Environmental pollutants that are known to cause cancer in rat mammary tissues are present in human breast milk, according to scientists in Canada. It is the first time that aromatic amines (AAs), which are used in many industrial processes, have been detected in human milk.
Researchers are not yet sure of the implications of the finding, saying it needs further investigation, but expressed concern that the substances may be a cause of breast cancer as well as a risk to nursing infants. They stress that the nutritional benefits of breast- feeding still outweigh the risks.
The finding is explained in the web edition of the peer-reviewed journal Chemical Research in Toxicology, published by the American Chemical Society -- the world's largest scientific society. It will appear in the print version of the journal on Dec. 21.
"Chronic exposure of the general population to AAs is a matter of public health importance," write P. David Josephy and Lillian DeBruin from the University of Guelph along with Janusz B. Pawliszyn at the University of Waterloo. "The presence of AAs in human milk implies that breast ductal epithelial cells, the target of mammary carcinogens, are also exposed."
AAs are used in the production of plastics, dyes, pesticides, and pharmaceuticals. Environmental sources for AAs include in industrial waste, air and water pollution, tobacco smoke, and some foods.
The study tested milk samples from 31 lactating mothers living near Guelph in Ontario, none of whom reported occupational exposure to AAs. All of the samples contained levels of AAs ranging from less than 0.01 to 7.44 parts per billion. Surprisingly, levels did not vary between smokers and non-smokers. Finding one particular AA, o-toluidine, may be of special significance because it is known to induce mammary tumors in female rats.
"We need to discover the major sources of these exposures," says Josephy. "Control of such exposures might ultimately help to lessen breast cancer risk, and possibly the risk of some other cancers."
Also troubling is the possibility that infants are being exposed to carcinogens through breast milk. However, Josephy adamantly adds, "Our results should in no way be taken to discourage breast-feeding, which has great health benefits for babies regardless of these trace contaminants."
The scientists plan to broaden their research to include women in other geographical areas. Previous studies have shown large variations in the breast cancer incidence, with especially high rates in the industrialized northeastern United States.
This research was supported by the Canadian Breast Cancer Foundation.
A nonprofit organization with a membership of more than 155,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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