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Chemical Pollution and Mother's Milk

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More than 85,000 chemicals are registered for use in the United States today, and because of inadequate testing, we really have no idea if most of these chemicals have insinuated themselves into our environments, our bodies or our breast milk. Most of the studies on contaminants in breast milk have focused repeatedly on a small number of chemicals already known to be a problem.

Those studies that have focused on specific chemicals in breast milk, however, show cause for concern. Generally speaking, they have found that man-made chemicals referred to as persistent organic pollutants (POPs) invade the environment; spread through our water, air and soil; are taken in and stored by fish and animals; and eventually reach the top of the food chain -- humans. Once there, they seek out and attach themselves to our fat, which is critical to the production of nursing mothers' breast milk. As mothers breastfeed their babies, these pollutants enter their babies' systems.

In the links below, you can read detailed information on each of the POPs, as well as on certain metals and solvents that are also cause for concern in breast milk. Remember, however, that the absence of a chemical from these pages does not mean that the chemical poses no threat; it may simply mean that no scientist has tested for it in breast milk.

Despite the shortcomings of research on pollution in breast milk, scientists have detected many different pesticides in breast milk throughout the world. The organochlorine class of pesticides poses the most significant threat. It includes DDT and nearly a dozen other chemicals similar to it, most of which came into widespread and heavy use in the 1940s and 1950s. Most of the organochlorine pesticides are POPs, persisting in the environment and bioaccumulating their way up the food chain. For that reason, most countries have banned or seriously limited the use of organochlorine pesticides. Some are still used on crops or for mosquito control in developing countries, however, and even in countries where they have been banned, detectable levels persist in blood and breast milk.

The good news is that countries that banned the use of these organochlorine insecticides have been rewarded with significant decreases in their levels in breast milk over the last 10 to 20 years, proof that eliminating the production or use of a persistent, hazardous chemical can make a significant difference in exposure levels. Not surprisingly, in those countries that continue to use organochlorines, levels of these contaminants in breast milk remain high.

Organochlorine pesticides pose many health risks. At high levels, they are toxic to the brain and nervous system, resulting in seizures, twitching and other signs of acute poisoning. At lower levels, many interfere with such hormones as estrogen and testosterone. In general, several organochlorines have a feminizing influence (at least, on laboratory animals) by mimicking estrogen and by blocking male androgens in the body. A number of pesticides of this class have also been linked to birth defects and cancer in animals.

Other chemicals found in breast milk are not pesticides, although dioxins, PCBs, PBDEs and toxic metals share some of the properties of organochlorine pesticides -- accumulating in the environment and concentrating in human bodies and in milk. The dioxins and PCBs are known or suspected cancer-causing chemicals, and can interfere with development of the brain in early life, possibly by blocking the normal effects of thyroid hormones. Dioxins are toxic to the immune system. The brominated flame retardants known as PBDEs share many of the properties of the PCBs and dioxins, but in contrast to the PCBs and dioxins, the levels of these PBDE chemicals have been increasing in breast milk. Chemicals that are widely used in fragrances for consumer products have also been reported to accumulate in breast milk. These musk-xylenes and nitro-musks have not yet been widely studied, and there is very little information about their possible health effects. Perchlorate, a chemical used in rocket fuel, fireworks and road flares, has made its way into drinking water supplies, and is also accumulating in irrigated crops. Studies have detected this chemical in breastmilk at surprisingly high levels. Finally, such metals as mercury and lead can be found in breast milk, although they tend to be at higher levels in blood. These metals are known to be toxic to the developing brain.

The precise health risks from the levels currently found in breast milk are very hard to estimate. For women in countries where these chemicals have been banned, the risks are quite low, and are certainly exceeded by the many benefits of breastfeeding. These chemicals are therefore examples of a partial success story: elimination of their use has resulted in partial clearing of women's breast milk. But this accomplishment comes with the certain knowledge that those countries that still permit the use of organochlorines need to phase them out in order to protect babies from dangerous exposures in their first few months of life. We also know that some chemicals, including the brominated flame retardants, are on the rise in breast milk, and that untold numbers of chemicals have never been looked for, making it impossible to know if they do or do not pose an exposure risk.

The following graph of breast milk levels of harmful chemicals illustrates Sweden's experience. Note that levels of PBDEs in breast milk increased markedly over the last quarter century, while levels of banned chemicals have gone down just as sharply. Women in Sweden have among the highest breastfeeding rates in the world, and the discovery of rising levels of PBDEs in breast milk did not make women stop breastfeeding. Instead, the discovery provoked a public outcry, and within one year the offending chemicals were banned in Sweden, resulting in the rapid decline of PBDEs in Swedish breast milk.

Figure 1

Figure 1

One of the things that scientists have learned about the persistent organic pollutant contaminants in breast milk -- chemicals such as dioxins, PCBs, PBDEs and the organochlorine pesticides -- is that the levels in breast milk tend to be higher in first-time mothers and also tend to be higher during the early months of breastfeeding. Mothers who breastfeed for a long period of time, or who nurse more than one child, can have lower concentrations of pollutants in their breast milk than mothers who breastfeed for shorter periods of time, or who breastfeed only one child. Obviously, many factors influence the levels of contaminants in breast milk in any given woman, but research studies need to account for duration of breastfeeding and number of children in order to have consistent and comparable results. For example, figures 2 and 3 show higher concentrations of pollutants measured in the breast milk of first-time mothers in Japan, South Korea and Mexico.1 First-time mothers are called primiparas, and mothers with multiple children are called multiparas.

Figure 2

Figure 2

Figure 3

Figure 3

Figure 4 shows the results of a study done in the United States, in which breast milk pollutant concentrations in one mother nursing twins were found to decrease significantly over a 38-month period. 2

Figure 4

Figure 4

Follow these links to learn more about the specific chemicals that invade mothers' breast milk.

Dieldrin, Aldrin and Endrin
Nitro Musks
Dioxins and Furans
Lead, Mercury, Cadmium and Other Metals

Related Information on the Web

  • The World Wildlife Fund maintains a website with information on persistent organic pollutants.

  • The International POPs Elimination Network is a global network of public interest non-governmental organizations united in support of a strategy to eliminate chemicals that persist in the environment and accumulate in our bodies.

Back to Top | Next: Links


1. Iida et al., Polychlorinated Dibenzo-P-Dioxins and Related Compounds in Breast Milk of Japanese Primiparas and Multiparas, Chemosphere, vol. 38, no. 11, (1999): pp. 2461-2466; Yang et al., PCDDs, PCDFs and PCBs Concentrations in Breast Milk from Two Areas in Korea: Body Burdens of Mothers and Implications for Feeding Infants, Chemosphere, 46, pp. 419-428; Waliszewski et al., Organochlorine Pesticide Residues in Human Breast Milk from Tropical Areas in Mexico, Bulletin of Environmental Contamination and Toxicology, vol. 57, (1996): pp.22-28.

2. Schecter et al., Decrease in Levels and Body Burden of Dioxins, Dibenzofurans, PCBs, DDE and HCB in Blood and Milk in a Mother Nursing Twins Over a Thirty-Eight Month Period, Chemosphere, vol. 37, nos. 9-12, (1998): pp.1807-1816.

last revised 3.25.05

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