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By Eddy Ball, NIEHS
The Duke University Integrated Toxicology and Environmental Health Program held its annual fall symposium Oct. 24 in the Searle Center Lecture Hall.
Speakers at the symposium shared their latest findings involving a new paradigm of nonmonotonic dose response (NMDR) involved in low-dose exposures to hormones and endocrine-disrupting chemicals. The paradigm, which remains controversial, is counterintuitive for classical toxicologists, who point to the contention by Paracelsus, “The dose makes the poison,” as a guiding principle.
Supporters of the nonmonotonic paradigm argue that exposure to endocrine-disrupting chemicals at low doses can have significant effects that are not seen at higher dose levels. Advocates point to mechanisms unique to the endocrine system, such as receptor saturation and feedback inhibition, that blunt the effects of higher doses.
“Interpretation of these new [low-dose] results is challenging, particularly within regulatory landscapes and risk assessment frameworks that operate under the assumption of a linear relationship between exposure dose and adverse effect,” said symposium chair Heather Stapleton, Ph.D., of Duke University, as she opened the meeting.
Stapleton introduced a program of researchers supported by NIEHS and the U.S. Environmental Protection Agency (EPA), who discussed their findings against a backdrop of two important documents — a draft state-of-the-science paper written by EPA in June 2013 and the external peer review of that paper published by the National Research Council (NRC) earlier this year…..