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Population-Weighted Exposure to 
174 Air Toxics in a Representative Sample 
of the United States Population 1999 – 2010 
B...
What is the nationwide 
outdoor exposure 
to air toxics?
Modeled Exposure 
 US EPA National-Scale Air Toxics Assessment 2005 
 Nationwide estimate of chronic inhalation exposure 
...
NATA 2005 Process 
Ambient Monitoring 
National Emissions Inventory 2005 
Point  Mobile Sources 
HEM3/AERMOD 
Exposure Con...
Now that we have 
exposure estimates, 
what if we could 
associate them with 
where people live?
National Population Sample 
 National Health and Nutrition Examination Survey 
 1999 — 2010 
 Health conditions and behavi...
National Population Sample
National Exposure Estimates
NATA-NHANES Data Merge 
Merge by 
Census 
Tract 
NATA 
Air Toxics 
Exposure 
NHANES 
Residence 
Merged 
NATA-NHANES 
Data
NATA 2005  NHANES 1999-2010 
 NATA outdoor exposure concentration for 
residence census tract 
 NHANES subjects 
 6 years-...
Loge Boxplots 
133 Air Toxics, Ranked by Median 
Ln Exposure [nmol/m3]
Medians
Exposure 6Nanomolar: Urban 
Urban Rural 
nmol/m3 μg/m3 μg/m3 
FORMALDEHYDE 54.20 1.63 1.02 
ACETALDEHYDE 32.90 1.45 1.10 
...
Exposure 6Nanomolar: Rural 
Rural Urban 
nmol/m3 μg/m3 μg/m3 
FORMALDEHYDE 34.00 1.02 1.63 
ACETALDEHYDE 25.00 1.10 1.45 
...
Median Nanomolar: 
Urban vs. Rural 
Air Toxic 
Urban 
[nmol/m3] 
Rural 
[nmol/m3] 
Urban 
[μg/m3] 
Rural 
[μg/m3] 
FORMALD...
Compare regions?
Which regional scheme?
Correlated Groupings 
 Method 
 Principle components analysis 
 Factor analysis 
Levy I, Mihele C, Lu G, Narayan J, Brook ...
Strengths 
 Comprehensive assessment of 174 air toxics 
 Population-weighted 
 Large sample 
 National geographic coverage...
Limitations 
 Uncertainty of NATA exposure estimates 
 NATA appropriate for determining: 
 Which pollutants or sources mig...
NATA 2005 Process 
Ambient Monitoring 
National Emissions Inventory 2005 
Point  Mobile Sources 
HEM3/AERMOD 
Exposure Con...
Approaches to 
Exposure Assessment 
Modeling 
Exposure 
Assessment 
Measurement Biomarker
URL to Presentation LinkedIn Contact 
B. Rey de Castro, Sc.D. 
+1 770 488 0162 
rdecastro@cdc.gov 
For more information pl...
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Population-Weighted Exposure to 174 Air Toxics in a Representative Sample of the United States Population 1999 – 2010

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BACKGROUND: The 1990 Clean Air Act regulates air toxics because they are known to or suspected of causing cancer or other serious health problems. US EPA’s 2005 National-Scale Air Toxics Assessment (NATA) provides a “snapshot” estimate of chronic inhalation exposure for numerous air toxics at each US census tract. The National Health and Nutrition Examination Survey (NHANES) obtains a complex, multistage probability sample of human subjects representative of the US population. AIMS: Estimate reference exposure concentrations of 174 air toxics, including diesel engine emissions, for a representative sample of the United States population. METHODS: Publicly available US EPA NATA 2005 air toxics exposure concentrations estimated at the census tract were geographically merged with geocoded residences of participants in NHANES 1999 – 2010 (n = 62,160). Population-weighted statistics were estimated for each air toxic. RESULTS: For a selection of air toxics, the population-weighted geometric mean (GM [GSD] in micrograms per cubic meter) of exposure concentration were estimated to be: toluene 1.6 [0.089]; formaldehyde 1.5 [0.036]; acetaldehyde 1.4 [0.027]; benzene 0.75 [0.027]; diesel engine emissions 0.24 [0.019]; acrolein 0.021 [0.0012]; and PAHs 0.0061 [0.00042]. Statistics grouped by metropolitan and non-metropolitan census tracts are also available. CONCLUSIONS: This analysis provides a comprehensive assessment of air toxics exposure for the US population potentially useful for prioritizing pollutants for further evaluation of public health impact.

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Population-Weighted Exposure to 174 Air Toxics in a Representative Sample of the United States Population 1999 – 2010

  1. 1. Population-Weighted Exposure to 174 Air Toxics in a Representative Sample of the United States Population 1999 – 2010 B. Rey de Castro, Sc.D. Statistician before the International Society for Exposure Science Modeling Sources and Exposures of Air Toxics Monday, 13 October 2014 Cincinnati, OH National Center for Health Statistics Division of Laboratory Science ID: Mo-O-A4-02
  2. 2. What is the nationwide outdoor exposure to air toxics?
  3. 3. Modeled Exposure US EPA National-Scale Air Toxics Assessment 2005 Nationwide estimate of chronic inhalation exposure Census tract resolution 174 Hazardous air pollutants Diesel particulate matter Cancer and non-cancer health effects
  4. 4. NATA 2005 Process Ambient Monitoring National Emissions Inventory 2005 Point Mobile Sources HEM3/AERMOD Exposure Concentrations HAPEM Risk Assessment Cancer Non-Cancer Nonpoint Sources ASPEN Photochemical Pollutants CMAQ Ambient Concentrations
  5. 5. Now that we have exposure estimates, what if we could associate them with where people live?
  6. 6. National Population Sample National Health and Nutrition Examination Survey 1999 — 2010 Health conditions and behaviors Biomonitoring Tobacco use Diet Representative sample of United States, nationwide Non-institutionalized Civilian Cross-sectional
  7. 7. National Population Sample
  8. 8. National Exposure Estimates
  9. 9. NATA-NHANES Data Merge Merge by Census Tract NATA Air Toxics Exposure NHANES Residence Merged NATA-NHANES Data
  10. 10. NATA 2005 NHANES 1999-2010 NATA outdoor exposure concentration for residence census tract NHANES subjects 6 years-old and over ~62,000 subjects Urban/rural stratification Urban: ~53,000 subjects = 237 million USA Rural: ~9,000 subjects = 51 million USA
  11. 11. Loge Boxplots 133 Air Toxics, Ranked by Median Ln Exposure [nmol/m3]
  12. 12. Medians
  13. 13. Exposure 6Nanomolar: Urban Urban Rural nmol/m3 μg/m3 μg/m3 FORMALDEHYDE 54.20 1.63 1.02 ACETALDEHYDE 32.90 1.45 1.10 TOLUENE 23.60 2.17 0.66 METHYL CHLORIDE (CHLOROMETHANE) 18.60 0.94 0.93 METHANOL 12.70 0.41 0.08 BENZENE (INCLUDING FROM GAS) 11.00 0.86 0.40 XYLENES (MIXED ISOMERS) 7.91 0.84 0.14 CARBON TETRACHLORIDE 3.09 0.48 0.48 HEXANE 3.09 0.27 0.04 2,2,4-TRIMETHYLPENTANE 3.07 0.35 0.06 METHYLENE CHLORIDE 2.92 0.25 0.10 HYDROCHLORIC ACID (GAS) 1.99 0.07 0.02 ETHYLENE GLYCOL 1.96 0.12 0.02 1,1,1-TRICHLOROETHANE 1.85 0.25 0.15 ETHYLBENZENE 1.67 0.19 0.03 METHYL ISOBUTYL KETONE (HEXONE) 1.59 0.16 0.03 1,3-BUTADIENE 1.10 0.06 0.02
  14. 14. Exposure 6Nanomolar: Rural Rural Urban nmol/m3 μg/m3 μg/m3 FORMALDEHYDE 34.00 1.02 1.63 ACETALDEHYDE 25.00 1.10 1.45 METHYL CHLORIDE (CHLOROMETHANE) 18.50 0.93 0.94 TOLUENE 7.21 0.66 2.17 BENZENE (INCLUDING FROM GAS) 5.06 0.40 0.86 CARBON TETRACHLORIDE 3.09 0.48 0.48 METHANOL 2.58 0.08 0.41 XYLENES (MIXED ISOMERS) 1.29 0.14 0.84 METHYLENE CHLORIDE 1.19 0.10 0.25 1,1,1-TRICHLOROETHANE 1.11 0.15 0.25
  15. 15. Median Nanomolar: Urban vs. Rural Air Toxic Urban [nmol/m3] Rural [nmol/m3] Urban [μg/m3] Rural [μg/m3] FORMALDEHYDE 54.20 [41.90, 68.20] 34.00 [27.20, 48.60] 1.63 [1.26, 2.05] 1.02 [0.82, 1.46] ACETALDEHYDE 32.90 [26.30, 40.10] 25.00 [19.70, 36.00] 1.45 [1.16, 1.77] 1.10 [0.87, 1.59] TOLUENE 23.60 [14.50, 35.30] 7.21 [5.91, 9.99] 2.17 [1.34, 3.25] 0.66 [0.54, 0.92] METHYL CHLORIDE (CHLOROMETHANE) 18.60 [18.50, 18.70] 18.50 [18.40, 18.60] 0.94 [0.93, 0.94] 0.93 [0.93, 0.94] METHANOL 12.70 [5.71, 24.20] 2.58 [0.78, 6.69] 0.41 [0.18, 0.78] 0.08 [0.03, 0.21] BENZENE (INCLUDING FROM GAS) 11.00 [7.87, 15.30] 5.06 [4.01, 6.71] 0.86 [0.61, 1.20] 0.40 [0.31, 0.52] XYLENES (MIXED ISOMERS) 7.91 [3.67, 13.8] 1.29 [0.70, 2.46] 0.84 [0.39, 1.47] 0.14 [0.07, 0.26] CARBON TETRACHLORIDE 3.09 [3.08, 3.11] 3.09 [3.07, 3.11] 0.48 [0.47, 0.48] 0.48 [0.47, 0.48] HEXANE 3.09 [1.57, 5.58] — 0.27 [0.14, 0.48] — 2,2,4-TRIMETHYLPENTANE 3.07 [1.34, 5.86] — 0.35 [0.15, 0.67] — METHYLENE CHLORIDE 2.92 [1.92, 4.48] 1.19 [1.08, 1.49] 0.25 [0.16, 0.38] 0.10 [0.09, 0.13] HYDROCHLORIC ACID (GAS) 1.99 [0.90, 4.89] — 0.07 [0.03, 0.18] — ETHYLENE GLYCOL 1.96 [0.89, 4.13] — 0.12 [0.06, 0.26] — 1,1,1-TRICHLOROETHANE 1.85 [1.34, 3.12] 1.11 [1.03, 1.29] 0.25 [0.18, 0.42] 0.15 [0.14, 0.17] ETHYLBENZENE 1.67 [0.77, 2.97] — 0.19 [0.09, 0.35] — METHYL ISOBUTYL KETONE (HEXONE) 1.59 [0.62, 3.15] — 0.16 [0.06, 0.32] — 1,3-BUTADIENE 1.10 [0.69, 1.69] — 0.06 [0.04, 0.09] —
  16. 16. Compare regions?
  17. 17. Which regional scheme?
  18. 18. Correlated Groupings Method Principle components analysis Factor analysis Levy I, Mihele C, Lu G, Narayan J, Brook JR. 2014. Evaluating multipollutant exposure and urban air quality: pollutant interrelationships, neighborhood variability, and nitrogen dioxide as a proxy pollutant. Environ Health Perspect 122:65–72.
  19. 19. Strengths Comprehensive assessment of 174 air toxics Population-weighted Large sample National geographic coverage Census tract resolution Generalizable to US population
  20. 20. Limitations Uncertainty of NATA exposure estimates NATA appropriate for determining: Which pollutants or sources might be associated with higher relative risks than others But not for determining: How many people are exposed to levels of absolute risk Which air toxic is safe or not NATA hazard estimates available
  21. 21. NATA 2005 Process Ambient Monitoring National Emissions Inventory 2005 Point Mobile Sources HEM3/AERMOD Exposure Concentrations HAPEM Risk Assessment Cancer Non-Cancer Nonpoint Sources ASPEN Photochemical Pollutants CMAQ Ambient Concentrations
  22. 22. Approaches to Exposure Assessment Modeling Exposure Assessment Measurement Biomarker
  23. 23. URL to Presentation LinkedIn Contact B. Rey de Castro, Sc.D. +1 770 488 0162 rdecastro@cdc.gov For more information please contact Centers for Disease Control and Prevention 1600 Clifton Road NE, Atlanta, GA 30333 Telephone: 1-800-CDC-INFO (232-4636)/TTY: 1-888-232-6348 E-mail: cdcinfo@cdc.gov Web: http://www.cdc.gov The findings and conclusions in this presentation are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. National Center for Environmental Health Division of Laboratory Sciences

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