Blacktop sealant from driveways and parking lots may be washing off into nearby waterways as hazardous waste, according to a recent broadcast on Minnesota Public Radio.

The main chemicals of concern in blacktop sealants are polycyclic aromatic hydrocarbons, or PAHs. These potentially cancer-causing chemicals, which are formed during combustion, can also be found in grilled meat. Yum!

According to the report, PAHs are turning up in local waterways due to an effort by environmental regulators to keep groundwater cleaner by damming up runoff from roadways and parking lots and redirecting it into stormwater retention ponds. The problem is the ponds were only meant to grab common agricultural chemicals like fertilizer, not PAHs.

“Probably it's only recently that we started to get a little concerned about everything else that might be going along with the typical nitrogen and phosphorus that we would expect to be in the particles, and the sand and grit that we would expect to be coming off the roads,” said Dale Thompson, who runs the Minnesota Pollution Control Agency's Municipal Stormwater Unit. “We started to see some other things showing up.”

The PAH is likely coming from sealant made from coal tar, a waste material that's useful for making products like shampoos that treat itchy, flaky scalps and ointments that help clear up eczema, psoriasis and other skin disorders, according to the Mayo Clinic.

Of course, coal tar is also used in blacktop sealant to help protect asphalt from the elements like rain and sun, but it doesn't always stay put. Eventually, it makes its way into nearby waterways.

According to this handout by the Minnesota Pollution Control Agency, PAHs cause tumors in some fish, disrupts the reproduction of aquatic organisms and causes some water-bottom species to avoid sediment altogether.

In addition, PAHs can also pose some health risks to humans.

“There [are] different kinds of PAHs that we're looking at,” explained Judy Crane, a water quality scientist at the Minnesota Pollution Control Agency, to the Michigan radio station. “We're looking at metals, and we're looking at some endocrine-disrupting compounds with octylphenols, nonylphenols and nonylphenol ethoxylates. There's like this whole big list.”

But Minnesota’s not the only state taking a hard look at the sealant’s environmental effects. According to the report, coal tar sealant has been under scrutiny from many governmental organizations over the past decade.

As a result,  some states have banned coal tar sealant, while others are trying to figure out how to clean it out of waterways and store it in landfills, at a potential cost of hundreds of millions of dollars to taxpayers.

Lowe’s and Home Depot have even stopped selling coal tar sealant as a switch to cheaper coatings takes hold.

As far as Minnesota is concerned, the state’s not taking any chances. It plans to stop using coal tar on roads next summer, though there’s no word yet on what will be taking its place.

In the meantime, the Minnesota Pollution Control Agency recommends that consumers consider asphalt-based sealcoat over the coal-tar based variety as the latter can contain up to 1,000 times more PAHs. 

Blacktop sealant raises concerns
Hazardous chemicals travel from parking lots and driveways into nearby ponds and streams.