In a motion filed in federal district court, the Environmental Working Group and Women’s Voices for the Earth allege that the Food and Drug Administration has failed to act on dangerous hair straighteners that contain unsafe levels of formaldehyde and pose a significant health hazard to consumers and salon workers.   The July 28 motion is part of the groups' lawsuit against the FDA for its failure to act on a six-year-old petition requesting an investigation into hair smoothing treatments...