Superfund Research Program
Indoor Air Concentration Dynamics and Vapor Intrusion
Project Leader: Eric M. Suuberg
Grant Number: P42ES013660
Funding Period: 2009-2021
Studies and Results
This project is focused on providing a better understanding of organic vapor exposure pathways and involves two complementary activities. One is related to gaining a better understanding the properties of the tar-like contaminant mixtures found on a great many Superfund and brownfields sites, and the other is concerned with "vapor intrusion" into structures built atop or near organics contaminated sites.
The researchers have looked into very basic questions concerning the thermodynamic properties of what are commonly termed "tars" or "tar mixtures." These contaminants are composed of what are termed polycyclic aromatic hydrocarbons (PAHs), several of which are already identified as carcinogens. The question that needs further examination is: How do people come into contact with the harmful PAHs? Except for those who work with tars, ordinary contact with skin is not the main concern. Rather, it is the vaporization of the more volatile components that can then be inhaled or trapped onto inhaled dusts or the dissolution into groundwater that is then consumed. The researchers study what is termed the partitioning of such compounds into air and water. During 2013, they published two book chapters on the topic (J. Fu, J.W. Rice, E.M. Suuberg, "Phase Behavior and Thermochemical Properties of Polycyclic Aromatic Hydrocarbons and Their Derivatives" and J.W. Rice, J. Fu, E.M. Suuberg, "Thermodynamic and Phase Behavior of Polycyclic Aromatic Hydrocarbon Mixtures," both in the Handbook of Polycyclic Aromatic Hydrocarbons: Chemistry, Occurrence, and Health Issues, New York: Nova Publishers) and a refereed paper (Fu, Jinxia and Eric M. Suuberg. 2013. Thermochemical and vapor pressure behavior of anthracene and brominated anthracene mixtures. Fluid Phase Equilibria. 342:60-70. [Abstract]) on the complicated phase behavior of polycyclic aromatic mixtures. The last cited article is an example of how the researchers' interests evolved to including compounds of concern in connection with use of brominated flame retardants.
This project also continues a major effort in the direction of developing modeling tools for characterization of vapor intrusion of hazardous materials from in-ground sources. During 2013, the researchers published 12 refereed papers on the topic of vapor intrusion and indoor air quality-related problems. One example of their work is a review paper they prepared on the topic (Yao, Yijun, Rui Shen, Kelly G. Pennell, and Eric M. Suuberg. 2013. A review of vapor intrusion models. Environmental Science & Technology. 47(6):2457-2470. [Abstract]). The purpose of this work is to develop mathematical modeling tools to the point that they become a usual part of field investigations of vapor intrusion. The researchers have explored issues ranging from how transient events, such as rainfall, influence the phenomena, to how biodegradation of contaminants in the soil can help mitigate the problem. Project researchers have also developed simple approximation methods that can be utilized in lieu of running the actual numerical code. As part of this effort, they presented two workshops, co-sponsored with the Northeast Waste Management Officials Association (NEWMOA), that introduced regional (state-level) regulators and environmental consultants to the advantages that such modeling work can offer in understanding the hazard posed by vapor intrusion to homes or businesses built atop contaminated sites.
This work has spun off a new series of projects concerned with use of passive samplers for characterizing sediment contamination. The relationship to the main thrust of this project is the fact that PAHs are often characterized using such methods. Two refereed papers describe the application of different passive sampling modalities to the problem (e.g., Perron, Monique M., Robert M. Burgess, Eric M. Suuberg, Mark G. Cantwell, and Kelly G. Pennell. 2013. Performance of passive samplers for monitoring estuarine water column concentrations: 1. Contaminants of concern. Environmental Toxicology and Chemistry. 32(10):2182-2189. [Abstract]), and Jim Rice received a K.C. Donnelly award on this topic. (Jim is involved in both this project and the program's Research Translation Core; see a description of this in the Research Translation Core report.
The significance of these efforts is in the direction of helping better characterize exposure pathways of people to contaminants that have been released to the environment surrounding where they live and work. Broadly speaking, the work falls into the general area of understanding fate and transport of contaminants in the environment. More specifically, the vapor intrusion research is aimed at helping better characterize the scope of the problem at particular sites. Right now, environmental practitioners in the field rely heavily upon empirical characterization procedures, which fail to always provide complete enough understanding of the problem, particularly on complex sites (and thus limit the choice of mitigation or remediation approaches). Mathematical models offer much greater insight into what drives the processes of contaminant vapor entry into structures and promise to be an important addition to the field practitioners' tools for assessing the risk posed by vapor intrusion. Meanwhile, providing reliable thermodynamic data on contaminants of concern is always valuable to those who need to understand and model the exposure routes. Here, the focus on mixtures is the critical aspect since the existence of many contaminants together often leads to unexpected exposure profiles that cannot be predicted from earlier single component studies.