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(NECN/NBC News: Monica Robbins) - During the summer, Patricia Barley's kids are outside for hours on end.
Concerned mother Patrica Barley said, "My children spend a lot of time on their driveway."
It turns out that it could pose a threat to their health.
"I had no idea," said Barley.
Asphalt driveways like the Barley's are common, and a common type of sealant used to maintain pavement contains coal tar pitch which is considered a human carcinogen. You'll know it from the smell.
Michael Pemberton, owner of Unique Paving Materials said, "There's a very strong vapor that comes off the coal tar."
Pemberton used to apply coal tar sealants.
"When you put coal tar down, it can really burn you if you get it on your skin," said Pemberton.
Studies suggest coal tar sealant is a major source of suspected carcinogens, polycyclic aromatic hydrocarbon, or PAH.
Exposure occurs when, over time sealants crumble into dust and can be inhaled or washed into water ways.
One study estimates the lifetime risk for people who live adjacent to coal tar sealant is 38 times higher than someone who doesn't.
Is Pemberton worried about how much exposure he’s had to it?
"Yeah, I'd say based on some of the studies I've read and everything, I've put a lot of tar sealer down when I was a young man," said Pemberton.
Unique Paving stopped using the sealant two decades ago and developed what they claim is a superior alternative for customers.
"It's asphalt-based and that has no tar in it."
Two states have banned the use of coal tar sealants altogether and across the country, more individual communities are banning the product or restricting its use.
Home Depot, Lowes and Ace Hardware no longer sell coal tar sealants.
"Our thought was, well, there's a product out there that pretty much everyone agrees does not have environmental impacts, so let’s give it a shot and see how it goes," said Pemberton.
Consumers do have a choice.
"They should ask their contractor is what they're using is tar based or asphalt based," said Pemberton.