Webinar series addresses early-life exposures
By Emily Zhou
An NIEHS Superfund Research Program (SRP) webinar Feb. 3 explored the potentially adverse effects of exposure to brominated fire retardants (BFRs) during critical windows of susceptibility. Hosted by SRP Director Bill Suk, Ph.D., the Risk eLearning Web Seminar was the first in a continuing series on the long-term health consequences of early-life environmental exposures.
According to the presenters, BFRs are present everywhere in the environment, and exposures to these chemicals at an early age can lead to a range of detrimental health effects later in life, either by increasing susceptibility to disease or by initiating disease processes.
Fire retardant chemicals in the environment
The first speaker in the webinar was NIEHS/NTP Director Linda Birnbaum, Ph.D., a leader in research on polybrominated diphenyl ethers (PBDEs), a group of chemicals widely used as fire retardants. “BFRs do not bind chemically to polymers in textiles and plastics,” Birnbaum said. “They leach out or evaporate from flame retarded products,” spreading widely in dust, water, and air.
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From consumer products, furnishings, and building materials, PBDEs enter air and dust in indoor environments, while landfills and waste treatment facilities carry the chemicals into the food chain, affecting wildlife, plants, and water. Birnbaum pointed to a number of animal and recent human studies that have found correlations between PBDEs and impaired reproductive function, altered neurological development, obesity, and diabetes.
The European Union has banned use of all PBDEs, and the U.S. is soon to follow with a voluntary phase out, but they are persistent chemicals and many PBDE-treated products are still in use. A rapid increase in BFR use in Asian markets has contributed to global concern about ongoing exposures, as have studies showing elevated levels of PBDE in people working in electronics waste disposal sites in China and Nicaragua.
High exposure of toddlers to chemicals that mimic thyroid hormone
“PBDEs are present in much higher quantities in [household] dust than in soils,” said the second speaker, Heather Stapleton, Ph.D. Stapleton is an SRP grantee, an NIEHS Outstanding New Environmental Scientist awardee, and an assistant professor at the Duke University Nicholas School of the Environment. Because children are spending more time indoors and have a greater number of hand-to-mouth contacts with household dust and treated products, toddlers are the most highly exposed age group for PBDE exposure, which is associated with altered thyroid regulation that may be playing a role in deficits in neurological development.
Taking blood samples, as well as samples from hand wipes and house dust, Stapleton’s laboratory conducted studies of birth outcomes in pregnant women and of toddlers. Study results showed the presence of PBDEs in all serum samples and a strong association between PBDEs in serum and PBDE residues on hand wipes. Exposure patterns change with age, Stapleton said, from mother’s milk for infants, to dust for toddlers, and to diet for older children and adults, but dust is a key route of exposure for all age groups. Observing an association between socioeconomic status and PDBE level, Stapleton speculated that PBDE’s might also be an environmental justice issue.
PBDEs as a neurotoxicant and possible carcinogen
Although Birnbaum and Stapleton had also raised the question of whether PBDEs, because of their structural similarity to polychlorinated biphenyl (PCBs), could be neurotoxic and even carcinogenic, the final speaker of the seminar, Prasada Kodavanti, Ph.D., addressed the issue in greater detail from the perspective of neurotoxicology. Kodavanti is a senior researcher in the Neurotoxicology Branch at the U.S. Environmental Protection Agency.
As Kodavanti explained, PBDEs have chemical structures that are very similar to known cancer-causing and neurotoxic compounds, such as PCBs, dioxins, and other persistent organic pollutants, and that levels of PBDEs are doubling every two to five years, quickly approaching the levels of PCBs in humans. The mechanisms of action are similar to those proposed for PCBs, with depression of serum T4, effects on intracellular signaling, and effects on neurotransmitters.
Kodavanti pointed to changes in the expression of proteins that related to energy metabolism, calcium signaling, and growth of the nervous system. He cautioned that PCBs and PBDEs might have synergistic effects on reproductive and neurological development.
(Emily Zhou, Ph.D., is a research fellow in the NIEHS Laboratory of Signal Transduction Inositol Signaling Group.)
Green chemical considerations for new flame retardants
Birnbaum closed her talk with a few caveats for developing safer flame retardants, with the following factors in mind:
- Alternative chemicals other than BFRs or other classes of fire retardants
- Minimized potential for hazard and exposure
- Low persistence and bioaccumulation for breakdown products, as well as parent chemicals
- Low toxicity, less potential for harm when exposure occurs
- Low exposure, less potential for release
Market considerations for flame retardant alternatives
Birnbaum also acknowledged alternatives need to be cost-effective and functional by addressing the following issues:
- Aesthetics and performance — appearance, durability, fire safety
- Process equipment cost
- Alternative technologies, barriers, surface treatments, graphite impregnated foams