-“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)
In the study, “Urban Sprawl leaves it PAH Signature” (Van Meter et al. 2000) states the following: “One intriguing possibility suggested by the results of this study is that urban growth or sprawl outside the watershed may adversely affect water quality within the watershed. This is most evident when a watershed has undergone only a relatively minor change in degree of urbanization. For example, Austin, TX, is one of the most rapidly growing cities in the country, but the majority of the growth there has occurred around the fringes of the city and outside of the watershed of Town Lake. This growth has contributed to large increases in vehicle traffic in the Town Lake watershed; traffic on MoPac Expressway, most of which lies within the watershed and which crosses Town Lake, almost doubled between 1990 and 1997. The large increases in traffic offer an explanation for why PAHs more than doubled in Town Lake from 1975 to 1990 while percent urban land use only increased by 5%. This suggests that urban sprawl in outlying areas may affect traffic patterns and water quality in the inner city”.
Also in the same study, “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 be the principal sources to the environment”.
In addition, “The increase in PAHs in new urban settings cannot be attributed solely to urbanization of the watersheds. This is most clearly illustrated by those watersheds in which urban levels are stable. The increase in PAH concentrations in these watersheds is, however, coincident with increases in automobile use. Among the sources of PAHs related to automobiles are tire wear, crankcase oil, roadway wear, and car soot and exhaust. Trends in PAH from the 1970s to the present compare well to trends in VMT on freeways and major arterial streets for the associated urban areas for all sites and ages of urban development”.
Historically the City of Austin has been routinely testing their water, soil and sediment for quality. PAHs were detected in areas of Town Lake (a segment of the Colorado River that flow through downtown Austin receiving water from other urbanized creeks) since 1991. Sediments in four urbanized creeks were sampled and identified at PAH “hot spots” by COA scientists. One of these “hot spots” was in the Barton Springs Pool.
It would appear that USGS became more involved with the refined tar sealer story around February 14, 2003.
It would appear at this point the City of Austin (COA) and USGS began to conduct a study based upon COA assumptions and findings that Refined Tar-Based Pavement Sealer was a major contributing source of PAH contamination to Austin’s waterways.
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”. (page 6)
The great majority of particles that are easily mobilized and washed off during a rainfall are removed by the first ≈2.6mm of rain or less. (pg. 1733)
Sources of contaminants were major roadways and roofing material. (pg. 1737-1738)
Yields of all the PAHs were elevated close to a major expressway. (pg. 1740)
This is the USGS study produced with COA:
Mahler, Van Metre and Wilson, 2004 [Revised 2007], Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) and Major and Trace Elements in Simulated Rainfall Runoff From Parking Lots, Austin Texas, 2003 (version 3): U.S. Geological Survey Open-File Report 2004-1208, 87p. [Online only].
As a result of the numerous errors contained in this original study, Pavement Coating Technology Council filed a Data Quality Act Challenge against USGS.
45 statements or topics were challenged:
Authors of the USGS study conceded in whole or in part to 33 issues.
USGS released Version 3 to replace previous versions.
Summary of the study:
-This study determined trends in hydrophobic organic compounds (including PAHs) since 1970 using sediment cores collected from 38 lakes across the country.
-Trends in concentrations of ΣPAH9 were examined.
-Increasing trends of PAHs in 42% of the 38 lakes sampled and decreasing in only 5%. Increasing trends in PAHs are almost exclusively in lakes with urbanized watersheds.
-“Van Metre et al., however, investigated PAH trends in 10 urban lakes, all of which are included in the study, and concluded most were coincident with urbanization and increases in vehicle traffic in the water shed. Here, we see increasing PAH trends in urban settings across the country”(pg. 5570).
-Changes in PAH assemblages indicate combustion sources are responsible for increasing trends in the urban lakes (pg. 5570).
-No mention of refined tar based sealer in this study.
-The study could not detect different PAH inputs from refined tar-based vs. asphalt based sealer in-use lots let alone from others sources of PAHs.
-There was no comparison to previously measured PAH loading settling from air.
-There was no comparison to rooftop runoff to drainage features
-There were no specified proportions of overall PAH loading to waterways.
-No chemical fingerprinting was performed. Only ΣPAH13 was utilized in study. Therefore, source(s) of PAHs is sheer speculation on the part of USGS. See Environmental Forensics under the PAHs section.
-Referenced that City of Austin claim that 2.5 million liters of sealcoat was used in the city annually. If you refer back to the Austin Studies section, you will see that is a gross overestimate.
-The study states that refined tar-based pavement sealer is made from crude coal tar. This is simply not true. Refined tar-based pavement sealer is made from refined tar or RT-12.
-This study claims “Here we present evidence suggesting that parking lot sealcoat would indeed be the dominate source of PAHs to watersheds with residential and commercial development” (page 5560).
-“Previously identified urban sources of PAHs, such as automobile exhaust and atmospheric disposition, have been difficult to control or even quantify because of their nonpoint source nature. In contrast, sealed parking lots are point sources, and use of the sealant is voluntary and controllable” (page 5565).
Pavement Coating Technology Council (PCTC) responded to the study with the following letter to the editor of ES&T:
To summarize these comments:
-The authors were unable to replicate the computations and identify valves used from the cited sources for a number of the data points represented in Figures 4-6 of ref. 1.
-With the PAH ratio analysis, they could not identify the source of the values presented for stream sediment samples and the values that they could identify from the City of Austin appear to contradict the interpretation developed by the authors.
-With regards to the mass balance analysis, they could not identify the source of the values presented from one watershed, the values presented for the other watersheds do not appear to match those from cited sources and previously published values suggest the relative contribution of PAHs from parking lot sources is substantially less than the “majority” source suggested by the authors.
Summary of study:
-Reiterates that refined tar based sealcoat was a major source of PAH to streams in Austin, TX. Not “could be” or “may be” but a statement of fact.
-The study presents new data from nine U.S. cities that show nationwide patterns in concentrations of PAHs associated with sealcoat. The study assumes that 100% of the PAH in the road dust that they gathered was attributed to refined tar based sealcoat. The PAH analysis that they ran cannot distinguish between used motor oil and other sources of PAHs.
-Again, the authors of the study would leave the reader to believe that refined tar based sealer is made from crude coal tar. This type of sealer is made from refined tar. Also, the amount of refined tar in sealer (concentrate) is 20-25%.
-Refined tar based sealer is typically sold only in the Midwest and the East Coast, not in all 50 states as the authors state.
-Total number PAHs analyzed were ∑PAH12. This is insufficient in performing a chemical fingerprint. Cannot determine source of PAHs based on the PAHs analyzed. See environmental forensics under the PAH section.
-Number of samples from sealed pavements out weighed number of samples from non-sealed pavements by over 3:1.
-Number of samples from Midwest and East Coast out weighed the number of samples from West Coast by 1.6:1. 66% of the West Coast samples were from on single location, Mountlake Terrace, WA (Seattle, WA).
-Authors never establish how they determined if a pavement was sealed with refined tar based pavement sealer or asphalt based pavement sealer.
-Authors state that elevated concentrations of PAHs in dust from sealcoated pavement in central and eastern cities cannot be attributed to urban sources of PAHs invoked in the past, such as used motor oil; burning of wood, coal and oil; tire-wear particles; and vehicle exhaust. As all of these sources are expected to affect both sealcoated and unsealcoated pavement, they cannot explain the large differences (80X) in concentrations from sealcoated and unsealcoated pavement in the central and eastern cities.
-The authors suggested regional differences in the role of refined tar based sealer as a source of sediment PAHs. This hypothesis is based on the observation of elevated PAH concentrations in some sediments collected in the eastern U.S. and sealed lot dust, together with an unreferenced claim of regional differences in the type of sealants used. However, the results of correlation evaluation indicate no regional treads linking sediment and sealant chemistry. Even in the eastern U.S., there is no apparent relationship between sediment any source correlation. Regional difference in the deposition of PAHs have been detected and seem to be attributed to factors such as the amount of coal used in industrial processes and electricity generation (EPA 2007). Coal-based industrial are the primary source of atmospheric PAHs in the Midwest, while vehicle exhaust dominates in California.
The below mentioned USGS study was the basis of the above mentioned studies:
Van Metre, Mahler, Wilson and Burbank, 2008, Collection and Analysis of Samples for Polycyclic Aromatic Hydrocarbons in Dust and Other Solids Related to Sealed and Unsealed Pavement From 10 Cities Across the United States 2005-07: U.S. Geological Survey Data Series 361, 5p.
Summary of Study:
-The study gives the reader the pre-conceived idea that the refined tar based pavement sealer were a major source of PAHs in streams.
-Sampling from sealcoated areas were from pavement scrapings which most certainly allowed for cross-contamination from other PAHs sources. This is a continuation of the notion that refined tar sealer is the primary contributor source of PAHs on a pavement.
-The authors mention other potential sources of PAH (incomplete combustion, vehicles, urbanization) and does not mention how these other source fit into the whole PAH picture. The authors then explain in detail about the Austin study and the biological effects study (Scoggins and others, 2007).
-Total number PAHs analyzed were ∑PAH12. This is insufficient in performing a chemical fingerprint. Cannot determine source of PAHs based on the PAHs analyzed. See environmental forensics under the PAH section. This would be considered a data gap.
-Authors of the study when using composite sampling utilized an approximation method (this was not explained) of sampling equal amounts within the composite sample.
-The authors offered no explanation how they determined how they determined if a lot was sealed with asphalt based sealer or refined tar based sealer.
-68.25% of the total samples were from sealed lots.
The study describes an evaluation of PAH in indoor and outdoor dust collected from apartments and their associated parking lots. Of 23 apartments tested, Mahler et al. (2010) determined that 11 had refined tar based pavement sealer (CT) and 12 were unsealed or coated with asphalt based sealer (NCT).
The Study found that median total PAH concentrations of 4,760 ppb and 9.0 ppb in dust collected from refined tar based pavement sealer lots (CT) and lots sealed with asphalt based sealer or no sealer at all (NCT), respectively. The median total PAH concentrations of 129 ppb (CT) and 5.1 ppb (NCT) are reported for indoor dust collected. The presence of refined tar based pavement sealer was reported to explain 48% variance total PAH concentrations in indoor dust. Other factors included land use, frequency of vacuuming, indoor burning, and more were evaluated. The study states that only urban land uses intensity near the sampled apartment has a significant relationship with total PAH concentrations.
Study states that tobacco smoking is a significant source of PAHs in urban homes only. There are scientific studies which state that this is false.
The study states that heating with coal, vehicle emissions and carpeting have not been demonstrated to be significant factors in PAH concentrations in settled house dust based up a review of scientific literature. There are scientific studies which state that that statement is false.
USGS incorrectly states that refined tar based pavement sealer is made from crude coal tar. It is made from refined tar.
USGS incorrectly states that refined tar based sealer is sold in all 50 states. This product is predominantly sold east of the Continental Divide.
The method utilized by USGS to determine if a coating was refined tar based or asphalt based was a rapid screening test (see Supporting Information from study). This rapid screening test is not recognized by any testing standards organization nor federal/state governments for this application.
USGS makes the assumption that all PAHs collected are from abraded refined tar based sealer and not from any of the thousands of other sources in the environment. Chemical fingerprinting would have been helpful to determine the source of the PAHs but USGS ran EPA’s 16 priority pollutant PAHs, which is insufficient to establish a chemical fingerprint.
USGS states that median concentration of PAHs in dust swept from parking lots in six cities was 2200 ppb. This is a reference to a previous USGS study (same authors) which implies that refined tar based sealer is a major PAH contributor in the United States. It should be noted that chemical fingerprinting analysis was not performed in this study and all PAHs in the dust gathered was attributed to refined tar based pavement sealer and no other source.
There was a lack of precision in selection of sample locations contributes to variability between the sampled areas and consequently, uncertainty regarding external influences when evaluating the results.
Small sample size (especially give lack of precision in sample location selection).
Particle size fraction evaluated not appropriate for dermal and ingestions exposures.
Dust loading (amount of dust) was not evaluated. Only PAH concentrations in settled house dust were evaluated. Both items need to be examined in order to do a proper evaluation.
Incomplete evaluation of independent variables.
The raw QA/QC data was not presented in the study. This information would be required for a proper evaluation of data quality. An example of this was why PAHs were detected in 20% of the blank samples.
Due to a lack of site selection or exclusion criteria other than presence or absence of refined tar sealer parking lots, other potential factors may have been overlooked or unaccounted for. For example, little or no information is presented to support the classification of the refined tar based sealed lot, which can affect the variability of the data.
Site selection was based solely on the rapid screening test (see introduction).
No criteria were provided for selection of specific sample locations within each parking lot other than avoidance of painted areas and drip lines.
Chemical Fingerprinting was not performed on the dust to verify the source of PAHs (combustion sources, crankcase oil, etc.). USGS assumes that all the PAHs in the dust are derived from refined tar based pavement sealer.
No criteria were provided for selection of apartments other than presence or absence of refined tar based sealed parking lots based on the coffee/tea test. Additional criteria such as apartment age, flooring type and age, and period of time occupied by current owner could have been used to obtain as uniform a sample population as possible and thereby improving comparability between samples.
It appears that the NCT apartments represent newer housing stock compared to CT apartments. To the extent that older apartments reflect longer-term accumulation of PAHs, for example if the apartment is located nearby a heavily traveled roadway, then apartment age may be a significant variable that has not be evaluated.
The study appeared that no field rinsate samples were collected as part of QA/QC procedures. Given the elevated levels of PAHs observed, it would have been helpful to evaluate the decontamination process by collecting rinsate samples to verify the collection equipment was being decontaminated correctly. Since standard operating procedures were not provided in the Supplementary Information, it is not known what measures (if any) were taken to reduce cross-contamination of samples.
The range in the area sampled among apartments (1.6-13 square meters indoor and 2.0-7.5 square meters outdoors). The rationale for this variability is not provided. This could bias the PAH concentrations high or low, depending upon the sampled location and the loading at that location.
USGS failed to utilize EPA and ASTM standards regarding sieved dusts samples that would obtain the size dust that would most likely adhere to skin surface.
USGS only provided the PAH analytical data in the Supplementary Information so the influence of the independent variables could not be verified.
Other variables that should have been considered but not reported include apartment and flooring age and degree of sealcoat wear.
If parking lot surface type is believed to be a significant factor in explaining indoor and parking lot dust PAH levels, one might expect that degree of sealcoat wear should also be a factor.
Other factors such as size of apartment complex or size of associated parking lot might also be expected to be factors in determining PAH levels in indoor dust, but this data was not presented.
PAH analytical data in the Supplementary Information was evaluated in an attempt to identify patterns in PAHs detected in CT and NCT samples. The information was insufficient to identify unique patterns in the dataset. Observations appear to most closely resemble what would be considered an “urban background” profile.
Metrics (measure) for Evaluating Dust Exposure
Both PAH concentration and dust loading for each living area are needed to assess exposures. While PAH concentrations are useful in providing the amount of PAH in dust, it does not provide information about the amount of dust that is available on an exposure are or surface. USGS only evaluated PAH concentrations.
EPA (2008) and ASTM (2005) and CS3 Inc.(vacuum manufacturer 2004) recommend evaluating both concentrations and loading metrics when evaluating exposures to dust. This was not done in the USGS study.
Although there are over 100 PAHs, seven of these PAHs have been classified as probable human carcinogens (Group 2B) by EPA (2010). Although studies in humans do not adequately demonstrate that benzo(a)pyrene is responsible for inducing carcinogenicity, there is sufficient animal data demonstrating carcinogenicity of these seven PAHs. To quantify the carcinogenicity of the seven PAHs, a relative potency factor of carcinogenicity was assigned to each of the seven PAHs with benzo(a)pyrene used as the standard compound.
Table 2 in Mahler et al. (2010) lists analytical results separately as the sum of total PAHs (16 PAHs total) and the sum of the seven carcinogenic PAHs. However, the seven carcinogenic PAHs have not been modified by their relative potencies to benzo(a)pyrene. This would mean that the total of the seven PAHs have been artificially inflated to yield a higher overall PAH concentrations.
Comparison to health-based Standards
As noted by Mahler et al. (2010), there is no regulatory standard for PAHs in indoor or outdoor dust. Mahler et al. (2010) relied on a German Federal Environmental Agency (FEA) value of 10 ppb for benzo(a)pyrene, established by their Commission for Indoor Air Quality. This FEA value is not health-based criteria. FEA selected this value as the maximum limit of benzo(a)pyrene in house dust in an attempt to minimize exposure to residents. In other words, exceedance of the FEA value does not provide information about residential exposure or risk level.
One additional item is that USGS stated is that coal tar based flooring adhesives were sold in the United States. Upon speaking with various individuals that have been involved with the carbon products and coatings industries with a combined experience of over 100 years, have never heard of such an adhesive being sold in the United States. This product may have been sold in Germany but in all likelihood not sold into the United States.
World Trade Center Criterion
Multiple federal, state and local agencies collaborated on development of indoor air and dust screening criteria for chemicals of potential concern (including the seven PAHs) in an attempt to assess environmental heath conditions or residences in the vicinity of the collapsed World Trade Center Buildings (WTC 2003). This health-based criterion is based on the toxicity of the seven PAHs relative to Benzo(a)pyrene and assumes exposure via both ingestion and dermal exposure pathways for an individual from age 1 through 31 years. The WTC criterion also takes into account ingestion of dust via hand-to-mouth contact.
The WTC health-based criterion of 34 ppb meters squared is considered relevant to residential indoor dust evaluations.
Using the Mahler et al. (2010) data and correctly adjusting for the relative potency factor of the seven PAHs, the median seven PAHs indoor dust loading level for an apartment with a refined tar based sealer parking lot is 3.4 ppb meters squared (the standard is 34 ppb meters squared). In other words, these levels are well below health-based standards derived in accordance with WTC methodology.
The exposure model described by Maertens et al. (2008) used in the USGS study, is not as sophisticated as that developed for the WTC criterion.
Dietary PAH Intakes
On average the ATSDR (1995) estimates that a total daily intake of PAHs includes 0.16-1.6 ppb from food, 0.207 ppb from air and 0.027 ppb from water. The World Health Organization (WHO 1998) provides a daily intake estimate from food of 0.1-8 ppb. The WHO (1998) notes that while PAHs may be found on fruits and vegetables due to atmospheric deposition and/or due to food processing such as frying and roasting, the highest levels of PAHs have been found in smoked meat (over 100 ppb) and fish (up to 86 ppb).
Assuming exposure to the seven PAHs in dust at the highest detected concentrations for a CT location reported by Mahler et al. (2010), the total daily intake of the seven PAHs would be 0.28 ppb. This intake not only is shown to be below an acceptable risk management level through comparison with the WTC criterion, but also consistent with other background exposures via food and air.
Short-comings in the study design introduced uncertainly in data quality and in the influence of other variables.
Both concentrations and dust loading are important factors in evaluating chemicals in dust. The USGS study did not evaluate dust loading.
Chemical Fingerprinting was not performed on the dust to verify the source of PAHs (combustion sources, crankcase oil, etc.). USGS assumes that all the PAHs in the dust are derived from refined tar based pavement sealer. USGS relied solely on the coffee/tea field screening test to determine if a lot contained refined tar pavement sealer or not. This coffee/tea test is not a standard recognized test so its accuracy in identifying refined tar based pavement sealer is uncertain.
The USGS did not compare PAH results to a health-based standard to determine the potential risk associated with the levels measured in house dust. Using the WTC criterion indicates that cancer-causing PAHs measured by Mahler et al. (2010) are below levels of concern. In fact, the highest level measured by Mahler et al. (2010) in indoor dust is half of the of the WTC screening level, even though PAH concentrations in dust may be overestimated due to selected sampling method.
Intake of cancer-causing PAHs in dust occurs ever day through the air that we breathe and food we eat. Levels measured by Mahler et al. (2010) that could be taken in via house dust are consistent with background intake levels via food, air and water.
USGS states that refined tar based pavement sealer might represent the most important, nondietary exposure pathway of the seven PAHs for children living at these residences. Based upon the more advance WTC criterion, we see that this statement is false.
USGS Podcast-03:17-BM-“Well, as we worked our way up the watershed and we looked at PAHs coming from roof tops, no they did not appear to be coming from roof tops. Are they coming from vehicle emissions? No, they don’t appear to be coming from vehicle emissions because when we started using catalytic converters on cars decreased PAH emission by 10 to 50 (??) and we don’t see that in the cores so that eliminated that”.
Furthermore, the author states that in another study that PAHs are increasing all over the county. Even though the authors content that refined tar based pavement sealer is available in all 50 states, that statement is incorrect. Refined tar based sealer is sold in the eastern United States and in the Midwest. How would the authors explain increases in PAHs in the Western US?
USGS Podcast-02:44-BM-“What got our attention that there were one group of contaminants that were increasing and that was the PAHs, polycyclic aromatic hydrocarbons, were increasing primary in urban lakes all across the United States”.
Lastly, on the USGS podcast, the interviewer asks the author what they should do if they have a refined tar based sealer on the pavement near their home:
USGS Podcast-06:32-Interviewer-“So if a person lives near a driveway or a parking lot that is covered by coal tar based sealer what should they do”?
USGS Podcast-06:37-BM-“Well, we haven’t done any studies that directly test any of these methods but I have read some other studies that say using a door mat to wipe your feet will certainly go a long way decreasing the particles that are being tracked in from the outdoors. Also, obviously taking your shoes off would prevent you from tracking particles indoors. That would be another strategy. In fact that would decrease in general the amount of dust and outdoor particles that are in your residence”.
-Again, the authors of the study would leave the reader to believe that refined tar based sealer is made from crude coal tar. Refined tar based sealer is made from refined tar, not crude coal tar. Also, the amount of refined tar in sealer (concentrate) is 20-25%.
-The authors claim that as sealcoat abrades into particles, they become mobile and be carried offsite by water, wind or mechanical tracking. The source of this information was the Austin Photographic Wear Study (see Austin Studies). The purpose of this study was to digitally determine the wear rate of refined tar based pavement sealer on a parking lot. This study did not determine the fate of abraded pavement sealer.
-The authors utilized a “rapid screening test” (see Supplementary Information, page 1) to determine if a pavement has been coated with asphalt based or refined tar based pavement sealer. This test has not been accepted as a standard test method by any of the Standards Organizations (such as ASTM).
Yang, Van Metre, Mahler, Wilson, Ligouis, Razzaque, Schaeffer and Werth, 2010, Influence of Coal-Tar Sealcoat and Other Carbonaceous Materials on Polycyclic Aromatic Hydrocarbon Loading in an Urban Watershed. ES&T: 44 (4), pp.1217-1223.
-Petrography classifies particles primary by size, shape and the optical properties color and fluorescence.
-Yang et al. used a statistical chemical correlation to identify similarities between sealed lot dust, sediments and some atmospheric sources.
-Yang et al. found PAHs in 6 out of the 10 sediment samples.
-Based on the methods presented and given the abundance of coal tar related material, in urban sediment, it was not possible to confirm that the material identified by Yang as refined tar in either soil or sediment was derived from refined tar based sealant.
-Yang et al. found statistical similarities between urban sediments in both refined tar based sealed lot dust and atmospheric source such as wood combustion products.