While the recycling numbers at the bottom of plastic items "are not meant to provide health information or risks, " Dr. Halden says, they can sometimes provide clues to the chemicals in them.

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Walk into a market in a depressed neighborhood, where the average income is low, most dwellings are rented, and the demographics feature higher numbers of minorities, and prices for basic items are often higher than they are at a massive supermarket in a thriving, mostly-white suburban neighborhood.

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