(Reuters Health) - In some U.S. cities, at least one in seven kids have unsafe levels of lead in their blood, indicating exposure to a toxic metal that can lead to lifelong physical, mental and behavioral health problems, a recent study suggests.

According to the Centers for Disease Control and Prevention (CDC), a blood lead level equal to or greater than five micrograms per deciliter of lead in blood is considered unsafe for children.

Researchers examined more than 5.2 million blood lead level test results for infants and children under 6 years of age over a six-year period ending in April 2015. They found 3.1 percent of boys and 2.8 percent of girls had blood lead levels exceeding what the CDC considers safe.

In six regions, more than 14 percent of kids had unsafe blood lead levels: Syracuse, Buffalo and Poughkeepsie in New York; Oil City and York in Pennsylvania and Cincinnati, Ohio.

“Many of these localities are old, industrial cities,” said Dr. Harvey Kaufman, senior medical director at Quest Diagnostics in St. Louis, Missouri, and an author of the study.

“There are many reasons why these localities could have the highest percentage of children who test with elevated blood lead levels, including more old housing stock, higher poverty rates and possibly fewer resources for remediation of older housing,” Kaufman added by email.

Even though lead was phased out of paint in the 1970s, many children in communities with older housing stock are still at risk for lead exposure because these buildings haven’t been inspected for lead or because the metal hasn’t been removed where it’s found, said Dr. Leonardo Trasande, a pediatrics researcher at New York University School of Medicine who wasn’t involved in the study.

“Insofar as old homes have not been evaluated or remediated, levels of lead in children’s blood are likely to be higher due to water ingestion, dust inhalation and contact with soil,” Trasande said by email.

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The study also identified five states with the largest proportion of tests indicating high blood lead levels: Minnesota (10.3 percent), Pennsylvania (7.8 percent), Kentucky (7.1 percent), Ohio (7.0 percent) and Connecticut (6.7 percent). California and Florida had the lowest rates, with 1.4 percent and 1.1 percent, respectively.

Over the course of the study, the proportion of children with high blood lead levels nationwide dropped slightly, from about 3.7 percent to 2.6 percent.

Even blood lead levels lower than the CDC threshold for unsafe exposure to the toxic chemical may put children at risk for reduced intellectual and academic abilities and attention deficit hyperactivity disorder, according to the American Academy of Pediatrics (AAP).

The AAP this week issued new lead screening recommendations that encourage doctors to step up testing efforts for children who live in neighborhoods with many homes built before 1960, when lead paint use was widespread. At the same time, the AAP called for strict standards to limit how much lead is allowed in air, water, soil, indoor dust and consumer products (bit.ly/28KV3rm).

“We must not treat children as ‘canaries in the coal mine’ where they are exposed first and then tested to see if they have been poisoned,” said Dr. Jennifer Lowry, chair of the AAP’s council on environmental health.

“Parents, healthcare providers and policy makers must ensure that children are protected before they live in a home with lead hazards,” Lowry added by email. “That is hardest on parents where they don’t know that lead hazards exist or don’t have the means to do this.”

One limitation of the study is the potential for children to be tested more frequently in communities where people are aware of the risk for lead exposure, the authors note in the Journal of Pediatrics. Some tests included in the study might also have been done because doctors suspected lead poisoning or because parents wanted to confirm initial screening results, the authors also point out.

Even so, the findings point to the need for parents to be vigilant about avoiding housing with lead paint and for pediatricians to screen children at risk for exposure, Kaufman said.

“The health impacts of lead poisoning on IQ, behavior, and brain development are irreversible, but lead exposure is preventable,” Kaufman said.