Not all driveway sealing products are created equal. These products often come in two basic formulations, with either asphalt or coal tar as their main ingredients. While neither product is free of toxic materials, a USGS study has shown that dust from surfaces coated with coal tar-based sealants contain hundreds to one-thousand times the concentration of a class of toxic chemicals known as Polycyclic Aromatic Hydrocarbons (PAHs) than dust from surfaces treated with asphalt-based products. Coal tar-based sealants were also the largest source of PAH contamination in 40 lakes studied by the USGS, acounting for more than half of the measured PAH pollution.
PAHs are a known carcinogen and a common byproduct of almost any combustion. PAHs can be found at levels ranging from low levels in ordinary burning candles and charred meats to highly toxic levels in coal ash/tar. Coal tar-based sealants have purportedly left PAHs on driveways at levels that would require a hazardous materials handling suit to remove them in the event of a toxic-waste cleanup of a site.
If your driveway is cracked and in need of sealing, please choose an asphalt-based sealing product if you are doing it yourself, or choose a professional who will use asphalt-based sealants for you. If your driveway is structurally fine and you just want to freshen its appearance with a fresh black coat, think twice about adding unnecessary and potentially toxic chemicals to your property.