Webinar on USGS research findings on Polycyclic Aromatic Hydrocarbons (PAH) contamination associated with coal-tar-based sealants and implications for environmental and human health. Dr.
Coal-Tar-Based Pavement Sealcoat, PAHs, and Environmental Health Active
Paint It Black
USGS researchers investigate releases of PAHs from coal-tar sealcoat into air and water
Featured Publication
Multiple lines of evidence point to coal-tar-sealcoat as the major source of PAHs and toxicity in Milwaukee streams
Just How Much Parking Lot Surface is Out There?
Unique data set on areal extent of U.S. parking lots and how that's changed
Sealcoat is the black, viscous liquid applied to many asphalt parking lots, driveways, and playgrounds in North America to protect and enhance the appearance of the underlying asphalt. Coal-tar-based pavement sealcoat is a potent source of polycyclic aromatic hydrocarbon (PAH) contamination in urban and suburban areas and a potential concern for human health and aquatic life.
BACKGROUND
Pavement sealcoat is a commercial product marked for use primarily on parking lots and driveways and is rarely used on public roads. Most sealcoat products are either coal-tar or asphalt emulsion. Coal tar and coal-tar pitch, both used in sealcoat products, have extremely high concentrations of PAHs, and both are classified as known human carcinogens. Coal-tar-based sealcoat products typically are 20 to 35 percent coal tar or coal-tar pitch. Asphalt and asphalt-based sealcoat products have much lower concentrations of PAHs.
For historical and economic reasons, coal-tar-based sealcoat is more common east of the Continental Divide (except in those states, counties, and municipalities where its use is prohibited), and asphalt-based sealcoat is more west of the Continental Divide. Coal-tar-based pavement sealcoat typically contains 35,000 to 200,000 mg/kg (parts per million, or ppm) PAHs, about 100 times more PAHs than in used motor oil and about 1,000 times more PAHs than in sealcoat products with an asphalt (oil) base. Levels of PAHs in dust swept from sealed parking lots to the east and west of the Continental Divide reflect this difference in use, with PAH concentrations in sealed-pavement dust the East about 1,000 times higher than concentrations in the West.
What are coal tar and coal-tar pitch?
Coal tar is a byproduct of the coking, liquefaction or gasification of coal. Coal-tar pitch is the residue that remains after the distillation of coal tar, that is, the thick black liquid remaining after various oils are removed from coal tar for use in the manufacture of industrial and consumer products. Coal-tar pitch is separated, or "refined", into 12 grades of viscosity. The most viscous grade, RT-12, is used in coal-tar-based sealcoat. The primary use of coal-tar pitch is in electrode manufacturing for the aluminum industry and for steel arc furnaces.
What are PAHs?
PAHs are a group of chemicals created by heating or burning material that contains carbon. There are many sources of PAHs to the environment, representing a wide range of PAHs concentrations, including asphalt (2-9 milligrams per kilogram, or mg/kg), tire particles (84 mg/kg), used motor oil (730 mg/kg), and coal-tar-based sealcoat (34,000-202,000 mg/kg). PAHs cause cancer, mutations, birth defects, and/or death in fish, wildlife, and invertebrates. Several PAHs are photoactivated, meaning that their toxic effects are greatly intensified when exposed to sunlight. The EPA has classified seven PAHs as probable human carcinogens, and 16 PAHs as Priority Pollutants.
AS SEALCOAT WEARS OFF, WHERE DOES IT GO?
Abraded dried sealcoat particles containing high concentrations of PAHs and related chemicals can be transported by rain, wind, car tires, and even our feet to surrounding areas, including our homes. Concentrations of PAHs in runoff, sediment, soils, and dust near coal-tar-sealcoated pavement are substantially higher than concentrations in those media near concrete pavement, unsealed asphalt pavement, and asphalt pavement with asphalt-based sealcoat.
POTENTIAL RISKS TO HUMAN HEALTH
PAHs from coal-tar-based sealcoat contaminate house dust. House dust is an important pathway for human exposure to many contaminants, including PAHs. This is particularly true for small children, who spend time on the floor and put their hands and objects into their mouths. In a study of 23 ground-floor apartments, PAH levels in house dust in apartments with parking lots sealed with a coal-tar-based product were 25 times higher than in house dust in apartments with parking lots with other surface types (concrete, unsealed asphalt, and asphalt-based sealcoat). No relation was found between PAHs in house dust and other possible indoor PAH sources such as tobacco smoking and fireplace use.
The pre-schooler living in a residence adjacent to coal-tar-sealed pavement who has relatively low hand-to-mouth activity consumes about 2.5 times more PAHs from house dust than from their diet. For the more active pre-schooler, whose hand-to-mouth activity is higher, the PAH intake from house dust is nearly 10 times more than the PAH intake from their diet. These findings upset the paradigm that diet is the greatest source of PAHs for small children.
POTENTIAL RISKS TO AQUATIC LIFE
Runoff from coal-tar-sealcoated pavement is acutely toxic to aquatic biota. Exposure to runoff from coal-tar-sealed pavement collected as much as 42 days after sealcoat application resulted in 100 percent mortality to two commonly tested laboratory organisms: day-old fathead minnows (Pimephales promelas) and water fleas (Ceriodaphnia dubia). In contrast, minnows and water fleas exposed to runoff from unsealed pavement experience no more than 10 percent mortality. When the minnows and water fleas were also exposed to simulated sunlight, which intensifies the toxicity of some PAHs, runoff collected 111 days (more than 3 months) after sealcoat application caused 100 percent mortality to both species, and caused 100 percent mortality to water fleas even when diluted to 10 percent of its original strength. These results demonstrate that runoff from coal-tar-sealcoated pavement continues to be toxic from aquatic organisms long after the 24- to 48-hour curing time.
A subsequent collaborative study by researchers at the National Oceanic and Atmospheric Adminstration (NOAA), U.S. Fish and Wildlife Service, and University of Washington reported that coal-tar-sealcoat runoff is acutely lethal to juvenile coho salmon (Oncorhynchus kisutch) and causes a wide spectrum of abnormalities to zebrafish (Danio rario) embryos. The study also reported that filtration of the runoff through a bioretention system substantially reduced toxicity.
COAL-TAR-BASED SEALCOAT, PAHS, AND STREAM AND LAKE SEDIMENT
Dust on coal-tar-sealed parking lots contains bits of abraded sealcoat particles, and measured concentrations of PAHs in the dust swept from coal-tar-sealed pavement typically are in the thousands of milligrams per kilogram. In some cases, stormwater runoff washes high-PAH pavement dust to a stormwater management device, such as a retention pond, leading to high costs of disposal. PAH-contaminated dust that is not trapped by management devices can be transported to streams and lakes, where it settles in the stream or lake bed. Application of a wide range of "forensic" methods has indicated that, in areas where it's used, coal-tar-based sealcoat is the primary source of PAHs to stream and lake sediment.
Analysis of lake sediment cores demonstrates that coal-tar-based sealcoat is a major contributor to upward trends in PAHs in urban lakes across the U.S. In Austin, Texas, coal-tar-sealcoat was banned in 2006—sediment cores collected in 2012 and 2014 from Lady Bird Lake, the primary receiving water body for the Austin area, showed a 58 percent decrease in PAH concentrations since the peak prior to the ban.
► Read more about use of sediment cores to reconstruct contaminant histories.
Other studies have used different approaches to determine the source of PAHs to urban stream and lake sediment and come to a similar conclusion regarding source. Those approaches include a land-use-based analysis and organic petroscopy. Those studies concluded that coal-tar-based sealcoat was the source of 70 to 80 percent of the PAHs in the sediment of the water bodies studied.
AIR QUALITY CONCERNS
Although unseen, releases of PAHs to the atmosphere (volatilization) from freshly coal-tar-sealed pavement are tens of thousands of times higher than from unsealed pavement. Volatilization is a potential human-health concern because inhalation is an important pathway for human exposure to PAHs. Volatilization of sealed surfaces is highest just after application and decreases rapidly over the following weeks. Nonetheless, volatilization continues long after application—PAH releases to the atmosphere from parking lots sealed from 3 to 8 years prior to sampling were on average 60 times higher than PAH releases from unsealed pavement. The results suggest that PAH emissions from new coal-tar-based sealcoat applications each year nationwide (~1000 Mg) are larger than annual vehicle emissions of PAHs.
ADDITIONAL RESOURCES
Follow the links below to access web pages related to coal-tar-based sealcoat, PAHs, and environmental and human health.
Water-Quality Trends From Lake Cores
Sediment-Associated Contaminants
Stream Ecology
USGS Research: PAHs and Coal-Tar-Based Pavement Sealcoat
Estimating the presence of paved surface parking lots in the conterminous U.S. from land use coefficients for 1974, 1982, 1992, 2002, and 2012
The USGS produces many types of multimedia products. Use the links below to browse our offerings of photographs, podcasts, and videos related to coal-tar sealant, PAHs, and environmental health.
Webinar on USGS research findings on Polycyclic Aromatic Hydrocarbons (PAH) contamination associated with coal-tar-based sealants and implications for environmental and human health. Dr.
USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
Pete Van Metre and Barbara Mahler discuss an experiment to assess release of Polycyclic Aromatic Hydrocarbons (PAHs) from coal tar pavement sealant after application on a parking lot. (Short Version)
Pete Van Metre and Barbara Mahler discuss an experiment to assess release of Polycyclic Aromatic Hydrocarbons (PAHs) from coal tar pavement sealant after application on a parking lot. (Short Version)
Once applied, sealcoat can be abraded by snowplows, as evidence here, or the abrasive action of car tires. Runoff carrying high-PAH sealcoat particles flows into storm drains, where it can be transported to streams and lakes.
Once applied, sealcoat can be abraded by snowplows, as evidence here, or the abrasive action of car tires. Runoff carrying high-PAH sealcoat particles flows into storm drains, where it can be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Sealcoated parking lot. Runoff from coal-tar-sealcoated pavement contains extremely high concentrations of polycyclic aromatic hydrocarbons (PAHs), and is toxic to aquatic life. Read more here.
Sealcoated parking lot. Runoff from coal-tar-sealcoated pavement contains extremely high concentrations of polycyclic aromatic hydrocarbons (PAHs), and is toxic to aquatic life. Read more here.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Carcinogenic compounds in a popular pavement sealer are tracked indoors, where they show up in high concentrations in house dust.
Listen as USGS hydrologist Barbara Mahler explains how she and her team identified the link between polycyclic aromatic hydrocarbons in coal-tar-based pavement sealcoat and house dust.
Carcinogenic compounds in a popular pavement sealer are tracked indoors, where they show up in high concentrations in house dust.
Listen as USGS hydrologist Barbara Mahler explains how she and her team identified the link between polycyclic aromatic hydrocarbons in coal-tar-based pavement sealcoat and house dust.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A driveway in an upscale residential community in the Lake in the Hills, Ill, is coated with coal-tar-based sealcoat. The driveway has a basketball hoop and a skateboard ramp.
A driveway in an upscale residential community in the Lake in the Hills, Ill, is coated with coal-tar-based sealcoat. The driveway has a basketball hoop and a skateboard ramp.
Many homeowners have their driveway sealcoat to protect and beautify the underlying asphalt. Coal-tar-based sealcoat, predominantly used east of the Continental Divide, is a potent source of polycyclic aromatic hydrocarbons (PAHs). Read more about coal-tar-based sealcoat and PAHs here.
Many homeowners have their driveway sealcoat to protect and beautify the underlying asphalt. Coal-tar-based sealcoat, predominantly used east of the Continental Divide, is a potent source of polycyclic aromatic hydrocarbons (PAHs). Read more about coal-tar-based sealcoat and PAHs here.
Dust swept from parking lots sealed with coal-tar-based sealant contains concentrations of polycyclic aromatic hydrocarbons (PAHs) about 1,000 higher than dust from parking lots with other surface types (concrete, unsealed asphalt, asphalt-based sealcoat).
Dust swept from parking lots sealed with coal-tar-based sealant contains concentrations of polycyclic aromatic hydrocarbons (PAHs) about 1,000 higher than dust from parking lots with other surface types (concrete, unsealed asphalt, asphalt-based sealcoat).
Sediment cores from lakes and reservoirs can be used to reconstruct contaminant histories in watersheds. Sediment-core analyses indicate that concentrations of PAHs in many U.S. urban lakes are increasing, and multiple lines of evidence indicate that the source of the PAHs in coal-tar-based pavement sealants.
Sediment cores from lakes and reservoirs can be used to reconstruct contaminant histories in watersheds. Sediment-core analyses indicate that concentrations of PAHs in many U.S. urban lakes are increasing, and multiple lines of evidence indicate that the source of the PAHs in coal-tar-based pavement sealants.
Dust was collected from sealcoated pavements across the U.S. Concentrations of polycyclic aromatic hydrocarbons (PAHs) in dust from sealed pavement in the East, where coal-tar-based products are used, was about 1,000 times higher than in dust from sealed pavement in the West, where asphalt-based products are used.
Dust was collected from sealcoated pavements across the U.S. Concentrations of polycyclic aromatic hydrocarbons (PAHs) in dust from sealed pavement in the East, where coal-tar-based products are used, was about 1,000 times higher than in dust from sealed pavement in the West, where asphalt-based products are used.
Newly applied coal-tar-based sealcoat is dark black, sharply contrasting with the unsealed asphalt parking lot below. Coal-tar-based sealcoat is a potent source of polycyclic aromatic hydrocarbons (PAHs).
Newly applied coal-tar-based sealcoat is dark black, sharply contrasting with the unsealed asphalt parking lot below. Coal-tar-based sealcoat is a potent source of polycyclic aromatic hydrocarbons (PAHs).
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
The abrasive action of car tires and snow plows causes sealcoat to wear off. Here, light-colored patches indicate where the sealcoat has worn off and the underlying asphalt shows through.
The abrasive action of car tires and snow plows causes sealcoat to wear off. Here, light-colored patches indicate where the sealcoat has worn off and the underlying asphalt shows through.
Use the links below to access USGS-authored publications on coal-tar-based sealcoat, PAHs, and human and environmental health.
Coal-tar-based pavement sealcoat—Potential concerns for human health and aquatic life
Coal-tar-based pavement sealants—a potent source of PAHs
Primary sources and toxicity of PAHs in Milwaukee-area streambed sediment
Coal-tar-based pavement sealcoat—Potential concerns for human health and aquatic life
Acute toxicity of runoff from sealcoated pavement to Ceriodaphnia dubia and Pimephales promelas
Exposure to runoff from coal-tar-sealed pavement induces genotoxicity and impairment of DNA repair capacity in the RTL-W1 fish liver cell line
Concentrations of polycyclic aromatic hydrocarbons (PAHs) and azaarenes in runoff from coal-tar- and asphalt-sealcoated pavement
PAH concentrations in lake sediment decline following ban on coal-tar-based pavement sealants in Austin, Texas
From streets to streams: Assessing the toxicity potential of urban sediment by particle size
You're standing on it! Coal-tar-based pavement sealcoat and environmental and human health
Cancer risk from incidental ingestion exposures to PAHs associated with coal-tar-sealed pavement
PAH volatilization following application of coal-tar-based pavement sealant
Coal-tar pavement sealants might substantially increase children's PAH exposures
Coal-tar sealant may protect roads, but it is problematic for people's health. Here are some news stories that address the toxicity of runoff waters from sealed roads.
Estimates of areal extent of U.S. parking lots now available
Parking lots may be a significant source of pollution, but up until now there has been no quantitative estimate of the areal extent of parking lots in the U.S.
- Overview
Sealcoat is the black, viscous liquid applied to many asphalt parking lots, driveways, and playgrounds in North America to protect and enhance the appearance of the underlying asphalt. Coal-tar-based pavement sealcoat is a potent source of polycyclic aromatic hydrocarbon (PAH) contamination in urban and suburban areas and a potential concern for human health and aquatic life.
BACKGROUND
Pavement sealcoat is a commercial product marked for use primarily on parking lots and driveways and is rarely used on public roads. Most sealcoat products are either coal-tar or asphalt emulsion. Coal tar and coal-tar pitch, both used in sealcoat products, have extremely high concentrations of PAHs, and both are classified as known human carcinogens. Coal-tar-based sealcoat products typically are 20 to 35 percent coal tar or coal-tar pitch. Asphalt and asphalt-based sealcoat products have much lower concentrations of PAHs.
For historical and economic reasons, coal-tar-based sealcoat is more common east of the Continental Divide (except in those states, counties, and municipalities where its use is prohibited), and asphalt-based sealcoat is more west of the Continental Divide. Coal-tar-based pavement sealcoat typically contains 35,000 to 200,000 mg/kg (parts per million, or ppm) PAHs, about 100 times more PAHs than in used motor oil and about 1,000 times more PAHs than in sealcoat products with an asphalt (oil) base. Levels of PAHs in dust swept from sealed parking lots to the east and west of the Continental Divide reflect this difference in use, with PAH concentrations in sealed-pavement dust the East about 1,000 times higher than concentrations in the West.
What are coal tar and coal-tar pitch?
Coal tar is a byproduct of the coking, liquefaction or gasification of coal. Coal-tar pitch is the residue that remains after the distillation of coal tar, that is, the thick black liquid remaining after various oils are removed from coal tar for use in the manufacture of industrial and consumer products. Coal-tar pitch is separated, or "refined", into 12 grades of viscosity. The most viscous grade, RT-12, is used in coal-tar-based sealcoat. The primary use of coal-tar pitch is in electrode manufacturing for the aluminum industry and for steel arc furnaces.
What are PAHs?
PAHs are a group of chemicals created by heating or burning material that contains carbon. There are many sources of PAHs to the environment, representing a wide range of PAHs concentrations, including asphalt (2-9 milligrams per kilogram, or mg/kg), tire particles (84 mg/kg), used motor oil (730 mg/kg), and coal-tar-based sealcoat (34,000-202,000 mg/kg). PAHs cause cancer, mutations, birth defects, and/or death in fish, wildlife, and invertebrates. Several PAHs are photoactivated, meaning that their toxic effects are greatly intensified when exposed to sunlight. The EPA has classified seven PAHs as probable human carcinogens, and 16 PAHs as Priority Pollutants.
AS SEALCOAT WEARS OFF, WHERE DOES IT GO?
Abraded dried sealcoat particles containing high concentrations of PAHs and related chemicals can be transported by rain, wind, car tires, and even our feet to surrounding areas, including our homes. Concentrations of PAHs in runoff, sediment, soils, and dust near coal-tar-sealcoated pavement are substantially higher than concentrations in those media near concrete pavement, unsealed asphalt pavement, and asphalt pavement with asphalt-based sealcoat.
POTENTIAL RISKS TO HUMAN HEALTH
PAHs from coal-tar-based sealcoat contaminate house dust. House dust is an important pathway for human exposure to many contaminants, including PAHs. This is particularly true for small children, who spend time on the floor and put their hands and objects into their mouths. In a study of 23 ground-floor apartments, PAH levels in house dust in apartments with parking lots sealed with a coal-tar-based product were 25 times higher than in house dust in apartments with parking lots with other surface types (concrete, unsealed asphalt, and asphalt-based sealcoat). No relation was found between PAHs in house dust and other possible indoor PAH sources such as tobacco smoking and fireplace use.
The pre-schooler living in a residence adjacent to coal-tar-sealed pavement who has relatively low hand-to-mouth activity consumes about 2.5 times more PAHs from house dust than from their diet. For the more active pre-schooler, whose hand-to-mouth activity is higher, the PAH intake from house dust is nearly 10 times more than the PAH intake from their diet. These findings upset the paradigm that diet is the greatest source of PAHs for small children.
POTENTIAL RISKS TO AQUATIC LIFE
Runoff from coal-tar-sealcoated pavement is acutely toxic to aquatic biota. Exposure to runoff from coal-tar-sealed pavement collected as much as 42 days after sealcoat application resulted in 100 percent mortality to two commonly tested laboratory organisms: day-old fathead minnows (Pimephales promelas) and water fleas (Ceriodaphnia dubia). In contrast, minnows and water fleas exposed to runoff from unsealed pavement experience no more than 10 percent mortality. When the minnows and water fleas were also exposed to simulated sunlight, which intensifies the toxicity of some PAHs, runoff collected 111 days (more than 3 months) after sealcoat application caused 100 percent mortality to both species, and caused 100 percent mortality to water fleas even when diluted to 10 percent of its original strength. These results demonstrate that runoff from coal-tar-sealcoated pavement continues to be toxic from aquatic organisms long after the 24- to 48-hour curing time.
A subsequent collaborative study by researchers at the National Oceanic and Atmospheric Adminstration (NOAA), U.S. Fish and Wildlife Service, and University of Washington reported that coal-tar-sealcoat runoff is acutely lethal to juvenile coho salmon (Oncorhynchus kisutch) and causes a wide spectrum of abnormalities to zebrafish (Danio rario) embryos. The study also reported that filtration of the runoff through a bioretention system substantially reduced toxicity.
COAL-TAR-BASED SEALCOAT, PAHS, AND STREAM AND LAKE SEDIMENT
Dust on coal-tar-sealed parking lots contains bits of abraded sealcoat particles, and measured concentrations of PAHs in the dust swept from coal-tar-sealed pavement typically are in the thousands of milligrams per kilogram. In some cases, stormwater runoff washes high-PAH pavement dust to a stormwater management device, such as a retention pond, leading to high costs of disposal. PAH-contaminated dust that is not trapped by management devices can be transported to streams and lakes, where it settles in the stream or lake bed. Application of a wide range of "forensic" methods has indicated that, in areas where it's used, coal-tar-based sealcoat is the primary source of PAHs to stream and lake sediment.
Analysis of lake sediment cores demonstrates that coal-tar-based sealcoat is a major contributor to upward trends in PAHs in urban lakes across the U.S. In Austin, Texas, coal-tar-sealcoat was banned in 2006—sediment cores collected in 2012 and 2014 from Lady Bird Lake, the primary receiving water body for the Austin area, showed a 58 percent decrease in PAH concentrations since the peak prior to the ban.
► Read more about use of sediment cores to reconstruct contaminant histories.
Other studies have used different approaches to determine the source of PAHs to urban stream and lake sediment and come to a similar conclusion regarding source. Those approaches include a land-use-based analysis and organic petroscopy. Those studies concluded that coal-tar-based sealcoat was the source of 70 to 80 percent of the PAHs in the sediment of the water bodies studied.
AIR QUALITY CONCERNS
Although unseen, releases of PAHs to the atmosphere (volatilization) from freshly coal-tar-sealed pavement are tens of thousands of times higher than from unsealed pavement. Volatilization is a potential human-health concern because inhalation is an important pathway for human exposure to PAHs. Volatilization of sealed surfaces is highest just after application and decreases rapidly over the following weeks. Nonetheless, volatilization continues long after application—PAH releases to the atmosphere from parking lots sealed from 3 to 8 years prior to sampling were on average 60 times higher than PAH releases from unsealed pavement. The results suggest that PAH emissions from new coal-tar-based sealcoat applications each year nationwide (~1000 Mg) are larger than annual vehicle emissions of PAHs.
ADDITIONAL RESOURCES
- Science
Follow the links below to access web pages related to coal-tar-based sealcoat, PAHs, and environmental and human health.
Water-Quality Trends From Lake Cores
Sediment cores let us look back in time at the contaminant history of a watershed. Learn about what lake and reservoir sediment cores tell us about trends in metals, organochlorine pesticides, polycyclic aromatic hydrocarbons, and other sediment-related contaminants.Sediment-Associated Contaminants
Stream, river, and lake bed sediment are reservoirs for many contaminants. These contaminants include some “legacy” contaminants, like DDT, PCBs, and chlordane, and chemicals currently in use, like the insecticide bifenthrin and many flame retardants. Learn about techniques used to study sediment-associated contaminants and their importance to aquatic biota.Stream Ecology
Who lives in your stream? Rivers and streams, even small ones, are teeming with a vast number of species, including fish, aquatic invertebrates, and algae. Stream ecology is the study of those aquatic species, the way they interrelate, and their interactions with all aspects of these flowing water systems.USGS Research: PAHs and Coal-Tar-Based Pavement Sealcoat
Coal-tar-based pavement sealant is a potent source of polycyclic aromatic hydrocarbons (PAHs), as documented by the USGS and other researchers. Coal-tar-based sealcoat products typically are 20 to 35% coal tar or coal-tar pitch—these materials are known human carcinogens that contain high concentrations of PAHs and related chemicals. Coal-tar-based pavement sealcoat typically contains 35,000 to... - Data
Estimating the presence of paved surface parking lots in the conterminous U.S. from land use coefficients for 1974, 1982, 1992, 2002, and 2012
Parking lots may be a significant source of pollution. Oil, sediments, and heavy metals may accumulate on their surface, then be flushed into rivers, streams, and lakes via rainfall. At present no dataset provides a mapping or estimation of parking lot area or locations nationwide. This product consists of a time series of five national 60-meter raster datasets which estimate the proportion of eac - Multimedia
The USGS produces many types of multimedia products. Use the links below to browse our offerings of photographs, podcasts, and videos related to coal-tar sealant, PAHs, and environmental health.
Filter Total Items: 23PAHs/Coal Tar Sealants Effects on Environment & Human HealthPAHs/Coal Tar Sealants Effects on Environment & Human HealthPAHs/Coal Tar Sealants Effects on Environment & Human HealthWebinar on USGS research findings on Polycyclic Aromatic Hydrocarbons (PAH) contamination associated with coal-tar-based sealants and implications for environmental and human health. Dr.
Webinar on USGS research findings on Polycyclic Aromatic Hydrocarbons (PAH) contamination associated with coal-tar-based sealants and implications for environmental and human health. Dr.
Testing Coal-Tar Sealcoats for Toxic PAH EmissionsTesting Coal-Tar Sealcoats for Toxic PAH EmissionsUSGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
Testing Coal-Tar Sealcoats for Toxic PAH EmissionsTesting Coal-Tar Sealcoats for Toxic PAH EmissionsA professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
Testing Coal-Tar Sealcoats for Toxic PAH EmissionsTesting Coal-Tar Sealcoats for Toxic PAH EmissionsA USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
Paint it BlackPete Van Metre and Barbara Mahler discuss an experiment to assess release of Polycyclic Aromatic Hydrocarbons (PAHs) from coal tar pavement sealant after application on a parking lot. (Short Version)
Pete Van Metre and Barbara Mahler discuss an experiment to assess release of Polycyclic Aromatic Hydrocarbons (PAHs) from coal tar pavement sealant after application on a parking lot. (Short Version)
Sealed parking lot with wear marks from snowplowOnce applied, sealcoat can be abraded by snowplows, as evidence here, or the abrasive action of car tires. Runoff carrying high-PAH sealcoat particles flows into storm drains, where it can be transported to streams and lakes.
Once applied, sealcoat can be abraded by snowplows, as evidence here, or the abrasive action of car tires. Runoff carrying high-PAH sealcoat particles flows into storm drains, where it can be transported to streams and lakes.
Sealcoated parking lot and storm drainRunoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Sealcoated pavement and storm drainRunoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Sealcoated parking lotSealcoated parking lot. Runoff from coal-tar-sealcoated pavement contains extremely high concentrations of polycyclic aromatic hydrocarbons (PAHs), and is toxic to aquatic life. Read more here.
Sealcoated parking lot. Runoff from coal-tar-sealcoated pavement contains extremely high concentrations of polycyclic aromatic hydrocarbons (PAHs), and is toxic to aquatic life. Read more here.
Sealcoated lot and adjacent storm drainRunoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
Runoff from this sealcoated lot will flow into the storm drain, where it will be transported to streams and lakes.
A Potent Pollutant is Tracked IndoorsCarcinogenic compounds in a popular pavement sealer are tracked indoors, where they show up in high concentrations in house dust.
Listen as USGS hydrologist Barbara Mahler explains how she and her team identified the link between polycyclic aromatic hydrocarbons in coal-tar-based pavement sealcoat and house dust.
Carcinogenic compounds in a popular pavement sealer are tracked indoors, where they show up in high concentrations in house dust.
Listen as USGS hydrologist Barbara Mahler explains how she and her team identified the link between polycyclic aromatic hydrocarbons in coal-tar-based pavement sealcoat and house dust.
Testing Coal-Tar Sealcoats for Toxic PAH EmissionsTesting Coal-Tar Sealcoats for Toxic PAH EmissionsA professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
A professional applicator applies coal-tar-based sealcoat to a test plot used to measure emission of polycyclic aromatic carbons (PAHs) into the air.
Sealcoated Driveway With Basketball HoopA driveway in an upscale residential community in the Lake in the Hills, Ill, is coated with coal-tar-based sealcoat. The driveway has a basketball hoop and a skateboard ramp.
A driveway in an upscale residential community in the Lake in the Hills, Ill, is coated with coal-tar-based sealcoat. The driveway has a basketball hoop and a skateboard ramp.
Driveway with black sealcoatMany homeowners have their driveway sealcoat to protect and beautify the underlying asphalt. Coal-tar-based sealcoat, predominantly used east of the Continental Divide, is a potent source of polycyclic aromatic hydrocarbons (PAHs). Read more about coal-tar-based sealcoat and PAHs here.
Many homeowners have their driveway sealcoat to protect and beautify the underlying asphalt. Coal-tar-based sealcoat, predominantly used east of the Continental Divide, is a potent source of polycyclic aromatic hydrocarbons (PAHs). Read more about coal-tar-based sealcoat and PAHs here.
Dust swept from coal-tar-sealed parking lot pavementDust swept from coal-tar-sealed parking lot pavementDust swept from parking lots sealed with coal-tar-based sealant contains concentrations of polycyclic aromatic hydrocarbons (PAHs) about 1,000 higher than dust from parking lots with other surface types (concrete, unsealed asphalt, asphalt-based sealcoat).
Dust swept from parking lots sealed with coal-tar-based sealant contains concentrations of polycyclic aromatic hydrocarbons (PAHs) about 1,000 higher than dust from parking lots with other surface types (concrete, unsealed asphalt, asphalt-based sealcoat).
Sediment core from lake for PAH analysisSediment cores from lakes and reservoirs can be used to reconstruct contaminant histories in watersheds. Sediment-core analyses indicate that concentrations of PAHs in many U.S. urban lakes are increasing, and multiple lines of evidence indicate that the source of the PAHs in coal-tar-based pavement sealants.
Sediment cores from lakes and reservoirs can be used to reconstruct contaminant histories in watersheds. Sediment-core analyses indicate that concentrations of PAHs in many U.S. urban lakes are increasing, and multiple lines of evidence indicate that the source of the PAHs in coal-tar-based pavement sealants.
Pouring dust from sealcoated pavement into sample jarPouring dust from sealcoated pavement into sample jarDust was collected from sealcoated pavements across the U.S. Concentrations of polycyclic aromatic hydrocarbons (PAHs) in dust from sealed pavement in the East, where coal-tar-based products are used, was about 1,000 times higher than in dust from sealed pavement in the West, where asphalt-based products are used.
Dust was collected from sealcoated pavements across the U.S. Concentrations of polycyclic aromatic hydrocarbons (PAHs) in dust from sealed pavement in the East, where coal-tar-based products are used, was about 1,000 times higher than in dust from sealed pavement in the West, where asphalt-based products are used.
Black newly applied sealcoat contrasts with unsealed asphaltBlack newly applied sealcoat contrasts with unsealed asphaltNewly applied coal-tar-based sealcoat is dark black, sharply contrasting with the unsealed asphalt parking lot below. Coal-tar-based sealcoat is a potent source of polycyclic aromatic hydrocarbons (PAHs).
Newly applied coal-tar-based sealcoat is dark black, sharply contrasting with the unsealed asphalt parking lot below. Coal-tar-based sealcoat is a potent source of polycyclic aromatic hydrocarbons (PAHs).
Worn sealcoat around a storm drain.Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Worn sealcoat in Milwaukee, WICoal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Coal-tar-based sealcoat, a potent source of polycyclic aromatic hydrocarbons (PAHs), abrades into fine particles with time. Here, runoff containing abraded particles goes down a storm drain and is delivered to a nearby lake. Read more about coal-tar-based sealcoat and PAHs here.
Sealcoat wear indicated by bare asphalt patchesThe abrasive action of car tires and snow plows causes sealcoat to wear off. Here, light-colored patches indicate where the sealcoat has worn off and the underlying asphalt shows through.
The abrasive action of car tires and snow plows causes sealcoat to wear off. Here, light-colored patches indicate where the sealcoat has worn off and the underlying asphalt shows through.
- Publications
Use the links below to access USGS-authored publications on coal-tar-based sealcoat, PAHs, and human and environmental health.
Coal-tar-based pavement sealcoat—Potential concerns for human health and aquatic life
Introduction Sealcoat is the black, viscous liquid sprayed or painted on many asphalt parking lots, driveways, and playgrounds to protect and enhance the appearance of the underlying asphalt. Studies by the U.S. Geological Survey (USGS), academic institutions, and State and local agencies have identified coal-tar-based pavement sealcoat as a major source of polycyclic aromatic hydrocarbon (PAH) coAuthorsBarbara Mahler, Michael D. Woodside, Peter C. Van MetreFilter Total Items: 25Coal-tar-based pavement sealants—a potent source of PAHs
P avement sealants are applied to the asphalt pavement of many parking lots, driveways, and even playgrounds in North America (Figure 1), where, when first applied, they render the pavement glossy black and looking like new. Sealant products used commercially in the central, eastern, and northern United States typically are coal-tarbased, whereas those used in the western United States typically aAuthorsBarbara Mahler, Peter C. Van MetrePrimary sources and toxicity of PAHs in Milwaukee-area streambed sediment
High concentrations of polycyclic aromatic hydrocarbons (PAHs) in streams can be a significant stressor to aquatic organisms. To understand the likely sources and toxicity of PAHs in Milwaukee-area streams, streambed sediment samples from 40 sites and parking lot dust samples from 6 sites were analyzed for 38 parent PAHs and 25 alkylated PAHs. Diagnostic ratios, profile correlations, principal comAuthorsAustin K. Baldwin, Steven R. Corsi, Michelle A. Lutz, Christopher G. Ingersoll, Rebecca A. Dorman, Christopher Magruder, Matthew MagruderCoal-tar-based pavement sealcoat—Potential concerns for human health and aquatic life
Introduction Sealcoat is the black, viscous liquid sprayed or painted on many asphalt parking lots, driveways, and playgrounds to protect and enhance the appearance of the underlying asphalt. Studies by the U.S. Geological Survey (USGS), academic institutions, and State and local agencies have identified coal-tar-based pavement sealcoat as a major source of polycyclic aromatic hydrocarbon (PAH) coAuthorsBarbara Mahler, Michael D. Woodside, Peter C. Van MetreAcute toxicity of runoff from sealcoated pavement to Ceriodaphnia dubia and Pimephales promelas
Runoff from coal-tar-based (CT) sealcoated pavement is a source of polycyclic aromatic hydrocarbons (PAHs) and N-heterocycles to surface waters. We investigated acute toxicity of simulated runoff collected from 5 h to 111 days after application of CT sealcoat and from 4 h to 36 days after application of asphalt-based sealcoat containing about 7% CT sealcoat (AS/CT-blend). Ceriodaphnia dubia (cladoAuthorsBarbara Mahler, Christopher G. Ingersoll, Peter C. Van Metre, James L. Kunz, Edward E. LittleExposure to runoff from coal-tar-sealed pavement induces genotoxicity and impairment of DNA repair capacity in the RTL-W1 fish liver cell line
Coal-tar-based (CTB) sealcoat, frequently applied to parking lots and driveways in North America, contains elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) and related compounds. The RTL-W1 fish liver cell line was used to investigate two endpoints (genotoxicity and DNA-repair-capacity impairment) associated with exposure to runoff from asphalt pavement with CTB sealcoat or withAuthorsAude Kienzler, Barbara Mahler, Peter C. Van Metre, Nathalie Schweigert, Alain Devaux, Sylvie BonyConcentrations of polycyclic aromatic hydrocarbons (PAHs) and azaarenes in runoff from coal-tar- and asphalt-sealcoated pavement
Coal-tar-based sealcoat, used extensively on parking lots and driveways in North America, is a potent source of PAHs. We investigated how concentrations and assemblages of PAHs and azaarenes in runoff from pavement newly sealed with coal-tar-based (CT) or asphalt-based (AS) sealcoat changed over time. Samples of simulated runoff were collected from pavement 5 h to 111 d following application of ASAuthorsBarbara Mahler, Peter C. Van Metre, William T. ForemanPAH concentrations in lake sediment decline following ban on coal-tar-based pavement sealants in Austin, Texas
Recent studies have concluded that coal-tar-based pavement sealants are a major source of polycyclic aromatic hydrocarbons (PAHs) in urban settings in large parts of the United States. In 2006, Austin, TX, became the first jurisdiction in the U.S. to ban the use of coal-tar sealants. We evaluated the effect of Austin’s ban by analyzing PAHs in sediment cores and bottom-sediment samples collected iAuthorsPeter C. Van Metre, Barbara MahlerFrom streets to streams: Assessing the toxicity potential of urban sediment by particle size
Urban sediment can act as a transport mechanism for a variety of pollutants to move towards a receiving water body. The concentrations of these pollutants oftentimes exceed levels that are toxic to aquatic organisms. Many treatment structures are designed to capture coarse sediment but do not work well to similarly capture the fines. This study measured concentrations of select trace metals and PAAuthorsWilliam R. Selbig, Roger T. Bannerman, Steven CorsiYou're standing on it! Coal-tar-based pavement sealcoat and environmental and human health
Coal-tar-based sealcoat—a product marketed to protect and beautify asphalt pavement—is a potent source of polycyclic aromatic hydrocarbons (PAHs) to air, soils, streams and lakes, and homes. Does its use present a risk to human health? Results from a new study by researchers from Baylor University and the USGS indicate that living adjacent to a coal-tar-sealed pavement is associated with significaAuthorsBarbara Mahler, Peter C. Van MetreCancer risk from incidental ingestion exposures to PAHs associated with coal-tar-sealed pavement
Recent (2009–10) studies documented significantly higher concentrations of polycyclic aromatic hydrocarbons (PAHs) in settled house dust in living spaces and soil adjacent to parking lots sealed with coal-tar-based products. To date, no studies have examined the potential human health effects of PAHs from these products in dust and soil. Here we present the results of an analysis of potential cancAuthorsE. Spencer Williams, Barbara Mahler, Peter C. Van MetrePAH volatilization following application of coal-tar-based pavement sealant
Coal-tar-based pavement sealants, a major source of PAHs to urban water bodies, have recently been identified as a source of volatile PAHs to the atmosphere. We tracked the volatilization of PAHs for 1 year after application of a coal-tar-based pavement sealant by measuring gas-phase PAH concentrations above the pavement surface and solid-phase PAH concentrations in sealant scraped from the surfacAuthorsPeter C. Van Metre, Michael S. Majewski, Barbara Mahler, William T. Foreman, Christopher L. Braun, Jennifer T. Wilson, Teresa L. BurbankCoal-tar pavement sealants might substantially increase children's PAH exposures
Dietary ingestion has been identified repeatedly as the primary route of human exposure to polycyclic aromatic hydrocarbons (PAHs), seven of which are classified as probable human carcinogens (B2 PAHs) by the U.S. EPA. Humans are exposed to PAHs through ingestion of cooked and uncooked foods, incidental ingestion of soil and dust, inhalation of ambient air, and absorption through skin. Although PAAuthorsE. Spencer Williams, Barbara Mahler, Peter C. Van Metre - News
Coal-tar sealant may protect roads, but it is problematic for people's health. Here are some news stories that address the toxicity of runoff waters from sealed roads.
Estimates of areal extent of U.S. parking lots now available
Parking lots may be a significant source of pollution, but up until now there has been no quantitative estimate of the areal extent of parking lots in the U.S.