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
By Water Resources Mission Area
March 1, 2019
Paint It Black
USGS researchers investigate releases of PAHs from coal-tar sealcoat into air and water
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
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
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?
Sources/Usage: Public Domain. View Media Details
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.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
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
Sources/Usage: Public Domain. View Media Details
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 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...
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: 23
PAHs/Coal Tar Sealants Effects on Environment & Human 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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Paint it Black
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)
Sealed parking lot with wear marks from snowplow
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.
Sealcoated parking lot and storm drain
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 pavement and storm drain
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
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.
Sealcoated lot and adjacent storm drain
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.
A Potent Pollutant is Tracked Indoors
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Sealcoated Driveway With Basketball Hoop
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.
Driveway with black sealcoat
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 coal-tar-sealed parking lot pavement
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 core from lake for PAH analysis
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.
Pouring dust from sealcoated pavement into sample jar
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.
Black newly applied sealcoat contrasts with unsealed asphalt
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).
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, WI
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.
Sealcoat wear indicated by bare asphalt patches
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.
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.
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?
Sources/Usage: Public Domain. View Media Details
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.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
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
Sources/Usage: Public Domain. View Media Details
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 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...
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: 23
PAHs/Coal Tar Sealants Effects on Environment & Human 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.
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 Emissions
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Paint it Black
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)
Sealed parking lot with wear marks from snowplow
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.
Sealcoated parking lot and storm drain
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 pavement and storm drain
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
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.
Sealcoated lot and adjacent storm drain
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.
A Potent Pollutant is Tracked Indoors
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.
Testing Coal-Tar Sealcoats for Toxic PAH Emissions
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.
Sealcoated Driveway With Basketball Hoop
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.
Driveway with black sealcoat
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 coal-tar-sealed parking lot pavement
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 core from lake for PAH analysis
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.
Pouring dust from sealcoated pavement into sample jar
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.
Black newly applied sealcoat contrasts with unsealed asphalt
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).
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, WI
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.
Sealcoat wear indicated by bare asphalt patches
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.
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.