How are people exposed to chemicals in driveway sealants?
Minnesota Public Radio clearly covered the health issue of PAH pollution from blacktop sealants but didn't fully explain how people can be exposed to the carcinogen.
On November 2, 2009, Tim Nelson of Minnesota Public Radio covered a water pollution problem in St. Paul that few have probably heard about before. His piece, "New concerns raised over blacktop sealant runoff," highlighted how chemicals that are found in blacktop sealants – called polyaromatic hydrocarbons or PAHs – are being washed off the surfaces and into stormwater ponds. PAHs in the ponds are a concern because some are known to cause cancer in humans and/or wildlife.
The broadcast did an excellent job of explaining why cancer-causing PAHs are found in stormwater ponds. The pollutants are part of the coal tar that is used to produce asphalt sealants and other consumer products such as dandruff shampoos. Stormwater, snow melt and water from hoses and sprinklers wash the PAHs and other pollutants along with the dirt off of driveways and into nearby streams, lakes or stormwater ponds.
The link between human use of asphalt sealants and the presence of PAHs in stormwater ponds in the city was clear, as was the message that it is important to decrease the use of PAH-containing sealants. Coverage like this will be critical for convincing people to choose products that are less harmful to their health and to the environment.
The main concern with the broadcast was the lack of an explanation of how people are exposed to PAHs from a variety of sources. This information could help reduce exposure.
PAHs are formed when coals, wood, oil, garbage, cigarette or gasoline are burned. They are created when meat is charred on the barbecue. Most people are exposed through the air. We breathe in PAHs from cigarette smoke and automobile exhaust so our exposure is higher if we smoke or live with smokers or near heavy traffic areas. We may also breath it from PAHs found in dust near sealed asphalt roads and parking lots. They are also formed during industrial processes so people can be exposed to them when drinking water that has been contaminated by industrial wastes. Some PAHs can also be absorbed by the skin from the products we use or when swimming in contaminated water, such as the stormwater ponds in St. Paul, as Mr. Nelson mentions.
There are many different kinds of PAHs. The ones in coal tar like to stick to particles rather than remain dissolved in water and will be found mostly in the sediments at the bottom of streams, ponds and lakes. Although bacteria in waters or sunlight can break down some of these chemicals, others are quite persistent and will accumulate over time. Aquatic animals living in the sediments can take them up into their bodies. Fish become exposed when they eat the PAH-contaminated prey.
Like humans, wildlife are affected by these combustion by-products. Young fish exposed to PAHs develop cardiovascular problems, and older fish are found with liver and skin tumors.
Nelson's main message is clear and correct. We should reduce our use of PAH-containing products to protect human and environmental health. People should consider non-PAH products and options for protecting asphalt or perhaps learn to appreciate fading pavement.
