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

 

Why endocrine disruption challenges
current approaches to regulation of chemicals.

Four of the most troubling aspects of endocrine disruption are that

  • some effects are demonstrable at very low exposures;
  • dose-response curves do not necessarily fit the classic monotonic assumption fundamental to regulatory toxicology;
  • under some (but not unusual) circumstances, there will be no threshold level below which there is no effect, and
  • contaminants exposures take place in mixtures and these mixtures can interact additively, synergistically or not at all.

These four aspects of endocrine disruption challenge fundamental elements of how risk assessment is currently practiced in the United States (and most other countries).  They mean that the current protective structure used to protect people from contaminants in the United States are fundamentally flawed.

The levels of contamination known to cause effects are dramatically lower than current testing procedures examine.  New data examining hormonal effects of bisphenol A, for example, suggest federal tolerances should be at least 25,000 times lower than current approaches would determine.
Endocrine disrupting chemicals violate a basic assumption of toxicology and modern risk assessment.  For classic toxicants, "the dose makes the poison."  As the dose increases so too does the effect. Dose - response is understood as a linear relationship. For some endocrine disrupting chemicals, however, effects may disappear at higher levels, or become different qualitatively, and may appear at levels below the no observable adverse effect level, or NOAEL. This means that high dose testing, the standard procedure of risk assessment, cannot reveal the health risks posed by endocrine disrupters.  And that means that most toxicological tests done for most regulatory decisions must be repeated at environmentally-relevant (i.e., much lower) levels. In the meantime, this means the US EPA, FDA, and industry are utterly lacking in scientific guidance for regulatory decisions about endocrine disrupters.

Traditional toxicology often assumes that there is some level of exposure, a threshold, beneath which small amounts of a contaminant have no effect. New research has demonstrated that endocrine disrupting compounds violate this assumption, that there is literally no threshold of effect for an endocrine disrupting compound when it is added to a hormone system that is already active. The crucial point is that traditional toxicants are thought to work by starting a process (or stopping one) by overwhelming the body's defense system. Up to some level of contamination, the body can defend itself against chemical assaults. Endocrine disrupting chemicals, in contrast, are adding to or subtracting from chemical signals that are directing processes already underway.

No one is exposed to just one chemical.  Our exposures come in mixtures whose compositions depend upon our life style, where we live, our age and many other factors.  Most research on the health impacts of contamination tests compounds one chemical at a time and thus are extreme simplifications of the real world.   Results emerging from research labs that test the combined effects of different chemicals are revealing complex interactions... sometimes additive, sometimes synergistic, and sometimes a canceling effect.  Even these experiments, the most complicated of which rarely involve more than a few chemicals simultaneously, pale in comparison with the uncontrolled "experiments" that are taking place in humans and wildlife today; as typical exposures involve several hundred chemicals simultaneously.

 

 

 

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