Typical Benzene Concentrations in Ambient and Indoor Air

Transcription

1 M E M O R A N D U M TO: FROM: Henry Schuver (US EPA) Bart Eklund (URS-Austin) DATE: February 13, 2004 SUBJECT: Typical Benzene Concentrations in Ambient and Indoor Air Vapor intrusion studies frequently involve the collection of indoor air and ambient air samples, as well as shallow soil gas samples. When evaluating such data, however, there are no guidelines as to what typical background levels may be encountered. Such information would be useful in evaluating whether a given measurement result is likely due to subsurface contamination or is due to other sources. This memorandum provides information about typical concentrations of benzene in ambient air and indoor air. Benzene is of particular concern for vapor intrusion studies due its occurrence in many petroleum products and its potential health effects. Information is summarized below for typical benzene concentrations in ambient air and in indoor air, followed by information about exposure guidelines for benzene. 1.0 Summary My best estimate of typical benzene concentrations in ambient urban air is 0.5 to 1.0 ppbv. My best estimate of typical benzene concentrations in indoor air is 1.5 to 2.0 ppbv for houses with non-smokers. These estimates are based on my 20+ years experience performing and evaluating air measurements for VOCs and my review of recent publicly available data. These estimates are annual average values; individual 8-hr or 24-hr measurements may be higher or lower. It is the annual average, of course, that is important for evaluation of chronic/long-term health impacts. 2.0 Benzene Concentrations in Ambient Air Information about benzene levels in ambient air was obtained and reviewed. Benzene is typically detected in ambient air samples collected in both urban and rural areas of the U.S. The best estimate of typical benzene levels in urban air currently is 0.5 to 1.0 ppbv. The concentrations have generally declined since the 1980 s. The US EPA summarized data from around the US in the National Air Quality and Emissions Trends Report for 1999 (US EPA, 2001). The annual average benzene concentration in metropolitan areas for 1999 was approximately 2.0 µg/m 3 (0.6 ppbv) with the 5 th percentile at about 1.0 µg/m 3 (0.3 ppbv) and the 95 th percentile at about 3.25 µg/m 3 (1 ppbv). In the same document, the annual average toluene concentration in Page 1 of 6

2 metropolitan areas for 1999 is shown as 5 µg/m 3 (1.2 ppbv). A toluene:benzene ratio of roughly 3:1 is typical of ambient air. The benzene data for the most recent available year (2000) shows little change from the 1999 data (see The US EPA estimates that benzene concentrations have decreased by 47% from 1994 through 2000, based on measurements at 95 urban monitoring sites. The National Trends Report for 1999 also shows the average annual benzene concentrations for metropolitan sites in California for 1990 to The highest values shown (the 95 th percentile values) never exceed 4 ppb (12 µg/m 3 ) for the 10-year period. These are average values; the range of individual measurement values for shorter time periods (e.g., 24-hr) will extend over a larger range and may include values >4 ppbv The US EPA maintains a database of ambient air monitoring (AAM) data from monitoring locations throughout the U.S. The air trends website for toxic air pollutants (see has the following plot of benzene levels for various US cities. Note: 3.2 µg/m 3 = 1 ppbv and 1 µg/m 3 = 0.31 ppbv. As shown in the figure, the average benzene concentrations in 2001 in these urban areas ranged from about 1.0 to 2.5 µg/m 3 (0.3 to 0.8 ppbv). Page 2 of 6

3 The literature review also identified several other government publications that summarized ambient benzene concentrations. The relevant data are summarized below, but the data in some cases is some years old and therefore may reflect higher benzene concentrations than more recent data. The US EPA website has a White Paper that contains information on ambient benzene concentrations (Goldstein, 2000). According to Dr. Goldstein, community outdoor benzene levels appear to range well below 10 ppb (32 µg/m 3 ). The most recent data cited in the paper is a 1999 study for EPA Region V that showed a median benzene level of 2.9 µg/m 3 (0.9 ppbv) and a 90 th percentile level of 5.6 µg/m 3 (1.8 ppbv). Also cited is a 1997 California Air Resources Board study that estimated an annual concentration of 2.3 µg/m 3 (0.7 ppbv). ATSDR summarized ambient air monitoring data for benzene in the Toxicological Profile for Benzene (ATSDR, 1997). The data in the ATSDR Tox Profile are largely from the 1980 s and therefore tend to be higher than more recent data reported by the US EPA. Values over 100 ppbv are reported for 24-hr average samples in urban areas. Data are reported for a study of 39 US urban areas in the mid-1980 s where the overall median was 12.6 ppbv. A 2 nd ATSDR document contains the following summary table (Gist and Burg, undated): Table 1. Levels of benzene in air. Location of Air Sample Level (ppb) Urban Remote/Rural Suburban residential-remote from traffic Indoor 1.8 Workplace 2.1 Near chemical plant 14.0 Near refineries 9.0 Gas stations < Page 3 of 6

4 3.0 Benzene Concentrations in Indoor Air Several summaries were identified that contain benzene concentrations for indoor air, but there are generally less data available for indoor air than for ambient air. The available information is summarized in Table 2. The values given in Table 2 are mean or median values; individual measurements may be higher or lower. For example, in one study not included in Table 2, the mean benzene concentrations were 3.9 µg/m 3 (1.2 ppbv) for 24 non-smoking homes and 5.5 µg/m 3 (1.7 ppbv) for 25 smoking homes. The maximum values, however, were 19 µg/m 3 (5.9 ppbv) for the non-smoking homes and 27 µg/m 3 (8.4 ppbv) for the smoking homes (ATSDR, 1997). Table 2. Typical Levels of Benzene in Indoor Air Type of Study Average Benzene Conc. (ppbv) Source Literature Review for US homes 1.6 US EPA, Houses in the US with non-smokers 2.2 ATSDR, Houses in the US with 1 or more smokers 3.3 ATDSR, Indoor air samples 1.4 CARB, 1997 Literature Review including non-us homes 1.6 Corsi, Health-Based Guidelines for Benzene As shown above, typical benzene concentrations in ambient air are approximately 0.5 to 1 ppbv. Benzene concentrations in indoor air typically are somewhat higher, with values of approximately 1 to 2 ppbv for US houses without smokers. Individual measurements up to an order of magnitude higher than these averages may be expected. The typical values are well above conservative screening levels that are sometimes used to evaluate inhalation risk. The EPA Region VI screening level for benzene in ambient air is 0.25 µg/m 3 (0.08 ppbv)(us EPA Region VI, 2003). The EPA Region III screening level for benzene in ambient air is 0.23 µg/m 3 (0.07 ppbv)(us EPA Region III, 2003). Values below the screening levels are considered to be safe for long-term exposure (30 years, 350 days/year). The US EPA IRIS database summarizes risk information for benzene (EPA, 2003). The reference concentration (RfC) for evaluation of non-carcinogenic effects of chronic Page 4 of 6

5 inhalation exposure is 3x10-2 mg/m 3, which is equivalent to 30 µg/m 3 (9.4 ppbv). The IRIS estimate for carcinogenic risk for inhalation exposure is shown in Table 3. Table 3. Air Concentrations at Specified Risk Levels for Benzene Risk Level Concentration E-4 (1 in 10,000) 13.0 to 45.0 µg/m 3 ( ppbv) E-5 (1 in 100,000) 1.3 to 4.5 µg/m 3 ( ppbv) E-6 (1 in 1,000,000) 0.13 to 0.45 µg/m 3 ( ppbv) Limits and guidelines for occupational exposures tend to be much higher than the screening levels shown above. Occupational exposure limits published by OSHA, NIOSH, and ACGH also shown in Table 4 for bezene (for comparison, toluene data also are shown). The OSHA Permissible Exposure Limits (PELs) are enforceable limits. The other values shown for comparison are the National Institute for Occupational Safety and Health (NIOSH) Recommended Expsoure Limits (RELs) and the American Congress of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs). The NIOSH and ACGIH values are guidelines that are updated more frequently than the OSHA values and tend to be more conservative. The values shown are time-weighted average (TWA) exposure concentrations for a conventional 8-hour (PEL, TLV) or up to a 10-hour (REL) workday and a 40-hour workweek. Table 4. Occupational Exposure Limits for Benzene and Toluene Analyte All values as ppbv OSHA PEL NIOSH REL ACGIH TLV Benzene 1, Toluene 200, ,000 50,000 Source: ACGIH, Page 5 of 6

6 5.0 References ACGIH. Guide to Occupational Exposure Values American Congress of Governmental Industrial Hygienists. Cincinnati, OH ATSDR. Toxicological Profile for Benzene. Agency for Toxic Substances and Disease Registry. September Available at: ATSDR. Health Consultation, St. Lucie Residences, St. Lucie, St. Lucie County, Florida. Agency for Toxic Substances and Disease Registry. November 13, Available at: CARB. Benzene fact sheet. California Air Resources Board. September Available at: Corsi, Richard. Review of BTEX and MTBE data for Residential Dwellings and a Recreation Center. July 20, [Personal communication to Bart Eklund, URS] Gist, G.L. and J.R. Burg. Benzene A Review of the Literature from a Health Effects Perspective. ATSDR. undated. Available at: Goldstein, B.D. Benzene White Paper. June 16, Available at: US EPA. Inside IAQ. EPA/600/N-98/002. Spring/Summer Available at: US EPA. National Air Quality and Emissions Trends Report, EPA 454/R US EPA, OAQPS, RTP, NC. March US EPA. Integrated Risk Information System (IRIS) Available at: US EPA Region III. EPA Region III Risk Based Concentration Table. October Available at: US EPA Region VI. Human Health Media-Specific Screening Levels. November Available at: Page 6 of 6