Polycyclic Aromatic Hydrocarbons Released from Sealcoated Pavement--An Evaluation of the Source and Fate of PAHs in Stormwater Runoff
1. We will conduct a side-by-side comparison of PAHs released from three differently treated parking lots, one treated with coal tar-based sealant, one with asphalt-based sealant, and one unsealed.
2. PAH loads in stormwater and vapor emmissions will be measured, and sealcoat wear rates will be estimated from cores.
3. PAH removal rates will be assesed for five common stormwater treatment technologies.
4. We will develop and disseminate recommendations for the future use of coal tar-based sealants, and for the treatment of PAHs in stormwater.
Sealcoat is applied to pavement to protect and enhance the appearance of the surface, but a recent study found that coal-tar based sealcoats contain up to 20% PAHs by weight. The proposed study will measure PAH concentrations in stormwater runoff from parking lots sealed with coal-tar and asphalt based sealcoat, will evaluate the effectiveness of common stormwater treatment technologies in removing PAHs from runoff, and will provide recommendations to planners and regulators about the future use of sealcoat.
UNH researchers engaging with sealcoat companies to encourage marketing environmentally friendly products
N.H. Sea Grant-funded research determined that stormwater samples collected from parking lots treated with coal tar-based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed. These results have contributed to nationwide research and dialogue about the impacts of coal-tar-based sealcoat, leading to proposed legislation calling for local, state and nationwide bans, and encouraging voluntary market reduction. In 2013, researchers engaged with local sealcoat applicators and buyers who were interested in improving their understanding of the study results in order to market more environmentally friendly products. This engagement is a step toward reducing PAHs in waterways while helping local sealcoat businesses remain profitable when they employ more sustainable and environmentally responsible practices.
NHSG-Supported Research Leads to Proposed Legislation to Ban Coal Tar-Based Sealcoat
RELEVANCE: NHSG-funded research determined that stormwater samples collected from parking lots treated with coal tar-based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed.
RESPONSE: Researchers from the UNH Stormwater Center have added to national research and dialogue documenting the environmental and human health impacts of PAHs coming from coal tar sealcoat.
RESULTS: In addition to previous sealcoat bans in a few cities and states, the U.S. House of Representatives is now considering legislation that would call for a nationwide ban on coal tar sealcoat based in part on research conducted using NHSG funds. Researchers are supporting US EPA education and outreach to reduce coal tar-based sealant use, and are working with the local sealcoat companies to encourage voluntary reduction of coal tar sealcoat use.
RECAP: NHSG-funded research contributed to nationwide research and dialogue about the impacts of coal tar-based sealcoat, leading to proposed legislation calling for local, state and nationwide bans, and encouraging voluntary market reduction.
PAHs in Environment Reduced by Coal Tar-based Sealcoat Bans
RELEVANCE: NHSG-funded research determined that stormwater samples collected from parking lots treated with coal-tar based sealcoat contained significantly higher polycyclic aromatic hydrocarbon (PAH) concentrations than those treated with asphalt-based sealcoat or those left unsealed.
RESPONSE: Researchers discussed their findings in numerous workshops and conferences throughout the nation and worked with NHSG staff to produce a pamphlet explaining the potential impacts of sealcoat to homeowners.
RESULTS: Sealcoat has been banned in Austin, Texas, Minneapolis/St. Paul, Minn., and the state of Washington, and several counties in Illinois and the state of Minnesota are considering banning sealcoat based in part on research conducted by the UNH Stormwater Center using NHSG funding.
UNH Researchers Determine that Coal Tar-based Sealcoat is a Source of PAHs in Stormwater Runoff
RELEVANCE: Previous research demonstrated that coal tar-based sealcoats contain up to 20% PAHs by weight. In the environment, they attach to organic matter such as leaves and inorganic particles like silt and clay, from where they may be ingested by organisms or buried in sediments. PAHs do not easily break down and may persist in the environment for decades. If PAHs enter waterways, they can increase the contaminant burden of aquatic ecosystems and could become a human health issue for people who are regularly exposed to it.
RESPONSE: Researchers at the UNH Stormwater Center studied the impact of sealcoat PAHs on stormwater runoff. Portions of a parking lot were covered with coal tar-based sealcoat, while the remainder was left unsealed. The PAH concentration of the stormwater runoff was measured in the water draining from the sealcoated and unsealed parking lot sections, both before and after applications. In addition, waterway bed sediments were also sampled and tested for PAHs.
RESULTS: The sealcoat parking lots led to a rapid increase in PAH concentrations in the initial runoff up to 5,000 parts per billion (ppb), significantly higher than the 10 ppb levels considered as the background concentration from the unsealed lot. However, concentrations decreased after several rainstorms. The PAH concentrations in the sediments mirrored these trends; the concentrations immediately downstream of the coal tar-sealed lot increased by nearly two orders of magnitude within the first year.
RECAP: Researchers have determined that coal tar-based pavement sealcoat is a significant source of PAHs in the environment and are working with the EPA, the sealcoat industry and others to ameliorate the situation.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
- Watts, A., T. Ballestero, R. Roseen and J. Houle (2010). Polycyclic aromatic hydrocarbons in stormwater runoff from sealcoated pavements. Environmental Science & Technology 44(23):8849-8854, December 2010.
- Mahler, B., P. Van Metre, J. Crane, A. Watts, M. Scoggins and E. Williams. Coal-tar-based pavement sealcoat and PAHs: implications for the environment, human health, and stormwater management. Environmental Science & Technology 46(6):3039-3045, March 2012.
- Thinking about sealcoating your driveway? Get the facts!
- Stormwater, coal-tar sealcoat, and polycyclic aromatic hydrocarbons (PAHs) - EPA's Stormwater Pollution Prevention Webinar Series. Presented June 14, 2012; available online.