At least 17 D.C. public school playgrounds were found to contain elevated traces of lead, and six had to be shut down over the summer, according to a city-commissioned study released this month.

The Department of General Services — which maintains playgrounds — hired an outside group to test them this summer. The report represents the city’s most comprehensive testing yet for potential lead exposure on playgrounds. The efforts came after a parent-advocacy group earlier in the year hired a company to test the playground at Janney Elementary School in Northwest. That study, the group said, found elevated lead levels.

General Services says it has thoroughly cleaned the playgrounds with specialized vacuums and power washers and that they are safe for children.

“I don’t think there is reason for any panic,” said Keith A. Anderson, the agency’s director.

The city has no record of a child who has tested positive for elevated lead levels as a result of contact with the playgrounds, according to Anderson.

Investigators focused on the 79 D.C. schools with “Poured-in-Place” playground surfaces — a rubber surface that often consists of synthetic materials popular in parks and playgrounds for their bright colors and ability to pad a child’s fall.

Anderson said that tests are ongoing, but that officials do not believe there are elevated lead levels in the core of the rubber material. Instead, Anderson said, much of the lead contamination came from outside sources, including dust from nearby construction sites and paint chips from surrounding buildings.

As a result, he said, the city will more frequently wash the District’s entire playground stock. Anderson also stressed that parents should ensure that children wash their hands after using the playgrounds.

According to the U.S. Environmental Protection Agency, lead in play areas cannot exceed more than 400 parts per million, though the American Academy of Pediatrics says children should not be exposed to any levels of lead.

D.C. investigators conducted four types of tests on the surface and core of the playground materials. The 17 playgrounds exceeded 400 parts per million on at least one test. Lead exposure can cause serious damage to the brain, nervous system, kidneys and red blood cells, particularly in babies and children.

“We are being proactive, and we are taking it seriously,” Anderson said. “The bottom line is that lead exposure is a difficult legacy for most urban environments. And it is one that will continue to be a challenge as we work to remedy this newly identified source on these playgrounds.”

The Washington Post reported last year that between March 2013 and March 2018, at least 41 D.C. families discovered that their homes, subsidized by housing vouchers and approved by inspectors, contained lead contaminants.

Between 2001 and 2004, the District’s water system was found to have alarming levels of lead when the Washington Aqueduct, which supplies city water, changed its treatment chemical from chlorine to chloramine. The city came under fire for its delay in informing residents about the water supply.

A coalition of parents, organized under a group called Safe Healthy Playing Fields Coalition, has pushed since 2017 for city officials to find alternatives to synthetic turf fields and rubber playgrounds, disputing claims that the material is not harmful.

Evan Yeats, a parent of two children at Thomson Elementary School downtown — one of the six schools that had a play area closed because of elevated lead levels — said he is concerned that the city deemed the playgrounds safe while testing is ongoing. He said the city should also address the lead-contaminated debris that drifts onto playgrounds.

“They reopened it without actually resolving the issue,” said Yeats, an advisory neighborhood commissioner in the Takoma neighborhood. “So no, I don’t feel 100 percent safe.”

Nicholas Arisco, a doctoral student at the Harvard University School of Public Health, co-wrote a study that examined lead levels in four popular playground materials in Boston. Boston has historically unsafe levels of lead in its soil, and the study found that soil had the highest levels of lead in the city. Rubber had the second highest levels, and mulch had the lowest levels.

“Exposure is not going to stop unless lead abatement occurs,” Arisco said.