Jaana Pietari

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

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.

Forensic Assessment of Refined Tar-Based Sealers as a Source of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Sediments

Atmospheric deposition of particles and their subsequent transport by stormwater are a major source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments. Recently, the results of forensic analysis have been used to promote a hypothesis that refined tar-based pavement sealers (RT-sealers) are another significant source. To evaluate this hypothesis, a suite of forensic methods was applied to a wider range of PAH data for this study. Sediments PAH profiles are no more similar to RT-sealers than they are to a number of other environmental inputs. While RT-sealers were not eliminated as a potential source in some locations, forensic methods did not differentiate their contribution from other sources of PAHs, indicating RT-sealers are not a unique or readily quantifiable source of PAHs to the urban environment.

Use of Receptor Models to Evaluate Sources of PAHs in Sediments

Receptor models are mathematical procedures for resolving one or more of these parameters in a mixed chemical system: (1) the number of sources, (2) their chemical characteristics, and (3) the relative contribution of each source in environmental samples. These models are being used increasingly to evaluate sources of polycyclic aromatic hydrocarbons (PAHs) in sediments. As with any mathematical model, understanding the underlying assumptions is critical in interpreting the output. Three assumptions that raise particular challenges when applying receptor models to evaluate multiple sources of pyrogenic PAHs are (1) identification of all important sources, (2) stability of source profiles, and (3) linear independence of each profile. Variability within source types, and similarities among the PAH profiles of different sources, create uncertainties that must be considered when evaluating the results of receptor models. Various procedures for evaluating uncertainties have been applied in the literature, but validation and standardization of such methods are often lacking. Using a case study, this article demonstrates how a more detailed evaluation of model output can produce conclusions that differ from those initially published. While not eliminating uncertainty, we recommend a multiple-lines-of-evidence approach that includes both mixing and unmixing receptor models, along with other environmental forensic techniques.

Atmospheric Fate and Behavior of POPs

Persistent organic pollutants (POPs) are often transported from primary and secondary sources through the atmosphere. Investigations into the sources, transport, fate, timing of releases, and apportionment of residual contamination require an understanding of emission characteristics of various sources, as well as relevant atmospheric chemical and physical processes. The researcher may also need to compare measured POPs concentrations in ambient air and settled dust with results from other studies in settings similar to the subject or condition. In this chapter, we provide a literature review of this information for five families of POPs: polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polybrominated compounds, polyfluorinated compounds, and polychlorinated dibenzo-p-dioxins (a.k.a. dioxins) and polychlorinated dibenzofurans (a.k.a. furans). For each of the chemical groups, we discuss sources to the atmosphere, chemical transformations during atmospheric transport, levels found in ambient air, and levels found in settled dust. Environmental forensic case studies are also presented for each type of POP.

Cautions on the treatment of non-detect results for environmental forensics

ABSTRACT While censored data (i.e., containing non-detect [ND] results) may provide useful information in the context of risk assessment, their utility in chemical forensics is less clear. Substitution of NDs can create invasive patterns and may obscure the true forensic features in the underlying chemistry and sample compositions. The effect of substituting numeric values for NDs on the results of common chemical forensics multivariate analyses is illustrated using synthetic simulated data and laboratory measurements of soil samples from Colorado. The analyses of simulated and laboratory data demonstrate the impact of substituting values for NDs on multivariate analyses and indicate the potential for incorrect conclusions about the true forensic features within the data. Recommendations are provided for how to investigate and visualize the impact of NDs on chemical forensic multivariate analyses.

Congeners: A Forensics Analysis

Analytical data must be reliable. Chemical fingerprinting methods, whether based on sample-specific comparisons of profiles, analyses of “diagnostic ratios,” or multivariate statistical analyses, are dependent on good quality analytical chemistry data and are thus vulnerable to data quality problems. Analytical data for the same compounds, but from different laboratories or derived by different methods, can introduce uncertainty in the comparisons. There are many chemical fingerprinting methods, which range from simple profile comparisons of individual samples to sophisticated multivariate analyses. Individual profile comparisons can be useful when the profiles are clearly different. However, the human eye has difficulty detecting subtle patterns between histogram plots of 10 PCDD/F homologs. Multivariate statistical analyses such as hierarchical cluster analysis and PCA are often used to condense and simplify a complex set of variables. These widely used and accepted techniques are scientifically defensible, although the underlying mathematics are complex.

Improving rigor in polycyclic aromatic hydrocarbon source fingerprinting

ABSTRACT Source identification of polycyclic aromatic hydrocarbons in environmental samples has advanced greatly in the last 20 years and continues to advance. To realize potential benefits and avoid possible pitfalls, however, great care is needed as one applies published diagnostic tools to data sets. This commentary reflects some recent observations, concerns, and recommendations.

Establishing the Chemical Footprint of Potential Injury from Petroleum Product Releases at Fuel Terminals

ABSTRACT Owners and operators of waterfront fuel terminals can be liable for natural resource damages (NRD) caused by releases from their facilities. While NRD assessments typically focus on measuring exposure and predicting injury, there is often insufficient consideration of two key issues: 1) adequate and specific consideration of the chemical background, and 2) establishing the release(s) footprint through linking sediment chemistry to the particular release(s). Recent changes in the legal framework used to assign and apportion remedial and NRD liability further increase the need to quantify a facilitys contribution to environmental harm. The goal of this paper is to discuss the changing legal framework and present a multiple lines of evidence approach both for characterizing the chemical conditions that would be expected in the absence of a release, and for identifying a facility-specific chemical footprint related to possible natural resource damages. Critical components include a thorough understa...