Assessing Exposure Factors of Asthmatic Children

Carvin D. Stevens, Ronald Williams and Thomas McCurdy
U. S. Environmental Protection Agency, National Exposure Research Laboratory

Research Triangle Park, NC 27711

Disclaimer: "Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy."

BACKGROUND

RESULTS

Introduction

Since 1980, there has been a 75% increase in the prevalence of asthma in
children in the U.S. The Tampa Asthmatic Children's Study (TACS) was
one of a number of pilot studies conducted to evaluate methods for
assessing asthmatic children's (< 6 yrs.) exposures to air pollutants.

PURPOSE

To develop and evaluate the accuracy of survey and direct measure
instruments to be used for the estimate of exposure, dose, and risk. The
evaluations used known facts, data, assumptions, inferences, and
professional observations of exposure scenarios.

MATERIALS AND METHODS

Nine asthmatic children who did not attend preschool or daycare programs
were recruited for personal, residential indoor and outdoor, and central site
monitoring. The concentrations of combustion related products, PM and air
toxics were monitored over a 4 day period, including weekdays and
weekends. Residence, participant and follow-up survey information were
collected, and the children's daily activities (including their locations) were
recorded every 15 minutes by the parents in a time activity diary (TAD).
The children wore an accelerometer on one ankle to obtain an objective and
direct measure of exertion (e.g. sedentary, light, moderate, and vigorous).
Data from the diaries were also used to estimate the activity exertion levels
and energy expenditures of the child. The ventilation rates and potential
dose were calculated using the following equations:

Eq. 1. Ventilation Rate (VE ) = EE x H x VQ

EE=energy expenditure,

H= average 02 uptake,

VQ= ventilation equivalent for 02

Eq. 2. Potential Dose (PD) =VE (m3/day) x PE (ug/m3)

VE = Ventilation Rate
PE = potential exposure

The concentrations of the monitored pollutants were within the
acceptable limits for the National Ambient Air Quality Standards
(Table.2). Variations in PM and peak concentrations measured with
continuous nephelometers were consistent with activity and exertion
information collected from the TADs. residence surveys, participant
surveys and follow-up questionnaires. Digital accelerometer exertion
data and time activity diary information were highly correlated (r 0.9).
On average, the children participated in sedentary activities 45% of the
time and spent 81% of their time indoors at home. Their estimated
ventilation rates averaged 39% less than the predicted rates for children
without asthma for the same age, gender and body mass class, as
determined using the Child Specific Exposure Factors Handbook
(Table. 1, figs.l & 2).

Table 2. Pollutant

Concentrj

ttions

Pollutants

Mean

Min

Max

(ppb)

Personal Ozone

9.6

3.1

28.2

Indoor Ozone

7.4

2.7

28.2

Outdoor Ozone

22.4

8.5

35.8

Ambient Ozone

32.5

11.5

70.5

Personal NOz

30.0

9.7

174.6

Indoor NOz

24.1

9.9

134.1

Outdoor NOz

38.3

8.0

163.9

Ambient NOz

38.3

18.3

170.7

Personal S02

2.5

0.5

14.5

Indoor S02

3.5

0.5

16.8

Outdoor S02

2.2

0.9

5.8

Ambient S02

2.6

1.4

7.2

Table 3. Exposure Factors

Exposure factors

Results

Age of Dwelling

Avg = 27 yrs

Air Conditioning

100%(Central
78To)

Heat source Electric

100%

Cooking fuel Electric

100%

Smokers in home

Mildew

Dust

56% med to
heavy

Carpet in child's room

55%

Pets

33%

Air exchange

Avg = 0.3/hr

CONCLUSIONS

The information collected from the surveys and questionnaires were
useful for identifying sources and activities that may impact asthmatic
children's exposures to air pollutants. The lower estimated ventilation
rates likely resulted in lower potential intake doses for the asthmatic
children, as compared with non-asthmatic children (fig.2). However,
lifestyle factors such as sedentary activities, housing factors, and the
amount of time spent indoors may have a greater influence on the
disease state. The observations support the need to collect data on
activities and lifestyle factors in large-scale asthma studies to model
asthmatic children's exposures and intake dose rates.

Table. 1. Potential Dose

Participant

Ventilation Rate
(\[:=n,7day)

Potential Exopsure
(ug/m3)

Potential Dose
(ug/day)

8.2

11.4

93.5

3.6

10.5

37.8

3.2

16.5

52.8

4.4

10.3

45.3

6.7

18.4

123.3

3.7

16.3

60.3

1.9

9.3

17.7

4.8

7.6

36.5

1. Ventilation Rates (participant's vs non-asthmatics)

12
10
8

VE 6-
4-
2
0

~ Study
¦ Predicted

1 3 4 5 6 7

Participant

fig.2. Potential Dose vs. Predicted Dose

200
150
ug/day 100
50

~ Dose

~ Predicted Dose

1 3 4 5 6 7!

Participant

BIBLIOGRAPHY

Lang, D.M. A. M. Butz, A.K. Duggan, and J.R. Serwint

Physical activity in urban school-aged children with asthma.

Pediatrics 2004; 113: e341-e346.

U.S. Environmental Protection Agency (EPA). (2002) Child-specific exposure factors handbook.
National Center for Environmental Assessment, Washington, DC; EPA/600/P-00/002B.

National Asthma Education and Prevention Program (National Heart, Lung, and Blood Institute)
Second Expert Panel on the Management of Asthma. Expert panel reports 2: guidelines for the
diagnosis and management of asthma. Bethesda, Md.: National Institutes of Health, 1997;
publication no. 97-4051.

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