A scientific revolution is brewing in the regulation of toxins. The revolution is over how standards are set. This new understanding comes from the study of endocrine disruptors such as bisphenol A, phthalates, polychlorinated biphenyls, dioxins, heavy metals, perchlorate, and pesticides. The revolution is not just about what constitutes an unacceptable exposure but the very scientific assumptions used in identifying risk.
Beginning over two decades ago with the publication of Our Stolen Future by Theo Colborn and her co-workers, a growing body of research has not only shown the toxic effects of endocrine disruptors but challenged the model used by regulators to set limits on toxic exposures. That regulatory model is based on the idea that large doses cause harm, small doses do not, and somewhere in between there’s a dose that is a safe boundary. What the challengers have found is that large doses do harm and intermediate doses do not but that small doses cause harm as well.
This new way of thinking creates a problem for regulators because these small doses are at levels that are commonly found in the human body as described by the CDC’s ongoing body burden study. It also creates a new concept for establishing safe limits: the environmentally relevant dose. In other words, what matters isn’t the dose you’re exposed to but the dose you have in your tissues.
The old thinking is that “the dose makes the poison.” What’s been found is that the timing of the dose matters too: endocrine disruptors have a greater impact during specific developmental stages— during fetal development, infancy, and puberty. So the new rule is “the dose and its timing make the poison.”
Another aspect to this revolution is that the old model of one toxin within one range of exposure leads to one health condition is grossly inadequate for understanding toxic effects. On the one hand, one toxin can be at the root of many dysfunctions and diseases. On the other hand, a single dysfunction or disease can be the result of exposure to a wide variety of endocrine disruptors. In other words, it’s not one toxin for one disease, but many toxins for many diseases.
And yet another aspect to this new way of thinking is the understanding that the many toxins in our bodies act together so that two toxins at levels lower than the safe limit on their own cause disruption when present together. In other words, by themselves they are not a risk but when combined are a risk.
These issues are discussed in the latest issue of Environmental Health Perspectives—although the word “paradigm shift” is used instead of “revolution.” After all, Environmental Health Perspectives is a government publication. Nevertheless, the director of the National Institute of Environmental Health Sciences, Linda Birnbaum, approvingly describes this new way of thinking in an editorial. Leading researchers in the field contribute an article in the issue titled “A Clash of Old and New Scientific Concepts in Toxicity, with Important Implications for Public Health.” This is all very good news.
But don’t start the victory parade.
The National Institute of Environmental Health Sciences funds research. Getting that science into practice is another story. If this science and its new way of thinking were implemented, more materials and processes will be found to be toxic and as a consequence more heavily restricted. Those who make money and wield power based on the use of those materials and processes will resist, as they have in the past with great effect.
An article in last week’s Science points to another problem. The article concerns e-waste, the vast stream of electronic devices that includes all the wonders of the wireless age such as cell phones and PDAs, devices that have a short life cycle and loads of toxins. The design of these products and the way in which they’re manufactured, as with virtually all products that carry toxins, is carried on with no thought to health risks. At the consumption end of the cycle, an estimated two thirds of consumers are completely in the dark about these products’ toxic load.
Sounds pretty bad.
However, in addition to the good news that the government agency responsible for funding research is taking a revolutionary position on the basic science of toxins, smart and dedicated people are working to bring this revolution to regulatory policy and practice, to industrial design, and to consumer education. For me, the take home message is that it is no longer “the dose that makes the poison” but “the dose, its timing, and its political economy make the poison.”
These issues are explored further in essays “Health and Plastic” and “Health Inequity and Toxic Load” and the essays in the sections on “Production” and “Natural Environments” in our book Too Much Medicine, Not Enough Health.