The substance is coal tar sealant, a waste product of steel manufacturing that is used to protect pavement and asphalt against cracking and water damage, and to impart a nice dark sheen. It is applied most heavily east of the Rockies but is used in all 50 states.
But scientists with the U.S. Geological Survey say the sealant — one of two types commonly used in the U.S. — doesn’t stay put. It slowly wears off and is tracked into homes on the shoes of residents.
Coal tar is known to cause cancer in humans. That finding dates to the 1770s, when chimney sweeps in London were found to have high levels of scrotal cancer. Late the next century, it was associated with skin cancers among creosote workers. PAHs themselves are listed by the U.S. Environmental Protection Agency as a probable human carcinogen, based on laboratory studies in which they caused cancer in animals.
Emerging evidence also suggests that babies exposed to PAHs while in the womb may be more prone to asthma and other ailments, and may have lowered IQs.
The new U.S.G.S. study compared house dust from 23 ground-floor apartments in Austin — 11 with coal tar-sealed parking lots and 12 coated with other substances, or not sealed at all. The study found that dust in the apartments next to the coal-tar-sealed lots had PAH pollution levels 25 times higher, on average, than the other lots.
More than half the apartments with the coal tar-sealed lots contained dust with levels of PAHs that would increase the risk of cancer if ingested by preschoolers, the researchers said. They came to this conclusion by comparing their results to a 2008 study that estimated those risks based on lab tests on animals. The increased risk means one additional child in 10,000 would develop cancer if exposed to that level of toxins over a lifetime.
Although adults are at risk from toxic pollutants in house dust, young children are especially vulnerable, studies have shown. That’s because they have a higher metabolic rate, they get a bigger dose per pound of body weight, their organs are still developing and they play on or near floors where carpets concentrate and retain toxics. Stanford University researchers have recorded children putting their hands on contaminated surfaces, such as floors, and then into their mouths up to 60 times an hour.
Components of coal tar escape parking lots and driveways — not from most public roads — and get into the environment, causing stunted growth in creatures that live in streams, scientists have shown. Research also reveals that the chemicals in coal tar kill tadpoles, cause tumors on fish and eliminate whole species of tiny aquatic creatures near the base of the food chain.
One congressman — Rep. Lloyd Doggett, D-Texas — is calling for a nationwide ban of the coal tar pavement sealants, which are applied by big contractors as well as operators with little more than a truck and a spray tank.
Not only was the toxic house dust found in apartment units surrounded by paved parking lots, but USGS researchers also measured contamination in dust from apartment house parking lots and the driveways of a few single-family homes. The most dangerous coal tar component — a PAH chemical called benzo[a]pyrene – was found in driveway dust at two suburban single family homes at thousands of times the level that would trigger a cleanup at a toxic-waste site.
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