Peter Van Metre and Barbara Mahler U.S. Geological Survey
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Transcript of Peter Van Metre and Barbara Mahler U.S. Geological Survey
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Peter Van Metre and Barbara Mahler U.S. Geological Survey
PAH sources to 40 U.S. urban lakes
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NAWQA – National Water Quality Assessment Program
Contaminant Trends in Lake SedimentsCTLS: http://tx.usgs.gov/coring/index.html
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Large group of organic compounds
Produced by combustion of organic matter
Many are carcinogenic, mutagenic, teratogenic, or toxic
PAHsPAHs(polycyclic aromatic hydrocarbons)
Phenanthrene
Benzo(a)pyrene
Pyrene
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How do sources compare?
• Tire wear particles– 175 (mean of 3 studies)
• Road dust– 59
• Brake lining particles– 9
• Air particles, major roadway– 104
• Fresh asphalt– 2
• Weathered asphalt– 9
• Fresh motor oil– 7
• Used motor oil– 726
• Diesel engine– 304 (mean of 2 studies)
• Gasoline engine– 35
• Coal-tar-based pavement sealant– 92,000
~1 to 50 mg/kg in urban lake sediment
All concentrations in mg/kg
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Upward trends in PAHs1970 to present
Van Metre and Mahler, 2005, Environmental Sci. & Tech.
Increasing concentrationsNo trendDecreasing concentrations
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What is sealcoat?• Used to protect asphalt
and improve appearance
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What is sealcoat?• Used to protect asphalt
and improve appearance
• First recognized as PAH source in 2005
• Coal-tar based and asphalt based products
• CT sealcoat is 5-10% PAH; 1,000x ASP sealcoat
• CT use greater east of Continental Divide; ASP in west
Mahler et al., 2005, Environmental Sci. & Tech.
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PAH in pavement dust
Van Metre et al., 2009, Environmental Sci. & Tech.
Coal tarAsphalt
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Modeling Approach
• Used CMB to determine recent (post-1990) sources for 40 lakes; long-term trends in 8 lakes
• Over 200 modeling runs; many combinations of sources, PAHs, and lakes
• Identified the 4 best performing models
• Summarized results for five source categories
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How CMB works • Uses proportional PAH
profiles (12 PAH) in many sources
• Adds source contributions to get best match of receptor profile (lake sediment) by minimizing Chi-squared (X2)
• Provides estimated mass loading and uncertainty for each source PAH, low to high molecular weight
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Sources Considered• Coal combustion
– Power plant emissions– Residential heating– Coke oven
• Vehicle related– Diesel vehicle emissions– Gasoline vehicle emissions– Traffic tunnel air– Used motor oil– Tire particles– Asphalt
• Fuel-oil combustion• Wood burning
– Pine-wood soot particles
• Coal-tar-sealcoat related– NIST coal tar standard– Sealcoat products– Sealcoat scrapings– Sealcoat dust (average, 6 cities)– Sealcoat dust, Austin
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PAH Sources to 40 U.S. Lakes
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PEC
0.09–1.4 mg/kg
6.9–81 mg/kg
PAH concentrations and sealcoat
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PAH Trends in New Urban Lakes
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All urban is not equal
Decker Lake2,090 people/km
SPAH 0.76 mg/kg
Tanasbrook Pond844 people/km
SPAH 1.34 mg/kg
Lake Anne2,095 people/km
SPAH 17.0 mg/kg
Palmer Lake939 people/km
SPAH 34.1 mg/kg