The United States began phasing out the use of tetraethyllead in gasoline in the mid 1970s (though it's still used in aviation and race car fuel). The pollution from TEL-enhanced gas, however, continues to linger in the soil, especially in cities, where concentrations of tailpipe emissions were higher. A recent study of New York City chickens found that lead from the soil was showing up in detectable levels in the chickens' eggs. The dose is low (though you probably don't want young children eating lots of those eggs), but it's a great example of how the effects of pollution don't vanish just because the pollution ends.

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