Coal-tar-based sealcoat being applied. Photo by Peter Van Metre.
We all have memories as children of being told to wipe our feet before coming in. Well, it might be more important than ever to follow that advice with a new study about what we may be tracking in.
Coal-tar-based sealcoal - that black, shiny stuff sprayed or painted on many parking lots, driveways, and playgrounds - has been linked to elevated concentrations of the contaminants polycyclic aromatic hydrocarbons (PAHs) in house dust.
Houses and apartments next to areas treated with this type of sealcoat contained dust with much higher concentrations of PAHs than those next to areas treated with other types sealcoats, according to the new study published by Environmental Science and Technology.
Asphalt-based sealcoat being applied. Photo by Guardtop.In contrast, “asphalt-based products have concentrations of PAHs that are 1,000 times less than what are in coal-tar-based products,” said Dr. Barbara Mahler, one of the authors of the study and a research hydrologist with the water resources division of the U.S. Geological Survey.
The concern is that “PAHs are highly potent carcinogens than can produce tumors in some organism at even a single dose. Mammals can absorb PAHs by inhalation, dermal contact or ingestion,” according to the U.S. Environmental Protection Agency.
“Fish exposed to PAH contamination have exhibited fin erosion, liver abnormalities, cataracts, and immune system impairments leading to increased susceptibility to disease,” adds the agency.
Working to assess water quality across the nation, “what caught our attention was there was one group of contaminants that was increasing, and that was the PAHs, which were primarily increasing in urban lakes in the U.S.,” said Mahler.
She went on to say that, “What we also found was that the PAH concentrations in the dust on these parking lots were extremely high, much higher than we had seen from any other PAH sources, including things like motor oil.”
The study found, “The concentration of Total-PAH measured in settled house dust from apartments with coal-tar-based sealcoated parking lots was significantly higher than that measured in the settled house dust from apartments with non-coal-tar-based sealcoated parking lots by a factor of 25. The difference greatly exceeds the sampling variability and analytical uncertainty.”
On a regional note, Mahler said, “More interestingly, coal-tar-based sealcoat is primarily used east of the Continental Divide, in the Midwest, Northeast, Southeast, but west of the divide, an asphalt-based sealcoat is used.”
Great Continental Divide. Stock Photo.
This study was conducted in Austin, Texas, which as of January 1, 2006, banned the use and sale of pavement sealants containing coal-tar within the city’s planning jurisdiction, with the exception that the sealant may be sold if the intended application area is outside the city. With regard to economic impact, the city’s justification was that effects “to the industry are mitigated by the availability of a less toxic alternative, asphalt-based sealants.”
Mahler said, “Here in the city of Austin, there are a lot of folks that have started up businesses to actually get sealcoat off, and then another possibility would be to put another layer of a different type of product on the sealcoat that doesn’t contain PAH.”
For those that aren’t in a position to do these things, Mahler suggested that, “using a doormat to wipe your feet will certainly go a long way to decreasing the particles that are being tracked in from the outdoors. Also, obviously taking your shoes off would prevent you from tracking particles indoors. In fact, that would decrease the general amount of particles that are in your residence.”
Beyond Austin, Danes County, Wis., and Washington, D.C. have also banned the use of coal-tar-based sealcoat in their jurisdictions, while asphalt-based sealcoat may still be used. Recent legislation in Minnesota bans the purchase of coal-tar-based sealcoat products by state agencies by July 1, 2010.
Recently, two national home improvement retailers - Lowe’s and Home Depot - took coal-tar-based sealcoat off their shelves.
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