For the first time, the Centers for Disease Control and Prevention has taken blood samples from a cross-section of Americans to look for a number of toxic substances. These substances show up in pollutants from industry and in products like cigarettes. NPR's John Nielsen reports some good news; chemicals from second-hand smoke seems to be appearing in blood less frequently. There's worrisome news too; there are lots of other chemicals in our blood about which we know very little.
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