Putting Things into Perspective: Coal Tar and PAH sources

It is important to reiterate the claims of City of Austin and USGS with regards to Refined Tar-Based Pavement Sealants:

It has been claimed that by banning refined tar-based pavement sealers this would result in an 85-90% reduction in PAH (Polycyclic Aromatic Hydrocarbon Hydrocarbon) loads.  In general, COA and USGS claim that almost all environmental PAHs are due to refined tar based sealer.

In the TCEQ Aquatic life studies, TCEQ found no impairment in the aquatic life in the year 2003. 

In 2003, US EPA, ATSDR, TDH and TCEQ stated that the sediment in Barton Springs Pool did not present a danger to humans.

Mahler said she’s certain that coal-tar sealants are the prime source of PAH in streams and apartments she surveyed.  “The only thing that it could be is coal tar,” Mahler said.
Columbus Dispatch, February 22, 2010.

COA and USGS continue to tie “higher” PAHs to use of refined tar sealers, even though through the use of environmental forensic analysis could identify the source of the PAHs in questions.  This type of analysis was not utilized by COA or USGS in any of their studies.

In a recent presentation by an official from City of Austin Watershed Protection Department (dated January 15, 2010) stated that Austin’s ban was a “precautionary” measure (implying that Austin’s ban was based upon the precautionary principle).

COA and USGS frequently state that refined tar based sealer is made from crude coal tar, when in fact it is not.  It is made from refined tar.

COA stated in one of its studies that coal tar is a hazardous waste by-product of the steel manufacturing industry.  That statement is false.  Neither crude coal tar or refined tar are hazardous wastes.

USGS Fact Sheet 089-03 entitled “Quality of Sediment Discharging from the Barton Springs System, Austin, Texas, 2000-2002. One of the finding of this study is that PAHs concentrations from sediments that were from more-urbanized areas were 10 to 100 greater than sediment from lightly-developed areas. The final conclusion of this study was “The results of the study described in this report indicate that urbanization of the watershed has not yet resulted in extensive degradation of the quality of sediment discharging from the Barton Springs System”.  

USGS Authors Recognize other PAH Sources:

Van Metre, Mahler and Furlong, 2000. Urban Sprawl Leaves its PAH Signature. ES&T 34: 4064.

“The presence and distribution of PAHs in the environment are largely a product of the incomplete combustion of petroleum, oil, coal and wood.  Anthropogenic (man-made) sources such as vehicles, heating and power plants, industrial processes, and refuse and open burning are considered to the principal sources to the environment.”

Another USGS study where the USGS authors recognize other PAH sources:  

Town Lake Bottom Sediments: A Chronicle of Water Quality Changes in Austin, Texas, 1960-1998. USGS: Peter Van Meter and Barbara Mahler, 1999.

-“PAHs are trace contaminants that occur naturally in crude oil, coal, and other hydrocarbons. They also are produced by combustion of hydrocarbons, resulting in many urban sources including: industrial and power plant emissions; car and truck exhaust; tires; and asphalt roads and roofs. Eliminating PAHs from urban runoff is difficult because of their varied sources”. (page 3)

-“Total PAH concentrations in recently deposited sediment in Town Lake are about 16 times the concentrations in 1960, increasing from about 700 ppb in 1960 to 11,400 ppb in 1998. The increase corresponds with increases in traffic in greater Austin”. (page 3)

-“The relation of PAH concentrations to Austin traffic is evidence of the importance of nonindustrial sources of PAHs to streams and lakes and indicates that vehicle emissions, road and tire wear, and engine oil leaks could be major sources of PAHs.” (page 3)

Yet another USGS study where the one of the USGS authors recognize other PAH sources:

Long, G., Ayers, M., Callender, E., Van Metre, P. 2003. Trends in Chemical Concentrations in Sediment Cores from Three Lakes in New Jersey and One Lake on Long Island, New York. U.S. Geological Survey Water-Resources Investigation Report 02-4272.

It states; “Concentrations of PAHs in sediment generally increased with population growth and urbanization, probably as a result of increased fossil-fuel combustion (gasoline and home-heating fuels and other uses (roads and parking lots paved with asphalt) associated with increased urban development and vehicular traffic. This finding is supported by low concentrations of PAHs in Packanack Lake sediments in the 1930’s, before the watershed was urbanized and when automobiles were comparatively rare. As vehicular use and urbanization increase in these watersheds, the general increase of PAH concentrations in lake sediments can be expected to continue.

Data from this study indicate that changes in population, land use, and chemical use in the urbanized watersheds over the period of sedimentary record have contributed to upward trends in concentrations of trace elements and hydrophobic organic compounds. Although downward trends were observed for some constituents in the years after their concentrations peaked, concentrations of most constituents in urban lake cores were higher in the most recently deposited sediments than at the base of each respective core and in the reference lake cores. Similar trends in concentrations of these constituents have been observed in sediment cores from other urban lakes across the United States”. (page 2)

And “As vehicular use and urbanization increase in these watersheds, the general increase in PAH concentrations in lake sediments can be expected to continue”. (page 21)

This is just a few of the hundreds of studies that recognize that there are other sources of PAHs in the environment and these sources make up the majority of environmental PAHs.

In the USGS study:

Mahler, Van Metre, Wilson and Musgrove, 2010, Coal-Tar-Based Parking Lot Seal Coat: An Unrecognized Source of PAH to Settled House Dust. ES&T: 44 (3) pp. 894-900.

USGS makes the claim that there is an increased risk of cancer in those apartments that utilized refined tar based sealer in the parking area.  USGS used an overly simplistic risk model in their analysis.  When using the peer-reviewed, more sophisticated model (WTC Criterion), the analysis showed that PAH (Polycyclic Aromatic Hydrocarbon Hydrocarbon) exposure risk was essentially at background levels.

In the MPCA paper, MPCA assumes that most environmental PAHs are from refined tar based pavement sealer (like USGS and COA).  When PCTC commissioned an Environmental Forensics expert to look at MPCA data the conclusion was the primary source of PAHs from the data was not from refined tar based pavement sealer and the general hypothesis that PAHs from refined tar based pavement sealer are a the primary source of environmental PAH is not supported by the data. 

COA claims that more that 660,000 gallons of refined tar-based sealant was applied annually in the Austin area.  COA summarized their watershed characteristic in the study PAHs in Austin, TX-Sediments and Coal-Tar Based Pavement Sealants. There are several interesting facts that can be derived from this summary:

?The total sealed parking area of the watershed is only 7.24% of the total watershed.

?Using COA total sealed parking area (in acres), industry accepted coverage rates and using several assumptions to derive an artificially high number.  This is a huge contrast to what COA and USGS have claimed. 

There are four graphs shown below which will help put Refined Tar-Based Pavement Sealer into perspective vs. other PAH sources:

Graph:  PAH Content from Various Sources (mg)

Graph:  PAH Content from Various Sources (mg)

As you can see, in terms of PAH content, Refined Tar-Based Pavement Sealer would be a minor contributor of Polycyclic Aromatic Hydrocarbon Hydrocarbons in the environment.

Graph:  Sources of PAH Contributions Equivalent to Rain Event on Freshly Sealed Residential Driveway (50 square meters)

Graph: Sources of PAH Contributions Equivalent to Rain Event on Freshly Sealed Residential Driveway (50 square meters)
-Sources: Mahler, Van Metre et al.2005 and Van Metre & Mahler 2003.

As you can see the one drop of used motor oil or Auto Exhaust (15 miles) contribute more PAHs to the environment than the washoff from a 50 square meter sealed driveway.

Graph:  Sources of PAH Contributions Equivalent to Rain Events on Freshly Sealed Residential Commercial Lot (1 acre)

Graph:  Sources of PAH Contributions Equivalent to Rain Events on Freshly Sealed Residential Commercial Lot (1 acre)

As you can see, one teaspoon of used motor oil and ½ oz. of Denorex contain more PAHs than the sealer washoff.  Five seconds of Austin vehicle exhaust contains the same amount of PAHs as the sealer washoff.

Another item that would help put PAH levels into perspective is to show that Austin waterbody PAH levels are not extraordinary; in fact they are quite typical.

Sources: Van Metre et al. 2000.  ES&T 34: 4064 ; Geismer Report.  COA unpublished results.

Graph: Austin Waterbody PAH levels are not extraordinary-Sediment measurement typical:

Graph: Austin Waterbody PAH levels are not extraordinary-Sediment measurement typical