Integrated Environmental Assessment and Management — Volume 10, Number 4—pp. 485–488 © 2014 SETAC

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In Response to O'Reilly et al. (2014) Peter C Van Metrey and Barbara J Mahler*z yHydrologist, US Geological Survey, Austin, Texas zResearch Hydrologist, US Geological Survey, Austin, Texas

(Submitted 16 April 2014; Accepted 25 April 2014)

* To whom correspondence may be addressed: [email protected] Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ieam.1547

from coal‐tar–sealed pavement extrapolated to the watershed scale for 4 watersheds more than accounted for total measured PAH loads in suspended sediment in the receiving streams. The statement in the abstract therefore is based on study results and national‐scale use of these products, and is supported by, but not based on, the similarity in ratios for PAHs in sealed pavement dust and in suspended sediment. Although the Case Study authors express concern about the local nature of the 2005 study, the conclusion reached has since been supported by studies in diverse locations (e.g., Watts et al. 2010, Yang et al. 2010; Crane 2013; Pavlowsky 2013; Selbig et al. 2013; Witter et al. 2014) and of national scale (e.g., Van Metre et al. 2009; Van Metre and Mahler 2010). The Case Study authors describe the scope of Van Metre et al. (2009) as based on “one sample from each of nine urban lakes” (p. 4) and criticize the use of only 1 forensic method. Van Metre et al. (2009) compared PAH concentrations and source ratios in 56 samples of parking lot dust, 6 samples of soils, and 10 samples of lake sediment, and their analysis relied on a combination of concentration, geospatial distribution, and chemical fingerprinting. For 6 central and eastern cities, where coal‐tar‐based sealcoat is predominantly used, median total PAH concentrations in dust from sealcoated and unsealcoated pavement were 2 200 and 27 mg/kg, respectively, demonstrating the potent source strength of the coal‐tar sealcoat products. For 3 western cities, where asphalt‐based sealcoat is predominantly used, median total PAH concentrations in dust from sealcoated and unsealcoated pavement were similar to one another and very low (2.1 and 0.8 mg/kg, respectively). Van Metre et al. (2009) note: “The elevated concentrations of PAHs in dust from sealcoated pavement in central and eastern cities cannot be attributed to urban sources of PAHs … 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 ….” In the same publication, Van Metre et al. (2009) reported higher PAH concentrations in bed sediment of lakes sampled in the central and eastern US than in bed sediment of lakes sampled in the western US for a given amount of urban land use. Finally, on a double‐ratio plot, samples of lake sediment and sealed parking lot dust from the central and eastern United States grouped together, and apart from 6 other commonly identified urban PAH sources, whereas samples of lake sediment and parking lot dust from the western US plotted in a group distinct from that of central and eastern samples, and closer to the six urban sources. In an earlier publication, O’Reilly et al. (2012), using a different set of ratios, illustrated the same phenomenon (Fig. 2, O’Reilly et al. 2012); their graphical results, as separate from their interpretation of those results, are consistent with the findings of Van Metre et al. (2009). We agree with the Case Study authors regarding the importance of multiple lines of evidence. USGS, other governmental, and academic research that has concluded that coal‐tar‐based pavement sealants are a major source of urban PAHs have relied on a wide array of forensic methods, including

Letter to the Editor

DEAR SIR: The Case Study article by O’Reilly et al. (hereinafter “Case Study authors”), published in Integrated Environmental Assessment and Management (O’Reilly et al. 2013) and funded by the Pavement Coatings Technology Council, includes a lengthy critique of US Geological Survey (USGS) research on environmental contamination associated with coal‐tar‐based pavement sealant. Coal‐tar‐based pavement sealant, a black liquid that is sprayed or painted on asphalt pavement, typically is 15% to 35% by weight coal tar or low‐ or high‐temperature coal‐tar pitch (CAS nos. 8007‐45‐2, 65996‐90‐9, and 65996‐ 93‐2, respectively). Coal tar and coal‐tar pitch, which are known human carcinogens (International Agency for Research on Cancer 2012; National Toxicology Program 2011), are complex mixtures of polycyclic aromatic hydrocarbons (PAHs) and other compounds (Agency for Toxic Substances and Disease Registry 2002). Research by the USGS and others has demonstrated that coal‐tar‐based pavement sealcoat, where it is used, is a major source of PAHs to soil; stormwater‐pond, stream, and lake sediment; house dust; and air (e.g., Watts et al. 2010; Yang et al. 2010; Mahler et al. 2012; Van Metre et al. 2012a, 2012b; Crane 2013; Pavlowsky 2013). The Case Study authors’ concerns with our research can be grouped into 3 categories: 1) scope of some USGS studies, 2) need for multiple lines of evidence, and 3) technical issues related to use of the contaminant mass balance (CMB) model (Van Metre and Mahler 2010). Here we respond to their major concerns to the extent space will allow; in regards to the Case Study authors’ statement that Drs. Van Metre and Mahler have been advocating bans in testimony, we direct the reader to the Letter to the Editor from USGS Acting Associate Director for Water Jerad Bales in this issue. In voicing their first concern (p. 4), the Case Study authors suggest that the results of some USGS studies do not support the scope of the conclusions drawn. The statement the Case Study authors refer to from the abstract of Mahler et al. (2005)—that coal‐tar‐based sealants “may dominate loading of PAHs to urban water bodies in the United States”—is described as based on ratio plots. The study reported that the mean total PAH concentration in particles in runoff from pavement with coal‐tar‐based sealants was 65 times higher than the mean for unsealed pavement. An estimated 320 million liters (85 million gallons) of coal‐tar‐based sealant are used annually (Scoggins et al. 2009), with most use in the central, southeastern, and northeastern US. The products typically contain 50 000–150 000 mg/kg PAH, and 1%–5% of urban watershed area typically is sealed (Pavlowsky 2013; Mahler et al. 2005). In Mahler et al. (2005), rain‐event loads of PAHs

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double‐ratio plots (Mahler et al. 2005; Van Metre et al. 2009; Crane 2013), principal components analysis (Watts et al. 2010), comparison of sealed and unsealed settings (Crane 2013; Mahler et al. 2005; Van Metre et al. 2009; Mahler et al. 2010; University of New Hampshire Stormwater Center 2010; Van Metre et al. 2012a, 2012b), organic petrography (Yang et al. 2010), profile correlation (Van Metre and Mahler 2010; Witter et al. 2014), geospatial correlation (Pavlowsky 2013; Witter et al. 2014), and quantitative source apportionment (Van Metre and Mahler 2010; Crane 2013). The third concern expressed by the Case Study authors regards “what conclusions may be warranted (p. 4)” from the CMB source‐apportionment modeling of Van Metre and Mahler (2010). In that study, the CMB model was applied to multiple lake‐sediment samples from 40 lakes across the US, testing 22 source input profiles and as many as 12 PAHs as variables. Coal‐tar‐based sealcoat was consistently identified as the most important overall source of PAHs to the lake sediment, accounting for about one‐half of PAH loading on average. Van Metre and Mahler (2014) demonstrated the robustness of the CMB model using data from Lady Bird Lake (formerly Town Lake) in Austin, Texas. The results from the CMB model had indicated that dust from coal‐tar‐sealed pavement was contributing about 75% of PAHs in lake sediment in 1998, 8 years prior to the citywide ban on coal‐tar‐sealant products in 2006 (Van Metre and Mahler 2010). In the 8 years since the ban, mean PAH concentrations in lake sediment have declined 58%. Additional CMB modeling indicates that existing stocks of coal‐ tar sealants continue to contribute the largest proportion of PAHs to the lake sediments, implying that PAH concentrations should continue to decrease as those stocks are depleted (Van Metre and Mahler 2014). The issues raised by the Case Study authors regarding the CMB model fall into 3 general categories: source profiles, modeling approach, and a principal components analysis (PCA) evaluation of model results. Van Metre and Mahler (2010) determined a mean source profile for dust from coal‐tar‐ sealcoated lots from data they had collected in 6 central and eastern US cities. (Without information as to which source or sources the Case Study authors find to have a profile similar to that of coal‐tar‐based sealant, we cannot evaluate their comment that the profile is not unique.) Input profiles for other sources were taken directly (i.e., not calculated) from the peer‐ reviewed literature (for sources, see Table 1, Van Metre and Mahler 2010). Some of these published input profiles are means from multiple studies or laboratories (e.g., National Institute of Standards and Technology 1992; Li et al. 2003), and some are mean values of multiple measurements from single studies (e.g., Schauer et al. 2001); the use of these published input profiles constitutes a logical approach for obtaining the best available estimate for a source profile. It is not clear whether the Case Study authors find issue with the fact that the source profiles used as model input were not from a single watershed, or that the samples themselves were not from a single watershed. If the Case Study authors’ concern is the former, their statement (p. 4) is incorrect—previously published applications of CMB do not limit the source input profiles to those collected in a single watershed. For example, Li et al. (2003) used data for vehicle emissions generated in Southern California, Japan, and Sweden, but their sediment data were from southeast Chicago. If the Case Study authors’ concern is the latter, CMB results are independent of sampling‐ site location—source inputs are for a source type (e.g., tire

particles, vehicle emissions) and are not specific to a particular watershed, and the model is applied to 1 sample at a time, not a set of samples (from, for example, a watershed). The Case Study authors also express concern that Van Metre and Mahler (2010) “used data from fresh emission sources for some profile inputs, but the RT [coal tar]‐sealer profile input used weathered sealer” (p. 4). We used the best source input profiles available; to our knowledge, source profiles are not available for weathered vehicle emissions, tire particles, or other sources for which we used published emissions profiles. As such data become available, they might improve source‐apportionment estimates, but there is no evidence that weathering of these sources will create a profile similar to that of coal‐tar‐based sealant or lake sediment. Finally, our use of correlation analysis indicated that source profiles for coal‐tar‐sealcoat scrapings and sealed parking lot dust were more similar to the mean profile for sediment from the 40 lakes than were the other input source profiles tested, including the profile for fresh sealcoat (Table 2, Van Metre and Mahler 2010). These results, however, did not cause us to eliminate the testing of less similar coal‐tar‐based sealcoat profiles in the model (p. 4, O’Reilly et al. 2013): sources with a low Pearson’s r and a high chi‐squared statistic (x2) were tested in model runs. In all, 22 PAH profiles, which include all major urban PAH sources, were tested as model inputs, the most to date in the published literature. Regarding the CMB modeling approach, the Case Study authors express concern about the number of modeling runs discussed in Van Metre and Mahler (2010) (p. 4) and the lack of a negative control (p. 5). In response to the Case Study authors’ concern that Van Metre and Mahler (2010) discussed in detail only 4 of 200 CMB model runs, it is common practice in modeling to try many different model runs to test various hypotheses and to determine the best‐fitting model, but not all model runs can or need to be discussed in detail in a publication. The 4 models discussed “are in general agreement with the vast majority of the 200 models tested in terms of the relative importance of the five major source categories consisting of 22 PAH profiles. All 4 have good model performance on the basis of x2, R2, and percentage of SPAH mass estimated, and all had no failures to converge on the 120 samples from the 40 lakes” (Van Metre and Mahler 2010). In response to the Case Study authors’ suggestion that a negative control be tested in the model (p. 5, col. 1), in a recent paper we ran the model for sediment from Lady Bird Lake both with and without a coal‐tar sealant dust profile as a source (Van Metre and Mahler 2014). The resulting model runs that included coal‐tar sealant dust had better measures of model performance than those that did not. Similarly, Crane (2013) reported a substantially improved model fit when coal‐tar‐ based sealant dust was included in CMB source apportionment for Minnesota stormwater ponds (mean x2 of 0.240 when the sealcoat profile was included, mean x2 of 0.955 when it was not). The ability to model a receptor profile by excluding a potentially important source profile (which the Case Authors refer to as “negative control”) does not prove that the excluded source is not an important contributor. As the Case Study authors themselves state (p. 3), “Inclusion of all important sources is critical as the model can assign the contribution of missing sources to those used as inputs.” When dust from coal‐ tar‐sealed pavement is included as a source in the CMB model, it is the dominant contributor of PAHs to urban lakes we sampled east of the Continental Divide (Van Metre and Mahler 2010).

In Response to O'Reilly et al. (2014)—Integr Environ Assess Manag 10, 2014

The results of Van Metre and Mahler (2010) are assessed by the Case Study authors by using PCA, but the lack of documentation precludes a comprehensive technical evaluation of the PCA results. The Case Study authors do not provide essential underlying information on the PCA, including which PAHs were used as variables, why only 7 were used, which pavement dust samples were used, why so few were used (5 dust samples in Figs. 1 and 5, 7 in Fig. 4; yet there are published data for more than 40 pavement dust samples [Mahler et al. 2010; University of New Hampshire Stormwater Center 2010; Mahler et al. 2004; Van Metre et al. 2008]), if or how the data were standardized, how outliers were handled, or whether substantial correlations were present. Although PCA is a useful tool for exploration of large data sets (i.e., 100þ samples), more direct and quantitative tools are available for comparing PAH profiles (e.g., correlation, x2 difference). Other shortcomings of the Case Study authors’ PCA are discussed in Crane (2014). The consistency between CMB results and ratio analysis was demonstrated in Van Metre and Mahler (2011) in response to O’Reilly et al. (2011). In conclusion, published academic and government research on effects of coal‐tar‐based pavement sealants has produced results consistent with those of the USGS (Mahler et al. 2012; Van Metre and Mahler 2010; Mahler et al. 2005; Van Metre et al. 2009). Research at Missouri State University demonstrated that concentrations of PAHs in stream sediment were strongly correlated with the percentage of coal‐tar–sealed parking lot area in the drainage basin upstream of the sampling site (Pavlowsky 2013). Researchers at the University of New Hampshire Stormwater Center reported that, during 2 years, approximately 30 times more PAHs were exported on a per area basis from coal‐tar‐sealed parking lots than from an unsealed parking lot (Watts et al. 2010). A Dickinson College study of streambed sediments in Pennsylvania determined that PAH profiles for samples collected in the urban part of the watershed were strongly correlated (r ¼ 0.94) to the profile for dust from coal‐tar‐sealcoated pavement (Witter et al. 2014). The Minnesota Pollution Control Agency used multiple environmental forensic techniques to identify sources of PAHs to sediment in 15 stormwater ponds and concluded that coal‐tar‐based sealant was the most important source (Crane 2013). Finally, PAH contamination concerns associated with coal‐ tar‐based sealcoat are not limited to stream and lake sediments. Coal‐tar‐based sealcoat can be the dominant source of PAHs to sediment that collects in stormwater‐management devices and ponds (Crane 2013; University of New Hampshire Stormwater Center 2010), greatly increasing the cost for disposal (Polta et al. 2006). Coal‐tar‐based sealcoat emits high concentrations of PAHs to air; the flux is particularly elevated immediately following application (45 000 mg m2 h1 1.6 hours after application) (Van Metre et al. 2012a) but remains elevated for months to years after application (about 88 mg m2 h1 for sealed lots, 1.4 mg m2 h1 for unsealed asphalt pavement) (Van Metre et al. 2012b). PAHs from coal‐tar–sealed pavement also become incorporated into house dust. The PAH concentrations in house dust from apartments with coal‐tar–sealed parking lots (median 129 mg/g) were 25 times higher than those in house dust from apartments with parking lots with other pavement surface types (median 5.1 mg/g) (Mahler et al. 2010). Children in these types of residences are estimated to ingest 2.5 times more of the 7 B2 (carcinogenic) PAHs by incidental (non‐dietary) ingestion of house dust than through their diet

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(Williams et al. 2012). In a companion study that considered non‐dietary ingestion of house dust and soils by those living in affected residences, average estimated lifetime cancer risk was increased by a factor of 38 relative to those living in unaffected residences (Williams et al. 2013). In short, multiple lines of evidence make a compelling case that coal‐tar‐based sealcoat is a major source of PAHs to many environmental compartments, including urban sediments. Disclaimer—The use of trade, firm, or industry names in this paper is for identification purposes only and does not imply endorsement by the US Government.

REFERENCES Agency for Toxic Substances and Disease Registry. 2002. Toxicological profile for wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles. US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, Atlanta (GA). [cited 2014 January 1]. Available from: http://www.atsdr.cdc.gov/ToxProfiles/tp85.pdf Crane JL. 2013. Source apportionment and distribution of polycyclic aromatic hydrocarbons, risk considerations, and management implications for urban stormwater pond sediments in Minnesota, USA. Arch Environ Contam Toxicol. Available from: DOI: 10.1007/s00244‐013‐9963‐8 Crane JL. 2014. Response to O'Reilly et al. (2014). Integr Environ Assess Manag 10:323–324. International Agency for Research on Cancer. 2012. Chemical agents and related occupations. IARC monographs on the evaluation of carcinogenic risks to humans, vol. 100F. 599 p. [cited 2014 January 1]. Available from: http:// monographs.iarc.fr/ENG/Monographs/vol100F/mono100F.pdf Li A, Jan JK, Scheff PA. 2003. Application of EPA CMB8.2 Model for source apportionment of sediment PAHs in Lake Calumet, Chicago. Environ Sci Technol 37:2958–2965. Mahler BJ, Van Metre PC, Bashara TJ, Wilson JT, Johns DA. 2005. Parking lot sealcoat: An unrecognized source of urban polycyclic aromatic hydrocarbons. Environ Sci Technol 39:5560–5566. Mahler BJ, Van Metre PC, Crane JL, Watts AW, Scoggins M, Williams ES. 2012. Coal‐ tar‐based pavement sealcoat and PAHs: Implications for the environment, human health, and stormwater management. Environ Sci Technol 56:3039– 3045. Mahler BJ, Van Metre PC, Wilson JT. 2004. Concentrations of polycyclic aromatic hydrocarbons (PAHs) and major and trace elements in simulated rainfall runoff from parking lots, Austin, Texas, 2003. US Geological Survey Open‐File Report 2004‐1208. 87 pp. [cited 2014 January 1]. Available from: http://pubs.usgs. gov/of/2004/1208/ Mahler BJ, Van Metre PC, Wilson JT, Musgrove M, Burtank TL, Ennis TE, Bashara TJ. 2010. Coal‐tar‐based parking lot sealcoat: An unrecognized source of PAH to settled house dust. Environ Sci Technol 44:894–900. National Toxicology Program. 2011. 12th Report on Carcinogens (RoC). US Department of Health and Human Services. [cited 2014 January 1]. Available from: http://ntp.niehs.nih.gov/ntp/roc/twelfth/profiles/coaltars.pdf National Institute of Standards and Technology 1992. Certificate of Analysis, Standard Reference Material 1597, Complex Mixture of Polycyclic Aromatic Hydrocarbons from Coal Tar. Gaithersburg (MD): National Institute of Standards and Technology. [cited 2014 January 1]. Available from: https:// www‐s.nist.gov/srmors/ O'Reilly K, Pietari J, Boehm P. 2011. Comment on “PAHs underfoot: Contaminated dust from coal‐tar sealcoated pavement is widespread in the U.S.” Environ Sci Technol 45:3185–3186. O'Reilly K, Pietari J, Boehm P. 2012. Forensic assessment of refined tar‐based sealers as a source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments. Environ Forensics 13:185–196. O'Reilly K, Pietari J, Boehm P. 2013. Parsing pyrogenic polycyclic aromatic hydrocarbons: Forensic chemistry, receptor models, and source control policy. Integr Environ Assess Manag 10:279–285. Pavlowsky RT. 2013. Coal‐tar pavement sealant use and polycyclic aromatic hydrocarbon contamination in urban stream sediments. Phys Geogr 34:392– 415. Polta R, Balogh S, Craft‐Reardon A. 2006. Characterization of stormwater pond sediments. Final project report. St. Paul (MN): Environmental Quality Assurance

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Department, Metropolitan Council Environmental Services. EQA Report 06‐ 572. Schauer JJ, Kleeman MJ, Cass GR, Simoneit BRT. 2001. Measurement of emissions from air pollution sources. 3. C1–C29 organic compounds from fireplace combustion of wood. Environ Sci Tech 35:1716–1728. Scoggins M, Ennis T, Parker N, Herrington C. 2009. A photographic method for estimating wear of coal tar sealcoat from parking lots. Environ Sci Technol 43:4909–4914. Selbig WR, Bannerman R, Corsi SR. 2013. From streets to streams: Assessing the toxicity potential of urban sediment by particle size. Sci Total Environ 444:381– 391. University of New Hampshire Stormwater Center 2010. Polycyclic aromatic hydrocarbons released from sealcoated parking lots: A controlled field experiment to determine if sealcoat is a significant source of PAHs in the environment. Durham (NH): University of New Hampshire Stormwater Center. 18 p. Van Metre PC, Mahler BJ. 2010. Contribution of PAHs from coal‐tar pavement sealcoat and other sources to 40 U.S. lakes. Sci Total Environ 409:334–344. Van Metre PC, Mahler BJ. 2011. Response to comment on “PAHs underfoot: Contaminated dust from coal‐tar sealcoated pavement is widespread in the U. S.” Environ Sci Technol 45:3187–3188. Van Metre PC, Mahler BJ. 2014. PAH concentrations in lake sediment decline following ban on coal‐tar‐based pavement sealants in Austin, Texas. Environ Sci Technol 48:7222–7228. Van Metre PC, Mahler BJ, Wilson JT. 2009. PAHs underfoot: Contaminated dust from coal‐tar sealcoated pavement is widespread in the United States. Environ Sci Technol 43:20–25.

Van Metre PC, Mahler BJ, Wilson JT, Burbank TL. 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– 2007. US Geological Survey Data Series Report 361. 5 p. Van Metre PC, Majewski MS, Mahler BJ, Foreman WT, Braun CL, Wilson JT, Burtank T. 2012a. PAH volatilization following application of coal‐tar‐based pavement sealant. Atmos Environ 51:108–115. Van Metre PC, Majewski MS, Mahler BJ, Foreman WT, Braun CL, Wilson JT, Burtank T. 2012b. Volatilization of polycyclic aromatic hydrocarbons from coal‐tar‐sealed pavement. Chemosphere 88:1–7. Watts AW, Ballestero TP, Roseen RM, Houle JP. 2010. Polycyclic aromatic hydrocarbons in stormwater runoff from sealcoated pavements. Environ Sci Technol 44:8849–8854. Williams ES, Mahler BJ, Van Metre PC. 2012. Coal‐tar pavement sealants may significantly increase children's PAH exposures. Environ Pollut 164: 40–41. Williams ES, Mahler BJ, Van Metre PC. 2013. Cancer risk from incidental ingestion exposures to PAHs associated with coal‐tar‐sealed pavement. Environ Sci Technol 47:1101–1109. Witter A, Nguyen MH, Baidar S, Sak PB. 2014. Coal‐tar‐based sealcoated pavement: A major PAH source to urban stream sediments. Environ Pollut 185:59–68. Yang Y, Van Metre PC, Mahler BJ, Wilson JT, Ligouis B, Razzaque M, Schaeffer C, Werth C. 2010. The influence of coal‐tar sealcoat and other carbonaceous materials on polycyclic aromatic hydrocarbon loading in an urban watershed. Environ Sci Technol 44:1217–1233.

In response to O'Reilly et al. (2014).

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