Post on 12-Aug-2020
Coal-Tar-Based Pavement Sealcoat, PAHs, and Environmental Health
1
What are PAHs and why do we care?
• Toxic to aquatic life and to mammals
• Cause tumors and mutations
• Cause birth defects
• Seven are probable human carcinogens (EPA B2 carcinogens)
• 16 are EPA Priority Pollutants
2
Benzo(a)pyrene
Pyrene Naphthalene
Contaminant Trends since 1970
Van Metre and Mahler, 2005, Environmental Sci. & Tech. 3
City of Austin measures PAH concentrations greater than 1,500 mg/kg
4
How much PAH in each source?
• Fresh asphalt 1.5
• Weathered asphalt 3
• Fresh motor oil 4
• Brake particles 16
• Road dust 24
• Tire particles 86
• Diesel engine 102
• Gasoline engine 370
• Used motor oil 440
All concentrations in mg/kg (averages of 1-6 studies)
Pavement Sealcoat •Asphalt Based ~ 50 •Coal-tar-based ~ 100,000
1,500 mg/kg in creek sediment
5
6
7
Sampled runoff from 13 parking lots
Analyzed particles and water for PAHs
PAH in runoff
Mahler et al., 2005, Environ. Sci. & Tech. 8
54
3,500
Mean Urban Lakes
12 mg/kg
Black R. Ohio, EPA Superfund
Site 1,100 mg/kg
Charles River
130 mg/kg
PAH in particles from parking lots
Mean concentration is
65-times greater
Tota
l P
AH
(m
g/k
g)
9
PEC
5.2
<13
2.1
3,000
570
3,200 3,400
3,200
1,300
Sealed pavement dust Total PAH (mg/kg)
Unsealed pavement dust
Asphalt Coal tar
8.5
<8.6
0.83
54
24
21 47
30
Asphalt Coal tar
Van Metre et al., 2009, Environ. Sci. & Tech. 10
?
11
0
0.05
0.1
0.15
0.2
0.25
Fra
cti
on
12 PAHs
CT dust
Lake Anne
0
0.05
0.1
0.15
0.2
0.25
Fra
cti
on
12 PAHs
Gas vehicle
Lake Anne
0
0.05
0.1
0.15
0.2
0.25
Fra
cti
on
12 PAHs
Coal
Lake Anne
Environmental Forensics: PAH fingerprints
r=0.60
r=0.68
r=0.94
12
Vehicle/traffic related Gasoline and diesel
soot and exhaust, tunnel air, used oil, tires, asphalt wear
Coal combustion Residential, power
plant, and coking Fuel oil combustion Wood burning Coal-tar based sealcoat
CMB source modeling
13
PAH sources to U.S. urban lakes
Coal-tar based
sealcoat
Probable Effect
Concentration
14
Sources of PAHs to Lake Anne
Lake Anne, Reston, Virginia
Date sediment deposited
1970 1980 1990 2000
PA
H c
oncentr
ation (
mg/k
g)
0
5
10
15
20
25
Lake Anne, Reston, Virginia
Date sediment deposited
1970 1980 1990 2000
PA
H c
oncentr
ation (
mg/k
g)
0
5
10
15
20
25
Lake Anne, Reston, Virginia
Date sediment deposited
1970 1980 1990 2000
PA
H c
oncentr
ation (
mg/k
g)
0
5
10
15
20
25
Lake Anne, Reston, Virginia
Date sediment deposited
1970 1980 1990 2000
PA
H c
oncentr
ation (
mg/k
g)
0
5
10
15
20
25
Lake Anne, Reston, Virginia
Date sediment deposited
1970 1980 1990 2000
PA
H c
on
ce
ntr
atio
n (
mg
/kg
)
0
5
10
15
20
25
Total PAH
Wood burning
Vehicles Coal burning
Coal-tar sealcoat
15
A large coal-tar-sealcoat contribution translates to high PAH concentrations
Probable effect
concentration
16
?
17
23 ground-floor apartments, dust indoors and out
18
5.1
9.0
129
4,760
Median total PAH [mg/kg]
n=12 n=11
Mahler et al., 2010, Environ. Sci. & Tech. 19
?
Air Quality?
20
Volatilization of PAH We used paired high volume air samples to measure PAH volatilization from sealcoated pavement
Ambient Air (AMB)
Surface air layer (HAT)
Solid phase
Gradient and estimated
flux 1.28 m
0.03 m
21
PAH in-use lots PAH8 in unsealed lots (geometric means)
HAT = 63 AMB = 26 ng/m3 flux = 1.4 g/m2 h
PAH8 in sealcoated lots
HAT=1,320 AMB = 138 ng/m3 flux = 88 g/m2 h
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Su
m P
AH
(n
g/m
3)
PAH in air in-use lots
AMB
HAT
22
Over freshly applied sealcoat
23
Concentrations in air
PAH8 2 hours after application
HAT = 300,000 AMB = 5,400 ng/m3
PAH8 149 days after (during winter)
HAT=291 AMB = 28 ng/m3
Trend after application
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
0 100 200 300 400
PAH
(n
g/m
3)
days since sealing
Concentration
HAT
AMB
25
0
10,000
20,000
30,000
40,000
50,000
0 100 200 300 400 PA
H8
flu
x (u
g/m
2 h
)
time (days)
Flux
summer winter summer
PAH loss from the sealant
26
0
5,000
10,000
15,000
20,000
25,000
30,000
0 100 200 300 400
PAH
8 (
mg
/kg)
Days since application
product
Volatilization shifts the PAH profile
0
0.05
0.1
0.15
0.2
0.25
0.3 F
rac
tio
n o
f to
tal P
AH
NIST-CT
Dust TX
Product
1 day
45 days
376 days
Ph
e
An
th
Flu
Pyr
BaA
Ch
ry
Bb
F
BkF
BeP
BaP
IP
Bg
P
3 ring 4 ring 5-6 ring
And a shift in emissions, too
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400
fra
cti
on
of
PA
H f
lux
days since sealing
Phe+An
the rest
PAH volatilized during drying
29
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
0 5 10 15 20
PAH
8 (
ug
/m2 h
)
time (days)
day-night
regression
measured flux
R2=0.95
PAH ~2.8 g/m2
PAH mass lost from the sealant
30
0
5,000
10,000
15,000
20,000
25,000
30,000
0 100 200 300 400
PA
H8 (
mg
/kg
)
Days since application
PAH ~5.8 g/m2
16 d
Total PAH emissions during drying
31
Annual coal-tar sealcoat use 85 million gal
Area covered ~440 km2
PAH emission rate 3 g/m2
PAH8 emissions/yr ~1,000 Mg
PAH16 vehicle emissions, 2010 840 Mg*
PAH8 vehicle emissions, 2010 ~50 Mg*
* Shen et al., 2011
32