SEATTLE (AP) - Soccer dad Mike Miller prefers the smooth, cushioned surface of synthetic turf because his 13-year-old daughter can play year-round, including in the long rainy season that closes Seattle's grass fields.

But as Caty Miller and her teammates dribble, pass and shoot, their cleats kick up tiny bits of ground-up tires that are used as filler between the blades of artificial grass.

Those recycled tires have some health experts, activists and parents from Seattle to Chicago to Stamford, Conn., worried that children may be exposed to chemicals by inhaling or swallowing the rubber granules. Some are calling for a moratorium until the issue is more fully studied.

"Rubber tires are made with chemicals that are known carcinogens. The question remains, does that raise the risk for cancer for children? We don't know that," said Dr. Susan Buchanan, associate director of Great Lakes Center for Children's Environmental Health and an assistant professor of public health at the University of Illinois at Chicago.

Artificial turf is often made of fake blades of grass with sand or ground up rubber tires used as fill to offer springy cushion. About 25 million used auto tires are recycled into turf each year, according to Synthetic Turf Council, the Atlanta-based trade group.

Local health agencies say that, based on available information, crumb rubber may contain chemicals that are potentially harmful but that health risks are extremely low or unlikely.

Supporters say the turf encourages increased outdoor play, reduces water and herbicide use and provides an even, predictable surface that's more cushioned than old-style AstroTurf.

"They drain well. They don't get as muddy. The ball bounces a little higher, goes a little faster," Miller said.

But potential health concerns have Connecticut and California conducting their own studies on the health effects of turf. New York City health officials recently commissioned a study to evaluate air quality above synthetic turf and found it didn't show appreciable impacts from contaminants in the crumb rubber.

"The crumb rubber that's used in many fills are safe," said Shira Miller, a spokeswoman for the Synthetic Turf Council.

But Dr. Philip Landrigan, professor and chairman of community and preventive medicine at Mount Sinai School of Medicine in New York, still wants a moratorium until more thorough studies are done.

Some scientific research studies in the U.S. and Europe have assessed potential exposure and health risks for people using turf and concluded that health effects are unlikely.

But Landrigan said he's aware of no studies that has evaluated how the chemicals affect actual children who play on turf field with crumb rubber.

"All those toxins are very available to kids, if kids are playing and running," he said. "All this chemical soup is going to get on their skins and their fingers."

Recycled tires contain metals like zinc, toxic chemicals such as benzene and butadiene and polycyclic aromatic hydrocarbons, which are in exhaust, smoke and soot.

Crumb rubber is also used for playground and track surfaces, but because they're in the form of a mat, there's less concern that it can get into kids, Landrigan said.

Heat emitting from the fields on hot days can also cause heat stress or heat stroke; temperatures have been recorded between 130 and 140 degrees on the fields, Landrigan said.

Last year, the U.S. Consumer Product Safety Commission investigated lead in artificial turf after New Jersey health officials found high lead content in some fields. The CPSC said none of the fields tested at levels that would be harmful to children, but it called for voluntary standards to eliminate lead in future products.

There are about 4,500 fields in use throughout the country.

In Seattle, the city is adding six new synthetic turf fields in the next year after reviewing current research on health or environmental risks.

The fields cost more to install than grass - about $800,000 each - but saves in maintenance costs and reduced herbicide and fertilizer use, said Dewey Potter, a Seattle parks spokeswoman.

Sports boosters say it allows more games to be played in the months when Seattle's trademark rain closes grass fields and pushes sports onto hated dirt and sand fields.

"We love natural grass, but it doesn't work for year-round and really intensive use," said Bill Farmer, a board member with Friends of Athletic Fields, a Seattle group.

The health concerns have become part of a larger debate in the Seattle area and elsewhere over whether the fields are a good idea. Some opponents don't want increased traffic in their neighborhoods, others object to spending taxpayer money. Still simply some prefer natural open space.

"Why have parks if you're going to pave them? They should be grass fields," said Chris Van Dyk, who led an unsuccessful attempt to block artificial turf fields on Bainbridge Island, Wash, just west of Seattle. Van Dyk said he doesn't want his sons playing on it.

In San Francisco last summer, health officials reviewed the available literature and found there wasn't enough evidence of risks from lead, bacteria or crumb rubber to warrant tearing up and replacing existing field. They also said where possible the city should consider alternative products, including turf that uses cork or coconut husks as fill.

On the sidelines of a Seattle scrimmage, soccer mom Beatriz Salgado said her daughter prefers grass because the turf can get too hot during the summer.

"In the summer, you can really smell it. It smells like tar," she said. "I would like to know more about what's in it."

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