We see the same thing with individual kinds of chemical exposures as well. One of our NIEHS grantees, Philippe Grandjean of Harvard University, followed women during their pregnancy, and then he followed their children. So he had blood samples before they were born from the mother. He had blood samples at birth, and he continued to follow the kids. What he found is that if those children had elevated exposure to PCBs [polychlorinated biphenyls used in electronics], they were less able to mount a normal response to a vaccination.
PCBs are considered likely carcinogens, but they are also endocrine disruptors, like bisphenol A or dioxin, which is something we've heard a lot about in the media lately. What is your definition of an endocrine disruptor?
An endocrine disruptor is anything that affects the synthesis of a hormone, the breakdown of a hormone or how the hormone functions. We used to think it had to bind with a hormone receptor but endocrine disruptors can perturb hormone action at other stages in the process.
Why are they such a big deal?
They're all around us, and I think they can affect us at very low levels. Our hormones control our basic homeostasis, our basic physiology. If you alter your hormone levels, you're not going to behave the same way physiologically, and that includes mentally and everything else. I think that there's growing evidence that some of the chemicals to which we are exposed are doing that to the population right now.
So we have this soup of endocrine disruptors, air pollution and other exposures, which has made epidemiology so difficult. What have you been doing at NIEHS to get to the bottom of these issues?
There are ways statistically that you can control for some of these factors, but I think we have to go beyond that and say, "Well, wait a minute. That's not real life." Maybe we need to look at whether there are interactions. In animal systems, from work that I did starting in the '80s and have continued ever since, we showed that for chemicals that have the same mechanism of action you can basically add up those chemicals to predict the toxicity. This is the toxic equivalency factor approach.
We've been finding with a lot of endocrine disruptors that if they impact the same health effect, such as decreased sperm production, you can just kind of add up chemicals. They may have a different mechanism, but they all affect sperm count. A lot of data show that if chemicals are estrogenic, you can add up their potency. If chemicals are anti-androgenic, you can add them up. If chemicals affect thyroid, you can add them up, too.
Nobody has tried to look even more broadly and say, "Well, I'm gonna take all these chemicals that somehow block male reproduction, and I'm also gonna add that to the chemicals that do something totally different." The way I think we're going to have to eventually get at that is through what we're calling "Tox21," which is this rapid-screening approach being developed with high-throughput screening of in vitro assays. They are cell-based assays looking at many, many, many different kinds of responses. Basically, we can screen up to 10,000 chemicals a year at 15 different dose levels for at least 70 or more different kinds of responses. We can begin now to do this with mixtures where we can make many different kinds of mixtures because we can test so many at a time.
How has spending 33 years studying toxic chemicals affected your outlook on the environment?
We do know that there are many chronic health conditions, non-communicable health conditions, which have increased too rapidly in the last 20 to 40 years. These are things like autism, ADHD and, of course, obesity and diabetes. We have identified chemicals clearly at play in the obesity epidemic. I am not in any way saying to people you can stop exercising and you don't have to watch what you eat, but the question I have is: Are we setting people up to fail because they're exposed to something that alters their ability to metabolize fats or sugars?
Overall, I'd say I'm a pragmatist. I think our air in this country is cleaner than it was, but it's not as clean as it needs to be. Our water is cleaner, but again not as clean as it needs to be. We've taken care of the really blatant environmental problems. We're concerned now about low levels of lead, not the very high levels that there used to be in our environment.—That's a good thing.