CHICAGO (Chicago Tribune) -- Children living next to driveways or parking lots coated with coal tar are exposed to significantly higher doses of cancer-causing chemicals than those living near untreated asphalt, according to a study that raises new questions about commonly used pavement sealants.

Researchers from Baylor University and the U.S. Geological Survey also found that children living near areas treated with coal-tar-based sealants ingest twice as many polycyclic aromatic hydrocarbons (PAHs) from contaminated dust tracked into their homes as they do from food.

The peer-reviewed study, and other new research documenting how coal-tar sealants emit high levels of troublesome chemicals into the air, comes as several cities in the Midwest, South and East are trying to ban the products' use on playgrounds, parking lots and driveways. Some major retailers have pulled the products from their shelves, but coal-tar sealants remain widely available elsewhere.

"There's been a long-held assumption that diet is the major source of exposure for children," said Peter Van Metre, a USGS scientist who co-authored the studies. "But it turns out that dust ingestion is a more significant pathway."

About 85 million gallons of coal-tar-based sealants are sold in the United States every year, mostly east of the Mississippi River, according to industry estimates. The sealants, promoted as a way to extend the life of asphalt and brighten it every few years with a fresh black sheen, are sprayed by contractors or spread by homeowners.

During the past decade, studies have identified coal-tar sealants as a major source of PAHs, toxic chemicals that can cause cancer and other health problems. Pavement sealants made with coal tar can contain as much as 50 percent PAHs by weight, substantially more than alternatives made with asphalt.

Anne LeHuray, executive director of the Pavement Coatings Technology Council, an industry trade group, said she was reviewing the new findings.

"It appears they have some other agenda here, which is to ban coal-tar-based pavement sealants," she said of the government scientists.

LeHuray and other industry representatives have argued that vehicle exhaust, wood smoke and grilled hamburgers are more significant sources of the toxic chemicals than coal tar.

But the latest USGS research estimates that annual emissions of PAHs from the application of coal-tar-based sealants exceed the amount from vehicle exhaust. Two hours after application, emissions were 30,000 times higher than those from unsealed pavement, one of the new studies found. Parking lots with 3- to 8-year-old sealant released 60 times more PAHs to the air than parking lots without sealant.

The studies are published in the scientific journals Chemosphere, Atmospheric Environment and Environmental Pollution.

(c)2012 the Chicago Tribune Distributed by McClatchy-Tribune News Service.