Post Publication Peer Review: Technical Evaluation of Van Metre & Mahler (2010)

Beginning in 2011, Dr. Kirk O’Reilly and his colleagues at Exponent® evaluated methods used by the USGS in their hypotheses that RTS is a “dominant” or “major” or “significant” source of PAHs in sediment in the US. The Exponent® team also reviewed the work of other scientists who adopted the USGS methods. Many of these evaluations and reviews have been published. In 2014, Dr. O’Reilly prepared a memorandum titled Technical Evaluation of Van Metre & Mahler (2010) to summarize the findings of the post publication peer review (PPPR) of the USGS publication that introduced the use of EPA’s Chemical Mass Balance (CMB) as a method of identifying PAH sources, and the percent contribution of those sources. The findings of the PPPR were:

Key findings include:
- CMB can match mixtures of the proposed sources to sediment PAH profiles whether or not a RTS source term is included.
 – When the RTS source profile is changed from one based on parking lot dust to another based on the chemical analysis of RTS, CMB eliminates it as a source from most of the sediments samples considered.
The evaluation indicates that the results of CMB do not provide support for the Mahler hypothesis. Because other researchers (Crane 2013; Witter et al 2014) have begun to apply the methods described in Van Metre and Mahler 2010, the USGS should consider retracting the article.


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