Chemical "Soup" Clouds Connection between Toxins and Poor Health

CHEMICAL CRUSADER: Through her leadership at NIEHS and NTP over the past three years, Linda Birnbaum has pursued a broad vision of environmental health that incorporates gene?environment interactions along with the impacts of disease, diet, stress and other factors. Image: Courtesy of the National Institute of Environmental Health Sciences (NIEHS)/Steve McCaw

From plastics to flame retardants, the ubiquitous chemicals of our daily lives have raised public health concerns like never before. Inside the Beltway, however, data-crunching scientists are often no match for industry lobbyists and corporate lawyers. The exception, no doubt, is Linda Birnbaum, the toxicologist who leads, two little-known scientific agencies, the National Institute of Environmental Health Services (NIEHS) and the National Toxicology Program (NTP).

Last April, Birnbaum sat inside a Capitol Hill conference room packed with poker-faced chemical industry executives ready for a showdown. The NTP had recently issued its report on carcinogens?a sort of name-and-shame list of chemicals on which no company wants to find its products. Charles Maresca of the Small Business Administration?taking a stand for the maligned styrene industry?argued that the report was "based on inaccurate scientific information" and faulty peer review.

North Carolina congressman Brad Miller (D) was unimpressed. He took the microphone and described Birnbaum's resume of more than 700 publications in public health, toxicology and environmental science. Removing his black reading glasses, he glanced at Maresca, and delivered the fatal blow with relish: "And you're a lawyer. Isn't that right?"

If Birnbaum got a kick out of the put-down, she didn?t show it. After 33 years working as a federal scientist at both the U.S. Environmental Protection Agency and the NIEHS, Birnbaum's career is a study in the way science becomes law and the ways lobbyists subvert science. She has watched her contributions to an EPA report on dioxin sit in limbo for 20 years, she has worked to study the health impacts of types of asbestos that are not legally recognized as asbestos and she has challenged the chemical industry in her pursuit for answers about the controversial chemical bisphenol A (BPA).

Through her leadership at NIEHS and NTP over the past three years, she has pursued a broad vision of environmental health that incorporates gene?environment interactions along with the impacts of disease, diet, stress and other factors. She has also tried to make the NIEHS quick on its feet: After the 2010 BP oil spill, she initiated the Gulf Long-Term Follow-Up (GuLF) study, the first extended review of the health effects of an oil spill.

Scientific American sat down with Birnbaum in Washington, D.C., to learn more about environmental health, toxic chemistry and the politics of chemical regulation.

[An edited transcript of the interview follows.]

How did you become interested in toxicology?
When I was in eighth grade at Benjamin Franklin Junior High School in Teaneck, New Jersey, I had a science teacher who was an attractive, peppy, young blonde woman who was also the cheerleading coach. I was a cheerleader, and that positive reinforcement made it okay to like science.

I became interested in thyroid hormones. I can't tell you exactly why, but I had written to a local pharmaceutical company and asked if they could give me some rats and some chemicals. That's something that would never happen easily today?but they did it! I got a letter from them that said, "Please come. We'd like to talk to you." The next thing I knew, I had 40 rats in four cages and feed and bedding and everything else, along with thyroid hormone and chemicals that block thyroid hormone.

They let you keep the rats at your house?
Yeah. We had them in my basement.

What did your parents say about that?
My parents were really incredibly supportive?even when one escaped. I eventually found its body and put it in the freezer figuring I'd dissect it at some point. But my grandmother went in thinking it was a package of ground beef. She had a little bit of a fright.

How much of human disease is due to environmental exposures?
The estimates vary, and it depends on how you define environment. People often say it's about 30 percent. I think that's defining environment fairly narrowly, considering only environmental chemical exposures, but your environment includes the food you eat, the drugs you take, the psychosocial stress you're exposed to and so forth. After all, what's the difference between a drug and an environmental chemical? One you intentionally take and the other one you don't. Considering all that, I would say then the environment is much more than 30 percent.

We also know?especially from studies of identical versus fraternal twins?that for many different diseases, genetics is not the whole story. Actually, I think it's time to stop asking, "Is this caused by genes or is this caused by the environment?" because in almost all cases, it's going to be both.

Why has it been so difficult to link environmental exposures to specific health consequences?
Nobody is exposed to one chemical at a time, right? I mean we live in a soup of chemicals and we live in a soup of exposures. Here, I'm having a lemonade. Well, it's not only lemon in here. I'm sure there's some sugar. There might be a preservative or something. I don't know what's in this. So think of all those things interacting, but when we test chemicals in the lab we tend to test them one at a time.

I guess we don't consider these other types of exposures.
Right. A high-fat diet, for example, can completely change the way your body handles chemicals. Exposure to a certain chemical may lower your ability to respond to an infection. At EPA we did a lot of studies exposing rats and mice to air pollutants and then to bacterial infections or influenza infections. Those who were exposed to pollution were more likely to die, whereas those in clean air recovered.

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