RECESS! Time for lava monster, freeze tag, four square, and foot races! Playing outside on playgrounds, driveways, or blacktops are central to a child’s healthy lifestyle, and we want to keep it that way. You may have heard or read that certain pavement sealants (“blacktop”) can cause cancer and are less environmentally friendly than alternatives. In this blog post, we will address this issue and give you the facts.
What is pavement sealant?
Pavement sealant, or sealcoat, is a liquid mixture that is sprayed or painted on to asphalt pavement for protection, preservation, and aesthetic improvement. It is used on driveways, parking lots, and playgrounds/blacktops. It is not used on roads. The base for sealcoat can be coal tar, asphalt, or acrylic. Typically, if you live west of the Continental Divide, (a dividing line running through the highest peaks of the Rocky Mountains), the sealcoat is asphalt-based. East of the Divide, coal tar-based sealcoats are more commonly used.
Because asphalt-based sealcoats are considered less hazardous, we will concentrate on sealcoats made from coal tar. Coal tar sealcoat contains coal tar pitch, 50% of which consists of polycyclic aromatic hydrocarbons (PAHs). According to the International Agency of Research on Cancer, coal tar pitch is a Class I carcinogen, which meansit is a known human carcinogen. The PAH concentration in coal tar-based sealcoat is 1000 times greater than the concentration in asphalt-based sealcoat.
What are PAHs?
PAHs are naturally found in coal and tar deposits. They are also byproducts from the burning of organic matter, so we encounter them in many places in our everyday lives, even in barbeque ribs! Breathing in or eating high levels of PAHs over a long period of time may increase the risk of cancer. Exposure to PAHs, especially early in childhood, has been linked to an increased risk of lung, skin, bladder, and respiratory cancers.
How are children exposed to the PAHs from coal tar based sealcoat?
After wear and tear of the pavement, sealcoat particles can be transported via wind, run off into water, get on clothes, and evaporate into air and be inhaled. According to one study, the amount of PAHs in storm water runoff was 65 times higher from parking lots sealed with coal tar sealant vs. storm water from unsealed parking lots. And coal tar sealcoat is the #1 source of PAH contamination in urban lakes.
After children play on pavement treated with coal tar sealcoat, they can get the particles on their clothes and track them into their homes. These particles can then become part of house dust, or they can get on food and be ingested. One study in Austin, Texas found that PAH concentrations in the dust of homes next to parking lots sealed with coal tar were 25 times higher than dust concentrations of homes next to parking lots sealed with asphalt. A child living in a home adjacent to a parking lot sealed with coal tar needs to ingest just 0.027 grams of house dust per day to exceed the US children’s average PAH ingestion. (Ingesting dust is easy for young children because they constantly put their toys and dust-covered hands in their mouths.)
How do I avoid exposure?
Be an informed consumer: when you get your driveway or parking lot sealed, ask the contractor if the sealcoat is coal tar-based or asphalt-based. Request asphalt-based instead of coal tar-based sealcoat. If you think your driveway might have been sealed with coal tar sealcoat in the past, you can appeal to your local government to get it cleaned up. Take a look at studies done by the United States Geological Survey about the exposure pathways and health implications of coal tar-based sealcoat (https://tx.usgs.gov/sealcoat.html).
As more information about the health effects of coal tar-based sealcoat becomes available, action is being taken. About 85 million gallons of coal tar-based sealcoat are used in the U.S. each year, but the states of Washington and Minnesota have banned its use. It has also been banned in numerous cities and counties across the US. Many Home Depots, Lowe’s, and Ace Hardware stores have stopped selling it. You can advocate for bans on coal tar-based sealcoat in your community.
Finally, a word about playground surface safety
According to the American Academy of Orthopaedic Surgeons, the type of surface on the playground is the most important factor in determining the number and severity of fall injuries. These injuries can be reduced by using softer surfaces such as wood mulch or chips, shredded tires, or sand. Asphalt and concrete result in the most severe injuries and are unsuitable for use under playground equipment. Soil, packed dirt, grass, and turf are not recommended for surfacing because their ability to absorb shock can be greatly affected by weather conditions and wear. Shredded products such as sneaker soles and cork have become more popular as questions about the safety of shredded rubber tires have been raised (see our blog post March 2011). Another recommended alternative for use under playground equipment is “pour-in- place” rubber or rubber tiles.
To conclude, playing outside is so important for children to develop socially and physically, and we want them to be safe while doing so. That is why we recommend switching to asphalt-based sealcoat for blacktops and driveways. Now go outside and play!
1. Mahler BJ, Van Metre PC, Bashara TJ, Wilson JT, Johns DA. Parking lot sealcoat: an unrecognized source of urban PAHs. Environmental Science & Technology 2005.
2. USGS Research: PAHs and Coal Tar-Based Pavement Sealcoat 2016. https://tx.usgs.gov/sealcoat.html
3. Mahler BJ, Metre PCV, Crane JL, Watts AW, Scoggins M, Williams ES. 2012. Coal‐tar‐based pavement sealcoat and PAHs: Implications for the environment, human health, and stormwater management. Environmental Science & Technology.
4. Williams ES, et al 2012. Coal-tar pavement sealants might substantially increase children’s PAH exposures. Environmental Pollution, 164:40–41.
5. American Academy of Orthopedic Surgeons, “Playground Safety Guide”. 2009. http://orthoinfo.aaos.org/topic.cfm?topic=A00313
January 2017. This blog post was written by Nathan Lin, Medical Student at the University of Illinois at Chicago, and edited by Dr. Susan Buchanan.