Many environmental issues are fairly well understood by the majority of people: global warming, extinction, sustainable resources, etc. If you ask your friends, co-workers, or next-door neighbors what they know about endocrine disruption, however, chances are you won't find the same breadth of knowledge in the topic. One of the best books written for the non-scientific populous that gives substantial depth to this topic is entitled Our Stolen Future, co-authored by Theo Colborn, Dianne Dumanoski, and JP Myers. I decided to read this book after we read a chapter in a toxicology course I took as an undergraduate. I found it to be a fascinating read and believe the field of endocrine disruption is one that should be more well-understood.
Over the past 30 years, we've seen many changes within science and research, including environmental toxicology. In the 1970's, toxicologists were borderline obsessed with cancer. Environmental scientists were constantly looking for links to cancer as caused by environmental pollutants, and grotesque pictures of tumor-ridden fish were not uncommon at toxicology research conferences. The problem with this mindset, however, was that it didn't really explain what other researchers were finding in the field. Cases of two female birds forming mating pairs, eggs that never hatched, skewed sex ratios, population levels declining sharply for no obvious reason.
When all of the pieces were put together, the answer became much more clear: pollutants in the environment were only causing cancer at extremely high doses: at lower doses (i.e. what would occur in the environment after an industrial spill or accident) they were acting as hormone mimics and disrupting the astutely-balanced endocrine system. Your endocrine system, in a nutshell, is responsible for regulating your sexual characteristics, fertility, and overall reproductive health. The endocrine system is also intricately linked with the central nervous system and the immune system, so anything that modulates the endocrine system can potentially affect the other two major systems as well.
One of the most surprising parst of this discovery was how many chemicals could act as hormone mimics or could offset hormonal homeostasis. Pesticides such as DDT, plastic additives such as polychlorinated biphenyls, industrial biproducts such as dioxin, and effluent from paper mills or agricultural activities. These chemicals were not designed to be hormones or hormone antagonists, yet by mechanisms which are only recently beginning to be understood they act as such. And not only are these chemicals acting by complex mechanisms, the nature of their chemical structures allows them to persist in the environment for long periods of time.
So these chemicals are in the environment and are impacting wildlife. So what? How does this impact human health? Both lab studies and empirical work demonstrates that these types of chemicals can elicit negative effects in human body. Human exposure to endocrine disruptors has been linked to reduced sperm counts, increased rates of reproductive cancers, and autoimmune diseases, to name just a few.
And if you think endocrine-disrupting chemicals are only found in the environment and not in your home or workplace, you are gravely mistaken. If you've purchased a plastic water bottle in the past year, you probably more manufacturers including labels that say "BPA free". Bisphenol A is a polycarbonate chemical developed to make plastic materials extremely strong (this was the first chemical that gave Nalgene the ability to make "indestructable" water bottles). Recent research, however, has shown that this chemical can act as a hormone mimic. BPA exposure can lead to health problems, especially in early infant or childhood development, and has even been linked to breast cancer. Thanks to increased research and public awareness of this chemical, the FDA is now re-assessing the potential hazards of this chemicals, as their initial assessment came to the conclusion that there were no negative affects associated with BPA exposure. Whether this compound will become regulated in the years to come is another story.
The authors of this book were an intricate of the paradigm shift from cancer to endocrine disruption, and Colborn and Myers lay out their story in an engaging and understandable manner. While some claim the book is too "sciency" for a general audience, if you consciously put an effort into comprehending what the authors are saying, you will have no problem understanding the take-home messages of the authors: endocrine disruption is a real trend that has the potential to have a huge negative impact on both human and environmental health, unless action is taken to regulate these chemicals.
On a personal note, I got the chance to meet with one of the scientists featured in Our Stolen Future, Dr. Richard Peterson of the University of Wisconsin-Madison. His work on the effects of dioxin on mouse development was featured in the book, and Dr. Peterson was one of the first researchers to realize the impacts of these chemicals, and even helped in coining the term "endocrine disruption." I also had a chance in February to listen to a lecture by Dr. Louis Guillette from the University of Florida. He was the first to discover endocrine disruption in a DDT-contaminated lake in Florida and his research on alligator reproductive physiology is both ground-breaking and incredibly interesting.
As science progresses and toxicologists delve into emerging fields of research, endocrine disruption will still be a significant chapter in our history and will likely influence the careers of many scientists-including myself-for years to come. If any progress is to be made, however, we will need to align scientific research with governmental regulatory institutions, and perhaps most importantly, continue to increase endocrine-disruption awareness in the non-scientific public.
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