Environmental Pollution xxx (2013) 1e2
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
Letter to the Editor
Article title misstates the role of pavement sealers a b s t r a c t Keywords: PAH Pavement sealer CMB Sediment
The claim made in the title of Witter et al. (2014) “Coal-tar-based sealcoated pavement: A major PAH source to urban stream sediments” is not supported by the data presented. The author’s use of Pearson correlation coefficients is insufficient to indicate causation. The application of spatial analysis and principle component analysis did not include sealer specific inputs, so provides no basis for the claim. To test the hypothesis that sealers are a source of PAHs in the stream studied, EPA’s Chemical Mass Balance (CMB) source evaluation model was applied to Witter’s sediment data. CMB found an excellent fit (R2 > 0.999) between measured and modeled PAH concentrations when sealers were not included as a potential source. This finding does not support Witter et al. (2014) claim that sealers are a major source of PAHs. Ó 2013 Elsevier Ltd. All rights reserved.
Editor I am writing to comment on the misleading title of Witter et al. (2014) “Coal-tar-based sealcoated pavement: A major PAH source to urban stream sediments”. The data presented in that article do not support the claim that refined tar pavement sealers (RTS) are a major source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments. Correction of the title is important because of the controversy concerning the role of RTS in urban sediments (USGS, 2013). While the authors refer to papers written by those who promoted the RTS hypothesis (Mahler et al., 2005; Van Metre et al., 2009; Van Metre and Mahler, 2010), they fail to cite those that challenge these findings (DeMott and Gauthier, 2006; DeMott et al., 2010; O’Reilly et al., 2011, 2012). As stated in the introduction, Witter et al. (2014) describes an investigation of the influence of urban land use on the PAH chemistry of a single stream. The spatial analysis contains no data on the use of RTS in the watershed. The only evidence of any relationship between RTS and sediment chemistry consists of calculated Pearson correlation coefficients between parking-lot dust samples containing PAHs of uncertain provenance (O’Reilly et al., 2013) and PAHs in local sediment samples. The results indicate that the PAH profiles of some of the sediment samples are more similar to the dust samples than to the published values for some combustion sources. Such similarity is not a sufficient basis to support a claim of causation, and any such claim ignores the fact that Pearson correlation coefficients between urban sediments and a number of PAH sources are consistent with those determined for RTS (Van Metre and Mahler, 2010; O’Reilly et al., 2012). Witter’s application of principal component (PCA) analysis indicates a difference between urban and rural samples, but provides no information concerning the role of RTS. Because of similarities among many pyrogenic PAH sources, PCA has been shown to be incapable of
differentiating among them (O’Reilly et al., 2012). PCA results have been shown to be inconsistent with claims that RTS are a local source (O’Reilly et al., 2013). The PAH source profiles used by Witter et al. (2014) are the same as those used in Van Metre and Mahler’s (2010) application of EPA’s Chemical Mass Balance (CMB) source evaluation model (Coulter, 2004). To test the hypothesis that RTS is a source of PAHs in the stream studied, CMB was applied using Witter’s sediment data and Van Metre’s source inputs (Van Metre and Mahler, 2010, model A). For a negative control, CMB was rerun without RTS as a source
Fig. 1. Plot comparing CMB-modeled to measured PAH concentrations of the Witter et al. (2014) sediment samples. CMB was run with and without RTS dust as a potential source. The modeling approach is described in Van Metre and Mahler (2010).
0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.11.029
Please cite this article in press as: O’Reilly, K., Article title misstates the role of pavement sealers, Environmental Pollution (2013), http:// dx.doi.org/10.1016/j.envpol.2013.11.029
2
Letter to the Editor / Environmental Pollution xxx (2013) 1e2
profile. In both cases, CMB found a solution that met model acceptability criteria for 26 of the 35 sediment samples. The fit (R2) between modeled and measured concentrations exceeded 0.999 whether or not RTS was included as a potential source (Fig. 1). The ability of CMB to fit sediment results without RTS as a potential source demonstrates that the data presented in Witter et al. (2014) do not support the claim made in the title. A title highlighting the land-use investigation would be more appropriate. References Coulter, C.T., 2004. EPA-CMB 8.2 Users’ Manual. U.S. Environmental Protection Agency, Washington, DC. EPA 452/R-04e011. DeMott, R.P., Gauthier, T.D., 2006. Comment on “Parking lot sealcoat: an unrecognized source of urban polycyclic aromatic hydrocarbons.” Environ. Sci. Technol. 40, 3657e3658. DeMott, R.P., Gauthier, T.D., Wiersema, J.M., Crenson, G., 2010. Polycyclic aromatic hydrocarbons (PAHs) in Austin sediments after a ban on pavement sealers. Environ. Forensics 11, 372e382. Mahler, B.J., Van Metre, P.C., Bashara, T.J., Wilson, J.T., Johns, D.A., 2005. Parking lot sealcoat: an unrecognized source of urban polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 39, 5560e5566. O’Reilly, K., Pietari, J., Boehm, P.D., 2011. Comment on “PAHs underfoot: contaminated dust from coal-tar sealcoated pavement is widespread in the U.S.” Environ. Sci. Technol. 45, 3185e3186.
O’Reilly, K., Pietari, J., Boehm, P., 2012. A forensic assessment of coal tar sealants as a source of polycyclic aromatic hydrocarbons in urban sediments. Environ. Forensics 13, 185e196. O’Reilly, K., Pietari, J., Boehm, P., 2013. Parsing pyrogenic PAHs: forensic chemistry, receptor models, and source control policy. Integr. Environ. Assess. Manag. http://dx.doi.org/10.1002/ieam.1506. USGS, 2013. Information Quality d Information Correction Request. U.S. Geological Survey. Available at: http://www.usgs.gov/info_qual/coal_tar_sealants.html. Reviewed November 13, 2013. Van Metre, P.C., Mahler, B.J., 2010. Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes. Sci. Tot. Environ. 409, 334e344. Van Metre, P.C., Mahler, B.J., Wilson, J.T., 2009. PAHs underfoot: contaminated dust from coal-tar sealcoated pavement is widespread in the United States. Environ. Sci. Technol. 43, 20e25. Witter, A.E., Nguyen, M.H., Baidar, S., Sak, P.B., 2014. Coal-tar-based sealcoated pavement: a major PAH source to urban stream sediments. Environ. Pollut. 185, 59e68.
Kirk O’Reilly Exponent, Inc., 15375 S.E. 30th Place, Suite 250, Bellevue, WA 98007, USA E-mail address: [email protected]. 20 November 2013
Please cite this article in press as: O’Reilly, K., Article title misstates the role of pavement sealers, Environmental Pollution (2013), http:// dx.doi.org/10.1016/j.envpol.2013.11.029
Contents lists available at ScienceDirect
Environmental Pollution journal homepage: www.elsevier.com/locate/envpol
Letter to the Editor
Article title misstates the role of pavement sealers a b s t r a c t Keywords: PAH Pavement sealer CMB Sediment
The claim made in the title of Witter et al. (2014) “Coal-tar-based sealcoated pavement: A major PAH source to urban stream sediments” is not supported by the data presented. The author’s use of Pearson correlation coefficients is insufficient to indicate causation. The application of spatial analysis and principle component analysis did not include sealer specific inputs, so provides no basis for the claim. To test the hypothesis that sealers are a source of PAHs in the stream studied, EPA’s Chemical Mass Balance (CMB) source evaluation model was applied to Witter’s sediment data. CMB found an excellent fit (R2 > 0.999) between measured and modeled PAH concentrations when sealers were not included as a potential source. This finding does not support Witter et al. (2014) claim that sealers are a major source of PAHs. Ó 2013 Elsevier Ltd. All rights reserved.
Editor I am writing to comment on the misleading title of Witter et al. (2014) “Coal-tar-based sealcoated pavement: A major PAH source to urban stream sediments”. The data presented in that article do not support the claim that refined tar pavement sealers (RTS) are a major source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments. Correction of the title is important because of the controversy concerning the role of RTS in urban sediments (USGS, 2013). While the authors refer to papers written by those who promoted the RTS hypothesis (Mahler et al., 2005; Van Metre et al., 2009; Van Metre and Mahler, 2010), they fail to cite those that challenge these findings (DeMott and Gauthier, 2006; DeMott et al., 2010; O’Reilly et al., 2011, 2012). As stated in the introduction, Witter et al. (2014) describes an investigation of the influence of urban land use on the PAH chemistry of a single stream. The spatial analysis contains no data on the use of RTS in the watershed. The only evidence of any relationship between RTS and sediment chemistry consists of calculated Pearson correlation coefficients between parking-lot dust samples containing PAHs of uncertain provenance (O’Reilly et al., 2013) and PAHs in local sediment samples. The results indicate that the PAH profiles of some of the sediment samples are more similar to the dust samples than to the published values for some combustion sources. Such similarity is not a sufficient basis to support a claim of causation, and any such claim ignores the fact that Pearson correlation coefficients between urban sediments and a number of PAH sources are consistent with those determined for RTS (Van Metre and Mahler, 2010; O’Reilly et al., 2012). Witter’s application of principal component (PCA) analysis indicates a difference between urban and rural samples, but provides no information concerning the role of RTS. Because of similarities among many pyrogenic PAH sources, PCA has been shown to be incapable of
differentiating among them (O’Reilly et al., 2012). PCA results have been shown to be inconsistent with claims that RTS are a local source (O’Reilly et al., 2013). The PAH source profiles used by Witter et al. (2014) are the same as those used in Van Metre and Mahler’s (2010) application of EPA’s Chemical Mass Balance (CMB) source evaluation model (Coulter, 2004). To test the hypothesis that RTS is a source of PAHs in the stream studied, CMB was applied using Witter’s sediment data and Van Metre’s source inputs (Van Metre and Mahler, 2010, model A). For a negative control, CMB was rerun without RTS as a source
Fig. 1. Plot comparing CMB-modeled to measured PAH concentrations of the Witter et al. (2014) sediment samples. CMB was run with and without RTS dust as a potential source. The modeling approach is described in Van Metre and Mahler (2010).
0269-7491/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.envpol.2013.11.029
Please cite this article in press as: O’Reilly, K., Article title misstates the role of pavement sealers, Environmental Pollution (2013), http:// dx.doi.org/10.1016/j.envpol.2013.11.029
2
Letter to the Editor / Environmental Pollution xxx (2013) 1e2
profile. In both cases, CMB found a solution that met model acceptability criteria for 26 of the 35 sediment samples. The fit (R2) between modeled and measured concentrations exceeded 0.999 whether or not RTS was included as a potential source (Fig. 1). The ability of CMB to fit sediment results without RTS as a potential source demonstrates that the data presented in Witter et al. (2014) do not support the claim made in the title. A title highlighting the land-use investigation would be more appropriate. References Coulter, C.T., 2004. EPA-CMB 8.2 Users’ Manual. U.S. Environmental Protection Agency, Washington, DC. EPA 452/R-04e011. DeMott, R.P., Gauthier, T.D., 2006. Comment on “Parking lot sealcoat: an unrecognized source of urban polycyclic aromatic hydrocarbons.” Environ. Sci. Technol. 40, 3657e3658. DeMott, R.P., Gauthier, T.D., Wiersema, J.M., Crenson, G., 2010. Polycyclic aromatic hydrocarbons (PAHs) in Austin sediments after a ban on pavement sealers. Environ. Forensics 11, 372e382. Mahler, B.J., Van Metre, P.C., Bashara, T.J., Wilson, J.T., Johns, D.A., 2005. Parking lot sealcoat: an unrecognized source of urban polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 39, 5560e5566. O’Reilly, K., Pietari, J., Boehm, P.D., 2011. Comment on “PAHs underfoot: contaminated dust from coal-tar sealcoated pavement is widespread in the U.S.” Environ. Sci. Technol. 45, 3185e3186.
O’Reilly, K., Pietari, J., Boehm, P., 2012. A forensic assessment of coal tar sealants as a source of polycyclic aromatic hydrocarbons in urban sediments. Environ. Forensics 13, 185e196. O’Reilly, K., Pietari, J., Boehm, P., 2013. Parsing pyrogenic PAHs: forensic chemistry, receptor models, and source control policy. Integr. Environ. Assess. Manag. http://dx.doi.org/10.1002/ieam.1506. USGS, 2013. Information Quality d Information Correction Request. U.S. Geological Survey. Available at: http://www.usgs.gov/info_qual/coal_tar_sealants.html. Reviewed November 13, 2013. Van Metre, P.C., Mahler, B.J., 2010. Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes. Sci. Tot. Environ. 409, 334e344. Van Metre, P.C., Mahler, B.J., Wilson, J.T., 2009. PAHs underfoot: contaminated dust from coal-tar sealcoated pavement is widespread in the United States. Environ. Sci. Technol. 43, 20e25. Witter, A.E., Nguyen, M.H., Baidar, S., Sak, P.B., 2014. Coal-tar-based sealcoated pavement: a major PAH source to urban stream sediments. Environ. Pollut. 185, 59e68.
Kirk O’Reilly Exponent, Inc., 15375 S.E. 30th Place, Suite 250, Bellevue, WA 98007, USA E-mail address: [email protected]. 20 November 2013
Please cite this article in press as: O’Reilly, K., Article title misstates the role of pavement sealers, Environmental Pollution (2013), http:// dx.doi.org/10.1016/j.envpol.2013.11.029
