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How do these findings apply to
<br />urban lakes and reservoirs?
<br />The concentrations of PAHs in
<br />lakes and reservoirs across the Nation are
<br />increasing, as indicated by USGS studies
<br />of 38 reservoirs and lakes conducted in
<br />18 metropolitan areas across the country
<br />(Van Metre and Mahler, 2005). Sedi-
<br />ment cores (vertical tubes of mud) were
<br />collected from reservoir and lake bottoms
<br />(see photo below); analysis of these cores
<br />provides a reconstruction of histori-
<br />cal water quality over time, much like
<br />using tree rings to reconstruct histori-
<br />cal climate. Runoff carries soil, debris,
<br />and attached contaminants to lakes and
<br />reservoirs, which settle to the bottom; as
<br />the sediment builds up, changes in water
<br />quality are recorded in the successive
<br />sediment layers.
<br />USGS findings show that concen-
<br />trations of total PAHs in the majority of
<br />lakes and reservoirs in urban and subur-
<br />ban areas across the Nation increased sig-
<br />nificantly from
<br />1970 to 2001.
<br />The increases
<br />were greatest
<br />in lakes with
<br />rapidly urban-
<br />izing water-
<br />sheds (urban
<br />sprawl); for
<br />example,
<br />over the last
<br />10 years, the
<br />concentrations
<br />of PAHs in
<br />Lake in the Hills (suburban Chicago, Illi-
<br />nois) increased ten -fold as the watershed
<br />was rapidly developed. Further study is
<br />needed to assess direct links between the
<br />use of sealcoat and PAH trends in these
<br />urban lakes and reservoirs across the
<br />Nation.
<br />What are the implications of these
<br />studies?
<br />The study of parking lot surfaces by
<br />the USGS and the City of Austin show
<br />that abraded sealcoat could be a major
<br />source of PAHs to urban and suburban
<br />water bodies in watersheds across the
<br />Nation where sealcoat is used. Such find-
<br />ings have implications that extend beyond
<br />Texas as sealcoat is used nationwide;
<br />further studies would help to evaluate
<br />the potential impacts of sealcoat on the
<br />aquatic environment in other parts of the
<br />country. Identification of this source may
<br />influence future strategies for controlling
<br />PAHs in urban environments. In the past,
<br />sources of PAHs in urban watersheds
<br />were thought to be dominated by numer-
<br />ous nonpoint sources, such as leaking
<br />motor oil, tire wear, vehicular exhaust,
<br />and atmospheric deposition. Such
<br />sources are difficult to quantify or control
<br />because of their diffuse nature. In con-
<br />trast, sealcoated parking lots are specific
<br />areas that contribute directly to urban
<br />stormwater runoff (see photo below),
<br />and the use of sealcoat is voluntary and
<br />controllable. To address PAH con-
<br />tamination in streams, the City of Austin
<br />Council banned the use of coal -tar based
<br />sealcoat, effective January 2006 (Nancy
<br />McClintock, written communication, City
<br />of Austin, November 2005).
<br />Possible alternatives to coal -tar
<br />based sealcoating of parking lots and
<br />driveways include the use of concrete and
<br />unsealed asphalt pavement, and the use of
<br />asphalt -based sealcoat that contains lower
<br />levels of PAHs.
<br />Currently, the use of coal -tar based
<br />sealcoat is not federally regulated. In
<br />1992, the U.S. Environmental Protection
<br />Agency excluded coke product residues,
<br />including coal tar, from classification as
<br />hazardous wastes if they are recycled.
<br />Under the Resource Conservation and
<br />Recovery Act, coal -tar based pave-
<br />ment sealants are products that contain
<br />recycled coal tar and, therefore, are not
<br />regulated.
<br />Contacts for additional information
<br />Peter Van Metre and Barbara Mahler
<br />U.S. Geological Survey
<br />8027 Exchange Drive
<br />Austin, Texas 78754 -4733
<br />(512) 927 -3506 or pcvanmet @usgs.gov
<br />(512) 927 -3566 or bjmahler @usgs.gov
<br />Mateo Scoggins
<br />City of Austin
<br />Watershed Protection and Development
<br />Review Department
<br />505 Barton Springs Road, 11th Floor
<br />Austin, Texas 78704
<br />(512) 974 -1917 or
<br />mateo.scoggins@ci.austin.tx.us
<br />Links to related publications, data
<br />and maps
<br />City of Austin Coal Tar Sealant
<br />Information
<br />http :Ilwww ci. austin.tx. uslwatershed/
<br />bs_coaltar..htm
<br />USGS frequently asked questions
<br />http: //water. usgs. gov /nawgalasphalt
<br />sealers.html
<br />Basic information on the toxicity of
<br />PAHs to biological organisms,
<br />U.S. Environmental Protection Agency
<br />(USEPA)—
<br />http:/Iwww.epa.gov/R5Super/ecologyl
<br />h tmI/toxprofiles. htrn#pahs
<br />General information on PAH
<br />exposure, Agency for Toxic Substances
<br />and Disease Registry (ATSDR)—
<br />http: /www atsdredc.govltoxprofiles/
<br />phs69.htinl
<br />References
<br />Mahler, B.J., Van Metre, P.C., Bashara,
<br />T.J., Wilson, J.T., and Johns, D.A.,
<br />2005. Parking lot sealcoat: An unrec-
<br />ognized source of urban PAHs: Envi-
<br />ronmental Science and Technology,
<br />vol. 39, no. 15, p. 5560 -5566.
<br />Van Metre, P.C. and Mahler, B.J., 2005.
<br />Trends in hydrophobic organic con-
<br />taminants in urban and reference lake
<br />sediments across the United States,
<br />1970 -2001: Environmental Science
<br />and Technology, vol. 39, no. 15, p.
<br />5567 -5574.
<br />City of Austin. 2005. PAHs in Austin,
<br />Texas. (http /www.ci.austin.tx.us/
<br />watershed/dawnloadslcoattar draft
<br />pah_study.pdf)
<br />U.S. Geological Survey
<br />2 City of Austin
<br />
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