Peter Van Metre and Barbara Mahler U.S. Geological Survey

PAH sources to 40 U.S. urban lakes

NAWQA – National Water Quality Assessment Program

Contaminant Trends in Lake SedimentsCTLS: http://tx.usgs.gov/coring/index.html

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

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

Upward trends in PAHs1970 to present

Van Metre and Mahler, 2005, Environmental Sci. & Tech.

Increasing concentrationsNo trendDecreasing concentrations

What is sealcoat?• Used to protect asphalt

and improve appearance

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.

PAH in pavement dust

Van Metre et al., 2009, Environmental Sci. & Tech.

Coal tarAsphalt

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

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

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

PAH Sources to 40 U.S. Lakes

PEC

0.09–1.4 mg/kg

6.9–81 mg/kg

PAH concentrations and sealcoat

PAH Trends in New Urban Lakes

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