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.