The study was small, sampling only seven child-care centers in Seattle. Nap mats in all but one of the centers contained flame-retardant chemicals, but replacing old mats slashed those levels.

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Afternoon naps are a time-honored tradition in many child-care centers, as toddlers snuggle up on soft mats to drowse, daydream or fidget.

The possibility that those mats could be exposing kids to toxic chemicals might come as a surprise to most parents and day-care workers. But a new analysis found potentially harmful flame retardants in the majority of mats at some day cares across Seattle.

The study was a small pilot, sampling only seven child-care centers in neighborhoods from the University District and Wallingford, to South Seattle and the Central District. Nap mats in all but one of the centers contained the flame-retardant chemicals.

Estimated exposures to children were generally below existing safety thresholds, though exposures to a few chemicals were higher. The researchers found that replacing older mats with new, greener versions lowered exposures dramatically by reducing chemicals in dust.

“This study shows that, clearly, we can reduce kids’ exposures to these chemicals linked to serious health problems simply by taking them out of the products,” said Erika Schreder, science director of the Seattle-based advocacy group Toxic-free Future and a co-author of the paper published Tuesday in the journal Environmental Pollution.

Public Health – Seattle & King County plans to work with Schreder’s organization and reach out to other child-care centers, including in-home operations, to see how many use older mats and what it would take to replace them, said an agency spokeswoman.

A growing body of research suggests that flame-retardant chemicals can cause a wide range of health problems, from obesity and cancer to hormone disruption, said co-author Amina Salamova, of Indiana University. There’s also little evidence that the chemicals in children’s products are effective in reducing fire danger, she added.

The chemicals have been widely used since the 1970s, promoted in large part by the tobacco and chemical industries. A Chicago Tribune investigation in 2012 found that Dr. David Heimbach, the former director of Harborview Medical Center’s Seattle burn center, fabricated tales of grievously burned children to convince state legislatures to require the use of flame- retardant chemicals.

Most people have traces of the chemicals in their bodies. Levels in children, who are more likely to ingest contaminated dust, are much higher than in adults, the study says.

Several types of flame retardants were phased out starting in 2004, but manufacturers replaced them with a dizzying array of alternatives, some of whose safety is also suspect, Schreder said. Washington’s 2016 Toxic-Free Kids and Families Act banned five flame-retardant chemicals from furniture and children’s products — but many other compounds are still on the market.

“It’s been a bit of a whack-a-mole problem with flame retardants in children’s products,” Schreder said.

It can be difficult for parents or day-care workers to tell whether products have the chemicals. The Child Learning and Care Center in the University District was the sole center in the study with retardant-free mats — but it was only by chance, said executive director Michele Sorenson.

“It was a surprise to me that this was something I would even have to worry about,” she said. “I didn’t make an informed decision.”

The mats at Interlake Child Care & Learning Center contained the chemicals, but director Marna Towle didn’t realize that could be a problem.

“So many things have flame retardants, you don’t think that’s necessarily going to mean it’s bad for you,” she said. “For us to learn that the mats could be actually emitting something harmful was a real eye-opener.”

The U.S. Consumer Product Safety Commission last year urged the public, especially pregnant women and children, to avoid a large class of fire-retardant chemicals, called organohalogens, which includes most of the chemicals found in Seattle day cares. The commission also took the first steps to eventually ban their use in furniture, electronics and children’s products.

Since 2013, when California changed its flammability standards, many companies have been manufacturing retardant-free products, including nap mats. But many older mats are still in use.

In the Seattle study, researchers cut up and analyzed mats and collected dust and air samples in the participating day-care centers, then replaced the older mats and repeated the dust and air sampling three months later.

Though estimated exposures to most of the chemicals were below levels considered unsafe, they don’t include any additional exposures kids encounter at home or elsewhere, Salamova pointed out. Also, there’s so little data on many of the compounds and their health effects that the so-called “safe” levels may not be trustworthy, Salamova cautioned.

“Since we know so little about the toxic effects, we should be careful about any exposures to these chemicals,” she said.

After the old mats were replaced, flame-retardant levels in dust dropped between 42 and 90 percent.

The day-care centers that participated in the study got new nap mats for free. A single, new mat can cost $50 or more, Towle pointed out.

“It’s a pretty big deal for day cares, because they are expensive,” she said.

Schreder advised concerned parents to speak with their day-care providers about the facilities’ nap mats. Older mats are much more likely to contain flame-retardant chemicals than mats purchased after 2013.

Salamova, whose own daughters are now 12 and 14, also recommends that parents check the ventilation and use of pesticides at their kids’ day care, and make sure their children wash their hands frequently.

For Sorenson, at Child Learning and Care Center, the study was a wake-up call that potentially dangerous substances can hide in innocuous products.

“It’s kind of discouraging when you work so hard to give the kids a really super-safe place, then you find out you could possibly be buying toxic things,” she said. “The take-away for me is to be more aware and not always trust what you’re buying.”