Young children's hand contact activities: An observational study via videotaping in primarily outdoor residential settings

Young children’s hand contact activities: An observational study via

videotaping in primarily outdoor residential settings

WILLA AUYEUNGa, ROBERT A. CANALESb, PALOMA BEAMERa, ALESIA C. FERGUSONc AND

JAMES O. LECKIEa

aDepartment of Civil and Environmental Engineering, Stanford University, Stanford, CA, USAbHarvard School of Public Health, Landmark Center, Boston, MA, USAcDepartment of Environmental and Occupational Health, College of Public Health, University of Arkansas for Medical Sciences, Little Rock,

Arkansas, USA

Microlevel activity time series (MLATS) data were gathered on hand contact activities of 38 children (1–6 years old) by videotaping in primarily outdoor

residential environments. The videotape recordings were then translated into text files using a specialized software called VirtualTimingDevicet. Contact

frequency (contacts/h), duration per contact (s/contact), and hourly contact duration (min/h) were summarized for outdoor hand contacts with 15

distinct object/surface categories (‘‘Animal’’, ‘‘Body’’, ‘‘Clothes/Towels’’, ‘‘Fabric’’, ‘‘Floor’’, ‘‘Food’’, ‘‘Footwear’’, ‘‘Metal’’, ‘‘Non-dietary Water’’,

‘‘Paper/Wrapper’’, ‘‘Plastic’’, ‘‘Rock/Brick’’, ‘‘Toys’’, ‘‘Vegetation/Grass’’, and ‘‘Wood’’) and two aggregate object/surface categories (‘‘Non-dietary

objects/surfaces’’ and ‘‘Total objects/surfaces’’). For outdoor both hand contacts with ‘‘Total objects/surfaces’’, contact frequencies ranged from 229.9 to

1517.7 contacts/h, median durations/contact ranged from o1 to 5 s, and hourly contact durations ranged from 42.6 to 102.2m/h.

The data were analyzed for significant differences in hand contact activities as a function of (1) age, (2) location, (3) gender, and (4) hand. Significant

differences (Pp0.05) were found for all four factors analyzed. Hourly contact durations with ‘‘Non-dietary objects/surfaces’’ and ‘‘Total objects/

surfaces’’ increased with age (P¼ 0.01, rs¼ 0.42 and P¼ 0.005, rs¼ 0.46, respectively), while contact frequencies and hourly contact durations with

‘‘Wood’’ decreased with age (P¼ 0.02, rs¼�0.38 and P¼ 0.05, rs¼�0.32, respectively). Location was found to affect contact frequencies and hourly

contact durations with certain objects/surfaces. For example, contact frequencies and hourly contact durations with ‘‘Fabric’’ were higher indoors

(P¼ 0.02 for both), while contact frequencies and hourly contact durations with ‘‘Vegetation/Grass’’ were higher outdoors (P¼ 0.02 and P¼ 0.04,

respectively). Girls had longer hourly contact durations with ‘‘Footwear’’ (P¼ 0.02), ‘‘Non-dietary objects/surfaces’’ (P¼ 0.03), and ‘‘Total objects/

surfaces’’ (P¼ 0.01) than boys. The right hand had longer hourly contact durations with objects that are often manipulated with the hand (e.g., ‘‘Toys’’

(P¼ 0.0002)), while the left hand had longer hourly contact durations with passively touched objects/surfaces (e.g., ‘‘Clothes/Towels’’ (P¼ 0.003) and

‘‘Floor’’ (P¼ 0.04)).

Journal of Exposure Science and Environmental Epidemiology (2006) 16, 434–446. doi:10.1038/sj.jes.7500480; published online 22 March 2006

Keywords: dermal exposure, non-dietary exposure, activity pattern, hand contact behavior, microlevel activity.

Introduction

Information about hand contact activities can help research-

ers understand how contaminants load onto the surface of

the hands. These chemicals may then enter the body via

dermal absorption or non-dietary ingestion. Microlevel

activity time series (MLATS) data capture the sequence

and duration of contact events and allow contact frequency

to be calculated (Ferguson et al., 2005). MLATS data can be

combined with environmental concentrations to create

sequential time exposure profiles that help researchers

determine contact activities that lead to peak exposure

(Ferguson, 2003; Riley et al., 2004).

Microlevel activity data are currently used in physical–

stochastic models which can account for temporal variability

in human exposure (Zartarian and Leckie, 1998). Models

include the Stochastic Human Exposure and Dose Simula-

tion (SHEDS) model developed at the United States

Environmental Protection Agency (USEPA) (Zartarian

et al., 2000), as well as the Dermal Exposure Reduction

Model (DERM) (Zartarian, 1996) and the Cumulative and

Aggregate Simulation of Exposure (CASE) model developed

at Stanford University (Canales, 2004).

Despite their usefulness, microlevel activity data are time-

and labor-intensive to collect. Thus, only a small number of

published studies on the collection and analysis of hand

microlevel activity data are available (Zartarian et al., 1997a;

Reed et al., 1999; Freeman et al., 2001, 2005). Furthermore,

previous studies collected data in primarily indoor environ-Received 19 August 2005; accepted 21 February 2006; published online 22

March 2006

1. Address all correspondence to: W AuYeung, Department of Civil and

Environmental Engineering, Stanford University, Stanford, P.O.Box

11226, Stanford, California 94309, USA. Tel.: þ 1 415 205 3337.

Fax: þ 1 650 725 3164. E-mail: [email protected]

Journal of Exposure Science and Environmental Epidemiology (2006) 16, 434–446

r 2006 Nature Publishing Group All rights reserved 1559-0631/06/$30.00

www.nature.com/jes

ments. This study aims to contribute to the field of exposure

assessment by providing an analysis of hand MLATS data

collected in primarily outdoor environments. This informa-

tion may be useful in assessing children’s exposure to

contaminants in outdoor environments. Statistical tests

were applied to analyze whether hand contact activities

differed by age, gender, indoor/outdoor environments, and

left/right hands. Similar analyses of hand-to-mouth and

other mouthing contacts can be found in AuYeung et al.

(2004).

Methods

Recruitment of SubjectsSubjects were recruited from the southern region of the San

Francisco Bay peninsula by calling telephone numbers

randomly extracted from the Pacific Bell residential telephone

directory for a 300–400 square mile region associated with

Redwood City, Menlo Park, and Palo Alto. To screen for

middle-class children, a phone survey was administered, and

families with children between 1 and 6 years of age who lived

in a residence with a lawn and whose annual household

income was greater than $35,000 were invited to participate

in the studies.

VideotapingStanford University’s Exposure Research Group videotaped

the 38 children between August 1998 and May 1999. The

subjects were videotaped only on days with fair weather (i.e.,

no rain). Parents were asked to keep their child outdoors for

the duration of the videotaping session (2 h) and videotape

data were collected for each child during ‘‘natural play’’ (i.e.,

unstructured play). In most cases, only one child was

videotaped during each session. In rare cases where two

children from the same household participated in the study,

two teams of researchers collected videotaping data in the

same session. Outdoor locations where videotaping occurred

include parks, playgrounds, and outdoor areas of the

children’s homes (e.g., back yard, front yard, patio).

Video-Translation Using VirtualTimingDevicetA hand contact was defined as any contact with the fingers,

palm, and/or back of the hands. Using a specialized software

package developed at Stanford University (VirtualTiming-

Devicet), the videotapes were ‘‘translated’’ or converted into

plain text files with sequential, second-by-second information

on microenvironments visited and objects/surfaces contacted

(Zartarian et al., 1997b; Ferguson et al., 2005). The

videotapes were translated separately for the left and right

hands. Contacts lasting less than 1 s were recorded as zeros.

Since contacts of zero duration represent short but real

contacts, they were included in the data analysis. The

location grid in the VirtualTimingDevicet palette (Figure 1)

used in this study was designed to capture the different

outdoor locations where children were likely to visit.

The 36 object categories in the objects/surfaces grid were

developed based on assumptions of objects/surfaces that

Location

Contact Type

Object/surfacecategories

RepetitiveConstant

Garage Other

ParkGarden

Patio Street/ Sidewalk

Yard Indoor

Head

Other

Grass Carpet/ Mat

Vegetation Food_ Cont

Wood_ Tool/Appl

Paper/ Wrapper

DirtWood_

Wall/FurnAnimal Sticky_

Food Plast_

Tool/Appl

Rck/Brk_ Wall/Furn

Porous_ Plast_Toy

Other_ Food

Metal_ Tool/Appl

Skin

Rck/Brk_ Floor

Fabric_ Wall/Furn

Fabric_ Toy

Water/ Beverage

Towel/ Washcloth

Wood_Floor Plastic_ Wall/Furn

Wood_Toy Pool_Water Clothes Not_

In_View

Tile/Linol_ Floor

Metal_ Wall/Furn

Hard_Toy Puddle_ Water

Footwear Nothing

Asphalt/ Sidewalk

Time: 10:00:00 AM Video ID: New Video Counter: Subject ID: New Subject

Index: 0 Coder ID: New CoderBoundary: Right_Hand

PAUSE OFF ON

Figure 1. VirtualTimingDevicet palette for the hands.

Children’s hand contact activities Auyeung et al.

Journal of Exposure Science and Environmental Epidemiology (2006) 16(5) 435

children most commonly come into contact with in outdoor

environments. The contact type grid allowed researchers to

designate contacts as either constant (e.g., holding a ball) or

repetitive (e.g., bouncing a ball). The ‘‘Repetitive’’ cell was

selected when contacts with an object/surface occurred at a

high rate.

Quality Control of Video-TranslationRigorous training and quality control protocols were applied

to ensure high quality data (Ferguson et al., 2005). Between

5 and 10% of the total number of translated files were

randomly selected to be checked by an experienced researcher

for agreement in object and location designations. In general,

if the two files had greater than 10% difference in total

duration with different object/location combinations, then

the translator had to retranslate the videotape segment. If

systemic errors were made (e.g., errors in the categorizations

of locations and objects/surfaces), then all segments where

the errors occurred were retranslated. The quality control

process reiterated until the retranslated segments met the

quality control standard.

In addition, as part of a separate study, researchers

rewatched the videotapes to assign contact configurations for

all hand contacts. Each recorded hand contact was examined

and a contact configuration (e.g., open hand grip, palm only

contact, etc.) was assigned to the contact. During this

process, any additional errors in location and object/surface

designations found in the activity files were corrected.

Data ProcessingThe translated plain text files were processed before the data

were analyzed. First, repetitive contacts were assumed to

alternate between contacts with the object/surface and air

(i.e., ‘‘Nothing’’). The contacts were assumed to alternate at

a rate of 0.5 s with ‘‘Nothing’’ and 0.5 s with the object/

surface. Secondly, the durations of continuous contacts in

different locations were joined to avoid overcounting the

number of contacts (Figure 2).

Object and location designations from the VirtualTiming-

Devicet palette (Figure 1) were grouped to form two

location and 15 object/surface super-categories (Table 1).

The ‘‘Other’’ location and ‘‘Other’’ object/surface categories

were not analyzed since they comprised less than 0.03%

and 0.2%, respectively, of the data set’s total duration.

In grouping the object/surface categories into super-cate-

gories, the surface type (e.g., ‘‘Metal’’, ‘‘Plastic’’, and

‘‘Wood’’) was assumed to be a more important factor in

differentiating the concentrations of contaminants on an

object/surface than the object type (i.e., ‘‘Tool/Appliance’’

vs. ‘‘Wall/Furniture’’). Therefore, the objects were grouped

by surface type. The only exception to this rule was objects in

the ‘‘Toys’’ super-category. All toys regardless of their

surface types were grouped into one super-category (i.e.,

‘‘Toys’’) because they are objects of contact unique to

children and chemical residue data are typically available for

this category of objects.

Data AnalysisContact frequencies, median duration per contact, and

hourly contact durations were calculated for each child,

hand (i.e., left and right hands), object/surface

super-category, and location super-category (i.e., ‘‘Indoor’’

and ‘‘Outdoor’’) combination. Time in view was calculated

as the duration of a videotape translation subtracted by

the total duration designated as ‘‘Not In View’’. Contact

frequencies and hourly contact durations for the left and

right hands were calculated separately following Equations 1

and 2, respectively. Contact frequencies and hourly

contact durations for combined left and right hands (i.e.,

both hands) were calculated by adding together the contact

frequencies or hourly contact durations for the left and

right hands.

Bodypart Activity Object Duration

Right_Hand Yard

Right_Hand Yard

Repetitive Hard_Toy 2

Constant Hard_Toy 3

Right_Hand Yard Constant Head 5

Right_Hand Patio Constant Head 5

Right_Hand Yard Constant Head 2

Bodypart Activity Object Duration

Right_Hand Yard Constant Hard_Toy 0.5

Right_Hand Yard Constant Nothing 0.5

Right_Hand Yard Constant Hard_Toy 0.5

Right_Hand Yard Constant Nothing 0.5

Right_Hand Constant Hard_Toy 3

Right_Hand Yard Constant Head 12

1

1

2

2

Repetitive contact

Continuouscontacts between locations

Repetitive contacts are expanded

Continuouscontacts are aggregated

Patio

Lacation

Lacation

Figure 2. Processing of repetitive and continuous contacts.

Children’s hand contact activitiesAuyeung et al.

436 Journal of Exposure Science and Environmental Epidemiology (2006) 16(5)

Equation 1. Contact frequency for left and right hands

Contact frequency ðchild; hand; objectÞcontacts

hour

� �

¼Number of contactsðchild; hand; objectÞ

Time in viewðchild;handÞ

Equation 2. Hourly contact duration for left and right

hands

Hourly contact duration ðchild; hand; objectÞminutes

hour

� �

¼P

Duration per contactðchild;hand;objectÞTime in viewðchild; handÞ

Contact frequency, median duration per contact, and

hourly contact duration were analyzed for significant

differences between age, gender, right/left hands, and

indoor/outdoor locations. Tree analysis was applied in S-

PLUS to test whether the data should be grouped by age and

non-parametric tests were used for all statistical analyses. The

two-tailed Wilcoxon rank sum test was applied to analyze

differences between male and female subjects, while the two-

tailed Wilcoxon signed rank test for matched pairs was

applied to test for differences between the right/left hands and

between indoor/outdoor environments (Rice, 1995). Spear-

man’s rank correlation coefficient was calculated to test for

correlations between hand contact activities and age (in

months). Only outdoor data were included in the statistical

analysis of differences in hand contact activities as a function

of age, gender, and left/right hands on hand contact

activities. Except when the data were analyzed for differences

between the left and right hands, all statistical tests were

applied only on data for both hands combined.

Results

SubjectsIn all, 38 children (1–6 years old) were recruited (Table 2). A

total of 30 children were recruited based on satisfaction of all

selection criteria and due to time constraints, an additional

eight children were recruited through acquaintances. The

only selection criteria for these eight children were that the

children were between 1 and 6 years of age, lived in Redwood

City, Menlo Park, or Palo Alto, and the families were willing

to participate in the studies.

All of the subjects lived in a suburban setting. The median

annual household income was greater than $100,000. Of the

31 households that provided ethnicity data, 55% were

Caucasian, 16% were Mexican American/Latino, 6% were

African American, and 23% belonged to other ethnicities.

Summary StatisticsUnlike hand-to-mouth contact behavior which have been

found to ‘‘naturally’’ separate into p24 and 424 months

old age bins (Tulve et al., 2002; AuYeung et al., 2004), no age

groupings were observed for hand contact activities. Instead,

the data were grouped by ‘‘Indoor’’ and ‘‘Outdoor’’

locations because recent studies (Freeman et al., 2001;

AuYeung et al., 2004; Black et al., 2005) found differences

in hand-to-mouth contact frequencies between indoor and

outdoor environments.

Summary statistics of hand-to-object/surface contact

frequency, median duration per contact, and hourly contact

duration for outdoor environments are provided in Tables 3–5.

For each object/surface super-category, contact frequency

Table 1. Super-category assignments of locations and objects/surfaces

VirtualTimingDevicet palette categories

Location super-

categories

Indoor Indoor

Outdoor Yard, Patio, Garden, Park, Garage, Street/

Sidewalk

Object super-categories

Animal Animal

Rock/brick Rock/Brick Wall/Furniture

Clothes/towels Clothes, Towel/Washcloth

Body Head, Skin

Fabric Fabric Wall/Furniture

Floor Dirt, Asphalt/Sidewalk, Rock/Brick Floor,

Wood Floor, Tile/Linoleum Floor,

Carpet/Mat

Food Sticky Food, Other Food, Food Container,

Water/Beverage

Footwear Footwear

Metal Metal Wall/Furniture, Metal Tool/Appliance

Non-dietary water Pool Water, Puddle Water

Paper/Wrapper Paper/Wrapper

Plastic Plastic Wall/Furniture,

Plastic Tool/Appliance

Toys Hard Toy, Porous Plastic Toy, Fabric Toy,

Wood Toy

Vegetation/Grass Vegetation, Grass

Wood Wood Wall/Furniture, Wood Tool/Appliance

Non-dietary objects/

surfaces

Everything listed above except objects/

surfaces in the Food super-category

Total objects/surfaces Everything listed above

Table 2. Age and gender of subjects (number of children)

Gender Age (years)

1 2 3 4 5 6 Total

Male 5 5 1 3 2 2 18

Female 3 3 3 4 3 4 20

Total 8 8 4 7 5 6 38

Children’s hand contact activities Auyeung et al.

Journal of Exposure Science and Environmental Epidemiology (2006) 16(5) 437

Table 3. Outdoor hand-to-object/surface contact frequency (contacts per hour)

Statistic Object/surface super-categories

n¼ 38 Animal Body Clothes/Towel Fabric Floor Food Foot-wear Metal Non-dietary

water

Paper/

Wrapper

Plastic Rock/Brick Toys Vegetation/

Grass

Wood Non-dietary

objects/surfaces

Total objects/

surfaces

Left hand

Range 0–11.8 5.4–93.8 4–100.3 0–14.4 0–448.4 0–47.1 0–12.1 0–268.1 0–4.2 0–54.7 0–152 0–14.7 0–270.6 0–75.5 0–49.4 20.2–767.2 20.2–769.4

Mean 1.4 38.5 39.2 1.7 34.2 7.2 1.7 29.1 0.3 3.6 28.5 1.3 79.1 18.6 11 288.9 296.1

5th percentile 0 13.5 14.2 0 1.1 0 0 0.5 0 0 0 0 7.5 0.7 0.7 186.6 199.3

25th percentile 0 26.8 25.7 0 3.4 0 0 3.2 0 0 9.1 0 38.5 6.3 2.4 238.3 244.7

50th percentile 0 35.6 33.9 0 16.8 1.5 0.8 7.4 0 0.6 22.4 0 68.7 10.8 6.4 269.1 271.9

75th percentile 0 46.4 55.1 1.6 33.8 9.8 1.7 36 0 3 39.9 1 104.3 25.1 14.5 329.4 333.2

95th percentile 9.6 73.6 80.8 7 113.6 26.6 6.2 100.7 1.4 12.2 58.7 5.9 167.3 61.3 41.1 424.2 424.3

99th percentile 11.4 90 95.5 12.4 334.5 45.7 11.4 217.2 3.7 40.1 129.9 13 262.9 72 47.4 645.5 647.2

Right hand

Range 0–11.5 6.3–97.9 5.8–98.8 0–17.1 0–492 0–45.3 0–12.9 0–198.1 0–3.2 0–49.1 0–172.6 0–13.3 0–387.2 0–95.8 0–60.3 160–745.5 160–748.3

Mean 1.2 36.3 34.5 2 31.6 7.4 1.9 29.2 0.2 3.7 28.2 1.1 82.2 22.1 11.4 286.4 293.7

5th percentile 0 13.9 10.1 0 0.7 0 0 0.7 0 0 0.5 0 13.1 0.5 0 179.5 181.9

25th percentile 0 22.2 21.8 0 3.2 0 0 3.9 0 0 8.5 0 37.8 5.7 2.8 205.6 214.3

50th percentile 0 30.6 30.7 0 14.7 3 0.7 8.5 0 0.9 21.6 0 63.7 14 5.3 250.4 268.5

75th percentile 0.7 44.9 43.6 2.7 27.2 8.8 3.1 37.2 0 3.3 39 1.5 96.8 28.1 14.4 347.9 349.5

95th percentile 7.7 76.9 63.3 8.4 83.1 26.9 5.5 113.7 1.5 13.7 64.5 5.1 205.5 66.9 34.9 482.9 482.9

99th percentile 10.2 95.5 91 14.1 360.9 39.8 11.9 180.7 3.2 38.7 144.4 10.4 348.8 88.5 55.7 650.9 652.7

Both hands

Range 0–23.3 17–191.7 17–199.1 0–31.5 0–940.4 0–88.7 0–23.1 0.6–466.2 0–7.4 0–103.8 0–324.6 0–28 0–657.8 0–138.7 0.6–100.9 225.1–1512.6 229.9–1517.7

Mean 2.6 74.8 73.7 3.7 65.8 14.5 3.6 58.3 0.5 7.3 56.7 2.4 161.3 40.6 22.4 575.3 589.8

5th percentile 0 27.1 27.4 0 1.9 0 0 1.1 0 0 0.6 0 26.7 1.1 1.3 368.8 387.6

25th percentile 0 48.8 46.9 0 8.1 0 0.6 8.2 0 0 18 0 72.7 13.2 5 443.9 449

50th percentile 0 65.1 65.7 0.4 27.9 4.9 1.5 16 0 1.5 47 0 129.4 27.8 12.7 526.3 540.8

75th percentile 0.7 94.3 97.4 3.9 60.1 18.3 4.7 72.3 0 7 74.1 2.1 201.3 56.2 32.6 644.1 644.1

95th percentile 13.8 150.4 132 14.7 182.7 56.2 11.4 206.4 2.9 21.4 121.1 10.3 372.8 128.1 79.8 889.2 889.2

99th percentile 21 185.5 186.5 26.2 683.7 81.2 22.8 384.9 6 73.6 274.4 22 611.7 135.8 93.1 1290.2 1293.4

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Table 4. Outdoor hand-to-object/surface median duration per contact (seconds per contact)

Statistic Object/surface super-categories

Animal Body Clothes/Towel

Fabric Floor Food Foot-wear

Metal Non-dietarywater

Paper/Wrapper

Plastic Rock/Brick Toys Vegetation/Grass

Wood Non-dietaryobjects/surfaces

Total objects/surfaces

Left hand n¼ 9 n¼ 37 n¼ 38 n¼ 19 n¼ 35 n¼ 25 n¼ 24 n¼ 35 n¼ 7 n¼ 23 n¼ 35 n¼ 14 n¼ 37 n¼ 37 n¼ 37 n¼ 38 n¼ 38Range 1–6 1–6.5 1–9 0.5–35 0–13.5 0–341 0–15 0–109.5 1–9 1–75 1–21 1–9 0–27 0–10.5 0–8.5 0–4 0–5Mean 3.2 2.1 2.8 7.7 3.3 22 3.4 8 3.5 15 5.3 3.4 6.4 4 3.6 3 3.1

5th percentile 1.4 1 1 1 0.7 1.6 0.1 0 1 2 1 1 2 1 0.9 1 125th percentile 2 1 2 1.8 1.8 4 1.9 2 1.3 4 2.5 1.6 4 2 2 2.3 2.350th percentile 3 2 2 4 3 7 2 4 2 9 4.5 2.8 5 3 3 3 375th percentile 3.5 2.5 3 11 4 11 4.3 6 5 19.3 6.3 3.8 6.5 4.5 5 4 495th percentile 5.6 3.2 5.5 21.5 7 33.8 8.8 18.1 8.4 52.3 11.9 9 18.6 10.1 7 4 499th percentile 5.9 5.6 8.8 32.3 11.3 268.2 13.6 80.4 8.9 70.6 18.6 9 24.1 10.5 8 4 4.6

Right hand n¼ 12 n¼ 38 n¼ 38 n¼ 17 n¼ 37 n¼ 25 n¼ 26 n¼ 37 n¼ 6 n¼ 23 n¼ 36 n¼ 13 n¼ 37 n¼ 36 n¼ 35 n¼ 38 n¼ 38Range 1–7 1–5 1–6 1.5–22 0–10 0–27 0–13 0–109.5 0.5–8.5 0–53.5 0–26 0.5–10 0–29.5 0–25 0–18 0–5 0–5Mean 3.3 1.9 2.4 6.5 3.1 8.7 3.8 7.7 4.1 9.6 5.7 3.1 7.1 4.5 4.1 2.9 3.1

5th percentile 1.3 1 1 1.5 0 1 0.3 0.8 0.6 1 0.9 0.8 1.8 0.8 0.7 0.9 0.925th percentile 2 1 2 2 2 4 1 2 1.3 1.8 3 1 4 2 2 2 2.350th percentile 3 2 2 5 2 6 2.8 3 3.8 5 4 1.5 6 3 3 3 375th percentile 4.6 2 3 7 4 11.5 5.8 6 6.6 9.5 5.5 4 9 6 5.5 4 495th percentile 5.9 4 4.2 15.6 9 23.5 9.4 16.8 8.1 38.2 15.5 10 15.2 9.4 8.6 5 599th percentile 6.8 4.6 5.6 20.7 9.6 26.6 12.1 83.8 8.4 50.3 22.9 10 26.8 20.5 15.3 5 5

Both hands n¼ 12 n¼ 38 n¼ 38 n¼ 20 n¼ 37 n¼ 26 n¼ 30 n¼ 37 n¼ 9 n¼ 26 n¼ 36 n¼ 16 n¼ 37 n¼ 37 n¼ 38 n¼ 38 n¼ 38Range 1.5–7 1–4 1–5 0.5–23.5 0–13 0–28 0–12 0–109.5 0.5–9 0–53.5 1–21.5 1–9 0–25.5 0–11 0–9 0–5 0–5Mean 3.2 2 2.5 5.9 3 7.6 3.3 7.3 3.3 9.4 5.1 2.8 6.5 3.7 3.7 3 3

5th percentile 1.8 1 1 1 0 0.3 0.5 0.8 0.7 1 1 1 2 1 0.9 1 125th percentile 2 1 2 1.9 2 4 1 2 1 2.1 2.9 1 4 2 2 2 2.350th percentile 2.5 2 2 3 2 6 2.5 3 2 4.3 4 2 6 3 3 3 375th percentile 4 2.4 3 8.8 4 9 4.9 6 5 13.3 6 3.3 7 5 5 4 495th percentile 6.5 3.2 4.6 15.4 6.5 20.8 8.1 15.8 8.2 28.1 12.8 7.5 13.5 9.1 8 4 4.299th percentile 6.9 4 5 21.9 10.7 26.8 11.1 79.8 8.8 47.5 19.2 8.7 24.8 10.5 8.6 4.6 5

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Table 5. Outdoor hand-to-object/surface hourly contact duration (minutes per hour)

Statistic Object/surface super-categories

n¼ 38 Animal Body Clothes/Towel

Fabric Floor Food Foot-wear

Metal Non-dietarywater

Paper/Wrapper

Plastic Rock/Brick Toys Vegetation/Grass

Wood Non-dietaryobjects/surfaces

Total objects/surfaces

Left handRange 0–1.4 0.4–6.7 0.6–14 0–3.3 0–12.9 0–10.7 0–2.8 0–17.4 0–1 0–11.8 0–12.9 0–1.4 0–28.6 0–9 0–13.6 5.8–49 5.8–49.7Mean 0.1 2.5 3.8 0.3 2.4 1.9 0.2 3.6 0.1 1 3.9 0.1 13 2.2 1.5 34.8 36.7

5th percentile 0 0.7 1 0 0.1 0 0 0 0 0 0 0 3.2 0 0 24.7 25.325th percentile 0 1.3 1.8 0 0.2 0 0 0.5 0 0 1.2 0 7.1 0.4 0.1 29.9 31.150th percentile 0 2 2.4 0 1.4 0.2 0 1.4 0 0.1 3.1 0 12.3 1 0.4 35 37.875th percentile 0 2.8 3.9 0.2 4 3.6 0.2 4.6 0 0.7 5.8 0 20.3 2.5 1.8 40.8 43.395th percentile 0.9 5.7 10.8 1.7 6.5 8.5 0.9 13.3 0.5 5.3 10.3 0.5 26.4 8.2 5.7 46.3 49.299th percentile 1.3 6.4 13.4 3 10.8 10.1 2.4 16.6 0.9 9.7 12.5 1.1 28.1 9 11 48.7 49.7

Right handRange 0–0.9 0.2–15 0.5–12.3 0–3.3 0–7.5 0–8.9 0–2.8 0–18.9 0–0.4 0–15.2 0–14.4 0–2.3 0–41 0–14.7 0–14.2 25.2–52.7 25.2–53.1Mean 0.1 2.5 3 0.4 1.6 2 0.3 3.8 0 0.9 4.1 0.1 16.8 2.9 1.6 38.1 40.1

5th percentile 0 0.7 0.5 0 0 0 0 0 0 0 0 0 4 0 0 27.9 28.925th percentile 0 1.3 1.4 0 0.2 0 0 0.7 0 0 1.1 0 9.5 0.8 0.1 31.8 35.350th percentile 0 2 2.1 0 1 0.3 0 1.7 0 0.1 3.1 0 16 1.5 0.7 38.3 40.875th percentile 0.1 2.9 3.5 0.3 2 3.8 0.3 6.3 0 0.6 6.5 0 23.6 4.2 1.9 42.9 4595th percentile 0.7 5.4 7.7 2.2 5 8.1 1.5 14.1 0.1 3 10.2 0.5 30.6 8.9 6.4 49.7 50.699th percentile 0.9 11.6 11.4 3 7.2 8.6 2.6 17.6 0.4 11.9 14 2 37.4 13.1 11.6 51.8 52.5

Both handsRange 0–2 0.6–17.8 1.4–26.3 0–6.6 0–16.4 0–17.3 0–5.6 0–36.3 0–1 0–27 0–26.3 0–3.7 0–63.1 0–21.5 0–27.8 42.6–101.7 42.6–102.2Mean 0.2 5 6.7 0.7 4 3.9 0.5 7.4 0.1 1.8 8 0.2 29.8 5.1 3.2 72.9 76.8

5th percentile 0 1.5 1.8 0 0.2 0 0 0 0 0 0.1 0 8.8 0 0.1 51 54.225th percentile 0 2.5 3.5 0 0.5 0 0 1.1 0 0 2.5 0 17.5 1.3 0.3 63.1 68.150th percentile 0 4.1 4.8 0 2.4 0.4 0 3.2 0 0.4 6 0 28.4 2.9 1.2 72.3 77.575th percentile 0.1 6.2 7.1 0.4 7.2 7 0.5 9.4 0 1.2 11.7 0 44.6 7.5 4 82.9 87.895th percentile 1.6 11.2 18.2 3.9 12.2 17 2 27.3 0.6 7.8 20.6 1 57 17.9 12.8 94.2 99.399th percentile 1.9 15.8 24.8 6 15.2 17.2 5 34.3 1 21.5 26.2 3 61.1 20.7 22.3 100.6 101.9

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(Table 3) and hourly contact duration (Table 5) were

calculated for all children (n¼ 38), while median duration

per contact (Table 4) could only be calculated for those

children who had contacts with that object/surface.

For the data analyses, the median time in view was 1 h and

40min for outdoor environments and 23min for indoor

environments. As this study focused on collecting outdoor

hand contact activities, only nine children in the data set

spent 15 or more minutes in view indoors. All indoor data

analysis were performed using only data from these nine

children, six of whom were between 4 and 6 years of age, and

three of whom were between 1 and 2 years of age.

Significant DifferencesContact frequencies, median contact durations, and hourly

contact durations were analyzed for significant differences as

a function of (1) age, (2) location, (3) gender, and (4) hand.

No significant differences or correlations (Pp0.05) in

median contact durations were found for any of the four

factors analyzed. However, significant findings were observed

for contact frequencies and hourly contact durations for all

four factors analyzed.

AgeAge (in months) was found to have significant correlations

with hand contact activity. Hourly contact duration increased

with age for contacts with ‘‘Non-dietary objects/surfaces’’

(P¼ 0.01, rs¼ 0.42) and ‘‘Total objects/surfaces’’ (P¼ 0.005,

rs¼ 0.46), but decreased with age for contacts with ‘‘Wood’’

(P¼ 0.05, rs¼�0.32). Contact frequency also decreased with

age for contacts with ‘‘Wood’’ (P¼ 0.02, rs¼�0.38).

LocationDifferences between indoor/outdoor environments were

examined using only data from the nine children who spent

more than 15min indoors. Differences between locations in

contact frequencies for both hands combined were found for

contacts with ‘‘Body’’, ‘‘Fabric’’, ‘‘Food’’, ‘‘Paper/Wrap-

per’’, ‘‘Vegetation/Grass’’, and ‘‘Wood’’. Differences be-

tween locations in hourly contact duration for both hands

combined were observed for contacts with ‘‘Body’’, ‘‘Fab-

ric’’, ‘‘Food’’, ‘‘Vegetation/Grass’’, and ‘‘Wood’’ (Table 6).

GenderDifferences between the genders were found for both hand

outdoor contact frequencies with ‘‘Body’’ and both

hand outdoor hourly contact durations with ‘‘Footwear’’,

‘‘Non-dietary objects/surfaces’’, and ‘‘Total objects/surfaces’’

(Table 7).

HandDifferences between the left and right hands were found for

outdoor contact frequencies with ‘‘Clothes/Towels’’ and

outdoor hourly contact durations with ‘‘Clothes/Towels’’,

‘‘Floor’’, ‘‘Toys’’, ‘‘Vegetation/Grass’’, ‘‘Non-dietary

objects/surfaces’’, and ‘‘Total objects/surfaces’’ (Table 8).

Discussion

MethodsThe videotaping and video-translation methods were used to

collect microlevel activity data because the duration of most

hand contacts is very short (on the order of a few seconds)

(Zartarian et al., 1997a; Freeman et al., 2005), and events of

such short duration may not be accurately captured via other

direct observational techniques like parental observation or

record-keeping (Timmer et al., 1985). Furthermore, the video-

taping and video-translation methods allow researchers to

retain a permanent record of the raw data, which can be used

for further analysis should future needs arise. It also allows

researchers to retranslate videotape segments and compare the

translated files in order to ensure high quality data.

Summary StatisticsFor both hand contacts with ‘‘Total objects/surfaces’’,

contact frequencies and hourly contact durations were very

high (229.9–1517.7 contacts per hour and 42.6–102.2min/h,

respectively), while the median durations per contact were

very short (o1 to 5 s/contact). Thus, children have a large

number of short contacts. The highest median contact

frequencies were with ‘‘Toys’’ (129.4 contacts/h for both

hands combined) followed by ‘‘Clothes/Towels’’ (65.7

contacts/h for both hands combined) and ‘‘Body’’ (65.1

contacts/h for both hands combined). This is not surprising

since nearly all of the children played with some type of toy

during the time they were videotaped and certain play

activities involving toys (e.g., bouncing a ball or tossing a

frisbee) involved high contact frequencies with the hands.

Contact frequencies with ‘‘Body’’ and ‘‘Clothes/Towels’’

were also high since all children had opportunities to contact

these objects/surfaces at all times.

Significant FindingsAs this study collected hand contact data mainly from

outdoor environments, some of the significant findings

regarding indoor/outdoor differences may be biased

due to the limited amount of indoor data collected. For

example, in this study, the children spent a large proportion

of their observed indoor time engaging in eating/

drinking events as a break from their outdoor activities.

Therefore, the significant differences in hand-to-food contact

behaviors between indoor/outdoor locations may be an

artefact of this bias towards recording an unusually high

frequency of indoor eating events. Despite the limitation just

mentioned, other significant differences between indoors/

outdoors environments seemed to make intuitive sense. That

is, contact frequencies and hourly contact durations with

Children’s hand contact activities Auyeung et al.

Journal of Exposure Science and Environmental Epidemiology (2006) 16(5) 441

Table 6. Significant differences in contact frequencies and hourly contact durations between indoor and outdoor environments for both hands combined

Location Statistic Object/surface super-categories

Indoor4outdoor Outdoor4indoor

Frequency (contacts per hour) Hourly contact duration (minutes per hour) Frequency (contacts per hour) Hourly contact duration

(minutes per hour)

Fabric

(P¼ 0.02)

Food

(P¼ 0.008)

Paper/

Wrapper

(P¼ 0.05)

Wood

(P¼ 0.004)

Fabric

(P¼ 0.02)

Food

(P¼ 0.03)

Wood

(P¼ 0.004)

Body

(P¼ 0.04)

Vegetation/

Grass

(P¼ 0.02)

Body

(P¼ 0.03)

Vegetation/

Grass

(P¼ 0.04)

Indoors Range 0–65.3 0–156.8 0–78.5 15.4–115.5 0–3.7 0–41.2 1.3–31.7 19.2–131.2 0–17.7 0.7–10.2 0–6.4

(n¼ 9) Mean 21.4 71.2 30.8 59.3 1.4 17.7 8.9 66.5 4.0 4.9 1.1

5th percentile 0 4.9 0.8 20.2 0 0.7 1.3 20.4 0 1 0

25th percentile 15.1 52.6 4.2 30.3 0.5 10.9 2.4 22.3 0 1.6 0

50th percentile 17.1 68.1 11.2 49.2 1.2 16.4 6.5 60.5 0 4.7 0

75th percentile 20.2 82.7 69 91.5 2.1 25.8 10.8 93 3.8 5.9 0

95th percentile 54.9 148.8 75 112.3 3.3 38.4 24.1 128.8 16.5 10.2 5.1

99th percentile 63.2 155.2 77.8 114.9 3.6 40.6 30.2 130.7 17.5 10.2 6.1

Outdoors Range 0–17.3 0–54.1 0–103.8 0.6–28.2 0–2 0–17.1 0–4.1 32.5–191.7 0–65.9 1.6–26.3 0–14.5

(n¼ 9) Mean 2.3 20.0 7.3 9.1 0.2 5.8 1.0 104.1 26.5 10.1 4.6

5th percentile 0 0.8 0 0.6 0 0 0 43.1 1.4 1.7 0

25th percentile 0 2.8 0 2.3 0 0.5 0.1 87.7 5.9 3.7 0.6

50th percentile 0 7.1 1.5 6.4 0 1.9 0.2 93.9 27.3 6.9 3.6

75th percentile 0.8 41.4 7 8.2 0 12.4 1.6 109.5 44.8 17.5 7.7

95th percentile 11.3 52.3 21.4 26.4 1.2 15.5 3.1 185 58 24.7 12

99th percentile 16.1 53.7 73.6 27.8 1.8 16.8 3.9 190.4 64.3 26 14

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‘‘Fabric’’ were higher indoors than outdoors because curtains

and sofas were more likely to be found indoors than

outdoors, while contact frequencies and hourly contact

durations with ‘‘Vegetation/Grass’’ were higher outdoors

because plants were more likely to be found outdoors

than indoors.

Table 7. Significant differences in outdoor contact frequencies and hourly contact durations between boys and girls for both hands combined

Gender Statistic Object/surface super-categories

Girls4boys

Frequency (contacts

per hour)

Hourly contact duration (minutes per hour)

Body (P¼ 0.007) Footwear

(P¼ 0.02)

Non-dietary objects/

surfaces (P¼ 0.03)

Total objects/surfaces

(P¼ 0.01)

Male Range 17–191.7 0–0.8 47.8–88.2 48.1–88.2

(n¼ 18) Mean 64.2 0.1 67.7 70.8

5th percentile 19.3 0 53.4 54.2

25th percentile 38.8 0 59.8 63.2

50th percentile 57.8 0 67.3 72.6

75th percentile 65.4 0.1 72.6 79.1

95th percentile 177.5 0.5 84.2 86.1

99th percentile 177.5 0.5 84.2 86.1

Female Range 28.4–146.1 0–5.6 42.6–101.7 42.6–102.2

(n¼ 20) Mean 84.3 0.8 77.6 82.2

5th percentile 44.6 0 51.2 57.9

25th percentile 63 0 68.7 72.6

50th percentile 88.6 0.2 79 85

75th percentile 99.4 0.8 90.8 93.4

95th percentile 126.1 4 98.9 101.3

99th percentile 126.1 4 98.9 101.3

Table 8. Significant differences in outdoor contact frequencies and hourly contact durations between the left and right hands

Hand Statistic Object/surface super-categories

Left4right Right4Left

Frequency (contacts

per hour)

Hourly contact duration

(minutes per hour)

Hourly contact duration (minutes per hour)

Clothes/towels

(P¼ 0.01)

Clothes/Towels

(P¼ 0.003)

Floor

(P¼ 0.04)

Toys

(P¼ 0.0002)

Vegetation/Grass

(P¼ 0.05)

Non-dietary

objects/surfaces

(P¼ 0.0001)

Total objects/

surfaces

(P¼ 0.0001)

Left Range 4–100.3 0.6–14 0–12.9 0–28.6 0–9 5.8–49 5.8–49.7

(n¼ 38) Mean 39.2 3.8 2.4 13.0 2.2 34.8 36.7

5th percentile 14.2 1 0.1 3.2 0 24.7 25.3

25th percentile 25.7 1.8 0.2 7.1 0.4 29.9 31.1

50th percentile 33.9 2.4 1.4 12.3 1 35 37.8

75th percentile 55.1 3.9 4 20.3 2.5 40.8 43.3

95th percentile 80.8 10.8 6.5 26.4 8.2 46.3 49.2

99th percentile 95.5 13.4 10.8 28.1 9 48.7 49.7

Right Range 5.8–98.8 0.5–12.3 0–7.5 0–41 0–14.7 25.2–52.7 25.2–53.1

(n¼ 38) Mean 34.5 3.0 1.6 16.8 2.9 38.1 40.1

5th percentile 10.1 0.5 0 4 0 28 28.9

25th percentile 21.8 1.4 0.2 9.5 0.8 31.8 35.3

50th percentile 30.7 2.1 1 16 1.5 38.2 40.8

75th percentile 43.6 3.5 2 23.6 4.2 42.8 45

95th percentile 63.3 7.7 5 30.6 8.9 49.7 50.6

99th percentile 91 11.4 7.2 37.4 13.1 51.8 52.5

Children’s hand contact activities Auyeung et al.

Journal of Exposure Science and Environmental Epidemiology (2006) 16(5) 443

Table 9. Summary of indoor median contact frequencies from previous studies (contacts per hour)

Study Method Location Length Age n Hand Object/surface categories

Carpet Clothing Hard

Floor

Paper Skin Upholstered

Furniture

Smooth

Surface

Textured

Surface

AuYeung

et al.

(current

study)

Videotaping;

computer

software

Primarily

outdoors

2 h (15–33min

for indoor data)

1–6 years 38 (n¼ 9 for

indoor data)

Left 7.9a 41b 3.2c 3.8 11.6 13.1d 61.9e 18.2f

Right 8.5a 25.2b 3.9c 7.4 9.9 7.7d 62.7e 22.1f

Both 28.4a 73.4b 7c 11.2 21.9 20.8d 116.9e 40.4f

Freeman

et al. (2004)

Videotaping;

computer

software

Primarily

indoors

4 h 2–4 years 10 Left F F F F F F F F

Right 1.1 41.9 10.3 21.8 26.4 19.3 88 4.1

Both F F F F F F F F

Freeman

et al. (2001)

Videotaping;

manual

recording

Primarily

indoors

4 h 3–12 years 19 (n¼ 10 for

3–6 years old)

Left F F F F F F F F

Right F F F F F F F FBoth F 22–26g F F F F 111–134g 20–40g

Reed et al.

(1999)

Videotaping;

manual

recording

Primarily

indoors

3–7 h 2–6 years 30 Left F F F F F F F F

Right F F F F F F F FBoth F 65 F F F F 80.2 16.3

Zartarian

et al. (1997)

Videotaping;

computer

software

Primarily

indoors

6–10 h 2–4 years 4 Left 2.5h 25h,i 10h 8.5h 14.5h 9h 35h,i F

Right 2.5h 26.5h,i 9h 16h 18.5h 11h 38.5h,i FBoth F F F F F F F F

aBased on contacts with ‘‘Carpet’’ .bBased on contacts with ‘‘Clothes’’.cBased on contacts with ‘‘Rock/Brick Floor’’, ‘‘Wood Floor’’, and ‘‘Tile/Linoleum Floor’’.dBased on contacts with ‘‘Fabric Wall/Furniture’’.eBased on contacts with ‘‘Wood Wall/Furniture’’, ‘‘Wood Floor’’, ‘‘Plastic Wall/Furniture’’, ‘‘Tile/Linoleum Floor’’, and ‘‘Metal Wall/Furniture’’, ‘‘Rock/Brick Floor’’, and ‘‘Rock/Brick Wall/

Furniture’’.fBased on contacts with ‘‘Carpet/Mat’’ and ‘‘Fabric Wall/Furniture’’.gMedians were reported separately for 3–4, 5–6, 7–8, and 10–12 years old children. Only medians for 3–4- and 5–6-year-old age groups are shown.hBased on the median of the four children’s average contact frequencies.iBased on contacts with ‘‘Other clothes’’.jBased on contacts with ‘‘Hard Surface’’.

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The right hand was found to have longer hourly contact

durations with objects that are often manipulated with the

hand (i.e., ‘‘Toys’’). On the other hand, the left hand had

longer hourly contact durations with objects/surfaces that did

not need to be manipulated (e.g., ‘‘Clothes/Towels’’ and

‘‘Floor’’). An explanation for this is that even though the

left hand was not used as often as the right hand to

manipulate objects, this did not mean that the left hand

did not touch objects/surfaces. The left hands of the

children were often observed to rest on or touch objects/

surfaces such as a table, clothes, the floor, etc. Occasionally,

the left hand was involved with object manipulation as well

(e.g., carrying a big ball). It is important to study the two

hands separately because differences in contact behaviors

between the left and right hands may lead to differences in

contaminant loadings between the hands. This in turn may

affect estimations of non-dietary ingestion exposure from

hand-to-mouth contacts if young children preferentially

mouth one of their hands.

Comparisons with Previous StudiesTable 9 compares results from this study with results from

previous studies. As all previous studies focused on indoor

environments, only the indoor data from the nine children

who spent more than 15min in view indoors are presented in

the table. It is worth noting that due to a number of factors

such as differences in data collection methods, object/surface

categorizations, as well as the subpopulations studied (both

in terms of the ages of the children studied and the regions/

locations where these studies were conducted), it is difficult to

compare results from different studies.

Zartarian et al. (1997a) collected hand-to-surface contact

frequency and duration data in the Salinas Valley of

California by videotaping four children in a primarily indoor

home environment and then transcribing the videotapes with

the VirtualTimingDevicet software (previously known as

VideoTraq). Reed et al. (1999) videotaped a total of 30

children aged 2–6 years in either a day-care center or a

residence in New Brunswick, New Jersey. Hand-to-surface

contact frequencies were then collected by manually record-

ing the frequency over 5-min intervals. Freeman et al. (2001)

employed the same data collection method as Reed and

collected data from 19 children in the residential home

environment. Freeman et al. (2005) videotaped 10 children

for approximately 4 h each in a primarily indoor home

environment and translated the videotapes using the

VirtualTimingDevicet software.

Despite the fact that only nine children were included for

indoor data analysis, indoor results from this study seemed to

agree well with those from previous studies. Contact

frequencies calculated from this study were systematically

higher than those reported by Reed et al. (1999) and

Freeman et al. (2001), but systematically lower than those

reported by Freeman et al. (2005) (except for ‘‘Carpet’’ and

‘‘Textured Surface’’). A possible explanation for the lower

contact frequency reported by Freeman et al. (2005) for

‘‘Textured Surface’’ is that their ‘‘Textured Surface’’ category

did not include contacts with ‘‘Carpet’’ or ‘‘Upholstered

Furniture’’, while contacts with these objects/surfaces were

included as ‘‘Textured Surface’’ for this study as well as the

studies by Reed et al. (1999) and Freeman et al. (2001).

Flooring type may have contributed in part to differences in

contact frequencies with ‘‘Hard Floor’’ and ‘‘Carpet’’

between this study and the study conducted by Zartarian

et al. (1997a). That is, contact frequency with ‘‘Hard Floor’’

from this study is similar to contact frequency with ‘‘Carpet’’

reported by Zartarian et al. (1997a) and vice versa.

Future StudiesSince the children in this study were videotaped for only 2 h

each and they were told by their parents to play outdoors for

the duration of the videotaping session, their activities may

not be entirely representative of how children spend time

outdoors. However, the data collected from this study

provides a rough description of children’s hand-to-object/

surface contacts in outdoor residential environments. In a

future study, the videotapes of the 38 children will be

rewatched and descriptions of general play activities will be

added to the MLATS file. Then, the MLATS data will

reanalyzed on an activity-specific basis (e.g., playing on

playground structure, riding bicycle, gardening) to further

refine information on children’s hand-to-object/surface con-

tacts in outdoor residential environments.

ConclusionThe results of this study suggest that in outdoor residential

settings, young children have a large number (median

frequency is 4500 contacts/h for both hands combined) of

short contacts (o5 s) with objects/surfaces. Differences in

hand contact activities were found for all four factors studied:

age (in months), gender, left/right hands, and indoor/

outdoor environments. Besides providing an account of

factors that affect hand contact activities, this study may also

help improve outdoor exposure assessments by providing

detailed summaries of hand-to-object/surface microlevel

activity data collected from outdoor environments.

Acknowledgements

The authors specially thank Kelly Naylor, Nolan Cabrera,

Sandy Robertson, Kevin Lee, Amy Munninghoff, Veronica

Vieira, Jessica Ramirez, and Angela Lin for their invaluable

help in collecting the data presented in this paper. This

project was supported by EPA STAR grant #R82936201,

ORETF Study #ORF018, USEPA Contract #QT-RT-99-

001182, and UPS Foundation grant #2DDA103. This

research has not been subject to federal peer and policy

Children’s hand contact activities Auyeung et al.

Journal of Exposure Science and Environmental Epidemiology (2006) 16(5) 445

review and therefore does not necessarily reflect the views of

the funding agencies. No official endorsement should be

inferred.

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