A closer look at lead and lead poisoning.

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The crisis in Flint, Mich., over lead in the city’s water supply has many focusing on the long-term effects of lead exposure for children. Lead exposure in childhood can have lifelong consequences. The Centers for Disease Control and Prevention (CDC) emphasizes that preventing exposure is critical, but so are prompt efforts to mitigate lead’s effects.

Here are some common questions about lead and lead poisoning.

Q: How are people exposed to lead?

A: In 1978, lead was banned in paint and other consumer goods made and sold in the United States. But lead paint in old buildings remains one of the most common sources of lead exposure for children and adults, often from the dust that may remain even after surfaces have been stripped or painted over.

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Other sources include:

• Soil contaminated with lead or food grown in it

• Lead water pipes or those soldered with lead, which can leach into the water supply

• Some canned goods, if the cans are soldered with lead

• Paint on some imported toys

• Some jewelry

Q: What are the symptoms of lead exposure?

A: Low levels of lead exposure usually have no obvious or immediate symptoms, meaning it can go undetected. But over time, even low levels of lead in blood can have profound effects on the brain and nervous system. Lower intelligence, difficulty in paying attention and with fine motor skills, and lower academic achievement have all been connected to elevated lead levels. Some studies have also linked lead exposure to violent behavior, and higher crime rates that can span at least two generations.

Q: Is there a treatment for lead poisoning?

A: There is no way of reversing damage done by lead poisoning, which is why pediatricians emphasize prevention. But a diet high in calcium, iron and vitamin C can help the body absorb less lead. And people with extreme lead poisoning can undergo chelation therapy, which involves injecting chemicals into the body that bind with lead so that it is excreted in urine. But research has found that chelation therapy cannot reverse damage already done to the brain or nervous system.

Q: What constitutes a dangerous level of lead?

A: The CDC uses a reference level of 5 micrograms per deciliter to identify children with blood lead levels that are elevated. Before 2012, children were considered to have a blood lead level “of concern” if a test result indicated 10 or more micrograms per deciliter. Experts now say no amount of lead in the blood is safe, and even low levels of exposure can harm cognitive function and have other adverse effects. The CDC recommends chelation therapy when a child’s blood lead level exceeds 45 micrograms per deciliter.

Q: How can I tell if my children or I have been exposed to lead?

A: Doctors recommend that children should be checked for lead with a blood test at age 1 and 2. But anyone at risk of exposure should be tested, including infants. Test results may not reflect the true extent of exposure, though, because lead does not linger in the blood for long before being absorbed by the bones and other organs.

Q: Aside From Flint, where else have people been exposed to lead on this scale?

A: Cities with an industrial past, including Baltimore, Cincinnati and Chicago, have long histories of exposure to lead in the air, soil and water, an environmental legacy of decades of manufacturing.

State testing found that 65,000 children in Baltimore had dangerously high blood lead levels between 1993 and 2013.

In the past 20 years, the overall rate of lead poisoning in Chicago has dropped significantly. But a study this year found that lead exposure in nearly 60,000 children in Chicago had been linked to lower, or failing, reading and math scores in the Chicago Public Schools.

Marc Edwards, a Virginia Tech professor who was instrumental in exposing the problems in Flint, was able to document the presence of high levels of lead in blood samples taken from children in Washington, D.C., between 2000 and 2003, which he linked to partly contaminated drinking water. A study in 2013 by Edwards found that Washington, D.C., women suffered from an abnormally high rate of late-term miscarriages and spontaneous abortions during that same time period.

A paper Edwards wrote in 2009 ran counter to a report by the Environmental Protection Agency in 2004 that deemed Washington, D.C.’s water safe to drink.