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Counterintuitive Toxicity

Increasingly, scientists are finding that they can't predict a poison's low-dose effects

2:07pm, January 16, 2007

For decades, researchers largely assumed that a poison's effects increase as the dose rises and diminish as it falls. However, scientists are increasingly documenting unexpected effects—sometimes disproportionately adverse, sometimes beneficial—at extremely low doses of radiation and toxic chemicals.

Consider the environmentally ubiquitous plastic-softening agent, di-2-ethylhexyl phthalate (DEHP). A German team recently found that in newborn male rats, the lowest DEHP doses tested suppressed the brain activity of an enzyme critical for male development. This was a surprise because higher DEHP doses stimulated that enzyme's action.

Anderson J.M. Andrade and his colleagues at Charité University Medical School in Berlin note that the enzyme's suppressive action would have been missed if they had done what most toxicologists do—project low-dose impacts from high-dose tests. The low dose that suppressed aromatase in the rodents was comparable to expo

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