PCTC Documents Flawed Methodology of USGS Austin Study, Asks Journal for Retraction

After years of waiting for the USGS to “do the right thing” by addressing its flawed science, which has created misconceptions and damages to business reputations, PCTC has submitted a request that the first of the USGS papers be retracted directly to the journal Environmental Science & Technology.  In addition, PCTC has posted the request along with documentation on the PubPeer web site. PubPeer is a site dedicated to Post Publication Peer Review of science papers. Additional PubPeer postings and requests for retraction are anticipated.

The paper by Mahler et al. (2005) marked the introduction of the hypothesis that refined coal tar-based pavement sealants (RTS) are a significant source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments in Austin and, by extension, throughout the US. The hypothesis was based on a small study conducted in Austin, TX. Background for the study can be found in an e-zine article at this link.

A Comment on this article was published by DeMott & Gauthier (2006) in Environmental Science & Technology (ES&T), available at this link.  The Comment made two essential points:

With regard to the PAH ratio analysis, we could not identify the source of the values presented for stream sediment samples, and the values that we could identify from the City of Austin appear to contradict the interpretation developed by the authors.

With regard to the mass balance analysis, we could not identify the source for values from one watershed, the values presented for the other watersheds do not appear to match those from the cited sources, and the previously published values suggest the relative contribution of PAHs from parking lot sources is substantially less than the “majority” source suggested by the authors.

Mahler et al. (2006) was represented as a Response to the Comment, but did not address the inability noted to identify the source of values used in Mahler et al. (2005).

ES&T has word limits for comments and access to the Comment may be limited by a pay wall. The Comment was based on a full post-publication peer review (P3R) of the work described in Mahler et al. (2005), as described in this post. This P3R evaluation of the study reported in Mahler et al. (2005) was commissioned by PCTC members. One of the conclusions of the P3R was that the Mahler et al. (2005) study was, at best, incomplete:

When the chemical fingerprints of PAHs from differing sources were compared to the measurements made from sediment samples, the patterns demonstrated that the PAH profile in sediments is distinct from that associated with coal tar-derived pavement sealer products and parking lot residues. The lack of a coal tar-derived pavement sealer signature in actual stream sediments further calls into question whether the proposed hypothesis that Austin stream inputs are dominated by coal tar-derived pavement sealer will be substantiated and points out the limitations of making predictions about stream sediment based solely on filter residue washed off parking lots. The results of this survey, from the field observations of stream conditions to changing concentrations associated with storm events and the PAH fingerprint patterns, reinforce through multiple approaches that the dynamics properties of sediment deposition, transport and mixing operating in Austin streams make it necessary for evaluations of urban impacts to be based on comprehensive studies of streams themselves.

Subsequent unsuccessful attempts to reproduce the Mahler et al. (2005) study by identifying PAHs from RTS in urban sediments from Austin, TX were published in a City of Austin-funded study (Scoggins et al., 2007) and a “before and after” study funded by PCTC (DeMott et al., 2010). The City-funded study included the following conclusions:

We attempted to identify the sources of PAH in the sediments of our study streams using ratio methods, but we were unsuccessful and found no significant clustering of field data with known source data. [Scoggins et al. (2007) p. 702].

We attempted to explain the magnitude of PAH contamination at the downstream study sites with spatial data. Neither total area of sealed parking lot nor its proximity to sampling locations were significantly correlated with PAH concentrations in the sediments at the downstream sites. [Scoggins et al. (2007) p. 705].

With the assistance of a letter to ES&T, the data used to represent urban sediment in Mahler et al. (2005) was identified. A response to a Freedom of Information Act (FOIA) request included an email explaining that those data were not chosen because they were believed to be representative of urban sediment, but were selected because they contained PAHs with signatures that “tended to group with [data from] the sealed parking lots.” The evidence that Mahler et al. (2005) selectively used data to confirm or generate a preferred hypothesis meets COPE’s criteria for “clear evidence that the findings are unreliable.”

After years of waiting for the authors’ institution, the United States Geological Survey (USGS), to address the situation, PCTC has made the case that the paper must be retracted directly to the editor of the journal, ES&T. PCTC’s retraction request letter is available here.


DeMott, R. P., and T. D. Gauthier, 2006, Comment on “Parking Lot Sealcoat: An Unrecognized Source of Urban Polycyclic Aromatic Hydrocarbons”: Environmental Science & Technology, v. 40, p. 3657-3658.

DeMott, R. P., T. D. Gauthier, J. M. Wiersema, and G. Crenson, 2010, Polycyclic Aromatic Hydrocarbons (PAHs) in Austin Sediments After a Ban on Pavement Sealers: Environmental Forensics, v. 11, p. 372-382.

LeHuray, A.P. 2014. Abuse of Science in Texas. American Thinker, Nov. 23. Available at http://www.americanthinker.com/articles/2014/11/abuse_of_science_in_texas.html

Mahler, B. J., P. Van Metre, T. J. Bashara, J. T. Wilson, and D. A. Johns, 2005, Parking Lot Sealcoat: An Unrecognized Source of Urban Polycyclic Aromatic Hydrocarbons: Environmental Science & Technology, v. 39, p. 5560 – 5566.

Mahler, B. J., P. C. Van Metre, J. T. Wilson, T. J. Bashara, and D. A. Johns, 2006, Response to Comment on “Parking Lot Sealcoat:  An Unrecognized Source of Urban Polycyclic Aromatic Hydrocarbons”: Environmental Science & Technology, v. 40, p. 3659-3661.

Scoggins, M., N. L. McClintock, L. Gosselink, and P. Bryer, 2007, Occurrence of polycyclic aromatic hydrocarbons below coal-tar-sealed parking lots and effects on stream benthic macroinvertebrate communities: Journal of the North American Benthological Society, v. 26, p. 694-707.

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