TABLE OF CONTENTS

6. OTHER NON-DIETARY INGESTION FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1 INTRODUCTION ............................................... 6-1

6.2 STUDIES RELATED TO NON-DIETARY INGESTION . . . . . . . . . . . . . . . . 6-2

6.2.1 Davis, 1995 .............................................. 6-2

6.2.2 Groot et al., 1998 .......................................... 6-5

6.2.3 Reed et al., 1999 .......................................... 6-6

6.2.4 Zartarian et al., 1997 and 1998 ............................... 6-7

6.2.5 Stanek et al., 1998 ......................................... 6-8

6.2.6 Freeman et al., 2001 ....................................... 6-10

6.2.7 Juberg et al., 2001 ........................................ 6-11

6.2.8 Greene, 2002 ............................................ 6-12

6.2.9 Tulve et al., 2002 ......................................... 6-13

6.2.10 Smith and Norris, 2003 .................................... 6-14

6.2.11 AuYeung et al., 2004 ..................................... 6-15

6.2.12 Black et al., 2005 ......................................... 6-16

6.3 RECOMMENDATIONS ......................................... 6-17

6.4 REFERENCES FOR CHAPTER 6 ................................. 6-19
LIST OF TABLES

Table 6-1. Extrapolated Total Mouthing Times Minutes per Day (time awake) . . . . . . . . . . 6-21

Table 6-2. Frequency of Contact (Contacts per Hour) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

Table 6-3. Prevalence of Non-Food Ingestion/Mouthing Behaviors by Child’s Age: Percent of

Children Whose Parents Reports the Behavior in the Past Month . . . . . . . . . . . . . . . 6-23

Table 6-4 Percent of Children with Reported Behaviors From the Telephone Survey Conducted

in the MNCPES (n = 168) .............................................. 6-26

Table 6-5. Median (Mean) Observed Activity Rate (Hand Contacts Per Hour) Based on 4 Hours

of Observation Per Person. ............................................. 6-26

Table 6-6. Comparison of Observed Activities for Boys and Girls (Mean). . . . . . . . . . . . . . 6-27

Table 6-7. Mouthing times for Pacifiers and Other Objects, by Age Category . . . . . . . . . . . 6-27

Table 6-8 . Average Mouthing Time by Object Category and Age (min/hr) . . . . . . . . . . . . . 6-28

Table 6-9. Mouthing Time Statistics for Various Objects (min/hr) . . . . . . . . . . . . . . . . . . . . 6-29

Table 6-10. Estimated Daily Mouthing Times for Various Objects (min/day) . . . . . . . . . . . 6-31

Table 6-11. Variability in Objects Mouthed for Different Age Groups. . . . . . . . . . . . . . . . . 6-32

Table 6-12. Mouthing Duration by Age Group for Pacifiers, Fingers, Toys, and 

Other Objects ........................................................ 6-33

Table 6-13. Indoor Mouthing Frequency (Contacts/Hour) . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34

Table 6-14. Outdoor Mouthing Frequency (Contacts/Hour) . . . . . . . . . . . . . . . . . . . . . . . . . 6-35

Table 6-15. Indoor Mouthing Contact Duration (Minutes/Hour) . . . . . . . . . . . . . . . . . . . . . . 6-36

Table 6-16. Outdoor Mouthing Contact Duration (Minutes/Hour) . . . . . . . . . . . . . . . . . . . . 6-37

Table 6-17. Videotaped Mouthing and Food-handling Activity as Median Hourly Frequency

(Contacts/Hour) and Median Duration (% of Tape Time) (Mean ± SD) . . . . . . . . . . 6-38

Table 6-18. Summary of Studies on Mouthing Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-39

Table 6-19. Summary of Mouthing Frequency Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-40

Table 6-20. Summary of Recommended Values for Total Mouthing Time 

(minutes per day) ..................................................... 6-42

Table 6-21. Summary of Recommended Values for Mouthing Frequency 

(contacts per hour) .................................................... 6-43

Table 6-22. Confidence in Mouthing Behavior Recommendations . . . . . . . . . . . . . . . . . . . . 6-44
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6. OTHER NON-DIETARY INGESTION FACTORS 

6.1 INTRODUCTION 

Young children (i.e., ages 6 months through approximately 4 years) have the potential for 

exposure to toxic substances through non-dietary ingestion pathways other than soil ingestion 

(e.g., ingesting pesticide residues that have been transferred from treated surfaces to the hands or 

objects that are mouthed). These children have an urge to mouth objects or their fingers in 

exploring their environment, as a sucking reflex and as a habit (Groot et al., 1998). Exposure via 

this route may exceed other routes of ingestion (i.e., food, pica, drinking water, breast milk) and 

dermal exposure, because non-dietary ingestion may result in higher ingestion rates of 

contaminated material (Weaver et al., 1998). This exposure route is also difficult to assess 

because there is little literature or research on mouthing behavior (Reed et al., 1999) and little 

information on the susceptibility of children to toxic substances (Weaver et al., 1998). 

Mouthing behavior includes all activities in which objects, including fingers, are touched 

by the mouth or put into the mouth except for eating and drinking, and includes licking, sucking, 

chewing, and biting (Groot et al., 1998). Children’s contact with surfaces is intermittent and 

nonuniform over different parts of the body and the nature of the mouthing itself is intermittent 

and nonuniform, making this pathway difficult to model (Zartarian et al., 1997). 

Children exhibit large differences in mouthing behavior (Groot et al., 1998). Infants are 

born with a sucking reflex for breast feeding, and within a few months, they begin to use sucking 

or mouthing as a means to explore their surroundings. Children will use both sucking and 

licking to explore their environment. Sucking also becomes a means of comfort when a child is 

tired or upset. In addition, teething normally causes substantial mouthing behavior— sucking or 

chewing— to alleviate discomfort in the gums. Each child is different, and large differences 

occur between children, even within the same family. 

Mouthing becomes critical in exposure to potentially toxic substances when it involves 

the behavior of a small child around potentially contaminated sources. Children play close to the 

ground and are frequently licking their fingers or mouthing toys or objects. As a result, 

mouthing becomes a potentially significant exposure route. Children may ingest more toxic 

constituents through this behavior than from dietary ingestion or inhalation because they may 

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place wet, sticky fingers on potentially-contaminated surfaces, and more toxic substances may 

adhere to the fingers than if the fingers were dry (Gurunathan et al., 1998). 

Gurunathan et al. (1998) estimated that young children spend as much as 90 percent of 

their days inside, so exposure to contaminants that may infiltrate the home through the vapor 

phase (e.g., volatile organic compounds (VOCs) and semi-VOCs (SVOCs)) may be of concern. 

This may be a significant pathway of exposure to SVOCs because these compounds can be 

deposited on surfaces in the home or become absorbed onto plastic toys or in stuffed animals 

where they can serve as reservoirs for toxic constituents (Gurunathan et al., 1998). 

Few studies have investigated this potential exposure route. The shortage of research and 

data may be due to the difficulty in observing very young children and the labor-intensive effort 

in gathering the data (Hubal et al., 2000). The applicable research efforts use two general 

approaches to gather data: real-time hand recording, in which trained persons observe a child and 

manually record information on a survey sheet or score sheet; and videotaping, in which trained 

videographers tape a child’s activities and subsequently extract the pertinent data manually or 

with computer software (Hubal et al., 2000). 

Some researchers express mouthing behavior in terms of frequency of occurrence (e.g., 

contacts per hour or contacts per minute). Others express mouthing behavior as a rate in units of 

minutes per hour of mouthing time. Both approaches have their use in exposure assessments. 

The former approach is more appropriate when studying children’s behavior during various 

microactivities. The latter, however, is more useful when studying children’s behavior during 

macroactivities. Macroactivities can be described by a child’s general activities such as 

sleeping, watching television, playing, and eating. Microactivities refer to the specific behavior 

a child is engaged in such as hand-to-surface contacts and hand-to-mouth behavior (Hubal et al., 

2000). Time spent in various macroactivities in several microenvironments (e.g., indoors at 

home) are presented in Chapter 9. 

6.2 STUDIES RELATED TO NON-DIETARY INGESTION 

6.2.1 Davis, 1995 

In 1992, the Fred Hutchinson Cancer Research Center under Cooperative Agreement 

with EPA, conducted a study to estimate children’s soil intake rates and collect mouthing 

behavior data. Originally, the study was designed with two primary purposes: (1) to describe 

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and quantify the distribution of soil ingestion values in a group of children under the age of five 

who exhibit behaviors that would be likely to result in the ingestion of larger than normal 

amounts of soil; and (2) to assess and quantify the degree to which soil ingestion varies among 

children according to season of the year (summer vs. winter). The study was conducted during 

the first four months of 1992 and included 92 children from the Tri-Cities area in Washington 

State. The children were volunteers among a group selected through random digit dialing and 

their ages ranged between 0 and 48 months. The study was conducted during a 7-day period. 

Because there was no standard methodology to study mouthing behavior, a pretest and a 

series of pilot studies were conducted to examine various aspects of the methodology. As a 

result of the pilot studies, it was determined that although parents could be taught to conduct 

observations using the instrument, the resulting ranking of children according to degree of 

mouthing behavior did not correspond very well to the rankings based on observations of the 

same children by trained staff observers. Therefore, using parents’ observations to select a group 

with high mouthing activity was not deemed appropriate. Funding constraints made it 

impractical to continue with the original design of screening a large number of children and 

conducting field work during two different times of the year. 

The Davis (1995) research recognizes that mouthing behavior is intermittent. Therefore, 

a practice called the “interval method” of observation was used. This method measures both 

frequency and duration of the behavior. Under this method, children were observed during 15 

second intervals, during which the mouthing behavior was recorded. Based on the types of 

behaviors observed in the testing of the instrument, two mouthing behaviors were selected for 

the full study. These included: 1) tongue contacts object; and 2) object in mouth. In addition 

four other behaviors were included in an attempt to better describe the types of behaviors that 

would likely result in soil ingestion: 1) hand touches ground; 2) child is repulsed by object in 

mouth and tries to get it out; 3) other person stops child’s contact with object; and 4) child is out 

of sight or view. To further characterize potential exposures to soil associated with the three 

types of mouthing behaviors, six object categories were included along with the behaviors: 1) 

hand, finger, or thumb; 2) other body parts, including toes, feet, arms; 3) natural materials, 

including dirt, sand, rocks, leaves; 4) toys and other objects, including books, utensils, keys; 5) 

surfaces, including window sills, floors, furniture, carpet; and 6) food or drink. An additional 

code was added to indicate whether an object was swallowed by the child. The type of activity 

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the child was engaged in during the observation period was also recorded. In addition to 

mouthing behavior data, information about how long the child spent indoors and outdoors each 

day, and the general types of outdoor settings in which the child played was collected. 

Mouthing behavior data were collected during a 4-day period. Both trained observers 

and one parent observed the children to record mouthing behavior data. Trained observers 

recorded mouthing behavior data for 1 hour during active play time, and the parent recorded 

mouthing behavior data for the first 15 minutes of that hour. 

The basic measure of each type of mouthing activity derived from the observation form 

was the percent of time spent in that activity. This measure was defined as the percentage of the 

total number of intervals observed that indicate such an activity took place. If there was no 

activity in an interval, that interval was excluded. For tabulating the object categories, multiple 

instances of the same object in a single interval were counted only once in that interval. 

Multiple instances of different objects in a single interval were counted separately under each 

object category. 

Based on the mouthing behavior data collected in this study, EPA calculated that during 

the period of observation (assumed to be 1 hour) the average mouthing activity was 6.2 minutes 

and the average tongue activity was 0.70 minutes. It is important to note that this is based on 

one hour of observation. In order to estimate the overall mouthing activity in a day, one would 

have to make some assumptions about the amount of time a child is involved in active play time 

in a day. These values may also be underestimates because they assume that all the children in 

the study were observed for one hour on each of the four days. If this were true, each child 

would have a total of 960 intervals of observations (i.e., 3,600 seconds x intervals/15 seconds x 4 

days). The data show that the number of intervals of observation ranged from 80 to 840. It can 

be concluded that some children were either observed for less than one hour or less than 4 days. 

In order to compare the values estimated by Groot et al. (1998) whose work also used 

time as a basis for measuring mouthing activity, it is necessary to multiply the Davis (1995) 

hourly estimate by an estimate of how long the children are awake during the day. According to 

Davis (1995), small children aged 0 to 48 months are awake approximately 8.9 hours per day. 

Based upon this estimate, the Davis (1995) findings translate into about 55 minutes per day of 

mouthing activity and 6 minutes per day of tongue activity. The 55 minutes compares favorably 

to the 37 minutes and 44 minutes estimated by Groot et al. (1998) for 3- to 6-month and 6- to 12­

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month old children, respectively, but is significantly above the 16.4 minutes and 9.3 minutes 

estimated for the 12- to 18-month and 18- to 36-month old children, respectively. The difference 

may be attributable to differences in sleep time between children at either end of the continuum 

of ages included in the study (0 to 48 months). 

Although the research included the largest sample population of the reviewed literature, 

92 sample points is still a small number considering the wide variability associated with 

mouthing in children. The random nature in which the population was selected probably 

provides a representative population of the northwest U.S., but not the national population in 

general. The interval time of 15 seconds would also appear to be small and potentially easily 

skewed for those children observed less than an hour. In addition, most other studies used 

observation times of 15 minutes to continuous observation throughout waking hours. 

6.2.2 Groot et al., 1998 

In this study, Groot et al. (1998) examined the mouthing behavior of infants and young 

children between the ages of 3 and 36 months in the Netherlands. The study was part of a larger 

effort to determine if PVC toys softened with phthalates could pose health risks to children from 

mouthing. As part of the effort, the investigators asked parents to observe their children and 

gather information that could be used to estimate how often children engage in mouthing and the 

duration spent mouthing during a day. Parents were asked to observe their children ten times per 

day for 15-minute intervals (i.e., 150 minutes total per day) for two days and measure mouthing 

with a stopwatch. In total, 36 parents participated in the study and 42 children were observed by 

their parents. For the study, a distinction was made between toys meant for mouthing (e.g., 

pacifiers, teething rings) and those not meant for mouthing. The time a child spent mouthing a 

dummy (e.g., pacifier) was not included in the time recorded. 

Although the sample size was relatively small, the results provide a first-order estimate 

on mouthing times during a day. The results (Table 6-1) show wide variation. The standard 

deviation in all four age categories except the 3- to 6-month old children exceeds the mean time 

estimated mouthing during a day. The large standard deviations is not unexpected given the vast 

behavioral differences from child to child and the small sample size of the study. The overall 

trend of the data, however, may be accurate in that it shows that as the children age, the time 

spent mouthing decreases. The 3- to 6-month children were estimated to mouth 37 minutes per 

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day and the 6- to 12-month children 44 minutes per day. After 12 months, the estimated 

mouthing time drops quickly to 16 minutes per day for 12- to 18-month children and 9 minutes 

per day for 18- to 36-month children. 

The study has several limitations that have an impact on the usability of the data. The 

initial drawback concerns the small size of the study. The authors of the study acknowledge this 

shortcoming and recommend further study using a larger sample population. In addition, the 

study also incorporated mostly higher-educated persons. The area where the study was 

performed consisted primarily of parents with higher education. The study had recruited persons 

of lower education and socioeconomic levels, but these persons chose not to participate in the 

study after recruitment. Therefore, the results do not reflect data from the full spectrum of the 

population. The study also recorded only the time spent mouthing and not the number of times 

that mouthing occurred and did not differentiate the types of objects mouthed. In addition, 

children were observed for a period of two consecutive days and may not reflect long-term 

behavior. Because this study was conducted in the Netherlands, it may not be representative of 

the U.S. population. 

6.2.3 Reed et al., 1999 

In this study, Reed et al. (1999) used videotaping to quantify the frequency and type of 

contacts children have during the course of an hour. The contacts included numerous categories: 

hand to clothing, hand to dirt, hand to hand, hand to mouth, hand to object, object to mouth, hand 

to smooth surface (e.g., counter tops, table tops), hand to textured surface (e.g., stuffed animal). 

A total of 30 children were observed in this study. Children were observed in both day care (20 

children 3-6 years old) and residential (10 children 2-5 years old) settings. Parents and daycare 

providers were also asked to complete questionnaires describing the behavior of the children. In 

addition, the study also differentiated between the use of right and left hands. 

Over the course of the research, the investigators found that the behavior of children in 

daycare and residential settings was similar except for the contact rate of hand to smooth 

surfaces. Children in residential settings had higher contact rates with smooth surfaces than 

children in day care centers. The results of the study are compiled in Table 6-2. The highest 

contacts were with object (123 contacts/hr), smooth surfaces (84 contacts/hr), and other (83 

contacts/hr). The two lowest contact rates were the hand-to-mouth (9.5 contacts/hr) and object6-6
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to-mouth (16.3 contacts/hr). Because the contact rates of hand-to-objects and smooth surfaces 

are high, these results indicate that the fingers would appear to provide a continual dose per 

hand-to-mouth contact because of constant touching of potentially contaminated surfaces. 

Pesticides and other SVOCs are partitioned between the vapor and deposited phases (e.g., on 

dust or absorbed on a plastic toy or stuffed animal) such that a child’s fingers, especially if wet 

from mouthing, will continually be acquiring doses of these types of constituents (Gurunathan et 

al., 1998). 

The investigators also noted that children acted equally on their environment with both 

hands with the exception of object-to-mouth behavior. Therefore, the compiled data are reported 

as combined right and left hand data. The object-to-mouth behavior showed a strong preference 

for the right hand over the left hand for nearly all children (Reed et al., 1999). The preference 

ratio for the right hand over the left hand for this category was 6.8 to 1. 

The advantages of this study is that it incorporates a wide variety of contacts that small 

children have, not just the hand-to-mouth or object-to-mouth. This information allows assessors 

to identify areas or surfaces that may serve as sources for toxic constituent transfer. This is 

especially important for exposure to SVOCs such as pesticides (e.g., chlorpyrifos) that have an 

affinity for absorption onto dust particles, plastic toys, and into the polyurethane foam (PUF) that 

is used in many stuffed animals (Gurunathan et al., 1998). Another strength of this study is the 

agreement it shows with earlier work by Zartarian et al. (1998) for the hand to mouth contacts. 

Some of the shortcomings are the small sample size of the study and the lack of comment as to 

the representativeness of the sample population to the U.S. population. The authors 

acknowledged the weakness in regard to the sample size and recommended further work with a 

larger population. The study makes no mention of the representativeness of the sample 

population or addresses the need for a representative population for any additional study. 

6.2.4 Zartarian et al., 1997 and 1998 

Zartarian et al. (1997, 1998) conducted a pilot study of four children of farm workers to 

investigate the applicability of using videotaping for gathering information related to children’s 

interaction with their environment. The evaluation of the videotaping included observation of 

the children’s contact frequency and duration with objects in their environment, duration spent in 

different locations, activity levels, and frequency distributions. 

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Four Mexican-American farm worker children— two girls and two boys between the 

ages of 2.5 and 4.2 years— were videotaped for 33 hours using hand-held cameras over the 

course of a single day in 1993. The videotaping gathered information on detailed micro-activity 

patterns of children to be used to evaluate software for videotaped activities and translation 

training methods The data were also reported by type of object/surface and by left or right hand. 

The investigators presented the data for their observations on a per child and per hand 

basis. None of the children had average contact frequencies for either hand, individually, lower 

than 3 contacts/hr for hand to mouth contact, and the investigators estimated the average as 9 

contacts/hr with an average range of 1 to 29 contacts/hr. As also reported by Reed et al. (1999), 

the most frequently contacted objects were toys and hard (i.e., smooth) surfaces. The average 

contact time with objects is only 2 to 3 seconds; therefore, according to the authors, 

questionnaires and diaries would be insufficient in gathering that level of activity. 

This study has several weaknesses. The sample population is very small, only four 

children; however, the work was reported as a pilot study completely acknowledging that further 

work was necessary. The effort was intended to evaluate the methodology of collecting 

observations, not the contact data itself. The data are not presented in a format that can be used 

to support other research or supply recommended estimates for contact frequency. This study 

may not reflect long-term behavior. In addition, the sample population is not representative of 

the U.S. population in general. 

6.2.5 Stanek et al., 1998 

Stanek et al. (1998) presented a methodology that characterizes the prevalence of 

mouthing behavior among healthy children . Data regarding the frequency of 28 mouthing 

behaviors were collected via face-to-face interviews over a period of 3 months from parents or 

guardians of 533 children ages 1 to 6 years old attending well-visits in Western Massachusetts. 

Three clinics participated in this study during the months of August, September, and October, 

1992: Kaiser Permanente’s clinic in Amherst, a private clinic associated with the Cooley 

Dickinson Hospital in Northampton, and the Bay State Medical Center clinic in Springfield. 

Participants were questioned about the frequency of 28 mouthing behaviors of the children over 

the past month in addition to exposure time (e.g., time outdoors, play in sand or dirt) and 

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children’s characteristics (e.g., teething). Response categories of the clinic questionnaire 

corresponded to daily, at least weekly, at least monthly, and never. 

The authors expressed the mouthing rate for each child as the sum of rates for responses 

to four questions on mouthing specific outdoor objects. Regression models with variables in a 

step-wise manner identified factors related to high outdoor mouthing rates. The authors first 

considered variables that indicated opportunity for exposure, then subjects’ characteristics (e.g., 

teething) and environmental factors, and finally, concurrent reported behaviors. 

Table 6-3 presents the prevalence of non-food ingestion/mouthing behaviors by child’s 

age as the percent of children whose parents reported the behavior in the past month. The table 

includes a column of data for the 3 to <6 year age category; this column was calculated by EPA 

as a weighted mean value of the individual data for 3-, 4-, and 5-year-olds in order to conform to 

the standardized age categories used in this Handbook. Outdoor soil mouthing behavior 

prevalence was found to be higher than indoor dust mouthing prevalence, but both behaviors had 

the highest prevalence among 1-year-old children and dropped quickly among children 2 years 

old and older. The investigators conducted principal component analyses on responses to four 

questions relating to ingestion/mouthing of outdoor objects (Table 6-3) in an attempt to 

characterize variability. Responses were converted to mouthing rates per week, using values of 

0, 0.25, 1, and 7 for responses of never, monthly, weekly, and daily ingestion. Outdoor 

ingestion/mouthing rates for were 4.73 per week and 0.44 per week for children 1 year of age 

and 2-6 years of age, respectively. The frequency with which children played in sand/dirt was 

estimated as a measure of potential exposure; 71% of the children were reported to have played 

in sand or dirt at least weekly, and 45% were reported to have played in the sand or dirt daily. 

The authors found that children who played in the sand or dirt had higher outdoor object 

ingestion/mouthing rates. Thus, children with higher direct exposure to sand or dirt were more 

likely to ingest or mouth outdoor objects. The investigators found similar results when 

comparing the time spent outdoors to reported outdoor ingestion and mouthing rates; the data 

indicate that 65% of one-year old children and 42 percent of children 2-6 years old spend less 

than 3 hours per day outdoors. A strength of this study is that it focuses on the prevalence 

of specific behaviors to quantify soil mouthing or ingestion among healthy children. The results 

of this study might have important health implications as it showed that 1-year-old children with 

high general levels of mouthing behavior have the potential for high risk soil ingestion. 

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A limitation associated with this study is that the data are based on recall behavior from 

the summer previous to the interview. Extrapolation to other seasons may be difficult. In 

addition, data were collected for children in Western Massachusetts and data were only available 

for the healthy children who were present for well-visits. 

6.2.6 Freeman et al., 2001 

As part of the Minnesota Children’s Pesticide Exposure Study (MNCPES), macroactivity 

and microactivity data were collected via questionnaire from the families of a group of 168 

children, and a subset of 19 of these children were videotaped for four consecutive hours during 

the months of August and September 1997. The children were between the ages of 3 and 12 

years old and were living in both urban and rural areas of Minnesota. For the time/activity 

questionnaires, the parents provided the responses for children ages 3 and 4, and collaborated 

with or assisted older children with their responses. The videotapes were analyzed using the 

methods reported by Reed (1999), and for comparison, four children’s videotapes were also 

analyzed using the VideoTraq transcription system described by Zartarian et al. (1995). 

Videotapes were transcribed once for the left hand and once for the right hand, and the frequency 

of six behaviors (hand-to-mouth, hand-to-object, object-to-mouth, hand-to-smooth surface, handto-textured surface, and hand-to-clothing) was recorded. The amount of time each child spent 

indoors, outdoors, in contact with soil or grass, and whether the child was barefoot was also 

recorded. Statistical analyses were performed using SPSS and Systat. 

For the survey responses, only eating food dropped on the floor was significantly greater 

for one age group (3-4 year olds), when compared to two other age groups (Table 6-4). When 

the survey responses were further broken down by age, the 3-year-olds had significantly more 

positive responses for all reported behavior compared to the other age groups. High response 

rates (>70%) to additional questions directed toward the 3- and 4-year-old children, regarding 

the use of blankets and toys indicated that these questions should also have been asked of the 

older children. 

Among the four age categories studied for the 19 videotaped children, object-to-mouth 

activities were significantly greater for the 3-year-olds than any other age group, with a mean of 

6 contacts per hour (P = 0.002) (Table 6-5). Contact with clothing was slightly more frequent 

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and contact with smooth surfaces less frequent among the two oldest groups of children, but 

neither of these differences was statistically significant. 

Gender differences were observed for some of the activities, with boys spending 

significantly more time outdoors than girls (Table 6-6). Hand-to-mouth and object-to-mouth 

activities were less frequent outdoors than indoors for both boys and girls. No significant 

differences were observed in the frequency of events recorded using the Reed manual counting 

system and the VideoTraq computer-based video transcription system. 

The advantage of this study is that it contains both survey and videotaped information on 

mouthing behavior, and that various ages were studied. The limitations of the study are that the 

sample size is small and was from a limited area (urban area of St. Paul/Minneapolis) not 

representative of the national population in general. 

6.2.7 Juberg et al., 2001 

Juberg et al. (2001) used a diary-based approach to record mouthing behavior in children 

up to three years of age. An initial pilot study involved 30 children, including 15 between the 

ages of 0 and 18 months and 15 between the ages of 19 and 36 months. A second phase of the 

study added 92 children to the younger group and 95 to the older group, for a total pooled data 

set of 107 and 110 persons, respectively. For the pilot and second study, diary forms were 

distributed to approximately 450 families; the distribution was split equally between a 

commercial child play research center and a nursery school/daycare center. Parents were asked 

to observe their child’s behavior on a single day of their choosing during a three-week period, 

and record the insertion of objects into the mouth by noting the “time in” and “time out.” 

Mouthed items were classified as pacifiers, teethers, plastic toys, or other objects. In the data 

analysis, pacifiers were examined as a separate category and data for all other items were pooled 

into a “non-pacifier” category. 

The results of the combined pilot and Phase II data are shown in Table 6-7. For both age 

groups, mouthing time for pacifiers greatly exceeded mouthing time for non-pacifiers, with the 

difference more acute for the older age group than for the younger age group. Histograms of the 

observed data show a peak in the low end of the distribution (0 to 100 minutes per day) and a 

rapid decline at longer durations. 

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A third phase of the study focused on children between the ages of 3 and 18 months and 

included only non-pacifiers. Subjects were observed for 5 non-consecutive days over a 2-month 

period. A total of 168 participants returned surveys for at least one day, providing a total of 793 

person-days of data. The data yielded a mean mouthing duration of 36 minutes per day; the mean 

was the same when calculated on the basis of 793 person-days of data as on the basis of 168 

daily average mouthing times. 

The advantages of this study are that it involved a large number of participants compared 

to other studies of mouthing behavior. It also exhibited consistency of results from the pilot 

study to the second and third phases. The potential sources of error include the limited 

geographic range of the study (western New York state) and the subjective nature of the 

observation and diary-based approach. Another limitation of this study is that it focused on 

object mouthing behavior and did not include hand-to-mouth behavior. 

6.2.8 Greene, 2002 

The U.S. Consumer Product Safety Commission (CPSC) investigated the potential health 

risks to children under three years of age from teethers, rattles, and toys made from polyvinyl 

chloride (PVC) containing various dialkyl phthalate (DAP) plasticizers. They conducted an 

observational study to quantify the cumulative time per day that young children spend mouthing 

objects, including toys and other children’s products. The study was conducted from December 

1999 through February 2001 in two geographical areas: Houston, TX and Chicago, IL. Subjects 

were recruited using telephone random digit dialing techniques. 

During the first phase of the study, the parent or legal guardian observed the child and 

recorded all mouthing behaviors for four 15-minute segments over two days. If the child was 

under 36 months of age, they were recruited to participate in phase II. During phase II, a trained 

observer recorded the child’s behavior for a total of four hours on at least two different days. 

The observations were done at different times of the day at home or a the child care facility 

attended by the child. A total of 491 children participated in phase I. The total number of 

participants in phase II was 169. The age of the children were between 3 months and 3 years of 

age. Of the 169 children in phase II, 109 participated in phase I. Data from phase I were 

analyzed and reported independently from phase II and were not provided by Greene (2002). 

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 Table 6-8 provides the average mouthing time by object category and age in minutes per 

hour. Mouthing time statistics by object categories and age are presented in Table 6-9. The 

average mouthing time for all objects ranged from 5.3 to 10.5 minutes per hour, with the highest 

mouthing time corresponding to children <1 year of age and the lowest to the 2-3 years of age. 

Among the objects mouthed, pacifiers represent about one third of the total mouthing time, with 

3.4 minutes per hour for the youngest children, 2.6 minutes per hour for the children between 1 

and 2 years and 1.8 minutes per hour for children over 2 years old. The next largest single item 

category was anatomy, representing children sucking fingers and thumbs. In this category, 

children under 1 year of age spent 2.4 minutes per hour and it declined with age, with the 1.2 

minutes per hours for the 2-3 years old. 

Daily mouthing times were estimated using a bootstrap procedure using a normally 

distributed random variable for the exposure time based on the child’s age. The bootstrap 

procedure is a statistical technique in which a set of collected data is randomly sub-sampled 

hundreds or thousands of times in order to empirically derive confidence limits on the mean of 

the main sample set. The empirical distribution of mouthing time was used to calculate statistics 

and confidence intervals and was selected independently of exposure time. The bootstrap 

th sampling was done 5000 times to generate mean, median, and 95 percentile daily mouthing

time for each age group and object category. The results of the bootstrap procedure are 

presented in Table 6-10. The estimated mean daily mouthing time for non-pacifiers ranged from 

37 min/day to 70 min/day with the lowest number corresponding to the 2-3 years old and the 

largest number corresponding to the 3 months -12 months old. 

6.2.9 Tulve et al., 2002 

In this study, previously unpublished data from the Fred Hutchinson Cancer Research 

Center, Seattle, Washington were analyzed. Data were collected by trained observers who 

described and quantified the mouthing behavior of 90 children in their home environment. The 

children ranged in age from 10-60 months. The observers recorded mouth and tongue contacts 

with hands, other body parts, natural objects, surfaces, and toys every 15 seconds for a minimum 

of 15 minutes. Children’s activities were coded as quiet or active play, and locations were coded 

as indoor or outdoor environments. The final data set that was analyzed for this study included 

only those children who were coded as engaging in quiet play in an indoor environment (72 

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children, ranging in age from 11-60 months). A total of 186 observations were included in the 

study, with the number of observations per child ranging from 1-6. Data analyses to evaluate the 

influence of age and gender were conducted using a linear SAS model (Version 8.02; SAS 

Institute, Cary, NC). 

Results of the data analyses indicated that there was no association between mouthing 

frequency and gender, but a clear association between mouthing frequency and age was 

observed. Using a tree analysis, children #24 months had the highest frequency of mouthing 

behavior (81 events/hour) and children >24 months had the lowest (42 events/hour) (Table 6-11). 

Both groups of children were observed to mouth toys and hands more frequently than body parts 

other than hands and surfaces. 

The advantage of this study is that mouthing data is provided for different age groups and 

for a variety of objects (mouth-body, -hand, -surface, and –toy). This study is limited in that it 

focuses on children involved in quiet play in an indoor environment. 

6.2.10 Smith and Norris, 2003 

Smith and Norris (2003) conducted a diary-based observational study of mouthing 

behavior among 236 children between the ages of 1 month and 5 years. Children were observed 

at home by parents, who recorded the time that mouthing began, the type of mouthing (licking, 

sucking, chewing, etc.), the type of object being mouthed, and the time that mouthing ceased. 

Children were observed for a total of 5 hours over a two-week period; the observation time 

consisted of twenty 15-minute periods evenly distributed through the week and throughout the 

child’s waking hours. Results of the study are shown in Table 6-12. While no overall pattern 

could be found in the different age groups tested, a Kruskal-Wallis test on the data for all items 

mouthed indicated that there was a significant difference between the age groups. Across all age 

groups and types of items, licking and sucking accounted for 64% of all mouthing behavior. 

Pacifiers and fingers exhibited less variety on mouthing behavior (principally sucking), while 

other items had a higher frequency of licking, biting, or other mouthing. 

The principal advantage of this study is its inclusion of the type of mouthing behavior in 

the survey. However, it suffers from the same limitations as many other survey-based studies, 

including observer bias, a relatively low sample size (especially when broken down by age), and 

a limited geographic scope. The study was conducted in the United Kingdom. 

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6.2.11 AuYeung et al., 2004 

AuYeung et al. videotaped 38 children (20 female and 18 male; ages 1-6 years) for two 

hours during indoor and outdoor play. Children were recruited for the study by calling telephone 

numbers randomly extracted from the telephone directory for an approximately 400 square mile 

portion of the San Francisco peninsula. Families who lived in a residence with a lawn and 

whose annual income was >$35,000 were asked to participate. Videotaping took place between 

August 1998 and May 1999. Most of the videotaping took place during outdoor play, however, 

data were included for several children (one child <2 years old and 8 children >2 years old) who 

had more than 15 minutes of indoor play during their videotaping sessions. The videotapes were 

translated into ASCII computer files using VirtualTimingDeviceTM software, which allowed the 

duration of very short mouthing events to be captured. 

For analysis, the mouthing contacts were divided into indoor and outdoor locations, and 

16 object/surface categories. Mouthing frequency, contact duration, and hourly duration were all 

analyzed by age and gender separately, and in combination. Mouthing contacts were defined as 

contact with the lips, inside of the mouth, and/or the tongue; dietary contacts were ignored. 

Nonparametric tests, such as the Wilcoxon rank sum test were used for the data analyses. 

Mouthing frequencies for indoor locations are shown in Table 6-13. For the one child 

observed that was #24 months, the total mouthing frequency was 84.8 contacts/hour; for children 

>24 months, the median indoor mouthing frequency was 19.5 contacts/hour. Outdoor median 

mouthing frequencies (Table 6-14) were very similar for children #24 months (13.9 

contacts/hour) and >24 months (14.6 contacts/hour). 

For the children in all age groups, the median duration of each mouthing contact was 1-2 

seconds, confirming the observations of other researchers that children’s mouthing contacts are 

of very short duration. For the one child observed that was #24 months, the total indoor 

mouthing duration was 11.1 minutes/hour; for children >24 months, the median indoor mouthing 

duration was 0.9 minutes/hour (Table 6-15). For outdoor environments, median contact 

durations for these age groups decreased to 0.8 and 0.6 minutes/hour, respectively (Table 6-16). 

Both age and gender were found to be associated with differences in mouthing behavior. 

Children #24 months had significantly longer hand-to-mouth contact durations than older 

children (p = 0.04), but no significant age-related differences were found in mouthing 

frequencies or hourly mouthing durations. Girls had significantly higher frequencies of 

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mouthing contacts with the hands and non-dietary objects than boys (p = 0.01 and p = 0.008, 

respectively). Girls’ hand-to-mouth contact durations were also significantly shorter than for 

boys (p = 0.04). 

This study is useful in that it provides distributions of outdoor mouthing frequencies and 

durations with a variety of objects and surfaces. Although indoor mouthing data are also 

included in this study, the results are based on a small number of children (n=9) and a limited 

amount of indoor play. 

6.2.12 Black et al., 2005 

In a recent study, the mouthing and food-handling behavior of 52 children (26 boys and 

26 girls) from 29 homes in the mid-Rio Grande Valley was videotaped as part of a year-long 

pesticide exposure study (Black et al., 2005). The children were grouped into four age 

categories: infants (7-12 months), 1-year-olds (13-24 months), 2-year-olds (25-36 months), and 

preschoolers (37-53 months). Detailed baseline and activity questionnaires were administered, 

and each child was videotaped for four hours. The children were followed by the videographers 

through the house and yard, except for times when they were napping or using the bathroom. 

Records were kept of any significant interruptions during videotaping. Virtual Timing Device 

software, a refinement of the videotape software described by Zartarian et al. (1997) was used to 

analyze the videotapes. Statistical Package for the Social Sciences software was used to analyze 

microactivity data and questionnaire results. 

Most of the children (49 of 52) spent the majority of their time indoors. Of the 39 

children who spent time both indoors and outdoors, all three behaviors (hand-to-mouth, objectto-mouth and food handling) were more frequent and longer while the child was indoors. Handto-mouth activity was recorded during the videotaping for all but one child, a 30-month-old girl. 

For the four age groups, the mean hourly hand-to-mouth frequency ranged from 11.9 (2­

year-olds) to 22.1 (preschoolers), the mean hourly object-to-mouth frequency ranged from 7.8 

(2-year-olds) to 24.4 (infants), and the mean hourly hand-to-food frequency ranged from 10.8 

(infants) to 17.2 (1-year-olds). Significant linear trends were observed for hourly object-tomouth frequency, which decreased as age increased (adjusted R2 = 0.179; P = 0.003), and handto-mouth frequency, which increased with increasing food contact frequency for children over 12 

months (adjusted R2 = 0.291; P = 0.002). Results of this study are shown in Table 6-17. 

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The advantage of this study is that it includes both survey and videotaped information on 

mouthing behavior. The limitations of this study are that the sample population was fairly small 

and was from a limited area (mid-Rio Grande Valley) not representative of the national 

population in general. In addition, the duration data in this study is presented as “% of tape 

time” and cannot be converted to a “minutes/day” format for comparison with other studies. 

6.3 RECOMMENDATIONS 

Due to the paucity of the available research data, mouthing frequency data should be 

used with caution. Table 6-18 summarizes the studies on mouthing behavior that were described 

in this chapter. Table 6-19 summarizes the mean mouthing time and frequencies for hand-tomouth, object-to-mouth, and totals from these studies. Table 6-20 and 6-21 summarize the 

recommended mean values for mouthing time and frequency, respectively, for the recommended 

age categories. The data for each of the standardized age categories in Table 6-20 and 6-21 are 

calculated as a weighted mean of values from studies in this chapter that are relevant to each age 

category. In some cases the age categories used in the studies did not correspond exactly to 

EPA’s recommended age groups. In those cases, the closest age group was used as indicated in 

the Tables 6-20 and 6-21. As mentioned earlier, the studies in this chapter use different units of 

reporting mouthing behavior. If the assessor is interested in estimating exposures during 

macroactivities, then the total amount of time engaged in mouthing behavior (Table 6-20) may 

be the unit of interest. If the assessor is interested in estimating exposures to various 

microactivities, then the number of contacts with hands or objects per unit of time (Table 6-21) 

may be the unit of interest. No data were available for infants from birth to <1 month old. There 

were also no recommendations presented for 1 to <3 months in Table 6-21 and 6-22 or for 3 to 

<6 years in Table 6-20. Smith and Norris (2003) included children from 1 - 5 years of age. 

However, the study is biased high because it included children who were sucking their thumb or 

finger. According to Smith and Norris (2003), this effect is more significant in the older children 

in the study. 

Total mean mouthing time ranged from 7 min/day to 65 min/day, with the lowest value 

corresponding to 2 to 6 years old and the highest value corresponding to 6 to <12 months old. 

Total mean mouthing frequency ranged from 5 contacts/hr to 54 contacts/hr, with the lowest 

value corresponding to the 6 to <11 years old and the highest value corresponding to the 1 to <2 

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years old. Mean hand-to-mouth contact ranged from 4 contacts/hr to 20 contacts/hr, with the 

lowest value corresponding to the 6 to <11 years old and the highest value corresponding to the 6 

to <12 months old. 

Table 6-22 presents the confidence ratings for the recommended values. The overall 

confidence rating was low because sample sizes were small for some of the age groups. 

Children’s behavior is difficult to measure and somewhat subjective because it depends on the 

experience of the observer. 

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6.4 REFERENCES FOR CHAPTER 6 

AuYeung, W; Canales, R; Beamer, P; Ferguson, AC; and Leckie, JO. (2004) Young children’s mouthing behavior: 

An observational study via videotaping in a primarily outdoor residential setting. J Children’s Health 2(3-4):271­

295. 

Black, K; Shalat, SL; Freeman, NCG; Jimenez, M; Donnelly, KC; Calvin, JA. (2005) Children’s mouthing and 

food-handling behavior in an agricultural community on the US/Mexico border. JEAEE. 15:244-251. 

Davis (1995). Soil Ingestion in Children with Pica (Final Report), EPA Cooperative Agreement CR 816334-01 

Freeman, CG; Jimenez, M; Reed, KJ; Gurunathan, S; Edwards, RD; Roy, A; Adgate, JL; Pellizzari, ED; 

Quackenboss, J; Sexton, K; Lioy, PJ. (2001) Quantitative analysis of children’s microactivity patterns: The 

Minnesota children’s pesticide exposure study. JEAEE 11:501-509. 

Greene, M.A. (2002) Mouthing times among young children from observational data. U.S. Consumer Product 

Safety Commission, Bethesda, MD. 

Groot M., Lekkerkerk M., Steenbekkers L. (1998) Mouthing behavior of young children - an observational study. 

H&C onderzoeksrapport 3. 

Gurunathan S., Robson M., Freeman N., Buckley B., Roy A., Meyer R., Bukowski J., and Lioy P. (1998) 

Accumulation of chloropyrifos on residential surfaces and toys accessible to children. Environ. Health Pers. 

106(1):9-16. 

Hubal, E.A.; Sheldon, L.S.; Burke, J.M.; McCurdy, T.R.; Berry, M.R.; Rigas, M.L.; Zartarian, V.G. (2000) 

Children’s exposure assessment: A review of factors influencing children’s exposure, and the data available to 

characterize and assess that exposure. Prepared by U.S. Environmental Protection Agency, National Exposure 

Research Laboratory, RTP, NC. 

Juberg, D.R.; Alfano, K; Coughlin, R.J.; Thompson, K.M. (2001) An Observational Study of Object Mouthing 

Behavior by Young Children. Pediatrics 107 (1) 135-142. 

Reed K., Jimenez M., Freeman N., and Lioy P. (1999) Quantification of children’s hand and mouthing activities 

through a videotaping methodology. JEAEE. 9:513-520. 

Smith, S.A., and Norris, B. (2003). Reducing the risk of choking hazards: mouthing behavior of children aged 1 

month to 5 years. Injury Control and Safety Promotion 10(3):145-154. 

Stanek, E.J.; Calabrese, E.J.; Mundt, K.; Pekow, P.; Yeatts, K.B. (1998) Prevalence of soil mouthing/ingestion 

among healthy children aged 1 to 6. Journal of Soil Contamination. 7(2):227-242. 

Tulve, NS; Suggs, JC; McCurdy, T; Cohen Hubal, EA; Moya, J. (2002) Frequency of mouthing behavior in young 

children. JEAEE. 12:259-264. 

U.S. EPA (1997) Standard operating procedures (SOPs) for residential exposure assessment. Washington, DC: 

Office of Pesticide Programs. 

U.S. EPA, National Exposure Research Laboratory. (1999) Children’s exposure assessment: A review of factors 

influencing children’s exposure, and the data available to characterize and assess that exposure. 

Weaver V., Buckley T., and Groopman J. (1998) Approaches to environmental exposure assessment in children. 

Environ. Health Pers. 106(3):827-831 

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Zartarian V., Ferguson A., and Leckie J. (1997) Quantified dermal activity data from a four-child pilot field study. 

JEAEE 7(4):543-553. 

Zartarian, VG; Ferguson, AC; Leckie, JO. (1998) Quantified mouthing activity data from a four-child pilot field 

study. JEAEE 8(4):543-553. 

6-20
Table 6-1. Extrapolated Total Mouthing Times Minutes per Day (time awake) 

Age (months) No. Children Mean Standard Dev. Minimum Maximum 

3 - 6 5 36.9 19.1 14.5 67 

6 - 12 14 44 44.7 2.4 171.5 

12 - 18 12 16.4 18.2 0 53.2 

18 - 36 11 9.3 9.8 0 30.9 

Note: The object most mouthed in all age groups in the fingers except for the 6 - 12 month group which mostly 

mouthed on toys. 

Source: Groot et al. (1998) 

6-21
Table 6-2. Frequency of Contact (Contacts per Hour) 

Variable Mean Median Minimum Maximum 90th Percentile 

Clothing 66.6 65 22.8 129.2 103.3 

Dirt 11.4 0.3 0 146.3 56.4 

Hand 21.1 14.2 6.3 116.4 43.5 

Hand to mouth 9.5 8.5 0.4 25.7 20.1 

Object 122.9 118.7 56.2 312 175.8 

Object to mouth 16.3 3.6 0 86.2 77.1 

Other 82.9 64.3 8.3 243.6 199.6 

Smooth surface 83.7 80.2 13.6 190.4 136.9 

Textured surface 22.1 16.3 0.2 68.7 52.2 

Source: Reed et al. (1999) 

6-22
Table 6-3. Prevalence of Non-Food Ingestion/Mouthing Behaviors by Child’s Age: Percent of Children Whose 

Parents Reports the Behavior in the Past Month 

Non-Food Prevalence Child’s Age (years) 

Ingestion/mouthing of 

Behavior 1 2 3 4 5 6 3 to <6 a All 

N=171 N=70 N=93 N=82 N=90 N=22 N= 265 N=528 

Outdoor “soil” mouthing/Ingestion 

Sand, stones % > Monthly 54 26 19 9 7 9 12 27 

% > Weekly 36 10 6 2 4 5 4 16 

% Daily 17 0 2 1 1 5 1 6 

Grass, leaves,

flowers % > Monthly 48 16 24 13 9 5 16 26 

% > Weekly 34 7 14 4 6 0 8 16 

% Daily 16 0 2 1 1 0 1 6 

Twigs, sticks, woodchips % > Monthly 42 23 13 13 11 5 12 23 

% > Weekly 29 7 9 5 7 0 7 14 

% Daily 12 0 0 1 0 0 0 4 

Soil, dirt % > Monthly 38 21 5 7 3 9 5 18 

% > Weekly 24 7 3 2 1 9 2 10 

% Daily 11 0 1 0 1 0 1 4 

Dust, lint, dustballs % > Monthly 14 4 2 0 0 5 1 6 

% > Weekly 7 1 1 0 0 0 0 3 

% Daily 2 0 0 0 0 0 0 1 

Plaster, chalk % > Monthly 8 10 3 2 3 5 3 5 

% > Weekly 5 3 0 1 0 0 0 2 

% Daily 2 0 0 1 0 0 0 1 

Paintchips, splinters % > Monthly 6 0 0 4 1 0 2 3 

% > Weekly 2 0 0 1 0 0 0 1 

% Daily 0 0 0 0 0 0 0 0 

General mouthing of objects 

Other toys % > Monthly 88 53 64 44 42 23 50 62 

% > Weekly 82 44 42 26 28 9 32 49 

% Daily 63 27 20 9 7 5 12 30 

Paper, cardboard,

tissues % > Monthly 71 37 32 23 18 14 24 41 

% > Weekly 54 23 20 12 7 9 13 28 

% Daily 28 9 8 5 2 5 5 13 

Teething toys % > Monthly 65 29 15 4 3 9 8 29 

% > Weekly 55 16 9 1 1 9 4 22 

% Daily 44 6 6 0 0 9 2 17 

6-23
Non-Food 

Ingestion/mouthing 

Prevalence 

of 

Behavior 

Child’s Age (years) 

1 2 3 4 5 6 3 to <6 a All 

N=171 N=70 N=93 N=82 N=90 N=22 N= 265 N=528 

Crayons, pencils, erasers % > Monthly 56 54 46 50 41 36 46 50 

% > Weekly 41 37 25 27 26 27 26 32 

% Daily 19 17 4 6 4 18 5 12 

Blankets, cloth % > Monthly 51 21 26 22 22 14 23 32 

% > Weekly 42 17 17 18 14 14 16 25 

% Daily 29 11 9 13 7 5 10 16 

Shoes, Footware % > Monthly 50 23 8 7 2 5 6 22 

% > Weekly 42 10 3 2 1 5 2 16 

% Daily 20 1 0 0 0 0 0 7 

Clothing % > Monthly 49 34 37 43 26 27 35 39 

% > Weekly 39 24 23 28 16 14 22 27 

% Daily 25 7 11 9 6 14 9 14 

Other items % > Monthly 41 30 30 23 21 27 25 31 

% > Weekly 35 26 24 15 10 14 16 23 

% Daily 22 11 15 7 6 5 9 14 

Crib, chairs,

furniture % > Monthly 37 11 8 10 4 5 7 17 

% > Weekly 26 9 3 5 2 0 3 11 

% Daily 13 3 1 1 0 0 1 5 

Sucking of fingers, etc 

Suck fingers/thumb % > Monthly 67 41 43 57 39 41 46 52 

% > Weekly 60 27 31 43 31 18 35 41 

% Daily 44 21 22 26 24 14 24 30 

Suck feet or toes % > Monthly 37 14 12 11 3 0 9 18 

% > Weekly 23 4 3 2 1 0 2 9 

% Daily 8 1 0 1 0 0 0 3 

Use pacifier % > Monthly 24 9 6 2 2 5 3 11 

% > Weekly 22 9 5 2 2 0 3 10 

% Daily 20 6 5 1 1 0 2 9 

Suck hair % > Monthly 1 3 8 9 10 5 9 5 

% > Weekly 1 3 2 2 4 5 3 2 

% Daily 1 1 1 0 2 0 1 1 

6-24
Non-Food Prevalence Child’s Age (years) 

Ingestion/mouthing of 

Behavior 1 2 3 4 5 6 3 to <6 a All 

N=171 N=70 N=93 N=82 N=90 N=22 N= 265 N=528 

“Disgusting” object mouthing/ingestion 

Soap, detergent,

shampoo 

% > Monthly 48 34 24 17 9 9 17 29 

% > Weekly 37 27 14 11 6 9 10 21 

% Daily 15 14 3 2 0 0 2 8 

Plastic, plastic wrap % > Monthly 32 19 8 7 9 0 8 17 

% > Weekly 22 11 3 4 4 0 4 10 

% Daily 7 4 1 0 1 0 1 3 

Cigarette butts,

tobacco % > Monthly 16 6 5 4 3 5 4 8 

% > Weekly 10 4 4 1 2 5 2 5 

% Daily 4 0 1 1 1 0 1 2 

Matches % > Monthly 6 4 1 4 1 0 2 4 

% > Weekly 2 3 1 1 1 0 1 2 

% Daily 1 0 0 0 0 0 0 0 

Insect % > Monthly 5 1 2 4 2 0 3 3 

% > Weekly 2 0 1 4 2 0 2 2 

% Daily 0 0 1 2 2 0 2 1 

Other ingestion and behaviors 

Toothpaste % > Monthly 63 97 92 94 93 86 93 84 

% > Weekly 60 94 91 93 92 86 92 82 

% Daily 52 87 86 93 89 82 89 77 

Chew gum % > Monthly 18 56 76 76 91 100 81 58 

% > Weekly 10 40 60 60 69 68 63 43 

% Daily 3 17 18 13 21 36 17 14 

Bite nails % > Monthly 8 26 31 29 33 59 31 24 

% > Weekly 5 23 24 20 26 45 23 18 

% Daily 2 7 12 9 10 14 10 7 

Suck hair % > Monthly 62 76 85 96 88 73 89 78 

% > Weekly 57 64 77 88 81 68 82 71 

% Daily 42 39 43 55 52 45 50 45 

a

Weighted mean of 3-, 4-, and 5-year-olds’ data calculated by EPA to conform to standardized age categories 

used in this Handbook. 

Source: Stanek et al. (1998). 

6-25 
Table 6-4. Percent of Children with Reported Behaviors From the Telephone Survey Conducted in the 

MNCPES (n = 168). 

Reported Behavior 3-4 Years (n=27) 

Percent Reported by Age Group 

5-9 Years (n=93) 10-12 Years (n=48) 

Hand-to-mouth 56 39 35* 

Non-feed items in mouth 52 31 37 

Eats food dropped on floor 48 10 4** 

Eats most food without 

utensils 

37 29 19* 

Puts paint chips in mouth 0 0 0 

x2 test, *P<0.10 between youngest and oldest groups; **significant difference across three groups. 

Source: Freeman et al., 2001 

Table 6-5. Median (Mean) Observed Activity Rate (Hand Contacts Per Hour) Based on 4 Hours of 

Observation Per Person. 

Observed Activity 

Age 3-4 (n=3)

Age Category (Years) 

 5-6 (n=7) 7-8 (n=4) 10-12 (n=5) 

Object-to-mouth*** 3 (6) 0 (1) 0 (1) 0 (1) 

Hand-to-mouth 3.5 (4) 2.5 (8) 3 (5) 2 (4) 

Touch clothing** 26 (34) 22 (26) 50 (54) 35 (53) 

Touch textured surface* 40 (52) 20 (32) 22 (58) 16 (24) 

Touch smooth surface 134 (151) 111 (120) 120 (155) 94 (96) 

Touch object 130 (153) 117 (132) 111 (164) 127 (179) 

Kruskal Wallis test comparison across four age groups: *P=0.1108; **P=0.0796; ***P=0.002. 

Source: Freeman et al., 2001 

6-26
Table 6-6. Comparison of Observed Activities for Boys and Girls (Mean). 

Observed Activity Boys (n=8) Girls (n=11) 

Hours since last hand wash 5.9 3.5 

Time spent outdoors (minutes)* 104.4 54.0 

Time spent indoors (minutes)* 134.3 186.0 

Hand-to-mouth indoors/hour* 4.7 8.1 

Hand-to-mouth outdoors/hour 1.7 2.3 

Object-to-mouth indoors/hour 1.0 2.6 

Object-to-mouth outdoors/hour 0.1 1.0 

*P<0.05 by Mann-Whitney test. 

Source: Freeman et al., 2001 

Table 6-7. Mouthing times for Pacifiers and Other Objects, by Age Category 

Object Type 

Age 0 to 18 months Age 19 to 36 months 

All Respondents 

(minutes/day) 

Doers Onlya 

(minutes/day) 

All Respondents 

(minutes/day) 

Doers Onlya 

(minutes/day) 

Pacifier 108 (n = 107) 221 (n=52) 126 (n=110) 462 (n=52) 

Non-Pacifier

 Teether 

 Plastic Toy

 Other Objects 

33 (n=107) b 

6 (n=107) 

17 (n=107) 

9 (n=107) 

not calculated 

20 (n=34) 

28 (n=66) 

22 (n=46) 

5 (n=110) b 

0 (n=110) 

2 (n=110) 

2 (n=110) 

not calculated 

30 (n=1) 

11 (n=21) 

15 (n=18) 

a

Doers only analysis refers to means calculated for the subset of the sample population that participated in the activity; zeroes are eliminated from

the calculation of the mean. b

Total for non-pacifiers may not equal sum of individual items due to rounding.

Source: Juberg et al., 2001 

6-27
Table 6-8 Average Mouthing Time by Object Category and Age (min/hr) 

Object Category All Ages 3-12 

months 

12-24 

months 

24-36 

months 

All Objects 7.7 10.5 7.3 5.3 

Pacifiers 2.6 3.4 2.6 1.8 

Non Pacifiers

 All Soft Plastic Items 

 Soft Plastic Items Not Food Contact

 Soft Plastic Toys, Teethers and Rattles

 Soft Plastic Toys

 Soft Plastic Teethers and Rattles 

Other Soft Plastic Items 

5.1 

0.4 

0.3 

0.2 

0.1 

0.1 

0.1 

7.1 

0.5 

0.4 

0.3 

0.1 

0.2 

0.1 

4.7 

0.4 

0.3 

0.2 

0.2 

0.0 

0.1 

3.5 

0.4 

0.2 

0.1 

0.1 

0.0 

0.1 

Soft Plastic Food Contact Items 0.1 0.0 0.1 0.2 

Anatomy 1.8 2.4 1.7 1.2 

Non Soft Plastic Toys, Teethers and Rattles 0.9 1.8 0.6 0.2 

Other Items 2.1 2.5 2.1 1.7 

Source : Greene, 2002 

6-28
Table 6-9. Mouthing Time Statistics for Various Objects (min/hr) 

Age Group Mean (SD) Median 95 Percentile th 99 Percentile th 

All Items 

3-12 months 

12-24 months 

24-36 months 

10.5 (7.3) 

7.3 (6.8) 

5.3 (8.2) 

9.6 

5.5 

2.4 

26.2 

22.0 

15.6 

39.8 

28.8 

47.8 

Non Pacifiers 

3-12 months 

12-24 months 

24-36 months 

7.1 (3.6) 

4.7 (3.7) 

3.5 (3.6) 

6.9 

3.6 

2.3 

13.1 

12.8 

12.8 

14.4 

18.9 

15.6 

All Soft Plastic Items 

3-12 months 

12-24 months 

24-36 months 

0.5 (0.6) 

0.4 (0.4) 

0.4 (0.6) 

0.1 

0.2 

0.1 

1.8 

1.3 

1.6 

2.5 

1.9 

2.9 

Soft Plastic Items Not Food Contact 

3-12 months 

12-24 months 

24-36 months 

0.4 (0.6) 

0.3 (0.4) 

0.2 (0.4) 

0.1 

0.1 

0.0 

1.8 

1.1 

1.3 

2.0 

1.5 

1.8 

Soft Plastic Toys, Teethers, and Rattles 

3-12 months 

12-24 months 

24-36 months 

0.3 (0.5) 

0.2 (0.3) 

0.1 (0.2) 

0.1 

0.0 

0.0 

1.8 

0.9 

0.2 

2.0 

1.3 

1.6 

Soft Plastic Toys 

3-12 months 

12-24 months 

24-36 months 

0.1 (0.3) 

0.2 (0.3) 

0.1 (0.2) 

0.0 

0.0 

0.0 

0.7 

0.9 

0.2 

1.1 

1.3 

1.6 

Soft Plastic Teethers and Rattles 

3-12 months 

12-24 months 

24-36 months 

0.2 (0.4) 

0.0 (0.1) 

0.0 (0.1) 

0.0 

0.0 

0.0 

1.0 

0.1 

0.0 

2.0 

0.6 

1.0 

Other Soft Plastic Items 

3-12 months 

12-24 months 

24-36 months 

0.1 (0.2) 

0.1 (0.1) 

0.1 (0.3) 

0.0 

0.0 

0.0 

0.8 

0.4 

0.5 

1.0 

0.6 

1.4 

6-29
Table 6-9. Mouthing Time Statistics for Various Objects (min/hr) 

Age Group Mean (SD) Median 95 Percentile th 99 Percentile th 

Soft Plastic Food Contact Items 

3-12 months 

12-24 months 

24-36 months 

0.0 (0.2) 

0.1 (0.2) 

0.2 (0.4) 

0.0 

0.0 

0.0 

0.3 

0.7 

1.2 

0.9 

1.2 

1.9 

Anatomy 

3-12 months 

12-24 months 

24-36 months 

2.4 (2.8) 

1.7 (2.7) 

1.2 (2.3) 

1.5 

0.8 

0.4 

10.1 

8.3 

5.1 

12.2 

14.8 

13.6 

Non Soft Plastic Toys, Teethers, and Rattles 

3-12 months 

12-24 months 

24-36 months 

1.8 (1.8) 

0.6 (0.8) 

0.2 (0.4) 

1.3 

0.3 

0.1 

6.5 

1.8 

0.9 

7.7 

4.6 

2.3 

Other Items 

3-12 months 

12-24 months 

24-36 months 

2.5 (2.1) 

2.1 (2.0) 

1.7 (2.6) 

2.1 

1.4 

0.7 

7.8 

6.6 

7.1 

8.1 

9.0 

14.3 

Pacifiers 

3-12 months 

12-24 months 

24-36 months 

3.4 (6.9) 

2.6 (6.5) 

1.8 (7.9) 

0.0 

0.0 

0.0 

19.5 

19.9 

4.8 

37.3 

28.6 

46.3 

Source: Greeene, 2002 

6-30
Table 6-10. Estimated Daily Mouthing Times for Various Objects (min/day) 

Age Group Mean 

(confidence 

intervals) 

Median

 (confidence 

intervals) 

95th Percentile 

(confidence 

intervals) 

99th Percentile 

(confidence 

intervals) 

Non Pacifiers 

3-12 months 

12-24 months 

24-36 months 

70.1 

(60.6 - 79.8) 

47.4 

(38.9 -57.1) 

37.0 

(27.0 - 48.5) 

65.6 

(52.3 - 78.2) 

37.0 

(28.7 - 49.9) 

23.8 

(18.4 - 29.3) 

134.4 

(117.1 - 153.2) 

121.5 

(85.2 - 166.0) 

124.3 

(70.9 - 173.3) 

153.1 

(129.6 - 180.6) 

180.3 

(123.6 - 235.5) 

167.9 

(104.0 - 208.0) 

Soft Plastic Items 

3-12 months 

12-24 months 

24-36 months 

4.4 

(3.0 - 6.1) 

3.8 

(2.8 - 4.9) 

4.2 

(2.5 - 6.1) 

1.5 

(0.3 - 3.7) 

2.2 

(1.0 - 3.8) 

1.5 

(0.2 - 3.0) 

17.5 

(12.2 - 23.3) 

13.0 

(9.6 - 17.8) 

18.5 

(9.6 - 29.4) 

23.0 

(16.2 - 30.1) 

18.9 

(12.8 - 23.8) 

28.0 

(15.9 - 37.6) 

Soft Plastic Toys 

3-12 months 

12-24 months 

24-36 months 

1.3 

(0.7 - 2.0) 

1.9 

(1.2 - 2.6) 

0.8 

(0.3 - 1.6) 

0.0 

(0.0 - 0.3) 

0.1 

(0.0 - 0.6) 

0.0 

(0.0 - 0.2) 

7.1 

(3.9 - 11.0) 

8.8 

(5.6 - 11.7) 

3.3 

(1.4 - 16.3) 

10.5 

(5.8 - 13.7) 

12.6 

(9.0 - 16.0) 

12.1 

(2.0 - 21.0) 

Note: Based on 5000 bootstrap samples. 

Source: Greene, 2002 

6-31
Table 6-11. Variability in Objects Mouthed for Different Age Groups. 

Variable All Subjects #24 Months >24 Months 

Meanb Median 95% CIc Meanb Median 95% CIc Meanb Median 95% CIc 

na (events/h) (events/h) (events/h) na (events/h) (events/h) (events/h) na (events/h) (events/h) (events/h) 

Mouth-body 186 8 2 2-3 69 10 4 3-6 117 7 1 0.8-1.3 

Mouth-hand 186 16 11 9-14 69 18 12 9-16 117 16 9 7-12 

Mouth-surface 186 4 1 0.8-1.2 69 7 5 3-8 117 2 1 0.9-1.1 

Mouth-toy 186 27 18 14-23 69 45 39 31-48 117 17 9 7-12 

Total events 186 56 44 36-52 69 81 73 60-88 117 42 31 25-39 

a

 Number of observations. b

 Arithmetic mean. 

c The 95% confidence limits apply to median. Values were calculated in logs and converted to original units. 

Source: Tulve et al., 2002 

6-32
Table 6-12. Mouthing Duration by Age Group for Pacifiers, Fingers, Toys, and Other Objects 

Item Mouthed 

Age Group, sample size (n), and Mouthing Duration (hours:minutes:seconds) 

1-3 

months 

3-6 

months 

6-9 

months 

9-12 

months 

12-15 

months 

15-18 

months 

18-21 

months 

21-24 

months 

2 years 3 years 4 years 5 years 

n = 9 n = 14 n = 15 n = 17 n = 16 n = 14 n = 16 n = 12 n = 39 n = 31 n = 29 n = 24

 Dummy (Pacifier) 0:47:13 0:27:45 0:14:36 0:41:39 1:00:15 0:25:22 1:09:02 0:25:12 0:32:55 0:48:42 0:16:40 0:00:20

 Fingers 0:18:22 0:49:03 0:16:54 0:14:07 0:08:24 0:10:07 0:18:40 0:35:34 0:29:43 0:34:42 0:19:26 0:44:06

 Toys 0:00:14 0:28:20 0:39:10 0:23:04 0:15:18 0:16:34 0:11:07 0:15:46 0:12:23 0:11:37 0:03:11 0:01:53

 Other Objects 0:05:14 0:12:29 0:24:30 0:16:25 0:12:02 0:23:01 0:19:49 0:12:53 0:21:46 0:15:16 0:10:44 0:10:00

 Not Recorded 0:00:45 0:00:24 0:00:00 0:00:01 0:00:02 0:00:08 0:00:11 0:14:13 0:02:40 0:00:01 0:00:05 0:02:58

 Total (all objects) 1:11:48 1:57:41 1:35:11 1:35:16 1:36:01 0:15:13 1:58:49 1:43:39 1:39:27 1:50:19 0:50:05 0:59:17 

Source: Smith and Norris, 2003 

6-33
Table 6-13. Indoor Mouthing Frequency (Contacts/Hour).a 

Age (months) n Statistic Hands Total non-dietary 

b 

#24 1 73.5 84.8 

>24 8 Mean 13.9 22.7 

Median 13.3 19.5 

Range 2.2 - 34.1 2.8 - 51.3 

All agesc 9 Mean 20.5 29.6 

Median 14.8 22.1 

Range 2.5 - 70.4 3.2 - 82.2 

a

 Shows data from children who had more than 15 minutes in view indoors.

b

 All object/surface categories included: animal, clothes/towels, fabric, hands, metal, non-dietary water,

paper/wrapper, plastic, skin, toys, vegetation/grass, and wood. c

 Ages 1-6 years.

Source: AuYeung et al., 2004

6-34
Table 6-14. Outdoor Mouthing Frequency (Contacts/Hour).

Age (months) n Statistic Hands Total non-dietary a

#24 8 Mean 13.0 20.4 

Median 7.0 13.9 

Range 1.3 - 47.7 6.2 - 56.4 

>24 30 Mean 11.3 17.7 

5 percentile th 0.2 0.6 

25 percentile th 4.7 7.6 

Median 8.6 14.6 

75 percentile th 14.8 22.4 

95 percentile th 27.7 43.8 

99 percentile th 39.5 53.0 

All agesc 38 Mean 11.7 18.3 

5 percentile th 0.4 0.8 

25 percentile th 4.4 9.2 

Median 8.4 14.5 

75 percentile th 14.8 22.4 

95 percentile th 31.5 51.7 

99 percentile th 47.6 56.6 

a

 All object/surface categories included: animal, clothes/towels, fabric, hands, metal, non-dietary water,

paper/wrapper, plastic, skin, toys, vegetation/grass, and wood. c

 Ages 1-6 years.

Source: AuYeung et al., 2004

6-35
Table 6-15. Indoor Mouthing Contact Duration (Minutes/Hour).a 

Age (months) n Statistic Hands Total non-dietary 

b 

#24 1 10.7 11.1 

>24 8 Mean 0.7 1.2 

Median 0.7 0.9 

Range 0 - 1.8 0.1 - 3.6 

All agesc 9 Mean 1.8 2.3 

Median 0.7 0.9 

Range 0 - 10.0 0.1 - 10.5 

a

 Shows data from children who had more than 15 minutes in view indoors.

b

 All object/surface categories included: animal, clothes/towels, fabric, hands, metal, non-dietary water,

paper/wrapper, plastic, skin, toys, vegetation/grass, and wood. c

 Ages 1-6 years.

Source: AuYeung et al., 2004

6-36
Table 6-16. Outdoor Mouthing Contact Duration (Minutes/Hour).

Age (months) n Statistic Hands Total non-dietary a

#24 8 Mean 2.7 3.1 

Median 0.4 0.8 

Range 0 - 14.7 0.2 - 15.0 

>24 30 Mean 0.4 0.7 

5 percentile th 0 0 

25 percentile th 0.1 0.2 

Median 0.2 0.6 

75 percentile th 0.4 1.0 

95 percentile th 1.2 2.1 

99 percentile th 2.2 2.5 

All agesc 38 Mean 0.9 1.2 

5 percentile th 0 0 

25 percentile th 0.1 0.2 

Median 0.2 0.6 

75 percentile th 0.6 1.2 

95 percentile th 2.6 2.9 

99 percentile th 11.2 11.5 

a

 All object/surface categories included: animal, clothes/towels, fabric, hands, metal, non-dietary water,

paper/wrapper, plastic, skin, toys, vegetation/grass, and wood. c

 Ages 1-6 years.

Source: AuYeung et al., 2004

6-37
Table 6-17. Videotaped Mouthing and Food-handling Activity as Median Hourly Frequency (Contacts/Hour) and Median 

Duration (% of Tape Time) (Mean ± SD) 

Age N Hand to mouth 

Frequency Duration 

Object to Mouth 

Frequency Duration 

Food 

Frequency Duration 

Infant 1 

3 

14 (19.8 ± 

14.5) 

3.0 (4.6 ± 6.0) 18.1 (24.4 ± 

11.6) 

3.1 (4.0 ± 2.4) 10.0 (10.8 ± 

9.0) 

3.9 (7.0 ± 7.4) 

1 year old 1 

2 

13.3 (15.8 ± 

8.7) 

2.2 (3.8 ± 7.0) 8.4 (9.8 ± 6.3) 1.3 (1.6 ± 1.2) 16.1 (17.2 ± 

14.0) 

5.2 (6.8 ± 5.8) 

2 year old 1 

8 

9.9 (11.9 ± 

9.3) 

1.3 (1.5 ± 1.3) 5.5 (7.8 ± 5.8) 0.9 (1.3 ± 1.1) 13.9 (14.7 ± 

10.9) 

5.6 (5.0 ± 3.8) 

Preschool 9 19.4 (22.1 ± 

22.1) 

1.5 (3.1 ± 3.4) 8.4 (10.1 ± 

12.4) 

1.9 (3.0 ± 3.9) 10.2 (15.7 ± 

11.8) 

5.6 (4.7 ± 2.6) 

Source: Black et al. (2005) 

6-38
Table 6-18. Summary of Studies on Mouthing Behavior 

Study Population Size Population Studied 

Groot et al. 1998 42 3-36 months in Netherlands 

children from well educated parents 

Reed et al. 1999 30 20 children 3-6 years 

10 children 2-5 years 

Day care and residential settings 

Zartarian 1997 and 1998 4 2.5-4.2 years 

children of farm workers 

Davis 1995 92 10-60 months 

Washington State 

Stanek et al. 1998 355 1-6 years 

private medical clinic 

Springfield, Massachusetts 

Juberg et al., 2001 Phase 1 & 2: 217 

Phase 3: 168 

Phase 1 & 2: less than 3 yrs old 

Phase 3: 3 to 18 months 

Western New York - research center and day 

care 

Freeman et al., 2001 168 3-12 years 

Urban and rural areas of Minnesota 

Greene, 2002 169 3 - 36 months 

Chicago and Houston metropolitan area 

Tulve et al., 2002 72 10-60 months 

Indoor home environment 

Smith and Norris, 2003 236 Ages 1 month to 5 years 

in-home 

Netherlands 

AuYeung et al., 2004 38 Ages 1-6 years 

Indoor and outdoor home environment 

San Francisco peninsula 

Black et al., 2005 52 7-53 months 

Mid-Rio Grande Valley 

Agricultural community 

6-39
Table 6-19. Summary of Mouthing Frequency Data 

Age (months) Mean Mouthing Frequency/Time Population Size Reference 

Hand-to-mouth Object-to-Mouth Total 

10-60 55 min/day EPA analysis based on 

Davis 1995 

2.5-4.2 years 9 contacts/hr 4 Zartarian 1997 

3-6 

6-12 

12-18 

18-36

 37 min/day 

 44 min/day 

16 min/day 

9 min/day 

5 

14 

12 

11 

Groot et al. 1998 

2-6 years 9.5 contacts/hr 16.3 contacts/hr 25.8 contacts/hr 30 Reed et al. 1999 

3-4 years 

5-6 years 

7-8 years 

10-12 years

 4 contacts/hr 

8 contacts/hr 

5 contacts/hr 

4 contacts/hr 

6 contacts/hr 

1 contacts/hr 

1 contacts/hr 

1 contacts/hr 

10 contacts/hr 

9 contacts/hr 

6 contacts/hr 

5 contacts/hr 

3 

7 

4 

5 

Freeman et al. 2001 

0-18 

18-36 

70 min/day a 

56 min/day a 

146 

40 

Juberg et al, 2001 

3-12 

12-24 

24-36 

2.4 min/hr; 26 min/day b 

1.7 min/hr; 18 min/day b 

1.2 min/hr; 12 min/day b 

70 min/day 

48 min/day 

37 min/day 

64 

60 

45 

Greene, 2002 

<24 18 contacts/hr 62 contacts/hr 81 ± 7 contacts/hr 28 Tulve et al. 2002 

>24 16 contacts/hr 26 contacts/hr 42 ± 4 contacts/hr 44 

6-40
c 

Table 6-19. Summary of Mouthing Frequency Data 

Age (months) Mean Mouthing Frequency/Time Population Size Reference 

Hand-to-mouth Object-to-Mouth Total 

1-3 

3-6 

6-9 

9-12 

12-15 

15-18 

18-21 

21-24 

2 years 

3 years 

4 years 

5 years 

50 min/day c 

96 min/day c 

77 min/day c 

98 min/day c 

36 min/day c 

39 min/day c 

80 min/day c 

113 min/day c 

148 min/day c 

199 min/day c 

171 min/day c 

543 min/day c 

29 min/day 

132 min/day 

251 min/day 

156 min/day 

157 min/day 

136 min/day 

99 min/day 

142 min/day 

304 min/day 

179 min/day 

96 min/day 

64 min/day 

79 min/day c 

228 min/day c 

328 min/day c 

254 min/day c 

193 min/day c 

175 min/day c 

179 min/day c 

255 min/day c 

452 min/day c 

378 min/day c 

267 min/day c 

607 min/day c 

9 

14 

15 

17 

16 

14 

16 

12 

39 

31 

29 

24 

Smith and Norris 2003 

#24 

2-6 

7 contacts/hr 

12 min/day b 

12 contacts/hr 

2 min/day b 

1 contact/hr 

1 min/day b 

8 contacts/hr 

1 min/day b 

9 contacts/hr 

12 min/day b 

20 contacts/hr 

3 min/day b 

9 

38 

AuYeung et al., 2004 d 

7-12 

13-24 

25-36 

37-53 

20 contacts/hr 

16 contacts/hr 

12 contacts/hr 

22 contacts/hr 

24 contacts/hr 

10 contacts/hr 

8 contacts/hr 

10 contacts/hr 

44 contacts/hr 

26 contacts/hr 

20 contacts/hr 

32 contacts/hr 

13 

12 

18 

9 

Black et al. 2005 

a

 Doers only from Table 6-8; totals calculated by adding all non pacifier objects b

 Daily mouthing estimated using 10 hours awake for children under 2 years old and 10.7 hours awake for children 2-3 years old from Greene (2002). 

Includes finger/thumb sucking 

d Includes indoor and outdoor data. 

6-41
Table 6-20. Summary of Recommended Values for Total Mouthing Time (minutes per day) a 

Age 

Mean Mouthing 

Time 

(min/day) 

Source 

birth to <1 month no data no data available 

1 to <3 months no data no data available ( Smith and Norris, 2003 were not used because thumb/finger 

sucking had a significant effect on results) 

3 to <6 months 27 Weighted mean of:

 Groot et al., 1998 and Reed et al. 1999 

6 to <12 months 65 Weighted mean of:

 Groot et al., 1998 and Greene, 2002 (used 3-12 months) 

1 to <2 years 39 Weighted mean of: 

Groot et al., 1998 (used 12-18 months) 

Greene, 2002 

AuYeung et al., 2004 (used #24 months) 

2 to <3 years 32 Weighted mean of: 

Groot et al., 1998 (used 18-36 month group) 

Greene, 2002 

3 to <6 years no data no data available (Smith and Norris (2003)data were not used because 

thumb/finger sucking had a significant effect on results) 

2 to 6 years 7 AuYeung et al., 2004 

a Excludes mouthing pacifiers 

6-42
Table 6-21. Summary of Recommended Values for Mouthing Frequency (contacts per hour) 

Age 

Mean Mouthing Frequency Reference 

Hand-to-Mouth Object-to-Mouth Total 

birth to < 1 mo no data no data no data 

1 to <3 mo no data no data no data 

6 to <12 mo 20 contacts/hr 24 contacts/hr 44 contacts/hr Black et al. 2005 

1 to <2 years 16 contacts/hr 38 contacts/hr 54 contacts/hr Weighted mean of: 

Tulve et al., 2002, AuYeung et al, 

2004, and Black et al., 2005 

2 to <3 years 12 contacts/hr 8 contacts/hr 20 contacts/hr Hand-to-mouth is weighted mean 

of Zartarian 1997 and Black et al. 

2005 

Object-to-mouth is based on Black 

et al. 2005 

Total is based on Black et al. 2005 

2 to 6 years 12 contacts/hr 8 contacts/hr 20 contacts/hr AuYeung et al, 2004 

3 to <6 years 14 contacts/hr 19 contacts/hr 32 contacts/hr Weighted mean of:

 Reed et al. 1999, Freeman et al. 

2001,Tulve et al. 2002, and Black 

et al. 2005 

6 to < 11 years 4 contacts/hr 1 contacts/hr 5 contacts/hr Based on weighted mean of 7-8 

and 10-12 years old from Freeman 

et al. 2001 

1 year 

2 years 

3 years 

4 years 

5 years 

6 years 

3 to <6 years 

Contact frequency with specific objects and surfaces (percent 

doing daily, weekly, and monthly) 

Stanek et al., 1998 (Table 6-3) 

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Table 6-22. Confidence in Mouthing Behavior Recommendations 

Considerations Rationale Rating 

Study Elements 

Peer Review There are eleven studies; nine of the studies are from 

peer-reviewed journals; one is an EPA analysis of raw 

data from a contractor's report to EPA and one is a 

government report 

High 

Accessibility Studies in journals have wide circulation. 

Contractor's report only available through EPA 

Medium 

Reproducibility Can follow analysis, but cannot reproduce the data 

unless raw data are provided. 

Medium 

Focus on factor of Interest Studies focused on mouthing behavior as well as other 

hand contacts. 

High 

Data pertinent to U.S. All but one of the studies were conducted in the U.S. High 

Primary data Analyses were done on primary data. EPA did the 

analysis of the raw data from Davis et al. (1995) and 

composited data from the Stanek et al. (1998) study to 

conform to standardized age groupings. 

High 

Currency Recent studies were evaluated. High 

Adequacy of data collection 

period 

Data were collected for a period of several days, not 

enough to represent seasonal variations. 

Medium 

Validity of Approach Measurements were made by observation methods. Both 

surveys and videotaping were used. Videotaping 

techniques may be more reliable, but resource intensive. 

Medium 

Representativeness of the 

population 

Data for some age groups were not available. An effort 

was made to consider age and gender, but sample sizes 

were small; SES factors not evaluated 

Low 

Characterization of variability An effort was made to consider age and gender, data for 

infants and older children are fairly limited. 

Low 

Lack of bias in study design Subjects were selected from volunteers. Medium 

Measurement error Measuring children's behavior is difficult and somewhat 

subjective and depends on the experience of the 

observer. 

Medium 

Other Elements 

Number of studies Eleven studies were evaluated Medium 

Agreement between researchers There is general agreement among the researchers. High 

Overall Rating Although there are eleven studies, for some of the age 

groups sample size was small, variability in the 

population cannot be assessed. Variation in behavior 

due to seasons cannot be evaluated. Measuring 

children's behavior is difficult. 

Low 

6-44