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Community exposures to chemicals through vapor intrusion: a review of past agency for toxic substances and disease registry public health evaluations.


Volatile contaminants in subsurface soil or groundwater can migrate up into buildings--vapor intrusion--and present a unique inhalation exposure pathway. As U.S. Environmental Protection Agency (U.S. EPA) and Agency for Toxic Substances and Disease Registry (ATSDR) awareness of this phenomenon increases, the large number of historical solvent and petroleum releases is resulting in an ever-increasing number of sites with a vapor intrusion component. This column summarizes information showing which chemicals occur most frequently above screening values at sites ATSDR has reviewed and how many of the sites with these contaminants were classified as a public health hazard. The potential for vapor intrusion and possible adverse health effects to building occupants are important pieces of information for communities to be aware of, especially during redevelopment activities and land use decision making.


Volatile organic chemicals (VOCs) are among the most common contaminants released into the environment from hazardous waste sites. In addition to contaminating groundwater and soil, these chemicals may off-gas from these two media and migrate up into the air of homes and commercial buildings. Figure 1 illustrates the potential vapor intrusion conduits into buildings. If vapors build up indoors levels may lead to the following health and safety issues: fire; explosion; and acute, intermediate, and chronic health effects (Agency for Toxic Substances and Disease Registry [ATSDR], 2008).



In 2009, an ATSDR intern reviewed 135 vapor intrusion public health assessments and consultations on 121 sites published on ATSDR's Web site between 1994 and 2009. Here we report the following: contaminant(s), maximum indoor air concentration, and health hazard category. ATSDR assigns one of five health hazard categories to summarize the risks of particular chemical exposures at a site. The categories range from "urgent public health hazard" to "no public health hazard (ATSDR, 2005)." Information on the source of indoor air contamination was also collected (e.g., groundwater, soil gas, crawl space gas, and outdoor air data).

We ranked chemicals detected in indoor air according to the frequency that they were found and the frequency in which they exceeded ATSDR comparison values (CVs). Our CVs are chemical and media-specific concentrations used by ATSDR health assessors and others to identify environmental contaminants at hazardous waste sites that require further evaluation. Evaluating chemicals present above CVs involves analysis of site-specific exposure factors and toxicologic studies (ATDSR, 2005). Lastly, we examined which chemicals resulted in sites being declared a health hazard.


Of the 135 reports evaluated (121 sites), 119 (88%) were written after U.S. EPA's 2002 draft guidance for evaluating vapor intrusion was published (U.S. Environmental Protection Agency [U.S. EPA], 2002). Figure 2 shows the increasing number of vapor intrusion site reports published each year since 1994.

Figure 3 shows these site locations and highlights those where ATSDR determined a public health hazard existed. As with many other types of ATSDR evaluations, the locations are highly concentrated in densely populated cities and areas historically associated with heavy industry. In addition, vapor intrusion sites have historically been more focused in the colder northern regions where the stack effect is considered more pronounced. In the stack effect, heated building interiors and higher winds at rooftops draw air out near the roof creating negative pressure inside the building and drawing in subsurface vapors.

Our review identified 119 VOCs and semivolatile organic compounds in indoor air, groundwater, ambient air, and soil gas. Ninety-five (80%) of the chemicals were detected in indoor air. Fifteen of these exceeded a CV or combustible hazard criteria and only five were responsible for declaring public health hazards (Table 1). The five chemicals associated with hazards were categorized in two chemical families: nonchlorinated and chlorinated VOCs. Three chemicals, benzene, tetrachloroethylene (PCE), and/or trichloroethylene (TCE) were found in at least one medium (indoor air, groundwater, crawl space air, or soil gas) at 95% of the sites. Nonchlorinated VOCs primarily come from petroleum sources, whereas the chlorinated VOCs come from a wider variety of sources, such as dry cleaning and degreasing operations.

Additionally, Table 1 lists each contaminant's detection frequency in indoor air, the number of sites with the chemical above the CV, and the number of sites declared a health hazard due to the contaminants. Ten of the 15 contaminants found above CVs were not the basis for declaring health hazards. This could be because other more hazardous contaminants were of higher concern or because of site-specific exposure scenarios (e.g., two hours of exposure per week compared with 24 hours of exposure per day, seven days per week).

Chlorinated ethylenes, PCE, and TCE resulted in the most health hazard conclusions (eight from indoor air measurements). Figures 4 and 5 compare maximum contaminant levels found with ATSDR CVs for nonchlorinated and chlorinated VOCs, respectively. Shaded symbols indicate contaminant concentrations exceed the CVs. Both figures display several "new" CVs. As toxicology and epidemiology science evolves, new findings may result in lowering or raising a contaminant's level of health concern. This may lead to changes in health conclusions. The presence of nonchlorinated VOCs (volatile petroleum products) resulted in health hazard conclusions due to benzene carcinogenicity or danger of fire and explosion.

Benzene, a carcinogen, is the more toxic constituent of the BTEX (benzene, toluene, ethylbenzene, xylene) petroleum chemical family (ATSDR, 2004). It was detected above CVs in indoor air at 28 sites and accounted for two sites with public health hazard conclusions. Confounding background sources are a concern at many benzene sites. The upper 95th percentile for benzene in indoor air, 29 [micro]g/[m.sup.3] (U.S. EPA, 2011), exceeds U.S. EPA's risk management range of 1 in 10,000 excess cancer cases. ATSDR provides health education on reducing background exposures to benzene and other indoor air contaminants when health based levels are exceeded (U.S. EPA, 2012).

Figure 4 illustrates that benzene exceeded its CV much more frequently (100%) than the remaining petroleum-related compounds (xylene = 20%, toluene = 14%, and ethylbenzene = 6%). Methane is not particularly toxic, but does pose a fire and explosion hazard if it accumulates to flammable or explosive levels. A public health hazard from methane was declared at one site because it was detected 1,000 times above the lower explosive limit. The petroleum VOCs were measured using a nonspecific photoionizing detector and therefore are estimates. Like methane, the levels present at the petroleum VOCs site were determined to be a fire and explosion hazard and possibly high enough to cause acute health effects.

As illustrated in Figure 5, of the chlorinated VOCs, the industrial solvent methylene chloride most often exceeded its CV. Levels were above the cancer risk CV 80% of the time it was detected. Vinyl chloride, another carcinogen (ATSDR, 2006), also had many measurements (70%) exceeding its CV



Of the 121 sites reviewed, 17 (14%) posed a "public health hazard," 83 (69%) posed "no apparent public health hazard," and 56 (46%) posed an "indeterminate public health hazard" (insufficient information precludes a conclusion). No sites posed an urgent public health hazard, ATSDR's highest conclusion category. Twelve of the 17 sites were classified as a public health hazard because of high indoor air measurements (Table 1). The five other sites that were deemed public health hazards exhibited relatively high soil gas, groundwater, or crawl space contamination.


Chlorinated ethylene pollutants and petroleum-related pollutants were the most frequently found chemicals at sites where the vapor intrusion pathway was investigated. Benzene, PCE, or TCE was found at 95% of the sites. Benzene most frequently exceeded its CV in indoor air for a chemical that resulted in health hazards. TCE, a chemical of increasing concern (Burk, Zarus, Grosse, Pugh, & Issacs, 2009), caused the highest percentage (14%) of health hazards due to toxicity when detected, though PCE was similar (13%). Petroleum VOCs and methane each resulted in one health hazard from the potential for fire or explosion. Vapor intrusion of a combined chloroform and carbon tetrachloride mixture also resulted in one public health hazard.

We encourage state, local, and federal stakeholders to increase awareness of historical sources of hazardous subsurface vapors in and near their communities. This issue is not just applicable to existing buildings--it should be considered in community revitalization and brownfields efforts and before abandoned property redevelopment decisions.



Editor's Note: As part of our continuing effort to highlight innovative approaches to improving the health and environment of communities, the Journal is pleased to publish a bimonthly column from the U.S. Agency for Toxic Substances and Disease Registry (ATSDR). The ATSDR, based in Atlanta, Georgia, is a federal public health agency of the U.S. Department of Health and Human Services and shares a common office of the Director with the National Center for Environmental Health at the Centers for Disease Control and Prevention (CDC). ATSDR serves the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and diseases related to toxic substances.

The purpose of this column is to inform readers of ATSDR's activities and initiatives to better understand the relationship between exposure to hazardous substances in the environment and their impact on human health and how to protect public health. We believe that the column will provide a valuable resource to our readership by helping to make known the considerable resources and expertise that ATSDR has available to assist communities, states, and others to assure good environmental health practice for all is served.

The conclusions of this article are those of the author(s) and do not necessarily represent the views of ATSDR, CDC, or the U.S. Department of Health and Human Services.

Since joining ATSDR in 2006, Tonia Burk has developed vapor intrusion tools, training materials, and professional presentations for the agency. She maintains an active role in interagency workgroups and provides technical assistance on vapor intrusion sites. Gregory Zarus has been an environmental health scientist with ATSDR since 1997 and currently leads the Atlanta-based team that assesses the health impact of environmental contamination for communities within the U.S. Environmental Protection Agency's Regions 7, 8, 9, and 10.

Acknowledgements: We thank the following ATSDR colleagues for their contributions, reviews, and suggestions: Arturo Rivera (intern), Janet Heitgerd, Ken Powell, Sarah Martin, Steve Bullard, Randall Young, and Arie Manangan.

Corresponding Author: Gregory Zarus, Division of Community Health Investigations, Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services, 4770 Buford Hwy. NE, Mail-stop F-59, Atlanta, GA 30341-3717. E-mail:


Agency for Toxic Substances and Disease Registry. (2004). Interaction profile for benzene, toluene, ethylbenzene, and xylenes (BTEX). Atlanta: U.S. Department of Health and Human Services. Retrieved from http://

Agency for Toxic Substances and Disease Registry. (2005). Public health assessment guidance manual (updated). Atlanta: U.S. Department of Health and Human Services. Retrieved from http://www.atsdr.cdc. gov/HAC/PHAmanual/index.html

Agency for Toxic Substances and Disease Registry. (2006). Toxicological profile for vinyl chloride. Atlanta: U.S. Department of Health and Human Services. Retrieved from tp20.pdf

Agency for Toxic Substances and Disease Registry. (2008). Evaluating vapor intrusion pathways at hazardous waste sites. Atlanta: U.S. Department of Health and Human Services. Retrieved from http://www.atsdr. intrusion.pdf

Burk, T., Zarus, G., Grosse, C., Pugh, K., & Issacs, S. (2009, May). ATSDR health assessment of TCE exposure by vapor intrusion at military facilities. Paper presented at the Environment, Energy & Sustainability Symposium, Denver, CO.

U.S. Environmental Protection Agency. (2002). OSWER draft guidance for evaluating the vapor intrusion to indoor air pathway from groundwater and soils (subsurface vapor intrusion guidance). Retrieved from http://www. eis/vapor.htm

U.S. Environmental Protection Agency. (2011). Background indoor air concentrations of volatile organic compounds in North American residences (1990-2005): A compilation of statistics for assessing vapor intrusion. Retrieved from documents/oswer-vapor-intrusion-background-Report-062411.pdf

U.S. Environmental Protection Agency. (2012). An introduction to indoor air quality (IAQ): Volatile organic compounds (VOCs). Retrieved from

Indoor Air Contaminants Found Above Comparison Values (CVs)
From Vapor Intrusion

Contaminants Sites (a) Lowest
 With CV
 Chemical (Type of
 Detected CV) in
 in Indoor [micro]g/
 Air [m.sup.3]]

Nonchlorinated VOCs (c)

Benzene 28 0.1 (CREG)
Toluene 21 300 (cEMEG)
Ethylbenzene 17 1000 (cEMEG)
Xylene 20 200 (cEMEG)
n-Hexane 9 2,100 (cEMEG)
1,3-butadiene 6 0.03 (CREG)
Combustibles Methane 2 10% LEL
 (c [double
 Petroleum 2 10% LEL
 VOCs ([double
Chlorinated VOCs
Tetrachloroethylene (PCE) 39 300 (cEMEG)
Trichloroethylene (TCE) 21 500 (iEMEG)
 (c [double
Vinyl chloride 10 0.11 (CREG)
Methylene chloride 20 2 (CREG)
Chloroform 10 0.04 (CREG)
Carbon tetrachloride 10 0.07 (CREG)
1,4-dichlorobenzene 7 60 (cEMEG)

Contaminants Sites (a) Sites
 With Declared
 Chemical a Public
 Above CV Health
 in Indoor Hazard
 Air Due to
 Air (b)
Nonchlorinated VOCs (c)

Benzene 28 (100%) 2 (7%)

Toluene 3 (14%) 0 (0%)

Ethylbenzene 1 (6%) 0 (0%)

Xylene 4 (20%) 0 (0%)
n-Hexane 1 (11%) 0 (0%)
1,3-butadiene 6 (100%) 0 (0%)
Combustibles Methane 1 (50%) 1 (50%)

 Petroleum 0 (0%) 1 (50%)

Chlorinated VOCs
Tetrachloroethylene (PCE) 5 (13%) 5 (13%)

Trichloroethylene (TCE) 1 (5%) 3 (14%)

Vinyl chloride 7 (70%) 0 (0%)
Methylene chloride 16 (80%) 0 (0%)

Chloroform 9 (90%) 0 (0%)
Carbon tetrachloride 9 (90%) 0 (0%)

1,4-dichlorobenzene 4 (57%) 0 (0%)

(a) Some sites have more than one chemical of concern, i.e.,
the sites are not mutually exclusive.

(b) Hazard frequency = the number of sites (and %) where the
chemical was declared a situation-specific health hazard.

(c) VOCs = volatile organic compounds; CREG = cancer risk
evaluation guides; cEMEG = noncancer chronic environmental media
evaluation guides; LEL = lower explosive limit; iEMEG = noncancer
intermediate environmental media evaluation guides.

([dagger]) The following updated CVs have recently been released:

Ethylbenzene: cEMEG = 260 [micro]g/[m.sup.3].

PCE: CREG = 3.8 [micro]g/[m.sup.3].

TCE: CREG = 0.24 [micro]g/[m.sup.3], reference concentration =
2 [micro]g/[m.sup.3].

Methylene chloride: CREG = 100 [micro]g/[m.sup.3], cEMEG =
1,000 [micro]g/[m.sup.3].

Carbon tetrachloride: CREG = 0.17 [micro]g/[m.sup.3].

([double dagger]) No Agency for Toxic Substances and Disease
Registry CV available. The National Institute for Occupational
Safety and Health has developed the immediately dangerous to
life and health

(IDLH) values for methane and petroleum distillates that are
10% of the LEL. Methane: IDLH = 5,000 parts per billion
(ppb) by volume; petroleum distillates: IDLH = 1,100,000 ppb.
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Title Annotation:DIRECT FROM ATSDR
Author:Burk, Tonia; Zarus, Gregory
Publication:Journal of Environmental Health
Date:May 1, 2013
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