True Confessions of an Inline Skater
By Dawn Pape
I have a confession. I love to rollerblade! My heart soars when I am out on a beautiful day
and I see a perfectly smooth, jet-black asphalt trail stretching out in front me. I know I can
go gliding along with the breeze on my face and I can relax a bit because I don’t need to
keep an eagle-eye watch out for those miserable cracks that can send me careening off
course. So where’s the confession? Surely, inline skating is not illegal, indecent or immoral.
Well, for the past 8 years, I have worked as the “Environmental Education Coordinator” at
the Rice Creek Watershed District with a central focus of educating the general public
about stormwater runoff and the negative effects it has on our waters. And, as it turns out,
those lovely coal-tar sealed asphalt trails (driveways and parking lots too) that I (secretly)
adore contain polycyclic aromatic hydrocarbons (PAHs) that are doing a number on our
lakes.
What’s the Issue?
Studies have identified coal-tar based sealcoat – the black, shiny emulsion painted or
sprayed on asphalt pavement – as a major and previously unrecognized source of PAH
contamination. Several PAHs are suspected human carcinogens and are toxic to aquatic
life.
Particles in runoff from coal-tar based sealcoated parking lots had concentrations of PAHs
that were about 65 times higher than concentration in particles washed off parking lots
that had not been sealcoated.
Biological studies indicated that PAH levels in sediment contaminated with abraded
sealcoat were toxic to aquatic life and were degrading aquatic communities, as indicated by
loss of species and decreased numbers of organisms. Identification of this source of PAHs
may help to improve future strategies for controlling these compounds in urban water
bodies across the country where parking lot sealcoat is used.
How was the study done?
U.S. Geological Survey (USGS) researchers sampled runoff at 13 parking lots. They also
took scraping samples of parking lot surfaces to compare source materials to particles in
the runoff. The researchers sprayed water on four different types of parking lot surfaces:
lots sealed with coal-tar based sealcost, lots sealed with asphalt-based sealcoat, unsealed
asphalt lots and unsealed concrete lots. The runoff was collected, pumped into containers
and filtered to collect particulates for analysis. It was found that concentrations of total
PAHs in particles in runoff from sealed parking lots greatly exceeded concentrations from
unsealed parking lots.
How does sealcoat get from parking lots in the environment?
Tires abrade parking lot sealcoat into small particles. These small particles are washed off
parking lots by precipitation and into storm sewers and streams. Sealcoat “wear and tear”
is visible in high traffic areas within a few months after application. Sealcoat
manufacturers recommend reapplication every two to three years.
What are potential environmental and human-health concerns?
PAHS are toxic to mammals (including humans), birds, fish, amphibians, invertebrates and
plants. Aquatic invertebrates are particularly susceptible to PAH contamination –
especially the bottom dwellers (benthic invertebrates) that live in the mud where PAHs
accumulate. They are an important part of the food chain and are often monitored as
indicators of stream quality.
Possible side effects of PAHs on aquatic invertebrates include inhibit reproduction, delayed
emergence and mortality. Possible adverse effects on fish include: fin erosion, liver
abnormalities, cataracts and immune system impairments.
The human health risk from environmental contaminants is often evaluated in terms of
exposure pathways. For example, people could be exposed to PAHs in sealcoat through
skin contact, inhalation of wind-blown particles and fumes that volatilize. PAHs in lakes
and streams rarely pose a human health risk via drinking water since PAHs attach to
sediment rather dissolve in water. In addition, because PAHs do not readily
bioaccummulate within the food chain, risks of exposure through the food chain is low.
City Bans on Coal-Tar Sealers
Support bans
Use alternative for your driveway (pervious, porous…)
Make the runoff from your driveway go into a raingarden
Where does that leave us?
If you need your driveway recoated, choose a non coal tar sealcoat
In 2009, the U.S. Geological Survey and the Minneapolis Park and Recreation Board
investigated contaminants in five Minneapolis lakes as part of a statewide study. Sedimnet
samples colled from the top five centimeter of lake bottom were collected from five lakes
and analyzed for organics and contaminants including a subset of PAHs. Source of PAHs
are diverse and include tire debris, gasoline, oil, asphalty and coal-tar sealcoat.