Are some chemicals more dangerous at low doses?

Scientific American Blog: "The basic premise of safety testing for chemicals is that anything can kill you in high enough doses (even too much water too fast can be lethal). The goal is to find safe levels that cause no harm. But new research suggests that some chemicals may be more dangerous than previously believed at low levels when acting in concert with other chemicals.

'Some chemicals may act in an additive fashion,' Linda Birnbaum said this week at a conference held at the Columbia Center for Children's Environmental Health at Columbia University. 'When we look one compound at a time, we may miss the boat.'"

For example, bisphenol-A (BPA), a primary component of some plastics, reacts with cells in the same way as the female hormone estrogen and could be acting synergistically with other pseudoestrogens in the bloodstream to produce heart disease, diabetes or liver failure. Such effects have been observed in animal studies in the lab as well as in frogs in the field for chemicals ranging from the phthalates (used to help perfumes scent linger and make plastics soft) to ubiquitous herbicides like atrazine, linked to malformation in frogs.