Background
Executive Summary
The report was submitted on behalf of PCTC in conjunction with a meeting with COA on January 14, 2004 regarding the voluntary elimination of refined tar sealers in Austin, TX.
Based on refined tar based sealers and other PAH containing materials, the PCTC does not agree with the COA conclusion that the elimination of refined tar sealers would eliminate PAH input into the Barton Creek/Springs watershed. In addition, PCTC felt that refined tar based sealers were being inappropriately singled out as the main source of PAHs in the springs which is contrary to the scientific consensus that the activities of urbanization (vehicle exhaust, rubber tires, asphalt roads, etc.) are the primary source of PAHs, not any single material.
The following conclusions were reached in this report
-PAHs associated with the subject parking lot/roadway area do not pose a health risk for users of Barton Springs pool.
In comparison to normal dietary intake of PAHs, consistent exposure to sediments containing the highest measured levels of PAHs (unlikely in any event given the concentrations were actually identified within a limited area of a drainage ditch) would represent an insignificant increase in average daily intake. For context, the PAHs associated with one grilled 6-ounce pork chop amounts to 65 times the average daily intake associated with the highest sample results reported.
Samples of soil and roadway runoff materials, even those with the highest detected PAH concentrations, are consistent with typical urban background levels.
Crankcase oil and vehicle emissions, not asphalt debris, are consistently identified as the primary source of PAHs transported in the environment from roadway runoff.
Elevated PAH levels identified in the area were restricted to samples that contained visible asphaltic materials, expected to contain PAHs, and were apparently not being transported substantially.
While refined tar based sealers and asphalt are expected to contribute PAHs in deposited roadway debris, the physical forms of these materials have low potential for leaching and are poorly taken up by biological organisms.
Appropriate prioritization of particular sources of PAHs would require chemical analyses for additional PAHs. The set of PAHs included in the COA-commissioned study were not sufficient to distinguish the potential contribution of CTE-based sealers from asphalt roadway material itself, typical parking lots debris (including tire particles, dust with adherent combustion byproducts, and motor oil) and discarded asphalt roofing
materials.
Prior to developing any source control or management strategies, it would be
necessary for the COA to complete a characterization adequate to identify significant contributions from particular sources in order to ensure that management efforts could have an impact.
Review of City of Austin's Current Testing Protocol
In summary, results were presented for 24 samples collected at 15 locations including soil samples at depths ranging from 0 to 22.5 feet in depth below ground surface as well as samples of material accumulating on a parking lot and scrapings of the parking lot surface.
The collection of accumulated material on top of a roadway/parking (S-1, S-3) and scrapings from such surfaces (S-4 and S-5) is not typically included in environmental site investigation and there are not standardize protocols for collecting/analyzing this type of sample. (page 3)
While standardized laboratory protocols do not pertain specifically for the handling, extraction, and analysis of samples scraped from roadways (S-4, S-5), the use of the standard soil protocol is probably sufficient for general identification of PAH compounds in known PAH containing materials. Any quantitative comparisons between results from these samples and results from standard soil samples should take into account the uncertainty associated comparing samples from distinctly dissimilar matrices.
The notable analytical limitation for this investigation is the lack of analytical results for a broader set of PAH compounds. The chemicals included in the laboratory analyses include only a small subset of PAHs. While the analyzed compounds are standard for generic environmental investigations, an investigation looking for specific PAH sources could have included an expanded set of analyses to help differentiate among potential sources. Different materials and original sources of PAHs produce distinct patterns (profiles) of PAH compounds, many of which are identifiable using expanded sets of PAH analyses. Most notably, the absence of results for methylated forms of PAHs precludes using a straightforward profiling approach to distinguish between the contribution from coal tar-derived materials (e.g., CTE sealers) versus petroleum derived materials (e.g., asphalt). Laboratories handling environmental samples can provide
analyses for methylated PAHs.
Boring B1 was located within the "area of primary concern" and the highest overall PAH concentrations (138.54 mg/kg – sum of reported PAHs) found were reported for the 0 to 0.5 foot bgs sample at this location. Because PAHs are naturally occurring and ubiquitous in the environment and in food through both environmental inputs and food processing, there is a normal dietary intake of PAHs that has been characterized. According to ATSDR (1995), the average intake of carcinogenic PAHs in the American diet is 1-5 μg (micrograms) per day. Exposure to the deposited materials at the surface at boring B-1 (the Geomatrix sampling location with the highest concentration of PAHs) for children playing in the outfall area would not significantly increase PAH intake beyond normal dietary intakes. Playing in this specific location over 6 years with the associated incidental ingestion of surficial particles would result in an increase of average daily intake by 0.04 μg per day over a lifetime. This value is based on a standard USEPA approach to characterizing incidental soil ingestion and the 90 percentile estimate for the amount of time per day 5-11 year-old children play in gravel or sand (i.e., 2 hrs) (USEPA 1997).
For example, from a typical dietary intake range of 1-5 μg/day, adding in routine exposure at the sampled location would yield a range of 1.04 –5.04 μg/day for overall intake of the corresponding PAHs. By way of contrast, the carcinogenic PAHs associated with one 6-ounce grilled pork chop amount to approximately 1.3 μg (ATSDR 1995). These comparisons point out the limited change in normal PAH intake that could correspond to exposure in the area with the highest PAH levels measured in the Geomatrix report (i.e., location B-1). Obviously, routine incidental ingestion of materials from this limited area is highly unlikely in any case.
The other samples evaluated in the Geomatrix report reflect sampling of the material
accumulated on a parking lot surface (S-1 and S-3) and scrapings of the parking lot surface (S-4 and S-5). As expected for roadways constructed and sealed with PAH-containing materials, PAH concentrations were reported above detection limits in all of these samples and were higher than those found in environmental (i.e., soil or sediment) samples. Samples S-1 and S-3 were noted to include a "high" percentage of abraded parking lot particles assumed to be surface sealant. Presumably, other normal parking lot debris containing PAHs (e.g., asphalt, motor oil, tire particulate) were present as well, and without definitive analyses of PAH profiles, the proportionate amount of total PAHs from the various sources cannot be established. Also, distinguishing between abraded tire particles and surface sealer particles is highly uncertain on normal visual inspection.
Interpretations
The results of the Geomatrix report indicate clearly that elevated PAHs are only found where observable roadway-associated, asphaltic materials were located. The report concludes that there is no active migration of PAHs to subsurface soils or groundwater. This conclusion is consistent with studies of PAH leachability from asphaltic materials that demonstrate there is very low potential for PAH transport via leaching from roadway materials (Kriech 2003; Townsend 1998). The limitation of detectable PAH levels to samples containing visible roadway materials in the parking lot and lack of a complete transport pathway is also consistent with the analysis of PAH levels downstream in the Barton Springs Pool area. An analysis conducted by the Agency for Toxic Substances and Disease Registry also provided a quantitative evaluation of potential health risks (ATSDR 2003). The ATSDR report concluded that PAHs found in the sediments of the Pool would contribute at most an excess lifetime cancer risk probability of 2.6 in one hundred million, well below the risk probability the USEPA uses to determine the need for comprehensive site specific considerations, i.e., one in one million excess lifetime risk. The ATSDR report was peer reviewed by the Texas Commission of Environmental Quality, the USEPA, and the Texas Department of Health. All three agencies concurred with the ATSDR's conclusion that the water and sediments of Barton Springs Pool did not pose a health risk to people swimming and playing in the pool.
While the report to the COA concludes specifically that the accumulation of asphalt seal
coating particles is the source of anomalously high PAH findings for the unnamed tributary, there is no presentation of an analytical approach used to distinguish between various expected sources of PAHs. Further, given the set of PAHs included in the analyses from the laboratories, it is not clear how refined tar based sealant PAHs could be readily differentiated from petroleum-derived (e.g., motor oil and road or roofing asphalt) PAHs.
In summary, the sampling and analysis sponsored by the COA supports the following
conclusions:
Elevated PAHs were only found in samples that contained visible asphaltic materials. In general, elevated PAHs were only found on the land (or parking lot) surface in samples with observable roadway (PAH-containing) material. Samples of soil and roadway runoff materials contained PAH concentrations consistent with typical urban background soil levels. PAHs found from the scraping or sediment samples from the paved parking lot were found at expected concentrations. PAHs bound in asphaltic materials have a low potential for leaching. PAHs associated with the subject parking lot/roadway area do not pose a health risk for users of Barton Springs Pool. An evaluation sufficient to distinguish the contribution of PAHs from CTE-based asphalt sealers, asphalt roadway material itself, typical parking lot debris (including tire particles, dust with adherent combustion byproducts, and motor oil) and discarded asphalt roofing materials has not been completed and would require chemical analyses for additional PAHs to differentiate the actual source(s).Review of refined Tar based sealers as potential PAH sources
There are several key factors regarding PAHs in the environment relevant to considering and communicating the potential significance of refined tar based sealers and other PAH-containing materials as sources of environmental chemical exposure. First, while PAHs are ubiquitous chemical compounds in our environment and are released through a wide range of natural and human activities (particularly any combustion-related activities), the general public does not recognize the types of chemical release and exposure resulting from these routine activities. Failure to recognize that some exposure to PAHs in the environment is routine and unavoidable can lead to concerns about particular materials that are disproportionate relative to their actual contributions to environmental PAHs. Failure to recognize that the predominant sources relate to normal modern activities such as operating motor vehicles, burning and energy production can also misdirect concerns. Familiarity and acceptance of the presence of cars and roads, for example, leads many people to differentiate between the importance of regulating roadway construction materials and runoff compared to "combustion byproducts and leachate in the environment" though the same chemicals end up in the environment.PAH Sources Associated with Roadways
Elevated levels of PAHs have long been understood to be associated with runoff from paved areas, such as roads and parking lots (Barrick 1982; Tetra Tech 1988; Eganhouse et al. 1981; Mulliss et al. 1996; Yamane et al. 1990). USEPA recognizes that the source of most PAH compounds in urban runoff is vehicles, including automobile and truck engines that drip oil (USEPA 1993). Another source of PAHs in urban runoff appears to be dust particles that accumulate on roads. It has been hypothesized that these particles are from atmospheric fallout processes and regional air pollutant emissions (Pitt and Barron 1990).A report sponsored by the U.S. Department of the Interior and the U.S. Geological Survey (Lopes and Dionne 1998) found that crankcase oil and vehicle emissions were consistently identified as the primary sources of semi-volatile compounds such as PAHs in storm water. It stated further that emission of PAHs from automobiles is directly related to their concentration in gasoline.
Another study evaluated the likely sources of PAHs found in rivers and estuaries (Zakaria 2002). Using fingerprint analysis of PAH profiles and the ratio of methylphenanthrene to phenanthrene found in sediments, they concluded that the major source of PAHs was petroleum. The likely source of the PAHs was determined to be crankcase oil that was either spilled or leaking from vehicles onto the road surface. The authors concluded that the fingerprint analysis excluded crude oil, fresh lubricating oil, asphalt, and tire-particles as major contributors to river and estuary sediments. The authors' conclusion is consistent with the limited mobility of roadway-associated particulate matter compared to light, liquid oil and combustion byproducts, for which waterborne and airborne transport is easier. A report by Pawluck and co-workers (2002) points out that PAHs are emitted frompractically every combustion source. These PAHs are then deposited either through wet or dry deposition on soil, vegetation and water. PAH residues on land, particularly impervious surfaces, are later transported with storm water runoff to water bodies and depositional areas. The specific traffic-related sources identified by Pawluck and coworkers (2002) were: tire wear, vehicle exhausts, asphalt and asphalt coatings, and lubricating oils and grease.
The Agency for Toxic Substance and Disease Registry's (ATSDR 1995) toxicological profile for PAHs lists the important sources of PAHs in surface water to include deposition of airborne PAHs, municipal waste water discharge, urban storm water runoff, runoff from coal storage areas, effluents from various industries, oil spills, and petroleum processing. ATSDR states further that most of the PAHs in soils are believed to result from atmospheric deposition after local and long-range transport. ATSDR concluded that the principal sources of PAHs in soils along highways and roads are from vehicular exhausts and emissions from wearing of tires and asphalt.Regardless of the ultimate source, PAHs have been consistently detected in urban runoff
from roads and associated with multiple sources. Thus, potentially significant sources of PAHs other than from the refined tar based materials are well known, and the presence of PAHs are not restricted to runoff from refined tar based materials.
Another study investigating the bioavailability (i.e., fraction of chemical available tobiological organisms) of PAHs from the same two types of sediments (Talley 2002) confirmed that PAH sorption to coal-related particles in sediments is associated with slow release rates compared to clay/silt particles. This study also found that biodegradation of coal particle-related PAHs is minimal compared to PAHs associated with clay/silt particles, indicating less bioavailability for PAHs associated with the coal derived fraction. This study supports the conclusion that the leachability of PAHs associated with refined tar based materials is expected to be low and further that the availability for biological uptake and metabolism of PAHs from these types of sources is low.
In summary, this analysis of sources of PAHs supports the following conclusions: There are numerous sources of PAHs that contribute to concentrations detected in theenvironment.
PAH content of road run-off is difficult to characterize as to the exact source because oflimited raw data.
Crankcase oil and vehicle emissions, not asphaltic debris, are consistently identified in the literature as the primary sources of PAHs transported in the environment from roadways. While refined tar based sealers are expected to contribute PAHs in deposited roadway debris through the coating on asphalt particles and abraded CTE particles, these physical forms have low potential for leaching and bioavailability and have limited contributions to environmental transport and typical environmental exposure relative to other PAH sources.Review of regulations for PAH containing runoff
There are state and federal regulations and screening/cleanup criteria pertaining to PAHs in soil and water. However, as noted above, these criteria are not applicable for samples containing 60-80% gravel. Criteria concentrations specifically derived for these types of samples would be significantly higher because the exposure potential is reduced compared to soils or sediments. Very little information was identified specific to managing PAH-containing runoff. The only relevant federal regulatory information found about runoff was in the USEPA's Management Measures Guidance (USEPA 1993) that were developed for states to incorporate into their coastal nonpoint source (NPS) pollution programs. One specific management measure that may apply is the Management Measure for Road, Highway, and Bridge Runoff Systems. This runoff measure requires that operation and maintenance systems include the development of retrofit projects, where needed, to collect NPS pollutant loadings from existing highways. It states further that poorly designed or maintained roads can generate significant erosion and pollution loads containing heavy metals, hydrocarbons, sediment, and debris that run off into and threaten the quality of surface waters and their tributaries. The measure states that in areas where such adverse impacts to surface waters can be attributed to adjacent roads, some type of remedial action may be necessary such as the installation of structural or nonstructural pollution controls. Areas with severe erosion and pollution runoff problems may require relocation or reconstruction to mitigate these impacts. The Texas Department of Transportation (TxDOT) also has a program for controlling NPS pollutants from highway construction and maintenance (TNRCC 1999). Their approach is to identify opportunities to improve existing urban runoff control structures in priority watersheds. Pollution prevention procedures are incorporated in the operation and maintenance activities for roads to reduce pollutant loading to surface water and sediments. TxDOT also has a program to assess water quality impacts resulting from transportation projects.No information was found regarding PAH-specific runoff regulations from the COA or
Travis County.
In summary, there are few federal, state or city regulations specific to PAH-containing runoff.
New: Polycyclic Aromatic Hydrocarbons (PAHs) in Austin Sediments After a Ban on Pavement Sealers, Robert P. DeMott; Thomas D. Gauthier; James M. Wiersema; Geoffrey Crenson, Environmental Forensics, Volume 11, Issue 4 December 2010 , pages 372 – 382.
http://dx.doi.org/10.1080/15275922.2010.526520
Abstract
Polycyclic aromatic hydrocarbon (PAH) concentrations were measured in stream
sediments collected before and after a municipal ban on the use of coal-tar based pavement sealers in Austin, Texas. Samples were collected in October 2005, prior to the ban, and again in April, 2008 – approximately two years after the ban. Differences in total PAH concentrations between samples collected before and after the ban show no net change in PAH levels in Austin stream sediments. Results of hydrocarbon fingerprinting reveal subtle differences in PAH profiles that appear to reflect the effect of the interval between rainfall events rather than a change in PAH sources
O'Reilly, Pietari and Boehm, 2010. Polycyclic Aromatic Hydrocarbons in Stormwater and Urban Sediments: A Review, in press.
Introduction
Polycyclic aromatic hydrocarbons (PAHs) commonly occur in the environment (Boehm 2006; Stout et al. 2004; Yunker et al. 2002) and as a result they are common constituents of municipal stormwater (Hwang and Foster 2006). Because PAHs are typically associated with particles, stormwater runoff can be a source of these compounds to surface waters and to sediments within those water bodies. The presence of PAHs in stormwater and sediments raises concerns because of the potential risk and impact of these contaminants on aquatic organisms. As a result of these risks, the presence of these compounds can result in regulatory demands for sediment assessment and remediation. In addition, the presence of PAHs in sediments can result in increased costs of sediment remediation and pond solids disposal. In addition, because of the recent interest in the issue of refined tar based pavement sealants as a source of PAHs (Mahler et al. 2005; DeMott and Gauthier 2006), research on this specific topic will be reviewed. Methods for treating stormwater will be discussed.
O'Reilly, Pietari and Boehm, 2010. A Forensics Assessment of Coal Tar Sealants as a Source of Polycyclic Aromatic Hydrocarbons in Urban Sediments, submitted.
Abstract
While atmospheric deposition is known to be a significant source of PAHs to urban sediment, recent studies suggest that coal tar-based pavement sealants may be another source. To evaluate this hypothesis, six chemical forensic methods were used to compare similarities and differences in the PAH chemistry of urban sediments and potential sources including coal tar sealants, particles from sealed parking lots, atmospheric deposition, soils, and highway runoff using data compiled from the literature representing more than 150 environmental samples. Atmospheric deposition and sealants could not be distinguished from each other using diagnostic source ratios or chemical correlations. Double ratio plots indicated a narrower range of results for sealant products compared to the environmental samples. While samples collected from roofs and roads were similar to sealants, atmospheric particles and urban sediments had the widest range of PAH ratio values, suggesting underlying atmospheric sources that differ by location. Principal component analysis also indicated similarities between the particles collected from sealed lots, roofs, and roads, and differences between those three sources and urban pond sediments. While not eliminating sealants as localized sources of PAHs, the results do not support the claim that they are a major contributor to urban sediment.
ENVIRON International Corporation, 2010. Review of "Coal-Tar-Based Parking Lot Sealcoat: An Unrecognized Source of PAH to Settled House Dust" by Mahler et al., published in Environmental Science and Technology, January 2010.
Study Summary
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 Review
Introduction:
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.
Study Design
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.
Analytical Methods
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.
Sampling Methodology
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.
Statistical Approach
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.
PAH Toxicity
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.
Conclusions
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.
An interview with USGS scientist Barbara Mahler can be heard in episode 116 of the USGS CoreCast.Link:
http://www.usgs.gov/corecast/details.asp?ep=116
Items of interest pertaining to the above mentioned Podcast:
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).
