From: Andy Soos, ENN
Published January 13, 2010 12:16 PM

Parking Lot Problems

Coal tar based seal coat, which is the black, shiny substance sprayed or painted on many parking lots, driveways, and playgrounds, has been linked to higher concentrations of the contaminants polycyclic aromatic hydrocarbons (PAHs) in house dust. Apartments with adjacent parking lots treated with the coal-tar based seal coat have house dust with much higher concentrations of PAHs than apartments next to other types of parking lots according to new research released today on-line by Environmental Science and Technology (ES&T).

The main purpose of using a quality sealer is that the sealer coats the asphalt surface protecting it from harmful ultra violet as well as road salts and engine oils which dissolve the asphalt and create soft spots. If untreated areas are ignored, deterioration will occur and you will end up spending much more money trying to patch and repair the asphalt than if you properly maintain it


Coal tar is a byproduct of the coking of coal, and can contain 50 percent or more PAHs by weight. PAHs are an environmental health issue because several are probable human carcinogens and they are toxic to fish and other aquatic life.

Small particles of seal coat, which contains high concentrations of PAHs, likely are tracked indoors by residents after they walk across the parking lot. The study found that apartments adjacent to coal tar seal coated parking lots contained concentrations of PAHs in house dust with that were 25 times higher than in house dust from apartments with concrete, asphalt, or asphalt-based seal coat parking lot surfaces. The study also found that dust directly on the coal tar seal coated parking lots had PAH concentrations that were 530 times higher than in dust on the parking lots without coal tar seal coat.

"These findings represent a breakthrough in our understanding of one of the important sources of these contaminants in house dust and how these contaminants can move from outdoors to indoors. The study provides evidence that will be potentially useful for policy makers," said Bob Joseph, Director of the USGS Texas Water Science Center.

Seal coat products are commonly applied to parking lots of commercial businesses (including strip malls and shopping centers), parking lots and residential driveways. The seal coat wears off of the surface relatively rapidly, especially in areas of high traffic, and manufacturers recommend resealing every three to five years.

There are three types of pavement sealer being produced in the industry today, they are: asphalt based, coal tar and acrylic.

Asphalt based sealers are made using asphalt emulsion which is asphalt cement emulsified with water using an emulsifier to homogenize and stabilize the emulsion. Asphalt cement is the binder used in asphalt pavement,. Therefore, when you use an asphalt based sealer you are using the same product that was used to hold the driveway aggregate in place to begin with and you are adding back asphalt particles to the pavement which acts like a rejuvenator. Asphalt Based Driveway Sealer have no PAH's.

Acrylic sealers are the least widely used pavement sealers in existence today. These sealers add nothing back to the asphalt pavement and while they are not carcinogenic, they are known to cause other health discomforts including dizziness, weakness, nausea, headaches, and even gastrointestinal problems. These sealers do however have a few good characteristics including their resistance to gas and oil.

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