New Environmental Threat: Parking Lots
24 June 2005
Research done by the USGS National Water-Quality Assessment (NAWQA) Program and the City of Austin has determined that parking lot sealcoat—a previously unidentified source of urban polycyclic aromatic hydrocarbons (PAHs)—may be the major source of PAH concentrations in urban water bodies in the United States.
Particles in runoff from parking lots with coal-tar emulsion sealcoat had mean concentrations of PAHs of 3,500 mg/kg, 65 times higher than the mean concentration from unsealed asphalt and cement lots. Contaminant yields projected to the watershed scale indicate that runoff from sealed parking lots could account for the majority of stream PAH loads.
PAH concentrations have been increasing over the past 30-35 years in many urban and suburban lakes across the United States.
Polycyclic aromatic hydrocarbons are a group of organic contaminants that form from the incomplete combustion of hydrocarbons, such as coal. Coal tar is a byproduct of the coking of coal, and can contain 50% or more PAHs by weight.
Sealcoat is a black liquid that is sprayed or painted on asphalt pavement in an effort to protect and beautify the asphalt. Most sealcoat products are coal-tar or asphalt-based. Many coal-tar sealcoat products contain as much as 30% coal tar by weight.
Small particles of sealcoat flake off as they are abraded by vehicle tires, and can wash into urban streams with rain and runoff. Sealcoat “wear and tear” is visible in high traffic areas within a few months after application, and sealcoat manufacturers recommend reapplication every 2 to 3 years.
According to the EPA, PAHs are highly potent carcinogens that can produce tumors in some organisms at even single doses. Their effects are wide-ranging within an organism and have been found in many types of organisms, including non-human mammals, birds, invertebrates, plants, amphibians, fish, and humans.
In aquatic systems, PAHs tend towards increased toxicity with increased molecular weight. Although the rate of uptake from the environment is variable among species, bioaccumulation tends to be rapid.
Bioaccumulation refers to the increase in concentration of a chemical in a biological organism over time, compared to the chemical’s concentration in the environment.
In the past, sources of PAHs in urban watersheds have been thought to be dominated by leaking motor oil, tire wear, vehicular exhaust and atmospheric deposition.
Although both unsealed and sealed parking lots receive PAHs from those same urban sources—tire particles, leaking motor oil, vehicle exhaust, and atmospheric deposition—the average yield of PAHs from sealed parking lots is 50 times greater than that from unsealed lots.
Estimates from the USGS study indicate that total loads of PAHs coming from parking lots in the studied watersheds would be reduced to about one-tenth of their current loads if all of the parking lots were unsealed.
The findings are scheduled to be published in the Aug. 1, 2005 issue of Environmental Science & Technology (ES&T), a journal of the American Chemical Society.
Resources:
Article Abstract: “Parking Lot Sealcoat: An Unrecognized Source of Urban Polycyclic Aromatic Hydrocarbons”
USGS FAQ on Sealers
EPA Toxicity profile on PAHs
Read a great piece by Paul Stamets about using mushrooms to break down toxins in the soil...compelling. While PAHs are a different compound than the one mentioned in the following linked article, Paul Stamets is working on adapting mushroom strains to consume different toxins....seems quite amazing...so maybe this type of work can provide a fix to the ridiculous practices of painting parking lots for pathetic cosmetic purposes.
URL: http://www.fungi.com/mycotech/mycova.html
Cheers,
Neal
Posted by: neal skapura | 24 June 2005 at 05:32 PM
Its not cosmetic no matter what these yutzes say its to seal the thing so water doesnt seep under and cause potholes. Saves a ton of money.
Posted by: wintermane | 24 June 2005 at 07:44 PM
In areas where it doesn't snow, why not use something closer to the "hybrid" permeable paver-grass lots / paver-gravel lots? They allow drainage through the lot instead of forcing all of it into a drain, thereby reducing erosion, concentrated pollution, and the like.
Sure, it causes trouble if you have to plow it, but in the deep south and the deserts out west, it seems like a way to reduce the impact of parking lots...
Posted by: stomv | 27 June 2005 at 11:10 AM