Environmental contaminants, including pesticides, industrial chemicals, and heavy metals are ubiquitous. Their long lasting, background presence in foods, soil, and dust results in ongoing consumption and exposure of virtually everyone, even long after use of a particular contaminant (e.g. DDT) has been discontinued. Concerns have been raised about the possible effects of these environmental contaminants on growth, sexual maturation, behavior and development, immunologic competence, and carcinogenic potential in the developing fetus, infant and child.
Little is known about levels and trends of environmental contaminants in breastmilk in the US Studies available from the US are geographically limited, based on small groups, and thus are not representative of the general population. Based upon studies from other countries, it appears that the concentration of some contaminants in breastmilk such as dioxin have declined worldwide since the 1970's. Fortunately, maternal exposure to environmental contaminants in the US is low except in women at specific occupational risk (pesticides in farm workers), women living in contaminated housing (lead in northeastern cities), accidental massive contamination of the food chain (PCB exposure via cow's milk and beef in Michigan in 1970's) or chronic ingestion of fish taken from waters with high levels of industrial contaminants (mercury or PCB in Lake Ontario, Hudson River).

Lipophilic, organochlorine contaminants, such as DDT compounds and PCB, are stored in body fat and accumulate over time. Exposure of the breastfeeding infant begins before birth by transfer of maternal contaminants present in maternal blood across the placenta. These contaminants, especially those stored in maternal fat (DDT, PCB), continue to be released into human milk throughout lactation. Maternal stores of these compounds are depleted as maternal fat is mobilized and the compounds are released into milk, thus transferring the contaminants from mother to the breastfeeding infant. Breastmilk levels of environmental contaminants decline substantially over the duration of breastfeeding and decrease with subsequent pregnancies, presumably reflecting the gradual depletion of maternal stores via breastfeeding. In general, larger amounts of contaminants are transferred postnatally via breastmilk than are transferred antenatally via the placenta. Despite this, the adverse physiologic effects of various contaminants appear to be greater with transplacental compared to lactational exposure in both humans and experimental animals. This greater susceptibility of the fetus may relate to the immaturity of affected systems at the time of antenatal exposure.
In experimental animals, organochlorine compounds (e.g., PCB, DDT) interfere with normal hormonal balance. Effects are variable and conflicting, depending upon the species, gender, age and immaturity of the animal studied Nevertheless, estrogenic, androgenic and anti-estrogenic effects have all been associated with exposure to DDT and PCB compounds. These effects include acceleration

continued on page 7