Dose-response Controversy
One major objection to the theory of endocrine disruptors is the dosage effect. There is a large gap between high exposures seen in a laboratory experiment versus the relatively low levels found in the environment. Critics argue that dose-response relationship data suggest that the amounts of the chemicals actually in the environment are too low to cause an effect. A consensus statement by the Learning and Development Disabilities Initiative rebuts this criticism arguing that "The very low-dose effects of endocrine disruptors can not be predicted from high-dose studies, which contradicts the standard 'dose makes the poison' rule of toxicology. Nontraditional dose-response curves are referred to as nonmonotonic dose response curves." Furthermore, endocrine disrupting effects have been noted in animals exposed to environmentally relevant levels of some chemicals. For example, researchers have found that a common flame retardant, PBDE-47, affects the reproductive system and thyroid gland of female rats in doses of the order of those to which humans are exposed.
The dosage objection could also be overcome if low concentrations of different endocrine disruptors were synergistic, which was asserted in a paper by Arnold. This paper was published in Science in June 1996, and was one reason for the passage of the Food Quality Protection Act of 1996. The results could not be confirmed with the same and alternative methodologies, and the original paper was retracted, with Arnold found to have committed scientific misconduct by the United States Office of Research Integrity. Subsequent papers by other authors demonstrated that low concentrations of endocrine disruptors can have synergistic effects in amphibians, but it is not clear that this is an effect mediated through the endocrine system.
The conventional relationship (more exposure equals higher risk) has been challenged by some studying endocrine disruptors. For example, it has been claimed that Tamoxifen and some phthalates have fundamentally different (and harmful) effects on the body at low doses than at high doses.
Read more about this topic: Endocrine Disruptor
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