Assessment of PAH Concentrations and Toxicity of Runoff from Sealed Asphalt Surfaces

Owners often apply asphalt sealants to parking lots and driveways to enhance appearance and protect the surface. There are two sealant types generally used in the United States today: asphalt emulsion and coal tar emulsion. Coal tar is a suspected human carcinogen and is detrimental to the health of a variety of organisms. Runoff from these surfaces may be a significant source of polycyclic aromatic hydrocarbons (PAHs) to the environment. The results from a field study of PAH concentrations and potential toxicity of runoff from asphalt surfaces sealed with coal tar sealant and asphalt emulsion sealant will be presented. The study assessed exposure concentrations and evaluated the short-term effects of leached PAHs on potential toxicity to receiving waters. The field study was conducted on an actively-used asphalt parking lot at EPA's Urban Watershed Research Facility (UWRF) in Edison, NJ. The lot was divided into three test plots: one sealed with coal tar sealant, one coated with asphalt emulsion sealant, and an unsealed control. Collected rainwater was homogenized and delivered to the plots for each test. Samples were collected immediately after running off the asphalt, as well as after mixing downstream at the end of a common trench drain. This was done in order to compare runoff from sealed asphalt surfaces to that which has been mixed and transported downstream. Samples were analyzed for a suite of PAHs, toxicity via the Microtox method, and water quality parameters including: solids, total organic carbon, and chemical oxygen demand. Both the runoff from the sealed surfaces and the coatings themselves were tested for toxicity using the Microtox light output procedure.