A study released by U.S. health officials yesterday showed for the first time that most Americans carry detectable levels of plastics, pesticides, and heavy metals in their blood and urine. The study by the U.S. Centers for Disease Control and Prevention measured the presence of 27 chemicals in humans and found levels in the average person that were far below those where problems with the toxics typically occur. Previously, researchers had only been able to measure the levels of many of these chemicals in air, water, and food. Levels of mercury were found to be lower than expected in children and higher among women of child-bearing age, though still below federal standards.