Our Stolen Futurea book by Theo Colborn, Dianne Dumanoski, and John Peterson Myers
 
 

 

In a report of a panel of experts (big .pdf file), the National Toxicology Program of the US National Institute of Environmental Health Sciences confirmed the existence of impacts of endocrine-disrupting compounds at levels below those of traditional concern.

NTP-NIEHS convened the panel to evaluate whether current testing procedures needed to be altered to reflect emerging data on low-dose effects, beneath those identified by traditional testing as thresholds for concern.

The panel concluded that "that there is 'credible evidence' that some hormone-like chemicals can affect test animals' bodily functions at very low levels – well below the "no effect" levels determined by traditional testing."

The strength of the evidence varies from compound to compound.

For example, the most contentious issue is about low dose effects of bisphenol A. The panel concluded that while several studies provide credible evidence of low-dose effects, other studies find no low-level effect, leaving them unable to reach a conclusion about this compound. [Additional evidence has emerged since the panel met suggesting (1) contaminated food supplies may have led some studies to find no impact; and (2) new independent corroboration of bisphenol A impacts at low levels.]

The panel agreed that the evidence was conclusive for a series of other estrogenic compounds, including estradiol, diethylstilbestrol (DES), methoxychlor, genistein and nonylphenol.

The overall conclusions of the panel were (taken from the reports Executive Summary, emphasis added):

  • Low-dose effects, as defined for this review, were demonstrated in laboratory animals exposed to certain endocrine active agents. The effects are dependent on the compound studied and the endpoint measured. In some cases where low-dose effects have been reported, the findings have not been replicated. The toxicological significance of many of these effects has not been determined.
  • The shape of the dose-response curves for these effects varies with the endpoint and dosing regimen, and may be low-dose linear, threshold-appearing, or non-monotonic.
  • The traditional multigeneration reproduction study protocol has not revealed major reproductive or developmental effects in laboratory animals exposed to endocrine active agents at doses approaching their NOAELs set by the standard testing paradigm. However, few multigenerational studies have been conducted over expanded dose ranges, and critical endpoints such as cancer have not been evaluated in multigenerational studies.
  • The Panel recommended additional research to replicate previously reported key low-dose findings, to characterize target tissue dosimetry during critical periods of development, to identify sensitive molecular markers that would be useful in understanding mechanistic events associated with lowdose effects, and to determine the long-term health consequences of low-dose effects of endocrine active agents.
  • The findings of the Panel indicate that the current testing paradigm used for assessments of reproductive and developmental toxicity should be revisited to see if changes are needed regarding dose selection, animal model selection, age when animals are evaluated, and the endpoints being measured following exposure to endocrine active agents.


 

 

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