Environmental Factor, September 2011, National Institute of Environmental Health Sciences
Birnbaum speaks at Dioxin 2011
By Eddy Ball
Both of Birnbaum's talks emphasized that NIEHS and NTP are not regulatory agencies. However, she also impressed upon her audience the importance of NIEHS/NTP scientific findings in shaping regulatory decisions by the U.S. Environmental Protection Agency, U.S. Food and Drug Administration, U.S. Consumer Product Safety Commission, and Occupational Safety and Health Administration. (Photo courtesy of Steve McCaw)
NIEHS/NTP Director Linda Birnbaum, Ph.D., was a featured speaker at two sessions during the weeklong Dioxin 2011(http://www.dioxin2011.org/sitecore/content/be-bruga/dioxin2011/programme.aspx) in Brussels, Belgium. The presentations were part of the 31st International Symposium on Halogenated Persistent Organic Pollutants (POPs), Aug. 21-25, and a post-symposium Flame Retardant Science and Policy Session sponsored by the Green Science Policy Institute(http://greensciencepolicy.org/) Aug. 26, as part of its Flame Retardant Dilemma series of workshops.
Birnbaum spoke on “The Potential Role of Developmental Chemical Exposures in Contributing to the Obesity Epidemic” Aug. 25, which she co-authored with her protégée, Michele La Merrill, Ph.D., of the Mt. Sinai School of Medicine. The next day she explored the question, “How scientists, government, and NGOs [non-governmental organizations] can work together so good science supports public policy.”
POPS as obesogens
Birnbaum framed her presentation on obesogens around a hypothesis that may explain the dramatic rise in rates of obesity worldwide, especially in economically developed countries and among urbanized populations. “Early life exposure to environmental chemicals,” she speculates, “is a contributing cause of the obesity epidemic, due to the potentially critical role of prenatal and perinatal metabolic programming in later risk of obesity.”
In the course of her presentation, Birnbaum reviewed research on the association between outcomes related to obesity and developmental exposure to several POPs in animals and humans. The research included studies of exposure to dioxins, polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), hexachlorobenzene (HCB), polybrominated flame retardants, and perfluorinated chemicals (PFCs).
While the results have been mixed, Birnbaum explained, a sufficient number of positive associations have been found to justify additional, longer range studies to explore the connection between early life exposures and outcomes in later adulthood.
“Experimental studies should extend into adulthood,” she concluded, “and prospective epidemiology studies should present data with and without adjustment by lipids, if experimental evidence suggests chemicals affect lipid homeostasis.”
Birnbaum also urged researchers to evaluate critically non-linear dose response, and build on preliminary findings about the roles of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and aryl hydrocarbon receptor (AhR) in obesity measures. PPAR-gamma, she explained, is considered a master regulator of adipogenesis, and AhR, the receptor found responsible for essentially all the effects of dioxin and dioxin-like compounds, appears to have an innate role in insulin and lipid homeostasis.
Science and public policy
Birnbaum moved seamlessly from the bench to public health considerations in her second talk in Brussels. She addressed the issue of flame retardants and their potential to affect human health, as a foundation for her discussion of the use of science in regulatory decision-making and the importance of working with communities.
As Birnbaum explained, halogenated fire retardants are a public health concern because of their widespread use in the U.S. in electronics, building insulation, polyurethane foam, and wire and cable. The chemicals have been found in breast milk, and research suggests that they are a potential thyroid hormone disruptor and developmental neurotoxicant. Some brominated fire retardants, she explained, are persistent and found in the blood of humans and animals living as far away from their sources as the Arctic. She cited studies indicating that levels have been doubling every two to five years since the 1970s.
Fire retardants brought Birnbaum to the importance of NIEHS funding for experimental studies in raising awareness of potential public health issues, and the role of NTP gold-standard chemical bioassays in providing science directly for regulatory use. Looking toward the emergence of predictive toxicology, she said, “Biological systems are incredibly complicated, and we need to look for perturbations in various developmental functions and consider multiple important endpoints.” To reduce chemical hazards and exposures, the regulatory framework must incorporate all available data.
Birnbaum concluded her presentation with a discussion of the importance of partnerships among NIEHS and the communities and stakeholders who have an interest in how science is used. These communities and stakeholders include organizations performing NIEHS-funded outreach and education, a powerful coalition of grassroots advocacy organizations known as Public Interest Partners, and the larger environmental health community that is the target audience for the NIEHS-funded journal Environmental Health Perspectives.