Are PAHs from coaltar sealants degrading Austin streams

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Are PAHs from coal-tar sealants degrading Austin
streams?

• Biological studies
• Laboratory toxicity study
• Microcosm community study
• Field community study

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Background Sealant work to date

• Coal tar sealants contain high concentrations of
  PAHs.
• Sealants abrade off of parking lots and wash off
  in stormwater.
• Concentrations and yields of sealant wash-off
  indicate it is a major source of PAHs in urban
  environments.

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1. Lab Study Are sealants toxic to aquatic
organisms?

• Sediment spiked with dried pavement sealant (low,
  medium high).
• 28 day exposure followed by UV.

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1. Lab Study
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1. Lab Study
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2. Microcosm Is coal tar toxic to aquatic
communities?

• Spiked at three treatment levels.
• Seeded with stream organisms.
• 24-day exposure period.

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2. Microcosm
PEC 23 ppm
Average Number of organisms
Control Low Medium High
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2. Microcosm
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3. Field Study Are PAHs degrading aquatic life
in Austin streams?

• Upstream and downstream of coal tar sealed lots.
• Biological communities and sediment chemistry
  sampled in 5 streams.

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3. Field Study
PEC 23 ppm
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3. Field Study
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3. Field Study
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3. Field Study
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Conclusions

• Coal tar sealants are concentrated source of
  PAHs.
• Sealants represent a major source of PAHs in
  urban streams.
• Ecological impacts demonstrated in Austin.
• Chemical tracing, toxicity, field verification
• Austin City Council Bans use and sale of coal tar
  sealant.

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Coal Tar vs. Asphalt Sealants

• Concentrations of PAHs in coal tar sealants 1,000
  times higher than asphalt-based sealants.
• Particulates washing off coal tar sealed lots had
  PAH concentrations 6.5 times higher than asphalt
  sealed lots.
• USGS PAH load estimates are 2x times higher from
  coal tar sealed lots than asphalt-sealed lots.
  Industry reports current asphalt formulations are
  less durable.
• Due to the concentrated source and local stream
  hydrology, higher concentrations from coal tar
  sealed lots would result in local hot spots.
• Toxicity was higher for coal tar compared to
  asphalt sealants at equivalent dilutions in lab
  studies.

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Field Study sampling locations
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Field Study
(TU0.8)
(TU2.6)
PEC 23 ppm
(TU1.1)
(TU1.4)
(TU0.8)
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Field Study