Pavement Sealcoat, PAHs, and the Environment: An Introduction

Barbara J. Mahler and Peter C. Van Metre U.S. Geological SurveySETAC, 9 November 2010

USGS NAWQA Program: PAHs in lake sediment are

increasing

Van Metre et al., 2000, ES&T; Van Metre and Mahler, 2005, ES&T

Increasing concentrationsNo trendDecreasing concentrations

Carcinogenic, teratogenic, mutagenic, and toxic

Produced by combustion of organic matter

Ubiquitous in the urban environment:

Used motor oilExhaust Industrial emissionsAsphaltTiresCoal-tar-based pavement

sealant

What Are PAHs?What Are PAHs?(polycyclic aromatic hydrocarbons)

The first clue: high PAH in Austin stream-bed sedimentThe first clue: high PAH in

Austin stream-bed sediment

Extremely high (>1,500 mg/kg) PAHs in some small drainages

Compare to Probable Effect Concentration (PEC) of 23 mg/kg

So … what’s upstream?

What is sealcoat?

• Asphalt-based product• West of the Continental Divide

• Coal-tar based product contains coal-tar pitch

• East of the Continental Divide

How do urban sources of PAHs stack up?

• 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

• Pavement sealcoat– Asphalt based ~ 50– Coal-tar-based ~

92,000 (mean of 4 products)

All concentrations in mg/kg

Environmental relevance

• Is use extensive?• Is the contaminant mobile?• Are concentrations elevated?

How extensive is sealcoat use?

• 200,000 gallons applied annually in Springfield, MO, area (applicator estimate)

• 1,400,000 gallons applied annually to New York Harbor watershed (New York Academy of Science estimate)

• 4,800,000 gallons (20,000 tons) of CT-based sealcoat applied in Texas annually (sealcoat industry estimate)

• Within watersheds:

– 4 watersheds in Texas: 1-2% area

– 1 watershed in Illinois: 4% of area• 42% of parking lot

area• 89% of driveway

area

Sealed570

3,800

3,400

1,3002.1

24

21

4730

0.8

Unsealed

Coal tarAsphalt

9 U.S. Cities: Pavement Dust PAH (mg/kg)

1,200

54

<13

5.2

8.5

<8.5

3,200

Van Metre et al., ES&T, 2009

23 ground-floor apartments

Ancillary Information Gathered

• Smoking• Incense/candles• Fireplace use• Type of stove/heat• Shoe wear in house• Indoor/outdoor pets• Distance to major

roadway• Intensity of urbanization

including

Out-CT = 530 x Out-NCTIn-CT = 25 x In-NCT

5.15.1

9.09.0

129129

4,7604,760

Median total PAH [mg/g]

n=12 n=11

Mahler et al., 2010, ES&T

Increasing trends in PAHs

What are the principal sources of PAHs to urban lakes?

Source-Apportionment Modeling

• Start with source profiles• receptor profiles• CMB model combines

sources to best match the receptor profile

• Results are the contribution of each source to each sediment sample

PhA-C

An-CFlA

-CPy-

C

BaA-C

Chy-C

BbF-C

BkF-C

BeP-C

BaP-C

IP-C

BgP-C

00.020.040.060.08

0.10.120.140.160.18

0.2

Lake in the Hills sediment

Example source

Example receptor

Phe FluBaA BbF BeP

IndP

y0.000.020.040.060.080.100.120.14

Traffic tunnel air

PA

H,

pro

po

rtio

nal

Sources Considered• Coal combustion

– Power plant emissions– Residential heating– Coke oven

• Fuel-oil combustion• Vehicle related

– Diesel vehicle emissions– Gasoline vehicle emissions– Traffic tunnel air– Used motor oil– Tire particles– Asphalt

• 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 Source Apportionment to 40 U.S. Lakes

Mass PAH contribution from coal-tar-based sealcoat

Van Metre and Mahler, STOTEN, in press

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