Not only are we potentially dragging toxic compounds into our homes, but children are also playing around these harmful chemicals.
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A widely used type of asphalt sealant derived from coal tar may be making its way into the house dust of homes, according to new research. Young children may actually be playing on coal-tar-sealed driveways and playgrounds, potentially raising their exposure to harmful chemicals.
The findings, presented at a meeting of the Society of Environmental Toxicology and Chemistry, concern a group of compounds called polycyclic aromatic hydrocarbons, or PAHs.
Toxic compounds appear in the sealants, which are used to create an even, deep black pavement surface. And coal tar contains a high proportion of PAHs, with levels about 1,000 times higher than in the alternative, asphalt-based sealant.
Past studies have demonstrated the harmful effects of PAHs on the skin and in the immune systems of animals that had short- and long-term exposure to these compounds. However, similar side effects have not yet been found in humans, although recent research has linked lower IQ in homes with higher exposure to PAHs.
Researchers from the city of Austin, Texas, were the first to realize that coal-tar-based asphalt sealant might be contaminating urban waterways with PAHs in 2003 when they found extremely high levels of the compounds in creeks downstream of parking lots in the city.
Follow-up research by U.S. Geological Survey researchers Peter Van Metre, Barbara Mahler and others showed that PAH levels were 65 times higher in dust from coal-tar-sealed parking lots than dust on unsealed lots.
In the new study, Van Metre and his team analyzed house dust from the floors of 23 ground-floor apartments, half of which had coal-tar-sealed parking lots and the other half of which did not.
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PAH levels were 25 times higher on average in dust from apartments with coal-tar-sealed lots.
"These numbers are at the high range for what's been found in indoor dust. ...We think this might account for a lot of these really high numbers," Van Metre added.
Van Metre and colleagues determined earlier that coal-tar-based sealant was more commonly used east of the Continental Divide. In one Chicago suburb that the team studied, 90 percent of the driveways were coated.
"The values in house dust are of big concern," said Mateo Scoggins of the City of Austin, who has worked with the USGS researchers on some of these studies.
"No one has really taken these values that they are finding, whether they're in scrapings from a parking lot, dust from a parking lot or dust from a house, and put any sort of risk to it," Scoggins added. "The values they are finding are high, but we still don't know if they are of significant concern.".
The city of Austin banned the use of coal-tar-based sealants in 2006, which may have saved the application of as much as 2 million gallons of sealant in the city since then, officials say.
Other communities have followed Austin's lead in attempting to ban or limit the use of coal-tar-based sealant.
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