This document summarizes a study that estimated population-weighted exposure to 174 air toxics for a representative sample of the United States population from 1999-2010. The study merged air toxics exposure estimates from the 2005 National-Scale Air Toxics Assessment with residence data from the National Health and Nutrition Examination Survey. The analysis found higher median exposure levels for several pollutants, such as formaldehyde and acetaldehyde, in urban areas compared to rural areas. While the study comprehensively assessed exposure to many air toxics, the exposure estimates have some uncertainty. The results are most useful for determining which pollutants or sources may pose relatively higher risks rather than absolute risk levels.

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. What is the nationwide
outdoor exposure
to air toxics?

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. 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. Now that we have
exposure estimates,
what if we could
associate them with
where people live?

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. National Population Sample

8. National Exposure Estimates

9. NATA-NHANES Data Merge
Merge by
Census
Tract
NATA
Air Toxics
Exposure
NHANES
Residence
Merged
NATA-NHANES
Data

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. Loge Boxplots
133 Air Toxics, Ranked by Median
Ln Exposure [nmol/m3]

12. Medians

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. 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. 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. Compare regions?

17. Which regional scheme?

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. Strengths
Comprehensive assessment of 174 air toxics
Population-weighted
Large sample
National geographic coverage
Census tract resolution
Generalizable to US population

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. 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. Approaches to
Exposure Assessment
Modeling
Exposure
Assessment
Measurement Biomarker

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