Persistent Organic Pollutants (POPs)
POPs are a family of chemicals manufactured either for a specific purpose (e.g., pesticides or flame retardants in electrical equipment or furniture) or produced as by-products of incinerated waste. Current and historic industrial emissions have deposited POPs into the air, soil, and water, where they find their way into the food chain. POPs are very stable compounds that are not readily degraded in the environment nor completely metabolized or excreted by organisms. As they are consumed and stored by one organism after another, these substances bioaccumulate in the food chain. Because humans are at the top of the food chain, we accumulate these chemicals over time, collecting what is referred to as a lifetime body burden. POPs are now ubiquitous but usually low-level contaminants in human beings worldwide. Although certain nations have banned particular POPs, their existence is not confined to areas of use, as distribution occurs through atmospheric and oceanic transfer, as well as through food sources. Even when production of these chemicals is halted, continued long-term exposure is certain.
The POPs family includes dioxins, which commonly refers to polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzodifurans (PCDF), as well as polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE), and other organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene ( Table 1 ).
The PCB subfamily consists of 209 different chemicals. They were first produced in the United States in the 1930s as insulators in electrical equipment, and for paint, carbonless copy paper, and pesticides until they were banned in 1977; however, production continues elsewhere. In industrialized nations, where the majority of PCBs have been manufactured, they are probably the most widespread and critical organochlorine contaminants in human milk. The levels of PCBs in the breast milk of Europeans and North Americans are generally higher than those of women in nonindustrialized nations. Their presence can be detected in meat and fish. Numerous advisories concerning freshwater fish consumption due to PCB contamination have occurred in the United States. In 1981, 93% of breast milk samples in one study exceeded the US Food and Drug Administration's limit for newborn ingestion of PCBs in mg/kg body weight.
The dioxin subfamily consists of 75 PCDDs and 135 PCDFs, 17 of which have been detected in humans. Dioxins are by-products of the production and combustion of chlorinated compounds, which include the manufacture of pesticides, paper bleaching, and incineration of waste. They usually occur as collections of several different dioxin compounds. The toxicity of PCBs and dioxins can be difficult to measure because of heterogeneous occurrence and is commonly referred to in toxic equivalencies, which refer to the degree that a particular sample of multiple compounds resembles the bioactivity of the most toxic dioxin. Dioxins have been studied in at least 36 countries, and like PCBs, levels of dioxins are higher in more industrialized countries. Time trend data suggest that breast milk levels of dioxins are decreasing in many countries; however, for some, including the United States, the data are too ambiguous to make definite conclusions. These results suggest that efforts to reduce emissions have notable effects. The main source of environmental exposure to dioxins is through food of animal origin, such as meat, dairy products, and fish.
PBDE is a flame retardant widely used in electrical appliances, foam, and textiles for furnishings. Its use is still unrestricted, and it is found in increasing levels in breast milk. PBDEs have a similar structure to PCBs and have similar properties. However, they are thought to be more susceptible to environmental degradation. That withstanding, levels of PBDE in human milk samples from American women are 10 to 100 times higher than European levels.
Organochloride pesticides include DDT, hexachlorobenzene, hexachlorohexane, chlordane, dieldrin, and heptachlor, among others. DDT is a well-known agricultural insecticide that has been used extensively for over 40 years. It was banned in many countries, including the United States in 1972, but it is still used in other nations, such as Mexico, for control of malaria-carrying mosquitoes. Dichlorodiphenylchloroethane (DDE) is a toxic metabolite of DDT that has estrogenic properties. Levels of DDT and DDE in human milk have decreased in areas where cessation of its use has occurred. The other organochloride pesticides have been used as agricultural and domestic pesticides and fungicides but are now banned in the United States because of their toxicity and biologic persistence. However, their use in other countries continues, and their existence is still detected in breast milk, although levels have decreased.
J Midwifery Womens Health. 2006;51(1):26-34. © 2006 Elsevier Science, Inc.
Cite this: Environmental Contaminants in Breast Milk - Medscape - Jan 01, 2006.