As scientific research on endocrine disruption has advanced, the scope of the research has broadened significantly. The list of hormonally active compounds is longer than anyone had previously imagined in the early days of the research. Not only are more compounds involved, but more hormone systems are now known to be vulnerable. And within each hormonal system, new mechanisms of interaction between compounds and receptor systems are being explored to understand how a compound exerts its effects. Research on leguminaceous plants and their symbiotic rhizobial bacteria show that chemical communication between organisms is also vulnerable to disruption by contaminants.

New compounds: Accidental discoveries and systematic testing have revealed a broader array of modern use compounds capable of interfering with the sex steroids hormones. New results come in regularly, identifying yet another hormonally-active compound.

Most notably, because of their ubiquity, certain compounds in plastics began to attract attention, especially nonylphenol and bisphenol-A (Our Stolen Future, Chapter 8). Nonylphenol is used widely as a surfactant (for example, in pesticides and detergents) and as an additive to certain plastics. Bisphenol-A, the basic building block of polycarbonate plastic, not only enters our lives in every objects made from polycarbonate, for example clear plastic baby bottles, it also enters children's mouths when their teeth are coated with polycarbonate to prevent cavities. And, like nonylphenol, bisphenol-A is used as a surfactant in pesticides. The ubiquity of exposure is breathtaking.

Concern began to turn to phthalates in the late 1990s after studies showed their potency as a reproductive toxicant during crucial windows a development. The first issues raised were about their use as additives to PVC plastics that make them flexible, and thus useful in children's toys and medical devices, among many uses. But then in mid-2000, the CDC opened a dramatic new chapter in the phthalate story with convincing demonstration of the ubiquity of phthalate contamination, and a particularly troubling revelation for women of child-bearing age.

Even bakelite (also known as bisphenol-F ), the first of the modern plastics, has been found to be estrogenic. This pushes widespread exposure to synthetic estrogens back to the first decade of the 20th century.

More hormone systems: The initial concern in endocrine disruption had focused on contaminants capable of interfering with the sex steroid hormones, especially estrogen. Research emphasized the classic estrogen mimics and antagonists--DES, certain PCBs, DDT, etc.

But hormone disruption is not limited to estrogenic compounds nor the estrogen receptor. To begin with, scientists have learned that there is more than one estrogen receptor. Furthmore, the mechanisms of disruption are diverse and complex; a compound may be an agonist (mimicking the actions of a hormone) or antagonist (interfering or blocking actions of a hormone); it may alter transport of a hormone; or it may bind to more than one hormone receptor. Research on the sex steroids has been broadened to include anti-estrogenic and anti-androgenic activities.

And, because every hormone system is potentially vulnerable to disruption or alteration, the list of hormone systems investigated has broadened beyond the sex steriods. Scientists have begun to look at other hormone signalling systems... thyroid, progesterone, retinoids, glucocorticoids, etc. Compounds capable of interfering with each of these systems have now been reported. And even though hormone disruptors have not yet been identified for every hormone system, the lack of data is most safely attributed to the diversity and sheer number of compounds yet untested.

Perhaps the most troubling aspect of many of these discoveries was their accidental nature. Acknowledging this and also the strong likelihood that many compounds might possess disruptive capabilities, the US Congress in 1996, unanimously passed the Food Quality Protection Act. FQPA established a new committee, the Endocrine Disruption Screening and Testing Advisory Committee (EDSTAC), to advise EPA on the development of a screening program that would systematically survey a variety (i.e, 15,000) of modern day use compounds whose effects on the endocrine system were virtually unknown.

Recent discoveries:

• EDCs disrupt the the symbiosis between legumes and Rhizobium, undermining nitrogen fixation, a process essential for life on earth.
• phthalate contamination is widespread in the American public.
• polybrominated diethyl ethers (PBDEs) are steroid and thyroid disruptors. They are used as flame retardants in many modern consumer products. They are more persistent than PCBs and have become ubiquitous contaminants throughout the world, including in remote ocean life.
• soccer shirts manufactured by a large consumer product firm contain tributyltin, an endocrine disrupting compound known to have dramatic impacts on marine life.
• methoprene (a common active ingredient in insecticides) and the breakdown products of methoprene interfere with retinoid signalling.
• Synthetic pyrethroids, widely used to combate ticks, mosquitos and even head lice, are powerful endocrine disruptors.

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