Agenda Item 5
September 11, 2012
Action
September 7,2012
MEMORANDUM
TO:
County Council
FROM:
SUBJECT:
Robert H. Drummer, Senior Legislative
Amanda Mihill, Legislative
Attomey~
Attome~
'I'fIIcJ
Action: Bill 21-12, Erosion, Sediment Control and Storrnwater Management
Coal Tar Pavement Products
Transportation, Infrastructure, Energy
&
Environment Committee recommendation (3-0):
enact Bill 21-12.
Bill 21-12, Erosion, Sediment Control and Storrnwater Management
Coal Tar Pavement
Products, sponsored by Councilmembers Rice, Navarro, Eirich, Riemer, and Ervin, was
introduced on June 19, 2012. A public hearing was held on July 17, at which speakers testified
in support and opposition to Bill 21-12 (see select written correspondence at ©39-54). A
Transportation, Infrastructure, Energy and Environment Committee worksession was held on
July
26.
Bill 21-12 would prohibit the use and sale of coal
tar
pavement products in the County and
require enforcement by the Department of Environmental Protection. Attached on
©
lOis a
recent study describing the problems caused by polycyclic aromatic hydrocarbons (P AH' s)
released into the environment through the use of a coal tar pavement product. Coal tar and coal­
tar
pitch are Group
1
carcinogens and the Environmental Protection Agency classifies
7
PAH
compounds as probable human carcinogens.
Background
What are coal tar, coal tar sealants, and polycyclic aromatic hydrocarbons (PAH)? Coal tar
is
a byproduct of the coking of coal for the steel industry and coal-tar pitch is the residue that
remains after the distillation of coal tar. Coal-tar pitch is at least 50% PAH's by weight and is
known to cause cancer in humans.
Pavement sealant
is a liquid that is sprayed or painted on some asphalt pavement to protect the
pavement surface. Sealcoat products generally have a coal-tar-pitch or asphalt base. Coal-tar­
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based sealcoat products are usually 20-35% coal-tar pitch and have about 1,000 times more
PAH's than sealcoat products with an asphalt base.
Polycyclic aromatic hydrocarbons (PAR'::.)
are a group of chemical compounds that form when
anything with a carbon base is burned (e.g., wood, gasoline, cigarettes, meat). PAH's are also in
materials (tires, coal tar).1 Of all known PAH sources, the highest concentrations are in coal tar
and the related compound creosote.
2
How do PAH's get released into the environment?
As the U.S. Geological Survey and the
American Chemical Society explain, sealcoat does not stay on a pavement permanently; sealcoat
manufacturers recommend reapplication every 1-2 or 3-5 years, depending on the product used.
Vehicle tires erode the sealcoat and it breaks into small particles. These particles can be washed
off the roadway by rain and carried through storm drains into streams, ponds, and stormwater
management devices. Other particles can be blown offsite by wind or tracked indoors on the
soles of shoes.
3
What are the environmental and health concerns with coal tar and PAH's?
Some PAH's are
toxic to fish, amphibians, and plants. Studies have looked at the effects of coal-tar-based
sealcoat. When sediment was spiked with coal-tar-based sealcoat, frogs had stunted growth,
delayed development, and mortality; salamanders had stunted growth, difficulty swimming or
righting themselves, and liver problems. As noted above, coal tar and coal-tar pitch are Group
1
carcinogens and the Environmental Protection Agency classifies 7 PAH compounds as probable
.
h
uman carcmogens.
4
At the public hearing, Bob Hoyt, Director of the Department of Environmental Protection,
endorsed Bill 21-12 on behalf of the County Executive. Mr. Hoyt noted that DEP recently
sampled the sediment from Lake Whetstone and Gunners Lake and found that the levels of
PAH's in the sediment exceeded the State's standard for restoring contaminated properties for
residential use. Mr. Hoyt noted that the PAH's in the sediment increase the costs of managing
the sediment after it is dredged by an estimated $1,120,000 for those two lakes alone (©39-40).
At a June 29 meeting of the Council sitting as the Board of Health, Councilmember Ervin asked
the County Health Officer to comment on the health effects of coal tar products. Dr. Tillman,
County Health Officer, forwarded studies by EPA and the Centers for Disease Control/Agency
for Toxic Substances (see cover pages and summary on ©55-59), but declined to offer an
"informed opinion" herself and deferred to D EP' s expertise on water quality issues.
How does the USGS link PAH's in the environment to coal tar sealants?
As described on
©17, the USGS collected sediment cores from 40 lakes across the country and analyzed the
samples for PAH's. USGS then determined the contribution ofPAH's from different sources by
using a chemical mass-balance model, which is based on chemical "fingerprinting". According
Coal-Tar-Based Pavement Sea/coat, PolycycliC Aromatic Hydrocarbons (PAH's), and Environmental Health.
U.S.
Geological Survey. Available at: !1ttp:!ipubs.lIsgs.govifs/201 !/3010/pdf'fs2011-3010.pdf (©17-22).
2
Coal-Tar-Based Pavement Sea/coat and PAH's:
Implications for the Environment, Human Health, and
American
Chemical
Society.
Available
at:
Stormwater
Management,
http://pubs.acs.org/doi/pdfplus/tO.102l!es203699x (©
10-16).
3
http://pubs.usgs.gov/fs/20 I
1/301
O/pdf/fs20
11-30
1O.pdf; http://pubs.acs.orgitioi/pd1l)tus!1 n.t
021 /es203699x.
4tillj:L;'Laillbs~~1.cs.org!dojftldti)lus!
I
0.1
021/cs'03699x.
I
2
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to the USGS analysis, on average coal-tar-based seal coat accounts for half of all P AH' s in the
lakes.
Presenting another viewpoint is a study on ©25. This study, funded by an industry organization,
the Pavement Coatings Technology Council (PCTC), concluded that "sediments' PAH profiles
are no more similar to refined tar sealers than they are to a number of other environmental inputs.
While refined tar sealers were not eliminated as a potential source in some locations, forensic
methods did not differentiate their contribution from other sources of P AH' s, indicating refined
tar sealers are not a unique or readily quantifiable source of PAH's to the urban environment."
On its website, the Minnesota Pollution Control Agency noted data-quality problems with this
study'S environmental forensic analysis and concluded that the study made inaccurate
comparisons between sediment data and stormwater runoff data in its analyses.
5
Are there alternatives to the use of coa1 tar sealants?
As the Environmental Protection Agency
noted, there are available alternatives to the use of coal-tar-based sealants (©23). These
alternatives include asphalt-based sealers, which contain 0.03% to 0.66% PAH's dry weight
(compared to 3.4% to 20% PAH's dry weight for coal-tar-based sealants). Additional
alternatives are permeable asphalt, gravel, and concrete.
What have other jurisdictions done?
According to the blog,
Coal Tar Free America,6
several
jurisdictions have restricted or banned the use of coal tar sealants (©37). Notable examples of
jurisdictions that have banned the product include Austin, Texas; Suffolk County, New York;
Washington, D.C.; and Washington State. Additionally, according to various sources, the Home
Depot and Lowes stores throughout the U.S. have stopped selling these products.
Issues/Committee Recommendation
1.
Should the use of coal tar sealants be banned?
The opposition to Bill 21-12 has chiefly
come from individuals and companies in the industry who are concerned about the economic
effect of a potential ban (see testimony, ©39). The County Finance Department indicated that
they do not expect Bill 21-12 to have an economic impact (©9). The manufactures of sealcoat
products that contain coal tar may experience negative economic impact if private contractors in
the County stop using those products.
A 2007 report by the Washington State Department of Transportation included the following
data regarding costs of sealcoat:
Cost per
Gallon
$3.00
$1.80
$1.65
Performance
History
8-10 years
6-8 years
4-6 years
Product
Coal Tar Pitch
Coal Tar Blend
Asphalt Emulsion
http://ww\\;.pea.state.ml1.us/incle x. php\vaterf\vater-tvpes-and-prooratnsstormwater/mlin ic ipal-stormwatericoal-tar­
based-sea leoat
-Ill
in nesota-Ioea
I-govern ment -
fag
s. htm 1
6The blog is at:
http://eoaltarfreeameriea.bJogspot.collli.
The blog is written by Thomas Ennis, Sustainability
Officer at the City of Austin, Texas.
5
3
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Councilmembers should weigh the environmental and health benefits of banning coal
tar
products against the economic impacts that the ban could have. Committee members were
persuaded by the information about environmental effects provided by the US Geological Survey
and the American Chemical Society.
Committee recommendation (3-0):
enact Bill 21-12.
2. Should the ban be limited to coal tar emulsion products?
Some companies suggested that
refined coal tar should not be subject to the coal tar ban because refined coal
tar
is different than
crude coal tar. The USGS fact sheet on ©22 notes that coal-tar pitch is "refined" into 12
different viscosities, including RT-12, which is used in coal-tar-based sealcoats. Council staff
has not found any evidence that "refined coal tar" should be excluded from the scope of this Bill.
The Council received correspondence from the manufacturer of PaveRx, seeking an amendment
to the proposed ban to prohibit only coal-tar emulsion sealers. The manufacturer argues that the
properties of PaveRx are different because it made of refined coal tar and doesn't chip, flake,
dust, peel, or spall and therefore doesn't raise the same environmental issues. However, the
manufacturer states that PaveRx must be reapplied every 5-7 years.
7
In Council staffs
understanding, this essentially means that the product will still be eroded over time by vehicle
tires and other means. In other words, the product may last longer than regular coal-tar-based
sealcoat but will still contribute to PAH's being released into the environment.
The Committee did not recommend
excluding this product from Bill 21-12. Councilmembers
could consider whether to allow a waiver from the coal tar ban
if
the applicant for the waiver can
If
convince DEP that their product does not release PAH's into the environment.
Council members want to allow such a waiver, Council staff recommends inserting the following
new subsection (d):
@
The
~tor
may waive the prohibitions of subsections (b) and ec) for a
product
if
the applicant for a waiver shows that ordinary use of the product
does not result in the immediate or eventual release of measurable
gyantities of polycyclic aromatic hydrocarbons into the air, water, ground,
or sediments.
The Committee did not discuss this language. After the worksession, Mike Leaman, President of
Total Asphalt, submitted a letter requesting that Bill 21-12 be amended to include this language
(©67).
7
The website of another company, HASCO Inc, indicates that PaveRx should be reapplied every 4-5 years. See
)l1aint<:lm.!1~~.
html.
.hlli2:!
J
\VWjy
.hasco2000 .com/iJtm
I/propeltv
4
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This packet contains:
Bill 21-12
Legislative Request Report
Fiscal Impact Statement
American Chemical Society Report
USGS Report
EP A fact sheet
Environmental Forensics report
Summary of laws in other jurisdictions
Select testimony/correspondence
Bob Hoyt, DEP Director
Total Asphalt
Chemtek
Seaboard Asphalt Products Co.
K.A.E. Paving Consultants
North Village Home Corp.
County Health Officer memo
News articles
Follow-up letter from Mike Leaman, Total Asphalt
Circle
#
1
4
5
10
17
23
24
37
39
41
43
49
52
54
55
56
67
F:\LAw\BILLS\1221 Erosion, Sediment Control-Coal Tar\Action Memo.Doc
5
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Bill No.
21-12
Concerning: Erosion, Sediment Control
and Stormwater Management - Coal
Tar Pavement Products
Revised: June 5, 2012 Draft No. -'--_ _
Introduced:
June 19, 2012
Expires:
December 19, 2013
Enacted: _ _ _ _ _ _ _ _ __
Executive: _ _ _ _ _ _ _ __
Effective: _ _ _ _ _ _ _ _ __
Sunset Date:
......:...!.No=.!n.!.!::e~
_ _ _ _ __
Ch. _ _, Laws of Mont. Co, _ __
COUNTY COUNCIL
FOR MONTGOMERY
COUNTY, MARYLAND
By: Councilmembers Rice, Navarro, EIrich, Riemer, and Ervin
AN
ACT to:
(1)
(2)
(3)
(4)
prohibit the use and sale of coal tar pavement products in the County;
require enforcement by the Director ofthe Department of Environmental Protection;
amend the titles of Chapter 19; and
generally amend the County laws regarding water quality.
By amending the titles of Chapter 19 and adding
Montgomery County Code
Chapter 19, Erosion, Sediment Control and Storm Water Management
Article VI. GeneraL
Section 19-68
By renumbering
Montgomery County Code
Chapter 19, Erosion, Sediment Control and Storm Water Management
Article VI. General.
Sections 19-68 and 19-69
Boldface
Underlining
[Single boldface brackets]
Double underlining
[[Double boldface bracketsD
* * *
Heading or defined term.
Added to existing law by original bill.
Deletedfrom existing law by original bill.
Added by amendment.
Deletedfrom existing law or the bill by amendment.
Existing law tmaffected by bill.
The County Council for Montgomery County, Maryland approves the following Act:
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BILL
No.
21-12
1
2
Sec.
1.
The titles in Chapter 19 are amended, a new Section 19-68 is
added, and Sections 19-68 and 19-69 are renumbered as follows:
Chapter 19, Erosion, Sediment Control and [Storm Water] Stormwater
Management.
3
4
5
*
*
*
*
6
7
Article II. [Storm Water] Stormwater Management.
*
19-68. Coal tar pavement products.
*
8
9
10
11
12
liD
Definitions.
As used in this Section:
Coal tar pavement product
means
f!
material that contains coal tar and is
intended to cover an asphalt or concrete surface, including
f!
driveway
or parking area.
13
14
15
Director
means the Director of the Department of Environmental
Protection or the Director's designee.
(Q}
Use gfcoal tar pavement products prohibited.
16
17
ill
ill
A person must not use
f!
coal tar pavement product.in the County.
Both the property owner and the applicator have violated this
Section if
f!
coal tar pavement product is applied to an asphalt or
concrete surface on the property.
18
19
20
21
(£}
Sale.
A person must not sell or offer for sale
f!
coal tar pavement product
in the County.
22
@
Enforcement.
The Director must:
23
24
25
ill
ill
publish
f!
list of alternative products for use on asphalt and
concrete that do not contain coal tar; and
generally enforce this Section.
26
27
(19-68] 19-69. Authority of department of environmental protection.
*
*
*
f:\Iaw\bHls\1221 erOSion, sediment control-coal tar\bill4.doc
@
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BILL
No. 21-12
28
29
[19-69] 19-70. Violations.
Any violation of this Chapter is a Class A violation.
However,
30
31
32
notwithstanding Section 1-19, the maximum penalty for a civil violation of Article I
is $1,000 for an initial or repeat offense. Each day a violation continues is a separate
offense.
33
*
Approved:
*
*
34
35
Roger Berliner, President, County Council
Date
36
Approved:
37
Isiah Leggett, County Executive
Date
38
39
This is a correct copy ofCouncil action.
Linda M. Lauer, Clerk of the Council
Date
f:\Iaw\bills\1221 erosion, sediment control-coal tar\bi1l4.doc
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LEGISLATIVE REQUEST REPORT
Bill 21-12
Erosion, Sediment Control and Stormwater Management
-
Coal Tar Pavement Products
DESCRIPTION:
Bi1l21-12 would prohibit the use of coal tar pavement products in the
County and require the Department of Environmental Protection to
enforce this law.
Coal tar and coal-tar pitch are Group 1 carcinogens and the
Environmental Protection Agency classifies 7 polycyclic aromatic
hydrocarbons (P AH) compounds as probable human carcinogens. Of
all known PAH sources, the highest concentrations are in coal tar and
related compound creosote.
To prohibit the use of coal tar pavement products.
Department of Environmental Protection
To be requested.
To be requested.
To be requested.
To be researched.
Bob Drummer, 240-777-7895
To be researched.
PROBLEM:
GOALS AND
OBJECTIVES:
COORDINATION:
FISCAL IMPACT:
ECONOMIC
IMPACT:
EVALUATION:
EXPERIENCE
ELSEWHERE:
SOURCE OF
INFORMATION:
APPLICATION
WITHIN
MUNICIP ALITIES:
PENAL TIES:
Class A violation.
(j)
f:\law\bills\1221 erosion, sediment contrOl-coal tar\legislative request report. doc
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069382
ROC~LE,
MARYLAND
'-­
c:::
MEMORAl'IDUM
July
11,2012
TO:
FRQM:
-<
Roger Berliner, President, COUJity Council
.
Jennifer
A.
Hughes, Director,
Office
of Management andB.udget
Joseph F. Beach, Director, Department ofFinance
~
ktkr
(J
SUBJECT:
Council Bil1
21-12 - Erosion,
Sediment
Contro1-~onnwater
Management­
Coal Tar Pavement Products
Attached
please rmd the fiscal and economic impact statements for the above-referenced
legislation.
JAH:nm
c: Kathleen Boucher, Assistant Chief
AdministTative
Officer
Lisa Austin, Offices oftbe County Executive
Joy
Nunni~
Special
Assistant to the County
Executive
Patrick
Lacefield, Director,
Public Information
Office
, A
lex
Espinosa"
Office
of
Management and Budget
­
Stan Edwards, Department ofEnviton:mental Protection
Greg Ossont, Department of
General Services
Patricia Brennan, Department ofHea1th and Human Services
Angela Dizelos, Office ofManagement and Budget
Naeem Mia,- Office ofManagement and Budget
David Platt, Department ofFinance
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Fiscal Impact Statement
Council BiU
21~
U - Erosion, Sediment Control and Stormwater Management­
.
Coal Tar Pavement Products
.
L Legislative Summary
Bill 21-12 would prohibit the use and sale ofcoal
tar
pavement products in the County and
require enforcement by the Department ofEnvironmental Protection (DEP). Coal
tar
and
coal-tar pitch are Group
1
carcinogens and the Environmental Protection Agency classifies
seven
(7)
polycyclic aromatic hydrocarbons
(P
AlI)
compounds as probable human
carcinogens.
Of
all
known
PM
sources., the highest concentrations (and greatest danger to
human
life)
are
in
coal
tar
and related compounds.
.
2.
An
estimate of changes in County revennes and expenditures regardless ofwhether the
revenues or expenditures are assumed
in
the recommended or approved budget.
Includes source of information; assumptions, and methodologies used.
Alternatives to coal tar-based sealants are readily available on
the
market. Neither
the
Department of General
~ervices
(DGS) nor
the
Department of Transportation
(DOT)
use coal
.
tar-based sealant products for any
County
activities.
Based on comparable bans ofcoal tar-based sealants in Waslrington, DC and Austin,
TX.
DEP estimates approximately 10 or less enforcement actions per year. Assuming ten (10)
enforcement actions per year and lab testing services at a cost of $400 per action, the
estimated nscal impact to expenditures
is
$4,000 per year,
in
the .first year of the
ban..
This
number of enforcement actions
is
not anticipated to result
in
any
staffing
impact to DEP.
DEP cannot currently estimate a fiscal impact to expenditures resulting from outreach efforts
to advertise the ban. However, DC has a similar ban and
has
previously contacted regional
distributors, home improvement
and
hardware stores> trade associations, contractors,
and
utility companies (mcIuding PEPCO and Washington Gas); many ofthese parties are
believed
to
have taken steps to
find
alternative products. Therefore; DEP believes
that
the
County's outreach efforts should be relatively easier.
Section
19-70
of
the
proposed
bill
authorizes a
maximum
penalty of $1,000 for
an
inital or
repeat offense. However, DEP does not anticipate
that
all violations
v-ill
result
in
a citation;
some violations may only carry a notice or warning (which does not
carry
a monetary
penalty). Based on a conservative estimate, DEP estimates a total of $9,000
in
revenues from
penalties (see
chart
directly below).
Yaar
1
2
Revenues
3
4
$5,900
$3,000
$1,000
$0
.
'*
Assumes each cltation
15
at the
maxlrrlUm
penalty of$1, 000.
1
5
6
TotaJ revenues
$0
$0
$9,000
Number of enforcement actions and citations"
10 enfo["gement actions, 5 of which result in citations
3 citations
1 citation
Coal
tar~roducts
are no longer on the market
Coal tar products are no longer on the market
Coal tar oroducts are no longer on the market
9 citations over &-years at max. penalty
I
I
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3. Revenue and expenditure estimates
covering
at least the next 6 fiscal years.
Revenues over the next 6 fiscal years are estimated to be $9,000 (see chart
in
item #2 above).
The number of enforcement actions
is
expected to decrease over subsequent fiscal years as
users switch to alternative products. The total impact to expenditures over the next six fiscal
years is $5,600 (see chart directly below).
Year
1
2
3
4
Exoendltures
,
$4,000
$1200
$400
$0
5
6
Expenditures
$0
$0
$5,600
.
mvolve
testing
at cost
of
$400
per test
However, not
.
*
Assumes
that all enforcement actlOns
.
all enforcement actions are likely
to
result
in
citations.
Although the cost ofoutreach cannot be estimated at this time, the fiscal impact ofoutreach
is
expected to be limited to the
fitst
year ofthe bill's implementation.
4. An actuarial analysis through the entire amortization period for each bill that would
affect retiree pension or
group
insurance costs.
Number of enforcement actions and testina*
10 enforcement actions/testing
3
enforcement actions/testing
1
enforcement actionsJtesting
Coal tar
products
are no lOl'!g_er on the market
Coal
tar
products
are no longer
on
the market
Coal
tar
products
are
no
longer
on the market
14
enforcement
actions
over6-yeam
at
max.
penalty
Not applicable.
5. Later actions that may affect future revenue and expenditures
if
the bill authorizes
future
spending.
The bill does not authorize futme spending.
6.
An
estimate of the stafftime needed to implement this bill.
Additional
staff
time required
by
this bill cannot
be
estimated,
but
DEP
win
utilize
existing
staff resources to absorb the additional workload.
7.
An
explanation of how the addition of new staff responsibilities would affect other
duties.
DEP
will
utilize existing staff resources to absorb the additional workload.
8. An estimate of
costs
when an additional
appropriation
is needed.
Additional appropriations are not needed.
. 9.· A description of
any
variable that could affect revenue and cost estimates.
Variables that could
affect
cost estimates include the cost and
scope
ofoutreach, which
cannot
be estimated at this time. The number ofenforcement actions in
any
given year is
also subject to wide variability.
.
2
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10. Ranges of revenue or expenditures that are uncertain. or difficult to project.
Although the bill allows forpenalties of up to $1,000 per violation (per day), actual penalties
may be lower. Furthennore, not all enforcement actions result
in
citations.
In
addition, the
cost of outreach cannot be estimated at this time.
11.
If
a bill
is
Hkely to
have no
flSeal
impact,
why
that
is
the
case.
Not applicable.
12.
Other fiscal impacts or comments.
.
Assumptions and estimates regarding revenues and expenditures are approximate only_ DEP
cannot
estimate with
certainty the number ofenforcement actions perfonned
in
a
given
year
.
and the number ofcitations issued.
Both the Departm.ent of General Services (DGS) and the Department Health and Human
Services (HHS) report no fiscal impacts to their budgets resulting
from
this bill.
13.
The following con1ributed to and concurred with
this
analysis:
Stan Edwards, Department ofEnvir()nmental Protection
Greg Ossont, Department of General Services
Patricia
Brennan,
Department of Health and Human Services
Angela Dizelos Office ofManagement and Budget
. Naeem Mia, Office ofManagement and Budget
j
(
3
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Economic Impact Statement
Council Bill 21-12
Erosion, Sediment Control and Stormwater Management - Coal Tar Pavement Products
Background:
This proposed legislation would prohibit the use and sale of coal tar pavement products
in
the County and require enforcement
by
the Department of Environmental Protection. .
Coal tar and coal-tar pitch are Group 1 carcinogens. Currently, the
Use
of these products
is
prohibited in
the
District. of Columbia.
1.
The
sources
ofinformation, assumptions, and methodologies used.
Based on information provided
to
the Department ofFinance·(Finance), major retailers
such
as The
Home
Depot
do
not
sell coal
tar
pavement products in the County. It
is
not
mown
if
private contractors currently use these products in the County, however, both
the Department of Transportation and
the
Department ofPennitting Services believe that
. the price difference between coal
tar
pavement products
anq
those that do not include
coal tar is not significant enough to haveari economic impact on
tlla!
sector.
2. A description of
~y
variable
that
could affect the economic impact eStimates.
The price of coal tar pavement products vis a
vis
those manufactured without coal tar
is
the
only variable.
3. The
Bill's positive or negative effect,
if
any
on employment, spending, saving.·
investment,
incomes, and property
values
in
the County.
There is
likely.no
economic effect at
smce the price of these products
(coal
tar and
non-coal
tar) is
not
materially
different
4. If
a
Bill
is
likely
to have no economic impact,
why
is that the case?
an.
See #3 above.
5. The folloVYing contributed to and concurred with this analysis: David Platt and 11ike
Coveyou, Finance.
Dat~
J
(j)
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{-saence
&
TeClino1ogg
and E. Spencer Williams
tU.S. Geological Survey, Austin, Texas
78754,
United States
tMinnesota Pollution Control Agency, St Paul, Minnesota
55155-4194,
United States
§University of New Hampshire, Durham, New Hampshire 03856, United States
IICity of Austin, Austin, Texas
78767,
United States
l.Baylor University, Waco, Texas
76798,
United States
£nVIRonmfnTAL
'iiMid
pubs.acs.orgiest
Coal-Tar-Based Pavement Sealcoat and PAHs: Implications for the
Environment, Human Health, and Stormwater Management
Barbara
J.
Mahler/'* Peter
C.
Van Metre,t Judy
L.
Crane,* Alison W. Watts
'
§
Mateo ScoO'oins
,
II
1.
OIY
INTRODUCTION
Driveways and parking lots are common features of cities,
suburbs, and small towns. Most Single-family residences in the
U.S. have paved driveways, and we encounter parking lots at
multifamily residences, schools, offices, and commercial busi­
nesses. Most people in developed countries, when outdoors,
probably spend as much time walking on pavement as on any
other type of surface.
There are differences among paved surfaces, however. Most
pavement is concrete or asphalt. The asphalt pavement of many
parking lots, driveways, and even some playgrounds in North
America is sprayed or painted with a black, shiny coating
referred to as "sealcoat," "pavement sealant," or "driveway
sealer" (Figure lA). Sealcoat is marketed as improving
pavement appearance and increasing pavement longevity. I
In
addition to making pavement black, however, one type of
commonly used pavement sealcoat contains refined coal tar and
is a potent source of polycyclic aromatic hydrocarbons
(PAHS).2-8 The contribution of pavement sealcoat to PAH
contamination of soils, lakes, and homes has only recently been
recognized.
4 ­ 6
Coal-Tar-Based Sealcoat: A Newly Identified Source of
PAHs.
The two primary sealcoat product types on the market
are refined coal-tar-pitch emulsion and asphalt emulsion. Coal­
tar pitch, a known (Group
1)
human carcinogen,9 is the residue
remaining after the distillation of crude coal tar (a byproduct of
the coking of coal), and contains about 200 PAH compounds.
lO
Most coal-tar-based sealcoat products consist of 20-35% coal­
tar pitch as the binder. Asphalt is the residue remaining after
the distillation of crude oil and is the binder
in
asphalt-based
sealcoat products. Although the two sealcoat product types are
similar in appearance, PAH concentrations in coal-tar-based .
sealcoat are about 1000 times higher than those in asphalt­
based sealcoae
l
(Table 1).
In the U.S., coal-tar-based sealcoat is used primarily east of
the Continental Divide, and asphalt-based sealcoat is used
primarily west of the Continental Divide.
3
Coal-tar-based
sealcoat also
is
used in Canada.
12
Geographic differences in use
in North America'likely are a historical and economic artifact of
the location of most coal-tar-distillation plants near steel mills,
which historically were (and are) in the central and eastern
United States.
An
estimated
85
million gallons (320 million
liters) of coal-tar-based sealcoat are used annually in the
United States.
lI
The pavement sealcoat issue has been evolving since 2000,
when PAH concentrations were discovered to be increasing in
many urban lakes across the United States,I5 even as
concentrations of other contaminants like lead,
r.0I~chlOrinated
bi­
phenyls (PCBs), and DDT were decreasing.
6,1
This
was
an
apparent reversal from earlier reports that PAH concentrations in
the U.S. were decreasing in
re~onse
to reduced emissions from
power plants and industries. IS,I The earlier studies, however, had
focused on lakes in undeveloped watersheds, whereas the upward
trends in PAHs were in lakes in urban and suburban watersheds.
This
meant, first, that reductions in PAH emissions caused by
changes in home-heating and power-generation'· technology had
been eclipsed in urban areas by some other urban source of
PAHs/ 5 and second, that this other source
was
specific to urban
and suburban areas.
A breakthrough in understanding urban sources of PAHs
came in 2003, when staff with the City of Austin, TX, noted
elevated PAH concentrations
(LP
AH
16
>
1000 mg/kg)
in some sediment samples collected from small tributaries
and drainages in largely residential areas?O Concentrations of
PAHs this high are typical of contaminated soils at some
1
manufactured gas plant Superfund sites/ but cannot be
accounted for by common urban sources (e.g., tire wear, vehicle
emissions, asphalt)? City of Austin staff connected the dots and
hypotheSized that the source of the elevated PAHs was particles
eroded from parking lots that were coated with coal-tar-based
sealcoat.
22
Since that time, an understanding has emerged of
relations between coal-tar-based pavement sealcoat and
PAHs
in the environment.
Published;
January
24, 2012
3039
dx.doi.orgl10.1021/e,203699x I
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Sci.
Technol.
2012, 46, 3039-3045
..;>
ACS Publications
©
2012 American Chemical Society
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Figure
1.
PAHs from coal-tar-based pavement sealcoat are transported by different pathways to various environmental compartments. Once dry, the
sealcoat product
(A),
which contains high concentrations of PAHs, is abraded into a powder and becomes part of the dust on th: pavement (B).
That dust is transported by storm runoff (C) to stormwater management devices (D) or to receiving stream.s and lakes (E).
~arking
lot dust also
adheres to tires (F) that track it onto unsealed pavement, and wind and runoff transport the dust to nearby soils (G). Dust particles
~lso
are
tr~cked
on shoes into residences, where they become incorporated into house dust (H). Volatile PAHs
in
coal-tar-based sealcoat are released mto the alI"
(1).
PAH concentrations associated with each compartment and literature sources are provided in Table
1.
WHAT
ARE POLYCYCLIC
AROMATIC HYDRO­
CARBONS crAHS)? PARs. are a large group of
organic compounds composed of two or more fused
benzene rings arranged in various configurations. Those
with a low molecular weight (two or three benzene
rings) tend to be more volatile, soluble,· and biodegrad­
able than those with a higher molecular weight (four or
more benzene rings). PARs occur naturally in coal and
petroleum products and are formed by the. incomplete
combustion of organic matter, from fossil fuels to wood
to cigarettes.PARs have many urban sources, including
used motor oil, automobile exhaust,. industrial atmos­
pheric emissions, tire particles, and asphalt.13,14 PARs
always occur as a mixture of different PAR compounds}
and are ubiquitous in the urban environment. Of all
known PAH sources, the highest concentrations are in
coal tar and the related compound creosote. Most
laboratories analyze only a subset of PARs, and
concentrations of total PARs are reported as the sum
of the subset analyzed as described in Table
1.
Migration of PAHs from Sealcoated Surfaces into the
Environment.
Sealcoat doesn't remain on the pavement sur­
face indefmitely, and different applicators recommend reappli­
cation from every
1
to 2 years (e.g., ref 23) to every 3 to 5 years
(e.g., ref
24).
Tires and snowplows, in particular, abrade the
friable sealcoat surface into fine particles.s,ll The overall annual
loss of sealcoat from parking lots in a warm climate is about
2.4%
of total sealcoat applied, with wear being most rapid (about
5% per year) in driving areas.
l l
Higher wear rates have been
noted in a cold-weather climate.
7
The mobilized sealcoat particles
and associated PARs are transported to various environmental
compartments (Figure I, Table
1).
The first compartment is the dust on the pavement surface
itself, generated as the sealcoat is abraded from the surface
3040
(Figure IB). Concentrations of PARs in fine particles (dust) on
pavement with coal-tar-based sealcoat are hundreds of times
higher than those in dust on concrete pavement or on asphalt
pavement that is unsealed or that has asphalt-based sealcoae- s
(Table
1).
PARs in dust on sealcoated pavement in the central
and eastern U.S. are about 1000 times higher than in dust on
sealcoated pavement in the western U.S., supporting anecdotal
reports of geographic differences in product use
3
(Figure 2).
Stormwater runoff transports abraded sealcoat particles off
sealed pavement (Figure IC, Table
1).
The PAR concentration
measured in particles in runoff from parking lots with coal­
tar-based sealcoat (3500 mg/kg) was
65
times higher on
average than the concentration in particles in runoff from
unsealed asphalt and cement lots.
2
Concentrations in unfIltered
stormwater runoff from coal-tar-sealcoated pavement are
particularly elevated during the months following sealcoat
application. The mean kPAHI6 in stormwater runoff from a
coal-tar-sealcoated parking lot during the 3 months follOwing
sealcoat application was 1357
ftg/L
and the 3-month
mea~
during the follOwing two years ranged from 17 to 116
jlg/L.
This relatively elevated concentration persists for years-the
median kPAH 18 in stormwater runoff from a parking lot in
Madison, WI, 5 years after the last application of coal-tar-based
sealcoat,
was
52 pg/L.2S That concentration is about 10 times
higher than that in runoff from a rrrixed-use strip mall, arterial
street, and unsealed parking lot (4.8-5.7 ftg/L), more than 20
times higher than in runoff from a minor arterial street and a
commercial rooftop
(1.8-2.4
ftg/L), and about 1000 times h}gher
than in runoff from a residential feeder street (0.05 pg/L).
In many communities, the first stop for stormwater runoff is
a stormwater-retention pond or other stormwater-management
device (Figure ID), where suspended sediment and associated
contaminants settle out. Stormwater ponds are designed to
efficiently collect sediment-associated contaminants, which
creates an unintended problem for many municipalities because
PARs accumulate in pond sediment.
In
5
000
ponds sampled in
the Minneapolis-St. Paul, MN, metropolitan area, concentrations
dx.doi.org/l0.l021/es203699x I
Environ. Sd. Technol.
2012, 46,3039-3045
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'ijM-
. PAM
(!Onc~ntiation
'(mediaiiorrilean) incoaI:­
,•• ,tar-baseds.ealcoat
Or .
.. ,affected medium
PM!
con';~ntr~tid~(me4ia~or
.
affected •...•.
mediUlt];'
or
associated
with
unsealed
......•
f'~vem,ent>
'
rn.eari)inasPhal~,seakoat,
Table
1.
Concentrations of PAHs as Reported in the Literature for Environmental Compartments Shown in Figure 1, and
Definitions of PAH Summations Used
A
B
sealcoat products
pavement dust
c
D
E
runoff, particles
runoff, unfiltered water"
stormwater-management.device
sediment
lake sediment"
66000
2200
4760
685
3500
71
SO
~PAHI6
~PAHI2
~PAHI6
~PAHI6
~PAHI2
11
9
<1
54
2
S
2
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
pg/L
flg/ L
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
ng/m
3
11,22
3
4
5
2
7
~PAHI6
52
646
33
1380
ZPAH I•
~PAH16
2S
5
0,4
3
2
F
G
H
I
tires
soil
d
settled house dust
air (0.03 m from pavement),
years after sealing
air (1.28 m from pavement),
years after sealing
air (0.03 m from pavement),
after
sealing
air
(1.28 m from pavement),
after
sealing
:EPAH CMB
ZPAH 16
~PAHI6
~PAH16
6
S
5
4
28
3-8
3-8
1.6 h
1.6 h
lOS
129
1320
138
5
66
26
28
29
29
297000
5680
66
26
Ql:PAH I2 is the sum of concentrations of the 12 parent PAH (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene,
fluoranthene, pyrene, benz[aJanthracene, chrysene, benzo[aJpyrene, and dibenz[a,hJanthracene), which are those PAHs used in computation of the
probable effects concentration (PEC) sediment-quality guideline,41 less 2-methylnaphthalene. :EPAH
16
is the sum of the concentrations of the 16
priority pollutants identified by the U.S. Environmental Protection Agency,42 equal to the sum of l:PAH
12
and concentrations of
benzo[b Jfluoranthene, benzo[ghiJperylene, benzo[kJfluoranthene, and indeno[1,2,3-cdJpyrene. :EPAH
18
is equal to :EPAH
16
plus concentrations
of 1-methylnaphthalene and 2-methylnaphthalene. :EPAH
CMB
is the sum of concentrations of phenanthrene, anthracene, f1uoranthene, pyrene,
benz[aJanthracene, chrysene, benzo[aJpyrene, benzo[b)f1uoranthene, benzo[ghi]perylene, benzo[kJfluoranthene, indeno[l,2,3-cdJpyrene, and
benzo[eJpyrene. :EPAH. is the sum of concentrations of phenanthrene, anthracene, 4,5-methylphenanthrene, 1-methylphenanthrene, fluoranthene,
pyrene, chrysene, and benzo[bJfluoranthene. On the basis ofPAH data from primarily combustion sources presented in Mahler et al.,4l:PAH
12
is
about 70-75% of :EPAH
16•
:EPAHI~
is similar to :EPAH I6, as the additional compounds in the summation either are not detected or are detected at
very low concentrations.
us
"Collected >3 months after sealcoat application. cMeans for urban lakes with >70% PAH from sealcoat and 0-20% from
sealcoat. dConcentration in soil adjacent to a sealed parking lot.
Figure 2. PAHs in dust swept from sealcoated p";'king lots show a
striking geographic difference. PAH concentrations
in
dust from
parking lots in central and eastern U.S. cities, where coal-tar·based
sealcoat is commonly used, are about 1000 times higher than in the
western U.S., where asphalt-based sealcoat
is
more commonly used.
Concentrations are the sum of 12 PAHs (:EPAH I2 ), in mg/kg. (Figure
adapted from ref 3, Figures 1 and 2).
of PAHs in sediment exceeded Minnesota's Level 2 Soil
Reference Value of 3 mg/kg benzo[a]pyrene equivalents
26
(BaPeq), greatly increasing the cost for disposal.
Even a
small amount of sealcoated pavement can be the dominant source
of PAHs to sediment that collects in stormwater-management
3041
devices, as demonstrated at the University of New Hampshire
Stormwater Center.s Sediment collected from a stormwater­
management device receiving runoff from a parking lot with
coal-tar-based sealcoat contained :EPAH
I6
of393-1180 mg/kgj
sediment
in
devices receiving mixed runoff (4% sealed pavement
and 96% unsealed pavement) contained 61-638 mg/kg :EPAH
16
i
and sediment in a device in the center of an adjacent unsealed lot
contained less than 4 mg/kg :EPAR
1/
Some sealcoat particles that are not trapped by stormwater
ponds or other collection devices are transported down streams
and rivers to lakes, where they are depOSited in lake sediment
(Figure IE). Do the PARs associated with the particles
constitute a majority of PAHs in urban lake sediments, and
might coal-tar-based sealcoat account for many of the upward
trends in PAHs reported by Van Metre et al.?15
An
initial
indication comes from a comparison of PAH ratios, or
"fingerprints", of the dust collected from parking lots in nine
U.S. cities to that of PAHs in sediment from lakes in the same
watersheds:'! In the central and eastern U.S., PAH fingerprints
of lake sediment and dust from seal coated parking lots were
Similar, and were different from fingerprints of lake sediment
and dust in the western U.S., ret1ecting regional differences
in sealcoat product type used.
A
more sophisticated source­
apportionment method-a statistical approach that quantifies
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the contribution of sources with known PAH profiles to an
environmental receptor-was used to quantify the contribution
of identified urban PAH sources to P AHs in bed sediment in
40 U.S. urban lakes.
6
Coal-tar-based sealcoat was estimated to
contribute about one-half of the PAHs in the lake sediment,
when averaged across the 40 lakes; vehicle-related sources and
coal combustion- also were important contributors. PAH
concentrations in lake sediment and the proportion contributed
from coal-tar-based sealcoat were greater in the central and
eastern U.S. than in the western U.S. Using sediment cores,
trends in P AHs were investigated for eight urban lakes; of the
six with Significant upward trends, source apportionment
indicated that coal-tar-based sealcoat was the cause of the
trend in all six of them.
Turning our attention back to sealed pavement, dust from
pavement with coal-tar-based sealcoat contaminates nearby
unsealed pavement, with concentrations decreasing with
distance from the sealed pavement. s A petrographic analysis
of dust from unsealed pavement in Fort Worth, TX, found that
coal-tar pitch was the dominant
(92%)
source ofPAHs in the
8
dust. Particles are transported by adhesion to vehicle tires and
by wind from sealed to unsealed surfaces-LPAH
l6
in particles
swept from tires driven over sealed lots were 400 times higher
than in particles swept from tires driven over unsealed lots
5
(Table
1,
Figure IF). Transport of abraded coal-tar-based
sealcoat particles by wind and tires might be one reason why
PAH concentrations in dust from unsealed parking lots in
the central and eastern U.S. (median LPAH
12
27
mg/kg), where
coal-tar-based sea1coat is predOminantly used, are Significantly
higher than those in dust from unsealed parking lots in the
western U.S. (median LPAH
12
0.8 mg/kg), where the asphalt­
based product is predominantly used?
PAHs in particles abraded from coal-tar-based seal coat also
are transported by wind, runoff, and snow removal to nearby
soils (Table I, Figure IG). LPAH I6 in surface soil adjacent to
coal-tar-sealed lots at the University of New Hampshire was as
high as 411 mg/kg, and concentrations decreased with distance
from the sealed lot to less than 10 mg/kg.s The highest
concentrations were measured in areas where snow was piled
adjacent to the lots during the winter months-snowplows
were scraping the sea1coat off with the snow. PAHs in surface
soils from commercial areas in Fort Worth, TX, were
dominantly (88%) from coal-tar pitch. s
PAHs from pavement sealed with coal-tar-based sealcoat can
contaminate the indoor environment (Figure IH) as well as the
outdoor environment. In a study in Austin, TX, apartments
with parking lots with coal-tar-based sealcoat had LPAH I6 in
house dust that was
25
times higher, on average, than LPAH 16
in house dust from apartments with parking lots with other
surface
~es
(concrete, unsealed asphalt, or asphalt-based
sealcoat) (Table
1).
The presence or absence of coal-tar-based
sealcoat on the apartment complex parking lot was strongly
correlated with PAH concentrations in house dust Although
tobacco smoking, candle and incense burning, and barbecue
and fireplace use have been suggested to affect PAH
concentrations in house dust, Mahler et a1.
4
found. no relation
between any of these and PAH concentrations in the house
dust. Concentrations of individual PAHs in house dust
collected from. apartments in Austin adjacent to pavement
with coal-tar-sealcoated parking lots were about 140 times
higher than those measured in a study of house dust in
27
California. Lower concentrations of PAHs in house dust in
California are consistent with the very low concentrations of
3042
'liMN
PAHs measured in pavement dust in the western U.S. (Figure 2),
where coal-tar-based sealcoat is not commonly used.
In addition to contaminating stormwater, sediment, soil, and
house dust, PAHs from coal-tar-based sealcoat contaminate air
(Figure 1I). Several of the lower molecular weight PAHs in
coal-tar-based sealcoat are volatile, which is why sealed parking
lots and driveways frequently give off a strong smell. A recent
studl
8
reported that the
flux
of LPAH
g
from in-use parking
lots with coal-tar-based sealcoat of various ages (mostly more
than 3 years old) was 60 times higher than that from unsealed
9
pavement on average. A second studl reported that LPAHg in
air just after seal coat application was hundreds to thousands of
times higher than that above unsealed parking lots (Table I),
and that one-quarter to one-half of the PAHs in the applied
sealcoat were lost to the atmosphere during the first 16 days
follOwing application. A mass balance indicated that LPAHg
emissions from new applications of coal-tar-based sealant each
year are larger than annual vehicle emissions of PAHs for the
U.S. 29
Biological Concerns.
The detrimental effects of PAHs on
30
terrestrial and aquatic ecosystems are well documented. For
example, when fish are exposed to PAHs, they exhibit chronic
effects, including fin erosion, liver abnormalities, cataracts, skin
tumors, and immune system impairments leading to increased
susceptibility to disease. 31 When benthic macroinvertebrates­
insects and other organisms that live at the bottom of rivers and
lakes and that make up the base of the aquatic food
chain­
are exposed to PAHs, they are susceptible to a number of
detrimental effects, including inhibited reproduction, delayed
emergence, sediment avoidance, and mortality.31 The most
important mechanism by which acute effects occur in benthic
invertebrates is a nonspecific narcosis-like mode of action that
32
results in the degradation of cell membranes. Ultraviolet
(UV) radiation greatly increases the toxicity of PAHs in a wide
.
.
.
vanety
0
f
aquatIC orgamsms.
33-36
As
the importance of coal-tar-based seal coat as a source of
PAHs has emerged, several studies have looked at potential
biological effects of this particular source of P AHs. When
sediment was spiked with coal-tar-based sealcoat to prOvide a
range of environmentally relevant PAH concentrations, frogs
(Xenopus laevis)
had stunted growth or delayed development at
30 mg/kg LPAHl(j, and complete mortality occurred at the
highest treatment of
300
mg/kg kPAH 16.
37
Salamanders
(Ambystoma maculatum)
and newts
(Notophthalmus viridescens)
exposed to sediment contaminated with coal-tar-based sealcoat
at PAH concentrations similar to the highest treatment in
the frog study had stunted growth, difficulty swimming or
righting themselves, and liver problems.
38
,39 These effects were
38
magnified by the addition of UV light. At the community
level, macroinvertebrate communities exposed to sediment
spiked with coal-tar-based sealcoat had Significant decreases in
species abundance and richness at LPAH 16 concentrations
exceeding
300
mg/kg.40 Similarly, in a study of urban streams,
aquatic invertebrate communities downstream from parking
lots with coal-tar-based sealcoat suffered losses of abundance
and diversity along a gradient of increasing total PAH con­
centration, starting near the
LPAH~~Erobable
effects concen­
tration (PEC) value of 22.8 mg/kg. ,I These studies demon­
strate that PAHs in sediment contaminated by coal-tar-based
sealcoat are bioavailable and that environmentally relevant con­
centrations adversely affect amphibians and benthic commun­
ities, two robust indicators of aquatiC ecosystem health. The
finding of adverse biological effects to biota when exposed to
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sediment with PAH concentrations near the PEC has wide­
spread relevance: Of the 40 U.S. urban lakes investigated
by
Van Metre and Mahler,6 sediment in the nine lakes with the
greatest mass loading of PAHs from coal-tar-based sealcoat had
concentrations of PAHs that exceeded the PEe.
Human-Health Concerns.
Coal tar and coal-tar pitch are
listed as Group 1 (carcinogenic to humans) carcinogens,9 and
the U.S. EPA currently classifies seven PAH compounds as
probable human carcinogens (Group B2): benz[
a
Janthracene,
benzo[aJpyrene, benzo[b ]fluoranthene, benzo[k]fluoranthene,
chrysene, dibenz[a,hJanthracene, and indeno[l,2,3-cdJ­
pyrene. 42 Coal tar itself is a powerful mutagen: The muta­
genicity index for coal tar is about 1000 times that of asphalt
cements. 43 However, although coal-tar-based sealcoat has been
on the market since at least 1960,6 little has been published
to date about the contribution of the sealcoat to PAH expo­
sures and the associated potential for adverse human-health
outcomes.
The elevated concentrations of PAHs in house dust, soil, air,
water, and sediment associated with coal-tar-based sealcoat
raise the possibility of several complete exposure pathways for
humans. Incidental ingestion of house dust and soil is
particularly relevant for small children, who Lut their hands
and objects into their mouths. A recent study reported that
children living in homes adjacent to pavement with coal­
tar-based sealcoat likely are exposed to about 14-fold higher
doses of PAHs through ingestion of house dust than are
children living in residences adjacent to unsealed pavement,
and that exposure from ingestion of PAH-contaminated house
dust is estimated to be more than double that from diet, even
under conservative assumptions. Ingestion of contaminated soil
is another way that children might be exposed to PAHs from
coal-tar-based sealcoat, particularly given that ingestion rates of
soil typically exceed those of house dust. 4s Incidental ingestion
of dust directly from sealed pavement also might be important,
because the extremely high concentrations of PAHs measured
in these materials (Table 1) could translate to substantial doses
from miniscule exposures. On a long-term basis, nondietary
ingestion of PAH-contaminated house dust and soil likely are
the most important routes of exposure, but a complete human­
health risk analysis is reqUired before the cancer risk associated
with ingestion of these media can be quantified.
Other routes of exposure to coal-tar-based sealcoat, in addition
to ingestion, might have implications for human health. Relatively
high acute exposures might occur from inhalation of wind-blown
particles or fumes that volatilize from sealed parking lots,
especially during sealcoat application. Sealcoat applicators, in
particular, might be subject to substantial inhalation exposures,
but such exposures have not yet beep characterized. Other
potential routes include skin contact with sealcoat and abraded
sealcoat particles and contaminated soil, sediment, dust, and
water. Such exposures likely would be relatively infrequent and
short-term. However, PAHs are readily absorbed through the
skin,46 and circumstances that increase the frequency or
magnitude of exposure events, such as daily activity on pavement
treated with coal-tar-based sealcoat, might be associated with
increased cancer risk.
Regulatory and Retail Actions.
Research to date, as
documented here, provides a compelling weight-of-evidence
that coal-tar-based sealcoat products are an important source of
PAHs to our environment. A patchwork of actions has been
taken to either ban or restrict the use of coal-tar-based sealcoat
in the United States. The first ban was implemented by the City
3043
ItiBl,,­
of Austin, TX, in 2006. 47
As
of January 2012, IS municipalities
and two counties in four states (Minnesota, New York, Texas,
and Wisconsin), the District of Columbia, and the State of
Washington had enacted some type of ban, affecting nearly 10.4
million people.48 Other local and state jurisdictions have used
voluntary or limited-use restrictions for certain groups (e.g.) city
government) to discourage the use of coal-tar-based sealcoat. 48
Minnesota, in particular, has been actively engaged in this issue
after mUnicipalities contacted state agencies and the Minnesota
Legislature for assistance addresSing PAH-contaminated storm­
water pond sediment,49 Costs for disposing of this sediment
could reach $1 billion
if
PAHs in sediment in just 10% of the
estimated 20 000 municipal stormwater ponds in the lYfinneap­
olis-St. Paul, MN, metropolitan area exceed Minnesota's Level 2
human-health risk-based Soil Reference Value of 3 mg/kg
BaPeqso (Donald Berger, Minnesota Pollution Control Agency,
written communication, 2011). The Minnesota Legislature passed
a bill in 2009 that provides small grants to local governments for
use in treating or disposing of contaminated sediment in storm­
water ponds, provided that the governments restrict the use of
undiluted coal-tar-based sealcoat.49
As
of January 2012, 13 muni­
cipalities had passed ordinances and three municipalities have
received grants for remediation of stormwater ponds.
Several national and regional hardware and home-improvement
retailers have voluntarily ceased selling coal-tar-based driveway­
sealer products. 48 Some private applicators have chosen to use
only asphalt-based sealcoat (e.g., refs 51,52). Many profeSSional
sealcoating companies in areas unaffected by bans or restric­
tions use coal-tar-based sealcoat, however, and coal-tar-based
sealcoat products are readily available online for purchase by
homeowners.
No action has been taken at a federal level to restrict the use
of coal-tar-based seale oat. Coke product residues, such as coal
tar, are not classified as hazardous waste under the Resource
Conservation and Recovery Act
if
the product is recycled,53
This exemption allows coal-tar pitch to be used in the
production of aluminum
(~9S%
of use), commercial carbon,
built-up roofing, and pavement sealcoat.
54
Because PAHs are a ubiquitous and persistent class of urban
contaminants, a decade or more might be required to assess the
effectiveness of bans, restrictions, and/or changes in the retail
aVailability of coal-tar-based sealcoat on reducing PAH
concentrations in urban water bodies. Research on trends in
the occurrence of PCBs and DDTs supports this concern.
FollOwing national bans on use of PCBs and DDT
in
the 1970s,
it was 10-15 years before concentrations in lakes and reservoirs
decreased by one_half.
17
,ss Unlike these chemicals, all sources of
PAHs in urban watersheds will not be eliminated by banning
coal-tar-based sealcoat. However, reductions in PAH loads over
~e
might be sufficient to provide more options for disposal of
dredged material from stormwater ponds and navigation
channels and reduce risk to terrestrial and aquatic ecosystems
and human health.
II AUTHOR INFORMATION
Corresponding Author
*E-mail: bjmahler@>usgs.gov.
Notes
The authors declare no competing fInancial interest.
dx.dOi.org!10.1021/e,203699x I
Environ. Sci. Technol. 2012,46. 3039-3045
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Environmental Science
&
Technology
'#111+
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Contamination of
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dx.doi.orgI10.1021
les203699x
I
Environ. Sci. Technol.
2012. 46. 3039-3045
@
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Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic
Hydrocarbons (PAHs), and Environmental Health
Studies by the U.S. Geological Survey (USGS) have identified coal-tar-based sealcoat-the black, viscous
liquid sprayed or p'ainted on asphalt pavement such as parking lots-as a major source of polycyclic aromatic
hydrocarbon (PAH) contamination in urban areas for large parts of the Nation. Several PAHs are suspected
human carcinogens and are toxic to aquatic life.
Seale oat is the black, viscous liquid sprayed or painted on the asphalt pavement of many parking lots, driveways, and playgrounds.
Key
Findings
• Dust from pavement with coal-tar-based sealcoat has greatly elevated PAH concentrations compared
to
dust from unsealed pavement.
• Coal-tar-based sealcoat is the largest source of
PAH
contamination
to
40 urban lakes studied, accounting
for one-half of all
PAH
inputs.
• Coal-tar-based sea1coat use
is
the primary cause of upward trends in
PAHs,
since thd 1960s, in urban lake
sediment.
• Residences adjacent to parking lots with coal-taI-based sealcoat have PAH concentrations in house dust
that are 25 times higher than those in house dust in residences adjacent to parking lots without coal-tar­
based sea1coat.
'
• PAHs
move from a sealcoated surface into our environment by many mechanisms: storm runoff, adhesion
to tires, wind, fOOL traffic, and volatilization.
Volatilization
Adhesion
Wind
Original graphic courtesy of Aaron Hicks, City of Austin, Texas.
Runoff
Printed on recycled paper
U,S. Department oftha Interior
U.S.
Geological Survey
®
FaCI Sheet 2011-3010
Fehruarv 2011
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What are Sealcoat, PAHs, and Coal
Tar?
Pavement
sealcoat (also called sealant) is a
black liquid that is sprayed or painted on some
asphalt pavement.
It
is marketed as protecting
and beautifying the underlying pavement, and is
used commercially and by homeowners across
the Nation. It
is
applied to parking lots associated
.
with commercial businesses, apartment and
condominium complexes, churches, schools, and
business parks, to residential driveways, and even
to some playgrounds. Most sealcoat products have
a coal-tar-pitch or asphalt (oil) base. Coal-tar-based
sealcoat is commonly used in the central,southern,
and eastern United States, and asphalt-based
sea1coat is commonly used in the western United
States.
.
PAHs
are
a
group of chemical compounds that
form whenever anything with a carbon base is
burned, from wood and gasoline to cigarettes and
meat. PARs also are in
~hjects
and miterials, such
as automobile tires and coal tar, the production
of which involves the heating of carbon-based
malerials. PAHs are of environmental concem
because several are toxic, carcinogenic, mutagenic,
and/or teratogenic (causing birth defects) to aquatic
life, and seven are probable human carcinogens
(U.S. Environmental Protection Agency, 2009) ..
How does Sealcoat get from Driveways
and Parking lots into Streams and
lakes, Homes, and the Air?
Friction from vehicle tires abrades pavement
sealcoat into small particles. These particles are
washed off pavement: by rain and carried down storm
drains and into streams. Other seaIcoat particles
adhere to vehicle tires and are transported to other
surfaces, blown offsite by wind, or tracked indoors
on the soles of shoes. Some of the PARs in sealcoat
volatilize (evaporate), which is why sealed parking
lots and driveways frequently give off a "mothball"
smelL Sealcoat wear is visible in high traffic areas
within a few months after application, and sealcoat
manufacturers recommend reapplication every
2
to
4 years.
Coal
tar
is a byproductofthe coking ofcoal
for
the steel industry and coal-tar pitch is the residue
remaining after the distillation of coal tar. Coal-tar
pitch is 50 percent or more PAHs by weight and·
is known to cause cancer in humans (International
Agency for Research on Cancer, 1980). Coal­
tar-based seal coat products typically are 20 to 35
percent coal-tar pitch. Product analyses indicate ..
that coal-tar-based sealcoat products contain about·
1,000 times more PAlls than scalcoat products with
an asphalt base (City of Austin, 2005).
Runoff from sealcoated pavement (black surface) enters storm
drains that lead to local streams. Drain grate Onset) is marl\ed
"DUMP NO WASTE" and "DRAINS TO WATERWAYS,"
Gray asphalt pavement shows through where sealcoat has worn off the driveway of an apartment complex.
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The East-West Divide
Regional Product Use Translates to Large Differences in PAH Concentrations
Does product type really matter?
PAH concentra­
tions in the coal-tar-based sealcoat product are about
1,000 times higher than in the asphalt-based product
(more than 50,000 milligrams per kilogram [mg/kg]
in coal-tar-based products and 50 mg/kg in asphalt­
based products [City of Austin, 2005]). Anecdotal
reports, such as Web sites, blogs, and comments
by industry representatives, indicate that the coal­
tar-based product is used predominantly east of the
Continental Divide and the asphalt-based product is
used predominantly west of the Continental Divide.
During 2007-08, the USGS swept dust from seal­
coated and unsealcoated parking lots in nine cities
across the United States and analyzed the dust for
PAHs. For six cities in the central and eastern United
States, the median PAH concentration in dust from
sea1coated parking lots was 2,200 mglkg, about 1,000
times higher than in dust from sealcoated parking
lots in the western United States, where the median
concentration was 2.1 mg/kg. Although both product
types are available nationally, these results confirm
the regional difference in use patterns (Van Metre and
others, 2009).
Concentrations of PAHs in dust swept from sealed parking lots in
central and eastern U.S. cities, where coal-tar-based-sealcoat
use dominates, were about 1,000 times higher than in western
U.S. cities, where asphalt-based-sealcoat use dominates.
Concentrations shown on the map are the sum of 12 PAHs, in
milligrams per kilogram (Van Metre and others, 2009).
UFingerprinting" Shows that Coal-Tar Sealant is the Largest Source of PAHs to
Urban Lakes
PAHs are increasing
;11
urbcm lakes across the
United States.
To better understand why this might
be happening, USGS scientists collected sedi­
. ment cores from 40 lakes in cities from Anchorage,
Alaska, to Orlando, Florida, analyzed the cores for
PAHs, and determined the contribution of PAHs from
many different sources by using a chemical mass­
balance model. The model is based on differences in
the chemical "fingerprint" of PAHs from each source.
Coal-tar-based sealcoat accounted for one-half of all
PARs in the lakes, on average, while vehicle-related
sources accounted for about one-fourth. Lakes with
a large contribution of PAHs from sealcoat tended
to have high PAH concentrations; in many cases, at
levels that can be harmful to aquatic life. Analysis
of historical trends in PAH sources to 8 of the 40
lakes indicates that sealcoat use is the primary cause
of increases in PAH concentrations since the 1960s.
Identifying where PAHs are coming from is essential
for developing environmental management strategies
(Van Metre and Mahler, 2010).
~
90::
I-r..!l
z~
_.J
100
80
60
40
20
........­ Coal-tar-based sea/coat
-()- Vehicle-related sources
Wood combustion
--+_.­
Fuel oil combustion
Coal combustion
~i:
wO::
0::
<to
20..
OV'l
uw
---+- .
-+--
o..r..!l
-.i
I<t
<to::
u~
0"::
r-:;e'
.:J
<>;-'
0
1930
1950
1970
1990
2010
DATE SEDIMENT DEPOSITED
Coal-tar-based sealcoat (orange symbol) is the largest contributor
to increasing concentrations of PAHs in Lake Killarney, Orlando,
Florida, as determined by chemical fingerprinting. Similar patterns
were seen in lakes across the central and eastern United States
(Van Metre and Mahler, 2010).
@
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From Outside to Inside
Coal~
Tar Pavement Sealant linked to PAHs in House Dust
House dust is all important source
for human
exposure to many contaminants, including PAHs.
This is particularly true for small children, who spend
time on the floor and put their hands and objects into
their mouths. In 2008, the USGS measured PAHs
in house dust from 23 ground-floor apartments and
in dust from the apartment parking lots. Apartments
with parking lots with coal-tar-based scalcoat had
PAH concentrations in house dust that were 25 times
higher, on average, than concentrations in house dust
from apartments with parking lots with other surface
types (concrete, unsealed asphalt, and asphalt-based
sealcoat). PAll concentrations in the dust from the
parking lots with coal-tar-based sealcoat were 530
times higher, on average, than concentrations on the
parking lots with other surface types.
Apartments with coal-tar-based sealcoat on the parking lot had
ml!ch higher concentrations of PAHs, both in indoor dust and
in parking lot dust, than apartments with an unsealed asphalt
or concrete parking lot or with a parking lot with asphalt-based
sealcoat. Concentrations shown are for the sum of the 16 U.S.
Environmental Protection Agency priority pollutant PAHs (Mahler
and others, 2010), in milligrams per kilogram (mg/kg).
Photograph obtained from Jupiter Images.
What about other sources ofPARs?
Although
tobacco smoking, candle and incense burning, and
barbecue and fireplace use have been suggested to
affect PAH concentrations in house dust, this study
found no relation between any of these, or the many
other factors considered, and
PAR
concentrations in
the house dust. The presence or absence of coal-tar­
based sealcoat on the apartment complex parking lot
was strongly conelated with
PAR
concentrations in
house dust; the only other variable that was related to
PAH concentrutions in house dust was urban land-use
intensity (the percentage of land near the apartment
dedicated to multifamily residential, commercial,
office, warehouse, or streets) (Mahler and others,
2010).
There are no U.S. health-based guidelines for
chronic exposure to PAHs in house dust.
The only
existing guideline is for a single PAH-benzo[a]­
pyrene-issued by the German Federal Environment
Agency Indoor Air Hygiene Commission (Hansen
and Volland, 1998). The guideline advises minimiz­
ing exposure to concentrations of benzo[a]pyrene
greater than 10 mg/kg in dust to avoid adverse health
effects. That guideline was exceeded for 4 of the
11 apartments with coal-tar-sealcoated parking lots
and for 1 of the 12 apartments with a parking lot with
a different surface type. Also of concern is expo­
sure to the sealcoated pavement surfaces themselves
through play activities. Dust on some of the seal­
coated parking lots had a concentration of benzoL
a]­
pyrene that was more than 50 times higher than the
German guideline.
Photograph courtesy of CLEARCorps, Durham, North Carolina.
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Our Environment and Us
What are the Concerns?
Some PAHs are toxic
to mammals (including
humans), birds, fish, amphibians (such as frogs
and salamanders), and plants. The aquatic inverte­
brates-insects and other small creatures that live in
streams and lakes-are particularly susceptible to
PAll contamination, especially those that live in the
mud w'here PARs tend to accumulate. These inver­
tebrates are an important part of the food chain and
are often monitored as indicators of stream quality
(analogous to the "canary in the coal mine" con­
cept). Possible adverse effects of PARs on aquatic
invertebrates include inhibited reproduction, delayed
emergence, sediment avoidance, and mortality. Pos­
sible adverse effects on fish include fin erosion, liver
abnormalities, cataracts, andinunune system impair­
ments. The Probable Effect Concentration (PEC) of
22.8 mglkg of total PAHs (MacDonald and others,
2000)-a widely used sediment quality guideline
that is the concentration in bed sediment expected to
have harmful effects on bottom-dwelling biota-is
exceeded in one-third of the central and eastern U.S.
urban lakes where PAH sources were studied.
When turned over, red
sported newts that had
been exposed to sediment
contaminated with
coal-tar-based seal coat
had difficulty righting
themselves (Bommarito
and others, 201 Db). Poor
reflexes could result
in decreased survival.
Photograph by Megan
Gibbons, Birmingham-
Tumors in brown bullhead catfish from the Anacostia River,
Washington, D.C., are believed to be related to elevated PAH
concentrations (Pinkney and others, 2009). Photograph by A.E.
Pinkney.
Human health risk
from environmental con­
taminants usually is evaluated in terms of exposure
pathways. For example, people could potentially
be exposed to PAHs in sealcoat through ingestion
of abraded particles from driveways, parking lots,
or play grounds, or through skin contact with the
abraded particles, either directly or by touching toys
or other objects that have been in contact with the
pavement. Inhalation of wind-blown particles and
of fumes that volatilize from sealed parking lots are
other possible pathways. PARs in streams and lakes
rarely pose a human health risk from contact recre­
ation or drinking water because of their tendency to
attach to sediment rather than to dissolve
in
water.
Southern College.
Scientific studies
have shown a relation between
coal-tar-based pavement sealcoat and harmful effects
on aquatic life.
• Aquatic communities downstream from storm­
water runoff from sealcoated parking lots were
impaired (Scoggins and others, 2007).
• Salamanders and newts exposed to sediment
contaminated with coal-tar-based sealcoat
had stunted growth, difficulty swimming or
righting themselves, and liver problems
(Bommarito and others, 201Oa, b).
• Frogs exposed to sediment contaminated
with coal-tar-based sealcoat died, had stunted
growth, or developed more slowly than usual
(Bryer and others, 2006).
Skin contact is one way humans can be exposed to PAHs.
Parking lots and driveways with coal-tar-based sealcoat have
concentrations of PAHs hundreds to thousands of times higher
than those with asphalt-based sealcoat or no sealcoat. Photograph
obtained from Corbis Images, Inc.
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FAn
Q)
Whot is
coal tar?
References
Bommarito, T. Sparling, D.W.. and Halbrook, RS., 2010u,
Toxicity of coal-tar pavement sealants and ultraviolet radia­
tion to
A mb}'stoma Af(leu/atum:
Ecotoxicology, v.
19,
no.
6,
p.1,147-1,156.
Bommarito, T, Sparling, D.W., and Halbrook, RS., 2010b,
Toxicity of coal-tar and asphalt sealants to eastern newts,
Notaphthalmlls l'iridescells:
Chemosphere,
Y.
81, no. 2,
p.187-193.
Bryer, PJ.. ElLiott,
IN.,
and Willingham, E.J., 2006,
The
effects
of coal tar based pavement sealer on amphibian development
and metamorphosis: Ecotoxicology, v. 15, no. 3, p. 241-247.
City of Austin, 2005. PAHs in Austin, Texas, sediments and
coal-tar based pavement sealants: Watershed Protection
Department, 55
p.,
accessed September 14, 2010.
at
htlp:/lrFww.craustin.tx.us/watershed1dO>'in/uadl'/cualtw·_
draji
yuh
_study.pdf.
Hansen. D., and Volland, G.,
1998,
Study about the contamina­
tion of PAH in rooms with tar
parquetry
adhesive: Otto-Graf­
Journal, v. 9, p. 48-60.
Inlernational Agency [or Research on Cancer, 1980, Coal tars
and coal tar pitches: accessed September 14, 2010,
at
http://
ntp.niehs.nih.govlntplroc!eleventhlprofilesls048coalpcil
MacDonald, D.D., Ingersoll, CG., and Berger, TA., 2000,
Development and evaluation of consensus-based sediment
quality guidelines for freshwater ecosystems: Archives
of Environmental Contamination and Toxicology, v. 39,
p.20-31.
Mahler, B.1., Van Metre, PC, Wilson, IT, Musgrove. M.,
Burbank, T.L., Ennis, TE., and Basham, TJ., 2010, Coal-tar­
based parking lot scalcoat-An unrecognized source of PAH
to settled house dust: Environmental Science and Technology,
v.44,p.894-900.
Pinkney, AE., Harshbarger, lC, and Rutter, M.A., 2009,
Tumors in brown bullheads
in
the Chesapeake Bay water­
shed-Analysis of survey data from 1992 through 2006:
Journal Aquatic Animal Health, v. 21, p. 71-8L
A) Coal tar is a thick, black or brown liquid that is a
byproduct of the carbonization of coal for the steel
industry or the gasification of coal to make coal gas.
Q)
H''hat is the d!flerence bet}l,;een crude
coal
ta;;
cool-tal' pitch, and "rejined" coal tar?
A) Coal-tar pitch is the residue that remains after
various light oils are distilled from crude coal tar for
commercial use. The coal-tar pitch is then separated
(refined) into 12 different viscosities, RT-l (the most
fluid) through RT-12 (the most viscous). RT-12
is the viscosity used in coal-tar-based pavement
sealcoat.
Q)
HOJ.i/
con
I
tell [fa product contains coal tar?
A) To determine if the product has a coal-tar base,
look for the Chemical Abstracts Service (CAS)
number 65996-93-2 on the product Material Safety
Data Sheet (MSDS). The words "coal tar," "refined
coal tar," "refined tar," "refined coal-tar pitch," or
other similar terms may be listed on the MSDS or on
the product container.
Q)
Is sea/coat used on roads?
A) Use on roads is extremely rare. Occasionally a
private property. such as a housing development, will
choose to have the roads sealcoated.
Q)
[<;
or
use ofcoal-tor-based sealant regulated?
Scoggins, M., McClintock, N., Gosselink, L., and Bryer, P.,
2007, Occurrence of polycyclic aromatic hydrocarbons below
coal-tac-sealed parking lots and effects on stream benthic
macroinvertebrate communities: loumal of the North Ameri­
can Benthological Society,
v.
26, no. 4, p. 694-707.
U.S. Environmental Protection Agency, 2009, Integrated Risk
Infonnation System (IRIS): accessed Septi!mber 14, 2010, at
http://c/j,mb.epa.gov/ncealirisiilldex.cj;n.
Van Metre, P.c., and Mahler, B.1., 2010, Contribution of PAlls
from coal-tar pavemi!n£ sealcoat and other sow'ces to 40 U.S.
lakes: Science of the Total Environment, v. 409, p. 334-344.
Van Metre, P.C, Mahler, B.J., and Wilson, LT, 2009, PAL-Is
underfoot-Contaminated dust from coal-tar sealcoated
pavement is widespread in the United States: Environmental
Science and Technology, v. 43, no.
1,
p. 20-25.
Any use of trade, product, or tirm names is for descriptive purposes
only and does not imply endorsement by the U.S. Government.
A) Several jurisdictions, including the City of Austin,
Texas, the City of \Vashington, D.C., Dane County,
Wisconsin, and several suburbs of Minneapolis,
Minnesota, have banned use of coal-tar-based
sealcoat. Similar bans are under consideration
in
other jurisdictions.
For more information on USGS researchoD PAHs and
coal-tar-based sealcoat go to
http://tx.lIsgs.gov/coring/
allth
illgssea
leoat.
Itt
ml.
Publishing support provided
by
Lafayette Publishing Service Center
-8..!
lVIahler (mdPC
Van
Afetre
@
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WHAT
ARE COAL TAR SEALANTS?
Coal tar sealants (CTS) are used to protect, maintain and beautify
asphalt pavement for driveways and parking lots.
BE INFORMED
For more information about
the effect of coal tar sealants
on the environment visit
http://water.usgs.gov/nawga/
asphalt sealers.html or
contact Barbara Mahler of the
U.S. Geological Survey at
bjmahler@usgs.gov.
WHY
ARE COAL TAR SEALANTS USED?
Asphalt pavement develops cracks over time, and sealants may
help protect the pavement surface. However, CTS are only one
method of maintaining pavement.
PROBLEMS
WITH COAL TAR SEALANTS
• Coal tars and coal tar pitches are
"known to be human
carcinogens"
according to the U.S. Dept. of Health and Human
Services
• CTS contain 3.4% to 20% polycyclic aromatic hydrocarbons
(PAHs) dry weight. PAHs are toxic to aquatic life, and several
are suspected human carcinogens.
• CTS are a source of PAHs in stormwater runoff
• PAH "hot spots" are found in streams adjacent to parking lots
using CTS
• CTS contribute more PAHs to runoff than viable alternatives
BE PROACTIVE
Municipalities may choose to
restrict the sale and/or use of
CTS in their community. It is
already happening! The City
of Austin, TX and Dane
County, WI have banned the
use and sale of CTS. Visit
http://www.cityofaustin.org/
watershed/coaltar ban.htm
for more information.
LIMITATIONS
OF COAL TAR SEALANTS
• Tend to dry, shrink and crack with time
• Need reapplication about every 2 to 5 years, depending on wear
• Can cause surfaces to become slippery when wet
ALTERATIVES
TO COAL TAR SEALANTS
• Consider using asphalt-based sealers, which contain 0.03% to
0.66% PAHs, much less than CTS
• Evaluate using permeable asphalt, which does not need
sealed and allows stormwater to infiltrate
• Explore using gravel and concrete, which do not require
sealant and reduce the urban heat island effect
• Promote shared driveways and parking lots to reduce the
need for paved surfaces
BE CREATIVE
Consider the alternatives.
Grid gravel and pervious
concrete provide added
benefits such as stormwater
management, groundwater
recharge, durability, and an
enhanced aesthetic quality.
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Environmental Forensics
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Forensic Assessment of Refined Tar-Based Sealers as a
Source of Polycyclic Aromatic Hydrocarbons (PAHs) in
Urban Sediments
Kirk O'Reilly
a ,
Jaana Pietari
a
8:
Paul Boehm
a
Exponent, Bellevue, WA, USA
b
Exponent, Maynard, MA, USA
Available online: 07 Jun 2012
b
To cite this article: Kirk O'Reilly, Jaana Pietari
8:
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Source of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Sediments, Environmental Forensics, 13:2, 185-196
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Environmental Forensics,
13:185-196,2012
Copyright
«)
Taylor
&
Francis Group, LLC
ISSN: 1527-5922 print
11527-5930
online
001:
10.1080115275922.2012.676598
Forensic AssessDlent of Refined Tar-Based Sealers as a Source of
Polycyclic Aromatic Hydrocarbons (PAHs) in Urban SediDlents
Kirk O'Reilly,
I
Jaana Pietari,
I
and Paul Boehm
2
IExponent, Bellevue, WA, USA
2Exponent, Maynard, MA, USA
Atmospheric deposition of particles and their subsequent transport by stormwater are a major source of polycyclic aromatic hydro­
carbons (PAHs) in urban scdiments. Recently, the results of forensic analysis have been used to promote a hypothesis that refined
tar-based pavement scalers (RT-sealers) are another significant source. To evaluate this hypothesis, a suite of forensic methods was
applied to a wider range of PAH data for this study. Sediments PAH profiles are no more similar to RT-sealcrs than they are to a number
of other environmental inputs. While RT-sealers were not eliminated as a potential source in some locations, forensic methods did not
diffcrcntiate their contribution from other sources of PAHs, indicating RT-sea1ers arc not a unique or readily quantifiable source of
PAHs to the urban environment.
Keywords: polycyclic aromatic hydrocarbons (PAHs), coal tar, refined tar, pavement sealers, sediments
Polycyclic aromatic hydrocarbon compounds (PARs) are ubiq­
uitous in the environment and are commonly found in aquatic
sediments (Stout et at, 2004; Rodenburg et al., 2010). Given the
multitude of natural and anthropogenic sources that may con­
tribute PAR compounds to sediments, identifying and character­
izing PAH sources has been the subject of significant research.
Efforts to evaluate contributions of various petrogenic (fossil
fuel-derived) and pyrogenic (high temperature and combustion­
derived) sourccs have consistently identified atmospheric de­
position as a significant source of PAHs to soils, paved areas,
and sediments in most urban environments (Hwang and Foster,
2006;
Li
et al.,
2003;
Lima et al.,
2005;
Simcik et al., 1996; Stein
et aI., 2006; Su et at,
2000;
Van Metre et al., 2000; Yunker et al.,
2002). Specifically, the higher molecular weight PAHs typical
ofcombustion-derived particulate matter, consistent with motor
exhaust, coal combustion products, or wood smoke, have been
found to dominate PAH profiles in sediments that are impacted
by "urban background" sources (Stout et al.,
2004).
A number of studies have demonstrated a link between at­
mospheric sources and PAHs in sediments. Evaluation of PAR
chemistry in sediment from lakes, creeks, and reservoirs from
across the United States report temporal links between changes
in PAH concentrations and increased automobile use and ve­
hicle emissions (Simcik et aL, 1996; Stein et al.,
2006;
Su et
al., 2000; Van Metre et al.,
2000;
Dickhut et aL, 2000). In
the upper Midwest, the mass and chemistry of PARs in lake
Address correspondence
to
Kirk O'Reilly, Exponent, 15375 SE 30th
Place, Bellevue, WA 98007n, USA. E-mail: koreilly@exponent.com
sediment could bc linked to specific atmospheric sourccs as­
sociated with activities such as steel production and motor
vehicle use (Su et aL, 2000, Simcik et al., 1999). Automo­
tive emissions have been shown to be a major source of par­
ticulate PAHs in aquatic systems in the Los Angeles basin
(Stein et at, 2006) and San Francisco Bay Area (Tsai et al.,
2002). Yunker et a1.,
(2002)
demonstrated a link between sedi­
ment chemistry and atmospheric sources throughout a regional
watershed.
Since 2005, several studies have hypothesized that refined
tar-based pavement sealer (RT-sealer) is another potentially sig­
nificant source ofPAHs to urban sediment (Mahler et al. 2005;
Van Metre et aL, 2009; Yang et a1., 2010; Van Metre and Mahler
2010; 2011; Watts et al.,
2010).
The hypothesis is based on ob­
servations of elevated concentrations of PARs' in particles and
runoff associated with RT sealer-treated parking lots and com­
parison of PAH compositions in sediment and potential source
samples. Mahler et aL (2005) presented data suggesting that
mean PAH concentrations of particles (p,g PAR per kg parti­
cle) associated with RT-sealed parking lots was up to 65 times
as high as the concentration of particles associated with non­
sealed lots. During artificial rainfall events, the mean yield
(Il-g
PAHlm
2)
within sealed lots was up to
44
times that of the un­
sealed lots. Offsite
flux
during actual rain events was not mea­
sured, but PAR concentrations decreased with distance from the
source (McClintock et al., 2005).
In
a study conducted by a
different USGS research team (Selbig,
2009),
the mean PAH
concentration (ll-glL) in actual runoff from a sealed lot was six
times that of an unsealed lot, but less than
2.5
times the con­
centration of runoff from a local roadway. Maximum total PAH
185
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186
K.
O'Reilly et
at.
concentrations for runoff from the sealed lot, 96
/lg/L,
and road­
way, 98/lg/L, were similar.
Thrcc PAH diagnostic ratios, fluoranthenc (Fl)/pyrcnc CPy),
benzo[a]pyrene (BaP)/benzo[e]pyrene (BeP), and indeno[1 ,2,3­
cdJpyrene (IDP)/benzo[ghi]perylene (BGP), were used to indi­
cate similarities and differences between parking lot and sed­
iment sample chemistries (Mahler et ai., 2005; Van Metre et
al. 2009). While there were overlaps in the observed ratios for
the sealed lot particles and sediments, other potential sources
that often have similar ratios were not considered. As noted by
DeMott and Gauthier (2006), ratios did not overlap between lots
and sediments from the same urban area.
Van Metre et al. (2009) evaluated PAH concentrations and
composition ofparking lot samples and sediments from 10 urban
watersheds. Higher particulate PAH concentrations measured
in dust collected from sealed lots in the eastern United States
compared to the west were attributed to a greater use of RT­
sealers in the east. Independent data on the relative use of sealer
types by region were not presented. A FliPy versus BaP/BeP
double ratio plot was used to suggest similarities between eastern
sediments and particles from RT-sealed lots.
In Van Metre and Mahler (2010), the United States Envi­
ronmental Protection Agency (US EPA) chemical mass balance
(CMB; Coulter, 2004) model was used to estimate the rela­
tive contribution of RT-sealers versus other PAH sources in the
sediments of 40 urban lakes. The model inputs were the PAH
profiles of five standardized source types including RT-sealers,
vehicle emissions, and wood, oil, and coal combustion-related
samples. Two significant problems exist with the RT-sealer in­
puts used in the modeL First, the authors admit that they assumed
the parking lots sampled were treated with RT-sealer, and sec­
ondly, the data were prescreened to select inputs that were the
most statistically similar to the sediment data set. Coal- and
vehicle emissions-related source types were not the results of
individual samples, but the averages of data from the literature.
It
appears that the averages were calculated by summing the
published average concentrations of subclasses of coal or vehi­
cle emission sources and then dividing by the total number of
published sources. Because this approach results in weighting
the influence of each subclass by numbers of publication, and
not by their environmental contribution, it is unclear that the
calculated value represents any real source. The authors of this
study have concerns about the results of this PAH apportion­
ment exercise because it appears that' model requirements of
source sufficiency and stability were violated (Galarneau, 2008;
US EPA, 2004). These critical assumptions for receptor models
require that all potential significant sources have been consid­
ered, and that the chemistries of the identified sources are stable.
The use of source chemistry at the point of emission instead of
atmospheric deposition ignores the effect of chemical reactions
that are known to occur in the atmosphere (Galarneau, 2008;
Katsoyiannis et aL, 2011; Ravindra et aL, 2008). Atmospheric
reactions such as photolytic decay, with half-lives as short as
1 or 2 hours, and processes including nonequilibrium
gas/particle partitioning complicate the application of receptor
models for PAH source apportionment (Gordon, 1988). Models
such as the CMB do not identify sources, but only statistically
fit mixtures of sources identified by the modeler to receptor
chemistry, so they have been described as "biased by
a priori
assumptions as to the number and nature of the contributing
sources" (Galarneau, 2008, p. 8146).
Because of uncertainties associated with the results of any
one single method, it is important to develop multiple lines of
evidence when using environmental forensics to characterize
source contributions (Stout and Graan, 2010). This approach is
especially true when potential sources have similar chemistries
such as those consisting of largely weathered pyrogenic PAHs.
The goal of this study is to evaluate the hypothesis concerning
the role of RT-sealers as a source of PAHs in urban sediments by
applying multiple methods and considering a wider range of en­
vironmental samples representing potential contributing inputs.
Possible outcomes of such analyses are that the results either
support the hypothesis that RT-sealers are a dominant source of
sediment PAHs (Mahler et ai., 2005), fail to support it, or dis­
prove the hypothesis. Results that fail to support a hypothesis do
not mean it is incorrect, only that other explanations can account
for the observed effects.
Experimental Section
Environmental chemical forensic methods are based on com­
paring the chemistry of the medium of interest, in this case sed­
iment, with the chemistries of potential sources (Li et aI., 2003;
Su et aL, 2000; Burns et al., 1997). For sediments, the term
source
can have two meanings, one of which is the
processes
that create the chemicals of interest,
such as coal combustion
or vehicle emissions; the second describes the
particulate mat­
ter that transport; chemicals from the broader environment to
sediments.
Each has advantages and disadvantages in source
allocation. While there may be a better understanding of the
processes resulting in the emission sources, they can be site
specific and do not account for changes that may occur be­
tween the source location and sediment. The opposite is true
for environmental particles: Whereas all the processes resulting
in the observed PAHchemistry may not be understood; they
better represent results of both generation and fate. Because of
uncertainties in primary source characteristics and the changes
that occur as a result of reactions in the atmosphere (Gordon,
1988; Galarneau, 2008; Ravindra et aI., 2008; Golomb et aI.,
2001), data on a range of environmental particulate materials
were evaluated as potential sources of PAHs. These sources
included fresh RT-sealer, particles from RT-sealed lots, atmo­
spheric particles, coal combustion and traffic related emissions,
road dirt, roof dust, urban soil, and highway runoff. PAH data
for both sediments and sources were compiled from the lit­
erature. Asphalt-based sealers were not included in this study
becausc thcy have not bccn suggested as a significant source
of PAHs (Mahler et aL, 2005). A list of the data sets used is
shown in Table 1. Except for fresh sealer material and a coal tar
standard, the data were derived from analysis of environmental
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Refined Tar-Based Sealers
Table
1.
Data sources used in this evaluation
FillY
l87
ID/BgPd
Max
1.30
1.66
1.64
Min
1.10
0.77
0.82
0.82
0.77
0.85
0.25
NA
0.81
NA
0.78
0.61
1.06
0.50
0.90
0.19
0.47
0.55
Max
0.81
1.48
0.95
'1.29
1.18
NA
1.00
NA
0.95
1.38
1.57
1.00
1.18
3.00
1.55
1.78
Material
Coal tar
Refined tar-based pavement CRT) products
RT-sealed lots
Air particles
Roofs
Roads
Soils
Sediments
Reference
I NIST 1597a
e
2 Mahler et al. (2005)
3 Mahler et aL (2004)
4 Selbig (2009)
5 NIST 1649b
e
6 Simciket at (1999)
7
Li
et al. (2003)
8
Van Metre and Mahler (2003)
9 Selbig (2009)
10 Van Mette and Mahler (2003)
II
Selbig (2009)
12 Breault et aJ. (2005)
13 Wilson et a1. (2006)
14 Polta et at. (2006)
15 Wilson et aL (2006)
16 Potta et at. (2006)
17 Van Mette et aL (2009)
18 Van Mette and Mahler. (2010)
n'
I
(:)
PAHI6?
b
y
y
Y
Y
y
N
Y
N
Y
N
Y
N
Y
Y
Y
Y
Y
N
Min
1.36
1.26
1.24
1.26
1.25
1.18
0.58
Ll8
1.23
20
15
I
2f
6
g
6
8
3
II
Ll8
1.28
1.27
1.12
0.40
1.23
0.00
0.66
0.72
5
6
4
12
50
8
40
h
1.25
2.52
1.27
1.30
1.38
1.67
1.52
1.34
LlO
1.42
1.42
1.48
1.52
Note: NA
=
Not measured
a
Number of samples
b
Does data sel include all
16
oflhe priority pollutant PAHs yes (y) or no (n)?
C
Fluoranthene / pyrene ratio
d
Indeno[ I ,2,3-cd]pyrene / benzo[ghi]perylene ratio
e National Institute of Standards and Technology (NIST), Gaithersburg, MD
r Both results are the mean of multiple samples from Figure 2 in Simcik et al. (\999).
g
Each sample represents an average of multiple samples for both traffic and coal combustion-related emissions.
h
Each sample presents an average of three samples.
samples. While most of the studies analyzed particles, some
such as Selbig (2009) analyzed unfiltered runoff, which would
include both dissolved and particulate-associated constituents.
Because organic carbon/water partitioning coefficients for the
compounds used in the forensic analysis range from 10
4
to more
than 10
6
(Hawthorne et aI., 2007), the
PAR
profiles of the unfil­
tered samples were assumed to represent the particulate phase.
Particulate bound PAHs have been shown to dominate over the
dissolved phase compounds in environmental samples (Hwang
and Foster, 2006).
The exact number and identity of PAH compounds analyzed
differed among the studies evaluated, but typically most or all of
PAHs ofthe 16 priority pollutant of the US EPA were included.
Because of detection limit issues, fewer PARs were reported in
some cases. Individual sample data were typically available, but
in some cases results were reported as the mean of a set of sam­
ples (Simcik et al., 1999;
Li
et ai., 2003; Van Metre and Mahler,
2010). Where a concentration was listed as an estimated value
or qualified with
"J,"
it was included in the forensic analysis. To
avoid skewing results based on detection limit issues, individual
samples were excluded from the analysis if fewer than ten PAHs
were detected. PAH diagnostic ratios were not calculated for
samples where an analyte of interest was undetected. To stan­
dardize results of analysis among samples of different media
and different contaminant levels, individual compound concen­
trations were converted to the relative fraction ofthe total PAHs,
Ci,
where the concentration of each compound, [PAH]i, is di­
vided by the sum ofthe individual PAH concentrations, as shown
in Equation (1):
Ci
=
[PAH]i/2:PAHx
(1)
Forensic Analysis
The data evaluation included diagnostic double ratio plots,
(Boehm, 2006; Mahler et aI., 2005) where the ratio oftwo PAHs
was plotted on the x-axis and the ratio of a second pair of PAHs
was plotted on the y-axis. Potential differences were identified
by comparing the coordinates ofsamples to each other, to known
sources, and to published values. Based on Mahler et aL (2005),
the two PAR diagnostic ratios selected were the 4-ringedeom­
pounds Fl and Py and the 6-ringed IDP and BgP. Both ratios
are commonly used in the PAR forensic literature to identify
sediment sources (Stout et ai., 2004; Yunker et ai., 2002). While
BaP/BeP has also been used to evaluate the influence of coal
tars (Mahler et ai., 2005; Van Metre et ai., 2009), BeP data
are available in fewer published studies because BeP is not one
of the priority pollutant PARs. When using double-ratio plots
for source identification, it is critical to include an appropriate
range of potential source materials to minimize the chance of
misidentification (Yunker et ai., 2002).
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188
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Pearson correlations were used to evaluate the similarities
between sediments and sources (Yang et al., 2010; Van Metre
and Mahler, 2010). For each sample pair, the Ci-values of each
compound in one sample were set as the x values, while the
Ci-values of each compound of the paired sample were set as
the corresponding y values. The average
Ci
result ofeach source
type was used. The student
t
test was used to compare data sets
consisting of the
r
values between each source and sediments
from 40 urban 'lakes with the null hypothesis that the mean of
the Pearson's correlation population for each source type was
the samc with 95% confidcnce levcl. Thc Pcarson correlation
r
was determined using statistical algorithms in Microsoft Excel
2007 (Microsoft, Redmond, WA) Pro-UCL (EPA, Washington,
DC) was used to conduct the
t
tests.
Principal component analysis (PCA) is a statistical technique
commonly used to compare sediment samples and suspected
source materials (Stout and Graan, 2010; Sofowote et a1., 2008).
The objective of PCA is to reduce the dimensionality of data
sets with a number of interrelated variables by transforming the
data into uncorrelated principal components that account for the
observed variance (Johnson et al., 2007). By plotting the results
of each sample against the primary and secondary factors, more.
and less similar samples are identified. PCA also allows for
identification of the compounds that contribute to the observed
differences between the samples. To allow inclusion ofsediment
data from Van Metre and Mahler (2010), 11 priority pollutant
PAHs were used as the input. PCA was conducted using Systat
12 (Systat Software, Chicago, IL).
The receptor model Unmix 6.0 (Norris et a1., 2007) was used
to evaluate the sediment data presented in Van Metre and Mahler
(2010). The inputs were either the 120 samples from 40 lakes
(3 samples per lake) or the 122 samples from the extended anal­
ysis of eight of these lakes (12-19 samples per lake). Unmix
solves a general mixture problem where the data are assumed
to be a positive linear combination of an unknown number of
sources of unknown composition. Using concentration data for
a given selection of chemical species, the model estimates the
number of sources, source compositions, and source contribu­
tions to each sample (Norris et al., 2007). Like the CMB, Unmix
was developed to evaluate atmospheric sources for air pollution
monitoring, but similar approaches have been used to evaluate
sediment source data (Bzdusek et al., 2004). A critical differ­
ence between the two models is that the chemistry of potential
sources is not an input to Unmix.
Results and Discussion
The results of forensic analysis depend on the chemistry of the
samples considered, so it is important to understand the over­
all nature of the PAH chemistry. Evaluation of the PAH con­
centration histograms can suggest whether a sample contained
PAHs from a petrogenic or pyrogenic source(s) and whether
the sample had weathered. PAH histograms also provide qual­
itative information about similarities and differences between
samples and sources. Challenges arise when potential sources
are similar, as it possible to misattribute the contribution of these
sources.
Figure 1 contains average compositional PAH histograms
for a number of environmental inputs and urban sediments.
The three sediments and the modeled RT-sealer contribution are
from Van Metre and Mahler (2010). The similarity among the
different source types stands out, especially in the patterns of
the 4- to 6-ringed compounds. This pattern is consistent with
PAHs originating from pyrogenic sources. The patterns for all .
these materials are well known in the sediment literature, and
are consistent with what is typically called "urban background"
(Stout et aI., 2004, p. 2987). Similarities between RT-sealers
and other environmental samples are not surprising, even if
sealers are not the source, because this pattern represents the
balance between the relative forces that generate and decay
PAHs.
The histograms indicate that fresh refined tar-based sealers
have a greater concentration of the lower molecular weight PAH
(;ompounds such as naphthalene, acenaphthene, fluorene, and
anthracene than environmental samples from studies listed in
Table 1. These four lower molecular weight PAHs are depleted
relative to the fresh product in most samples, including dust col­
lected at lots sealed with refined tar-based sealers. Differences in
PAH compositional patterns of fresh product and samples from
sealed lots can be explained by the weathering of the lighter
compounds (Bums et al., 1997).
Double-ratio plots for 40 urban lakes, RT-sealed lots, and
other environmental sample types are shown in Figure 2. Table
I shows the range of diagnostic ratios for each sample type. A
regional trend is observed in these lake sediments, with samples
from the central United States more toward the upper right
corner, samples from the west toward the lower left, and eastern
samples between the two. Van Metre et al. (2009) suggested
that such a trend could be explained by an unreferenced claim
of lower use of RT-sealers in the west compared to the other
two regions (Van Metre et al., 2009). Other regional differences,
such as the concentration of coal-based electricity generation,
might also account for the results. The apparent regional trend
may be an experimental artifact. In another study, 50 samples
collected from 10 ponds in a single metropolitan area (Polta et
al., 2006) had a similar range of ratios as those from the three
regions (Figure 3).
To more closely evaluate the double ratio results of the RT­
sealer and other environmental samples, sediment data were re­
moved from Figure 4. Samples from RT-sealed lots in Texas and
Wisconsin grouped closely with material such as roof dust and
highway runoff. While the possibility of the presence of some
sealer in these materials cannot be eliminated, it seems unlikely
for the roof dust, which is not in direct contact with tires that
might have driven on sealed pavement. If just these two diag­
nostic ratios are considered, one could argue that there may be
more similarity between the test plot samples with freshly ap­
plied sealer and the sediment samples from the central United
States, but forensic evaluation requires the use ofmultiple meth­
ods and, as will be seen in the PCA result, unique chemical
 PDF to HTML - Convert PDF files to HTML files
0.25
~
w
Refined tar sealer
0.20'
r
J
Refined Tar-Based Sealers
189
W_ _ AT - " "
parking Iota
UO,15
0.10
0.05
O~-r'-~~~~~~~~~~~~
0.25
eRoofdust
1. ...
...
11.11111,1
e
Atmospheric particles
0.20
_0,15
U
(UG
CO!:;
o~-.,-~~~~~~~~~~~~
1
llhlllll,1
.....
. , rban
sedlment-Modeled
U
RT~sealer
contribution 38%
1l.25
o
Soli
0.20
Q
0.15
0,10
{),05
o~~~~~~~~~~~~~~~
0..25
0..20
e
Urban sediment-Modeled
'RT·sealer contribution 52%
CD
Urban
sediment-Modeled
'AT.sea1er contribution 83%
Uo.·
15
0.10
Figure
1.
Polycyclic aromatic hydrocarbons (PARs) 'concentration histograms for five environmental inputs and three urban sediments. The modeled
refined tar-based pavement sealers (RT-sealers) contribution is from Van Metre and Mahler (2010).
similarity between sealers and sediment samples from the cen­
tral United States is not supported.
In prior studies (Mahler et al., 2005; Van Metre et al., 2009),
PAH ratio and double ratio analyses have been a primary forensic
methods applied to evaluate the hypothesis concerning sealers.
Because of uncertainties introduced by overlapping ranges for
various sources, these types of ratio analyses are more useful
for distinguishing between clearly different sources (such as pet­
rogenic and pyrogenic) than for differentiating among similar
ones such as a wide variety ofpyrogenic sources ofPAHs (Stout
et al., 2004; Boehm, 2006). A number of combustion sources
have been shown to have
FI/Py
ratios consistent with the range
for coal tar and RT-sealers reported by others and' included in
this paper (Costa and Sauer, 2005; Lima et al., 2005; Yunker
et aL 2002). All appropriate potential sources must be included
when evaluating the relative contribution of each to environ­
mental sinks such as sediment. Yunker et
aI.
(2002) considered
more than 20 source classes and a variety of chemical ratios in
an attempt to link combustion sources to sediment chemistry
throughout a regional watershed, and argued that a limited as­
sessment can result in misleading relationships between PAH
sources and sinks. In another study, 18 potential source types
were considered when evaluating the origin ofPAHs in sediment
samples (Burns et al., 1997).
The results ofthe CMB model (Van Metre and Mahler, 20 10)
and double ratio analyses are combined in Figure 5. If results
of the CMB model were consistent with results of the dou­
ble ratio method, one would expect there to be a relationship
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190
K.
O'Reilly et al.
1,00
1.60
Q.
1.40
·0
-
Q.
g
120
e
1.00
0,00
000&0-s.
II
III . .
.
II
II
.....
-l~
~
0
III
-
O'f£;A
.l>
..
-
..
I::.
tOO
1.60
a.
uo
-.
A
Q
1-.
.
0
eO
i
A
to
of6
e
1.20
1.00
••
0.80
0.60
III
0.00
O,40+---,--....---r----.--...,.---,----.
0.40 tt60 0.80 1.00 1.20 1.40 HID
1.80
O.40J--.,.---..---.---.....----,.----,.-----.
0.40
OJ:lO
0.80 1.00
1.20
1.40
1.60
1.80
FIIPy
LEGEND
• Central
(2)
Fl/Py
• RT sealant
(2)
AT lOt (4)
0
HIghWay
(13)
4
Test plot (3)
)C
Roof dust (10) .. Road dirt {14)
• RT
lot
(3)
• SolI
(lS.HI)
QEastem
IDWesfem
AT sealant
(2:)
(>
RTlot (4)
QHlgJway{1S)
4Tesl
plct
(3)
~
Roof
dUSt (10) •
Road
(lrt
(14)
• AT IIX
(3)
801(15.16)
il
*
Figure 2. Polycyclic aromatic hydrocarbon (PAH) double-ratio plot com­
paring urban sediments with RT sealer, dust from sealed parking lots,
atmospheric particles, roof dust, road runoff, and urban sediments. The
sediments arc classified by regions as identified in Van Metre and Mahler
(20 I0). The numbers in parenthesis refer to the reference in Table I.
Figure 4. Double-ratio plot highlighting the similarities between environ­
mental samples that may represent sources of polycyclic aromatic hydro­
carbons (PAHs) to urban sediments. The numbers in parenthesis refer to
the reference in Table L
between the PAH ratios and modeled fraction of sealer contri­
bution. No relationship was noted as samples within each of
four classes of percent RT-sealer contribution were calculated
using the CMB model (:::;25%, 26--50%,51-75%, :0::76%) are
spread across the range of PAH ratios. A similar lack of consis­
tency has also been demonstrated between CMB results and the
diagnostic PAH ratios FIIPy versus BaP/BeP (O'Reilly et aI.,
2011).
Based on the selection of sources, it is not surprising that
CMB results suggest that sealers are a major contributor to
sediments. As noted by the authors, for most model runs they
selected sealer sources for which they only assumed the pres­
ence of sealer, and of which the average Pearson coefficient
(r)
between source and the 40 lake sediments was greater than 0.95.
The remaining sources had
r
of 0.83 (wood smoke), 0.67 (tun­
nel air), 0.55 (coal emissions), and 0.43 (fuel oil combustion).
Sealer sources with average Pearson coefficients of 0.62, 0.55,
and 0.38 were reported by the authors but the results of CMB
modeling with these sources were not presented (Van Metre
and Mahler, 2010). Using the compiled data set showed similar
1.80
1,80
UIO
0..
1.40
<!J
.....
a..
e
411.20
1.00
.
.
+
1I
1.00
0..
At.
A.A
'l>
"tAO
• •
~
• • II.
tI>
0
III 1.20
<:>
(too
0.00
0.40+---.---...--..---..---.__-.-----.
0.40 0.60 0.80 1.00
t
.20
1.40 1.60 1.80
...
FIfPy
~
1.00
1
0.80
..
A
",t!' •
¢
Q
(:;
..o"e,
<>
. , .
OJiO
~
<
0.40,
,
0.40 0.00
0.801.00
UID
1.40
Hi\!
1.BO
LEGEND
• Central
o Eastem
FHPy
• Western
.. MN
ponds
LEGENg
¢
0-25%
&
51-7(}'1"
Figure 3. The range of polycyclic aromatic hydrocarbon (PAH) ratios for
10 ponds from one metropolitan area is simil ar to the range for samples
taken across the country.
• 26-5Q%
>7r:tr9
Figure 5. Comparison ofdouble-ratio plot results to chemical mass balance
(CMB) model output.
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Refined Tar-Based Sea]ers
Table
2.
t-test' results for comparison ofPearson coefficients for each lake sediment and source type.
Product
(n
6)
191
=
lLAir
(n
2)
=
WI Roof
(n
8)
WI Lots
(n
=
7)
Texas Lots
(n
=
8)