Post Publication Review: Did Austin’s RTS Ban Result in a Decline in PAH Concentrations in Lady Bird Lake Sediments?

In 2014, Van Metre & Mahler published a paper in the journal Environmental Science & Technology (ES&T) claiming that PAHs in Lady Bird Lake (or LBL, formerly called Town Lake) in the City of Austin, Texas, had declined because of the City’s RTS ban, which began on Jan. 1, 2006. The graph shown at the top of this post (Total PAH concentration versus time) is from the abstract of the paper. The graph illustrates a decline in total PAH concentrations in Lady Bird Lake sediments beginning in the late 1990’s to early 2000’s. The dashed vertical line represents January, 2006, when the RTS ban went into effect.

A decline in PAHs in urban sediments has been noted nationwide beginning in the 1990’s, and is attributed by most investigators to improved emission controls of the largest source of atmospheric PAHs (which are virtually always associated with particulate matter), vehicles and fossil fuel-fired electric plants, refineries, and other manufacturing facilities.  Van Metre & Mahler acknowledge that a decline in vehicle emissions has occurred, but dismiss its importance to the decline they posit in LBL sediments. As will be expanded on below, it is a puzzle why the decline in industrial emissions was not acknowledged.

PCTC has worked with scientists familiar with PAH concentrations in sediments in Austin waterways as well as with PAH source identification and apportionment methods used by Van Metre & Mahler in earlier publications. PCTC commissioned two post publication reviews from those different perspectives. As the results of both reviews indicated that formal Comments were warranted, the plan was to submit formal Comments on the Van Metre & Mahler paper to ES&T reflecting the two reviews. PCTC also planned to submit a third Comment based on the omission of a major source of PAHs from consideration – or even mention – in the Van Metre & Mahler paper. As it turned out, the first two Comments were submitted to ES&T, which immediately rejected both without further consideration on the grounds that ES&T apparently has a policy that no more than one Comment on any given paper will be published. The outcome of this development is that one of the Comments was re-submitted and subsequently published (DeMott & Gauthier, 2014), and the other two are relegated to informal publication on this web site and elsewhere. Each of the three Comments is summarized here.

DeMott & Gauthier (2014) expanded on three overall points:

Decreases in sediment PAH concentrations are shown to begin in the late 1990s, well before the city ban on CT sealants;

Decreases reported as significant1 were from differing and selected numbers of years by core (2009−2012 in core LBL.1; 2010−2012 in core LBL.2) and are not statistically significant when all postban years (2007− 2012) are included; and

PAH profiles in sediment samples are more consistent with typical parking lot/street dust profiles than CT sealer profiles.

DeMott & Gauthier’s review resulted in the following conclusion:

The timelines from sediment cores reported in the subject paper, other sampling by the COA [City of Austin], and a similar observed pattern of decreasing PAH concentrations beginning in the 1990s at a Texas lake where there was no CT-sealer ban (Fosdic Lake),6 all demonstrate that attributing the entire reported decrease to the ban in Austin is an incomplete explanation of the available data. The similarity of PAH profiles for the lake sediments to non-CT related dust sources also suggests an alternative explanation warranting consideration. The authors have incorporated a degree of conclusiveness to their interpretation of the Austin sealer ban effects that overlooks other available information.

In the second submitted Comment, available here, O’Reilly (2014, unpublished) notes the reoccurrence of  feature that is a hallmark of Van Metre & Mahler’s RTS papers- referring only to studies that support their hypotheses while ignoring work that might suggest some other explanation.

Consistent with their prior papers, Van Metre and Mahler described results in a way to promote a preconceived narrative instead of fully informing the reader. This is demonstrated in part by the references being dominated by papers generated by a small group of researchers who support their hypothesis concerning the role of refined tar pavement sealers (RTS) as a source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments while ignoring the body of literature describing PAH sources.  By not citing papers providing independent analyses and those that that have raised questions about the authors’ claims, the reader is not informed of the non-USGS data analyses and the findings that call aspects of their work into question. Van Metre and Mahler also fail to discuss their role in advocating for the product ban that their work evaluates, or that many of the sampling locations were adjacent to an electrical power plant that closed soon after the ban an important fact that supports a different causal analysis relating to the analytical findings in their work

O’Reilly goes on to describe the results he found using the same non-RTS model input parameters to the Chemical Mass Balance (CMB) model as Van Metre & Mahler, with two sets of different input values that unquestionably related to RTS used locally in Austin:

The critical finding is that RTS was indicated as a source only when the parking-lot dust PAH profile was used as a model input, but not when data that unquestionably represented RTS were used. The modeled source contribution of the fresh or test-plot RTS profiles was zero. Van Metre and Mahler argued that using fresh RTS as a source profile was not appropriate, because the material is known to weather in the environment. While this is true for RTS, it also true for all the other source profiles used. Using a weathered profile for RTS and unweathered profiles for the remaining sources is likely a major reason that Van Metre and Mahler’s application of CMB suggests an elevated RTS contribution to the typical weathered PAH profile of urban sediments.

Both the DeMott & Gauthier (2014) and O’Reilly (2014, unpublished) Comments are worthy of being read in full, so here again are the links, here and here.

A third Comment was planned and, given ES&T’s “one Comment per paper” policy, never submitted. As is evident in a 1999 publication by the same authors, Van Metre & Mahler, there was a large, fossil fuel-fired electric utility plant prominently placed on the shores of Lady Bird Lake, clearly visible in photographs included in Van Metre & Mahler (1999).   The photos show the Holly Street Power Plant. Indeed, Lady Bird Lake is an impoundment constructed as a cooling pond for the power plant. According to various histories, the plant regularly subjected neighbors to fires and spills. A 2011 newspaper account described living near the Holly Street Plant this way:

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With a power plant as its next door neighbor, the old house has endured half a century of loud, foundation-rattling clamor; regular dustings of soot; and a constant threat of fires and fuel spills that have marked much of the neighborhood’s perilous history

Both that newspaper story and a presentation by the City’s Parks & Recreation Department make clear that the plant’s closure in 2007 – not long after the City’s RTS ban went into effect – removed a potent source of PAHs, which would have been abundantly present in the soot, the fires, and the spills. PCTC is at a loss to understand how the authors of the USGS 1999 “Fact Sheet” on Lady Bird Lake failed to include closure of the plant in 2007 in an evaluation of a decline in PAH concentrations in cooling pond sediments adjacent to the Plant.

In summary, the answer to the question asked in the title of this post – Did Austin’s RTS Ban Result in a Decline in PAH Concentrations in Lady Bird Lake Sediments? – can be inferred to be “no.”


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