(Beyond Pesticides, March 16, 2012) A report published online this week in the journal Endocrine Reviews documents extensive scientific research showing that endocrine disrupting chemicals, or endocrine disruptors, can be toxic to humans even in minutely small doses. The report, three years in the making, was published Wednesday by a team of 12 scientists who study hormone-altering chemicals. Authors include the University of Missouri’s Frederick vom Saal, PhD., who has linked low doses of bisphenol A (BPA) to a variety of effects, Theo Colborn, PhD., who is credited with first spreading the word about hormone-disrupting chemicals in the late 1980s, and University of California at Berkeley’s Tyrone Hayes, PhD., who has documented the effects of the pesticide atrazine on frogs. Drs. Colborn, Hayes, and vom Saal are all former speakers at the National Pesticide Forum. One of the reporrtâ€™s authors is Pete Myers, PhD, the founder of Environmental Health News and chief scientist of Environmental Health Sciences.
Dozens of substances that can mimic or block estrogen, testosterone and other hormones are found in the environment, the food supply and consumer products, including plastics, pesticides and cosmetics. One of the biggest, longest-lasting controversies about these chemicals is whether the tiny doses that most people are exposed to are harmful.
In the new report, researchers led by Tufts Universityâ€™s Laura Vandenberg, PhD, concluded after examining hundreds of studies that health effects â€śare remarkably commonâ€ť when people or animals are exposed to low doses of endocrine-disrupting compounds. As examples, evidence is provided for several controversial chemicals, including BPA, found in polycarbonate plastic, canned foods and paper receipts, and atrazine, used in large volumes, mainly on corn.
The scientists conclude that scientific evidence â€śclearly indicates that low doses cannot be ignored.â€ť They cite evidence of a wide range of health effects in people â€“from fetuses to aging adultsâ€“ including links to infertility, cardiovascular disease, obesity, cancer, and other disorders. â€śWhether low doses of endocrine-disrupting compounds influence human disorders is no longer conjecture, as epidemiological studies show that environmental exposures are associated with human diseases and disabilities,â€ť the report says.
In addition, the scientists took on the issue of whether a decades-old strategy for testing most chemicals â€“exposing lab rodents to high doses then extrapolating down for real-life human exposuresâ€“ is adequate to protect people. The authors conclude that it is not and urged reforms. Some hormone-like chemicals have health effects at low doses that do not occur at high doses. â€śCurrent testing paradigms are missing important, sensitive endpointsâ€ť for human health, the report says. â€śThe effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.â€ť
Linda Birnbaum, PhD., director of the National Institute of Environmental Health Sciences, said the new report is valuable â€śbecause it pulls a tremendous amount of information togetherâ€ť about endocrine-disrupting compounds. Her agency is the main one that studies health effects of contaminants in the environment. Dr. Birnbaum said she agrees with their main finding: All chemicals that can disrupt hormones should be tested in ultra-low doses relevant to real human exposures, she said.
However, the scientists who wrote the report said that low-dose science “has been disregarded or considered insignificant by many.” They seemed to aim much of their findings at the National Toxicology Program and the U.S. Food and Drug Administration (FDA). The FDA in 2008 discounted low-dose studies when it concluded that BPA in consumer products was safe. Two years later, the agency shifted its opinion, stating that they now will more closely examine studies showing low-dose effects. The National Toxicology Program in 2008 found that BPA poses â€śsome risksâ€ť to human health but rejected other risks because studies were inconsistent.
Several of the reportâ€™s authors have been criticized by some other scientists and industry representatives because they have become outspoken advocates for testing, regulating, and replacing endocrine-disrupting compounds. The scientists, however, say they feel compelled to speak out because regulatory agencies are slow to act and they are concerned about the health of people, especially infants and children, and wildlife.
Endocrinologists have long known that infinitesimal amounts of estrogen, testosterone, thyroid hormones and other natural hormones can have big health effects, particularly on fetuses. It comes as no surprise to them that manmade substances with hormonal properties might have big effects, too. â€śThere truly are no safe doses for chemicals that act like hormones, because the endocrine system is designed to act at very low levels,â€ť Dr. Vandenberg, a postdoctoral fellow at Tufts Universityâ€™s Levin Lab Center for Regenerative and Developmental Biology, told Environmental Health News.
But many toxicologists subscribe to â€śthe dose makes the poisonâ€ť conventional wisdom. In other words, it takes a certain size dose of something to be toxic. They also are accustomed to seeing an effect from chemicals called â€śmonotonic,â€ť which means the responses of an animal or person go up or down with the dose.
The scientists in the new review said neither of those applies to hormone-like chemicals. â€śAccepting these phenomena should lead to paradigm shifts in toxicological studies, and will likely also have lasting effects on regulatory science,â€ť they wrote. In the report, the scientists are concerned that government has determined “safe” levels for â€śa significant number of endocrine-disrupting compoundsâ€ť that have never been tested at low levels. The authors urged â€śgreatly expanded and generalized safety testing.â€ť “We suggest setting the lowest dose in the experiment below the range of human exposures, if such a dose is known,â€ť they wrote.
For more information on the effects of pesticides on human health, see Beyond Pesticidesâ€™ Pesticide Induced Diseases Database.
Source: Environmental Health News
All unattributed positions and opinions in this piece are those of Beyond Pesticides.