. At ages 3 and 5, they determined the children’s IQ scores using a standard test.

The researchers controlled for a number of factors, such as home environment and mother’s IQ. They then compared the blood lead levels and IQ levels. They found a strong inverse relationship between lead levels and IQ. The association was even stronger when they only compared children who had levels consistently below 10 µg/dL. Each additional 1µg/dL of lead in the blood was associated with a 1.37-point decrease in IQ.

These findings suggest that not only are blood lead levels below 10 µg/dL associated with diminished IQ but these lower levels had a comparatively more significant impact than higher levels. Noted the researchers: “Most of the damage experienced by children with higher lead levels actually is due largely to the initial IQ loss at blood lead concentrations of 10 µg/dL or less.”

Canfield, RL, et al. “Intellectual Impairment in Children with Blood Lead Concentrations below 10 µg per Deciliter,”New England Journal of Medicine, April 17, 2003. For more information, go to www.protectingourhealth.org.

Birth Control Pills Can Harm Fish Reproduction

New evidence indicates that exposure to synthetic estrogen may harm the ability of male rainbow trout to reproduce. Adult rainbow trout were caged and exposed to water containing ethynylestradiol, a synthetic estrogen, at levels often seen in streams and rivers. After two months, the fish were removed from the contaminated water and spawned with female fish. The males exposed to the synthetic estrogen were only half as fertile as those that had not been exposed.

It is not clear what these findings mean for fish in the wild but there is growing concern that synthetic hormones may affect frogs, river otters, and other aquatic creatures. Like many other pharmaceuticals, synthetic estrogen from oral contraception is not captured at wastewater treatment plants – it is discharged into streams with the treated water from the plant.

Schultz, Irvin R, et al. “Short-Term Exposure to 17-Ethynylestradiol Decreases the Fertility of Sexually Maturing Male Rainbow Trout,” Environmental Toxicology and Chemistry, June 2003.

Compiled by Mary Beth Doyle, M.P.H.,
Ecology Center Environmental Health Campaign Director

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