A Contaminant in Mothers' Milk.

The Persistent Threat of PBDEs

A class of compounds known as polybrominated diphenyl ethers (PBDEs)--flame-retardant additives used in high-impact plastics, foams, and textiles--has recently sparked concerns among environmental health scientists. PBDEs are part of a superfamily of related toxic compounds known as persistent organic pollutants (POPs). Limited evidence suggests they may be associated with health effects including cancer, thyroid toxicity, and neurodevelopmental problems. In this issue, Kim Hooper, a research scientist with the Hazardous Materials Laboratory in the California Environmental Protection Agency, and Thomas McDonald, a staff toxicologist in the agency's Office of Environmental Health Hazard Assessment, discuss PBDEs and explore what prove to be many parallels between some PBDEs and other members of the POPs family [EHP 108:387-392].

The POPs family also includes compounds such as dioxins, furans, and polychlorinated biphenyls (PCBs), which have been found in humans, animals, and environmental media all over the world. Hooper and McDonald suggest that the toxicity of PBDEs is likely to be most similar to that of PCBs, causing similar effects.

According to Hooper and McDonald, the weak carbon-bromine bonds of PBDEs render them more susceptible to environmental degradation than the other POPs, most of which contain highly stable carbon-chlorine bonds. Nonetheless, PBDEs are persistent enough to bioaccumulate in fatty tissues as they make their way up the food chain to humans, where they can be passed directly to nursing infants via breast milk.

Of the three major commercial mixtures of PBDEs produced --deca-BDEs, octa-BDEs, and penta-BDEs--it is deca-BDEs (which have the least potential to bioaccumulate) that account for most commercial production. However, in sunlight, deca-BDEs degrade to penta- and tetra-brominated compounds, which bioaccumulate almost as well as PCBs. It is these lesser brominated compounds, particularly the tetra- to hexa-BDEs, that have been identified in Swedish breast milk.

Hooper and McDonald note that Swedish scientists report a doubling of concentrations of PBDEs in human breast milk samples from Sweden every 5 years since the first samples were taken 25 years ago. They warn that large gaps exist in what is known about PBDE toxicity, and suggest that the increasing presence of these compounds in biological tissues could pose a threat to human health. Based on the Swedish data set for PBDEs, Hooper and McDonald suggest that breast-milk monitoring programs are a valuable source of time-trend data that can be used to identify emerging pollutants (such as PBDEs), as well as track population-level changes in the tissue concentrations of known contaminants.

Hooper and McDonald suggest that such programs provide a convenient, noninvasive way to estimate body burdens of POPs in the mother, fetus, and breast-fed child. In addition, breast-milk monitoring programs can be used to identify geographical hot spots for POPs contamination and to identify groups of at-risk individuals that can be followed. Several European countries have operated breast-milk monitoring programs for as long as 30 years. These programs helped to identify PCBs and dioxins as important contaminants in humans. Currently, there are no systematic breast-milk monitoring programs in the United States, where little is known about PBDE concentrations in breast milk or PBDE body burdens.