Parsing pyrogenic polycyclic aromatic hydrocarbons: Forensic chemistry, receptor models, and source control policy

Abstract

A realistic understanding of contaminant sources is required to set appropriate control policy. Forensic chemical methods can be powerful tools in source characterization and identification, but they require a multiple-lines-of-evidence approach. Atmospheric receptor models, such as the US Environmental Protection Agency (USEPA)'s chemical mass balance (CMB), are increasingly being used to evaluate sources of pyrogenic polycyclic aromatic hydrocarbons (PAHs) in sediments. This paper describes the assumptions underlying receptor models and discusses challenges in complying with these assumptions in practice. Given the variability within, and the similarity among, pyrogenic PAH source types, model outputs are sensitive to specific inputs, and parsing among some source types may not be possible. Although still useful for identifying potential sources, the technical specialist applying these methods must describe both the results and their inherent uncertainties in a way that is understandable to nontechnical policy makers. The authors present an example case study concerning an investigation of a class of parking-lot sealers as a significant source of PAHs in urban sediment. Principal component analysis is used to evaluate published CMB model inputs and outputs. Targeted analyses of 2 areas where bans have been implemented are included. The results do not support the claim that parking-lot sealers are a significant source of PAHs in urban sediments.

In response to Bales (2014)

“…In an article reporting work funded by the Pavement Coatings Technology Council (PCTC) recently published in Integrated Environmental Assessment and Management (IEAM), O'Reilly et al () state “Over the last few years, [US Geological Survey (USGS) scientists] Van Metre and Mahler have been advocating bans [of refined tar‐based pavement sealant, RTS] in testimony to local, state, and federal entities.” The statement is based on observations made by O'Reilly and colleagues at hearings they attended to testify about the findings of polycyclic aromatic hydrocarbon (PAH) forensic evaluations of data concerning RTS. In a letter to the editor of IEAM , Dr. Jared Bales, Acting Associate Director of Water, USGS, wrote that the statement is “inaccurate and misrepresents the facts” because the testimony in question was subject to USGS internal review procedures.…”

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

“…The Case Study article by O'Reilly et al (hereinafter “Case Study authors”), published in Integrated Environmental Assessment and Management (O'Reilly et al ) 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.…”

Response to O'Reilly et al. (2014): Policy of the US Geological Survey on advocacy

“…The US Geological Survey (USGS) believes that the following statement in O'Reilly et al () is inaccurate and misrepresents the facts: “Over the last few years, [USGS scientists] Van Metre and Mahler have been advocating bans in testimony to local, state, and federal entities.”…”