Research Commentary: Human Milk Contamination
The Ribbon

Lillian S. DeBruin, J.B. Pawliszyn, P.D. Josephy. Chemical Research in Toxicology Volume 12, 78-82, January 1999.

The worldwide contamination of human breast milk is a well-kept secret. This is not to say that the topic has not been thoroughly studied. A quick computer search will turn up citations for hundreds of research papers, reviews, and reports. (Type "breast milk contamination" into a medline search and see for yourself.) These publications consistently document the presence of suspected carcinogens-especially fat-seeking, chlorinated organics-in the milk of nursing mothers from Kenya to Kentucky and the Arabian peninsula to the Arctic Circle. Indeed, because breast milk occupies the highest rung on the food chain ladder, it is the most contaminated of all human foods, with bioaccumulative toxics in mothers' milk reaching levels that far exceed their concentrations in animal-based foods (dairy, fish, eggs, and meat). And yet, in spite of this impressive accumulation of scientific knowledge, we hear almost no public discussion on the issue.

As a breastfeeding mother myself, I am dismayed by the silence. In my experience, childbirth educators, pediatricians, midwives, lactation consultants, and breastfeeding advocates such as La Leche League downplay the pollution of human milk in order to prevent women from choosing the bottle over the breast. But keeping secrets is never a good strategy for advancing public health. Mothers today confront a dismal Hobson's choice: Do we feed our babies the highly contaminated milk from our own bodies (which swarms with disease-fighting immune cells, brain-enhancing sugars, allergy-suppressing proteins, and bactericidal elements)? Or do we opt for a nutritionally inferior but lesser contaminated formula? The conventional wisdom-that the known benefits of breastfeeding in fighting infectious diseases outweigh the long-term, less understood risks of increased chemical exposure-is an untested supposition and a hardly reassuring one. The obvious third choice-that mothers should feed their babies human milk uncontaminated with carcinogens-is currently available to no woman on earth.

Happily, some brave breast cancer activists are beginning the much need public conversation that breastfeeding activists are apparently too fearful to initiate. The connection is a simple one: if toxic chemicals are ubiquitous in breast milk, then they are also present in the breasts of all women, lactating or otherwise, and may be contributing to cellular damage in the breast ducts. Such activists will want to take note of a new study published by researchers at the University of Guelph in Ontario, Canada. This study looks at a class of industrial chemicals that, heretofore, has not received close attention by breast cancer researchers: the aromatic amines.

Aromatic amines have many sources. They have long been used in the manufacture of dyes. They are also used to make plastic foams, pesticides, and pharmaceuticals. They are a byproduct of tobacco smoke. They are added to rubber during vulcanization, and they are used in color photography. They are called amines because the chemicals in this broad class are derived from ammonia. They are therefore distinguished by having both nitrogen and carbon in their molecules. "Aromatic" means that the chemical members of this class all possess a hexagonal ring of carbons (like benzene) rather than a single straight chain. Aromatic amines have already been identified as mammary carcinogens in laboratory rats. Human data is scarcer, but the authors point to some compelling occupational data. Women workers in a Russian dye-making factory, for example, showed excess rates of breast cancer.

In carrying out their study, the authors had to first establish an analytical method for measuring the presence of monocyclic aromatic amines in biological fluids. Indeed, they are the first team of researchers to detect such contaminants in human milk. As the authors themselves note, the implications of such a finding are gravely important. While environmental organochlorine pollutants (pesticides, dioxins, and PCBs) have been identified in human milk for decades, few organochlorine chemicals can, all by themselves, cause breast cancer in animals. Aromatic amines such as o-toluidine, on the other hand, are known to cause ductal carcinomas in rats. Their detection in human milk means that the ductal epithelial cells of the human breast are routinely being exposed to a class of chemicals for which the data on carcinogenicity is overwhelmingly clear.

The experimental methods used in the study were impressive. Detections of aromatic amines could be made by using solid-phase microextraction coupled with gas chromatography/mass spectrometry. The human milk in this study was collected from 31 lactating mothers without occupational exposure to aromatic amines. Some had been breastfeeding for only a few days; other for more than two years. Seven were smokers and 24 were non-smokers.

The results were unequivocal. Monocyclic aromatic amines were detected in milk samples from all mothers, both smokers and non-smokers. These included aniline, o-toluidine, and N-methylaniline. All mothers had aniline in their milk at levels ranging from 0.05 parts per billion to 5.2 parts per billion. (These concentrations are comparable to the average levels of some of the most common organochlorine breast milk contaminants.) The milk of eleven mothers contained both o-toluidine and N-methylaniline. Interestingly, levels of contaminants did not correlate with length of lactation, the fat or protein level of the milk, or with each other. There was no significant difference between smokers and non-smokers. Also, there were no differences in contamination between the milk of first-time mothers and those with more than one child. The authors did not, however, test for an association between mother's age and contaminant levels.

The authors end their report by asking some important questions for further study. Unlike organochlorines, aromatic amines have short half-lives and are readily excreted in urine (which is why they are also strongly linked to bladder cancer). Are the levels of these chemicals therefore the result of recent rather than long-ago exposures? (The lack of difference between contaminant levels in uniparous and multiparous mothers suggests such a conclusion and stands in stark contrast to the data on organochlorine levels in breast milk where levels fall dramatically as length of lactation and number of breast-fed children increase). If these exposures are indeed recent and ongoing, what is their ultimate source? Diet? Air? Water?

Breast cancer activists will find in this study renewed reasons to focus on environmental causes of the disease. Nursing mothers will find more reasons for heartache in the obvious question not addressed by this study: what is the effect of aniline-laced breast milk on my child? This is certainly the question in my mind as I watch the mouth of my nine-month-old daughter tug rhythmically and blissfully at my breast, her own rosebud nipples rising and falling with each swallow.

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Prepared by Sandra Steingraber, Ph.D., Visiting Assistant Professor
Cornell University Center for the Environment

Research Commentary: Human Milk Contamination The Ribbon

Research Commentary: Human Milk Contamination
The Ribbon