Coal Tar

Stormwater runoff is water from rain or melting snow that “runs off” across the land instead of seeping into the ground. This runoff usually flows into the nearest stream, creek, river, lake or ocean. The runoff is not treated in any way. Many cities are encouraging suppliers, buyers and communities to phase out the application of pavement seal coats containing coal tar pitch, in order to reduce the release into our air and water of potentially-harmful chemicals in those seal coats.

Runoff Contaminants
Runoff from all parking lots is contaminated with PAHS (polycyclic aromatic hydrocarbons) from leaking motor oil, tire particles, vehicle exhaust, and atmospheric deposition. PAHs are a group of organic contaminants that form from the incomplete combustion of hydrocarbons, such as coal.

Coal tar, which is primarily used for pavement sealcoating, is a byproduct of the coaking of coal and can contain 50% or more PAHS by weight. This is an issue because PAHs found in seal coats and other combustion-based materials are toxic to mammals (including humans), birds, fish, amphibians, invertebrates, and plants.

Health Risks
Human-health risk from environmental contaminants is often evaluated in terms of exposure pathways. For example, people could potentially be exposed to PAHs in sealcoat through skin contact with abraded particles from parking lots, inhalation of wind-blown particles, and inhalation of fumes that volatilize from sealed parking lots. Some of the chemicals, PAHs, are known to cause cancer in people and fish, and to harm the aquatic food chain.

Studies around the U.S. have shown that PAHs are released from coal tar-based seal coats into the air and homes, workplaces, and shopping centers, and also into ponds, lakes and streams. In addition to the potential health risk of PAHs, there can be substantial costs for cities and private property owners to manage sediment in storm water ponds that is contaminated with PAHs from coal tar-based sealants.

Seal coats are used commercially and by homeowners across the nation. It commonly is applied to parking lots associated with commercial businesses; apartment and condominium complexes; churches and schools; and on residential driveways.

Safer Alternatives
The most common and cheapest alternative to coal tar now on the market is petroleum asphalt-based seal coats. Asphalt seal coats contain PAHs, but at as little at 1/1000th the PAH level of coal tar seal coats. Good asphalt sealcoat emulsions are very affordable, will provide a black appearance for 1-2 years, and can provide less-visible protection for 2-4 years if properly applied.

Other alternatives such as Gilsonite®, acrylic and agricultural oil-based seals contain few or no PAHs, but they tend to be higher-priced and they have less of a performance track record than asphalt seals.

The National Water Quality Assessment study found that concentrations of PAHs were much higher in runoff from parking lots sealed with coal-tar based sealcoat than from all other types of parking-lot surfaces. The average concentration in runoff from coal-tar sealed lots was about 65 times higher than the average concentration in particles washed off parking lots that had not been seal coated.

The average concentration in particles washed off parking lots sealed with asphalt-based sealcoat was about 6 times less than coal-tar based sealcoat, but still 10 times higher than the concentration from unsealed parking lots.

Do your part to help manage the water quality of Mexico’s lakes and streams. Consider the effect of the product you may choose to use for your parking lot or driveway maintenance.