A Meta‐Analysis of Children's Hand‐to‐Mouth Frequency Data for Estimating Nondietary Ingestion Exposure

Abstract

Because of their mouthing behaviors, children have a higher potential for exposure to available chemicals through the nondietary ingestion route; thus, frequency of hand-to-mouth activity is an important variable for exposure assessments. Such data are limited and difficult to collect. Few published studies report such information, and the studies that have been conducted used different data collection approaches (e.g., videography versus real-time observation), data analysis and reporting methods, ages of children, locations, and even definitions of "mouthing." For this article, hand-to-mouth frequency data were gathered from 9 available studies representing 429 subjects and more than 2,000 hours of behavior observation. A meta-analysis was conducted to study differences in hand-to-mouth frequency based on study, age group, gender, and location (indoor vs. outdoor), to fit variability and uncertainty distributions that can be used in probabilistic exposure assessments, and to identify any data gaps. Results of this analysis indicate that age and location are important for hand-to-mouth frequency, but study and gender are not. As age increases, both indoor and outdoor hand-to-mouth frequencies decrease. Hand-to-mouth behavior is significantly greater indoors than outdoors. For both indoor and outdoor hand-to-mouth frequencies, interpersonal, and intra-personal variability are approximately 60% and approximately 30%, respectively. The variance difference among different studies is much bigger than its mean, indicating that different studies with different methodologies have similar central values. Weibull distributions best fit the observed data for the different variables considered and are presented in this article by study, age group, and location. Average indoor hand-to-mouth behavior ranged from 6.7 to 28.0 contacts/hour, with the lowest value corresponding to the 6 to <11 year olds and the highest value corresponding to the 3 to <6 month olds. Average outdoor hand-to-mouth frequency ranged from 2.9 to 14.5 contacts/hour, with the lowest value corresponding to the 6 to <11 year olds and the highest value corresponding to the 6 to <12 month olds. The analysis highlights the need for additional hand-to-mouth data for the <3 months, 3 to <6 months, and 3 to <6 year age groups using standardized collection and analysis because of lack of data or high uncertainty in available data. This is the first publication to report Weibull distributions as the best fitting distribution for hand-to-mouth frequency; using the best fitting exposure factor distribution will help improve estimates of exposure. The analyses also represent a first comprehensive effort to fit hand-to-mouth frequency variability and uncertainty distributions by indoor/outdoor location and by age groups, using the new standard set of age groups recommended by the U.S. Environmental Protection Agency for assessing childhood exposures. Thus, the data presented in this article can be used to update the U.S. EPA's Child-Specific Exposure Factors Handbook ...

Quantified outdoor micro-activity data for children aged 7–12-years old

“…Mouthing duration of hands, toys and non-dietary objects also decreased with age among the 1-12-year-old children. However, most current methods to estimate non-dietary ingestion incorporate frequency but not mouthing duration (Zartarian et al, 2000;Canales and Leckie, 2007;Nicas and Best, 2008;Stapleton et al, 2008;Tulve et al, 2010). It is likely with a longer mouthing duration that a greater surface area of the object or hand would be mouthed, which could lead to a greater amount of ingested contaminant.…”

“…It is not clear why the differences between the two studies exist. Xue et al (2007) conducted a meta-analysis of hand-to-mouth contact frequency that included Freeman et al (2001) and the data from our data set under age 6 (AuYeung et al, 2004). In this meta-analysis, they determined that hand-mouthing frequency did not vary between studies for the children r6 years.…”

“…These future studies should be designed to have an even number of males and females in each age group to reduce confounding of the results. In the meta-analysis by Xue et al (2007), mouthing frequencies were determined to be significantly different indoors compared with outdoors for children r6 years of age. Our current study consists only of children engaged in outdoor play.…”

“…Mouthing and hand contact frequencies are key parameters for estimating non-dietary ingestion and dermal exposure (Zartarian et al, 2006;Nicas and Best, 2008;Stapleton et al, 2008;Julian et al, 2009;Schleier et al, 2009;Macedo et al, 2010;Tulve et al, 2010), as well as soil/dust ingestion rates (Ö zkaynak et al, 2010) critical for most hazardous site clean-up risk assessments including Superfund sites (US EPA, 2004). Several studies have quantified these mouthing and hand contact behaviors in children (Zartarian et al, 1997aBrinkman et al, 1999;Reed et al, 1999;Freeman et al, 2001Freeman et al, , 2005Tulve et al, 2002;AuYeung et al, 2004;Black et al, 2005;Auyeung et al, 2006;Beamer et al, 2008); however, we know of only one other study that has reported any data on children over 6 years of age (Freeman et al, 2001).…”

“…Meta-analyses of the data collected from younger children have indicated that mouthing decreases with age and other studies have reported differences by age in the frequency, with which children contact different types of objects or fomites with their hands (Freeman et al, 2001;Auyeung et al, 2006;Beamer et al, 2008). There is a clear need to quantify the mouthing and dermal contact activity patterns for individuals older than 6 years of age for use in the exposure assessments, and to determine if these trends continue past early childhood (Firestone et al, 2007;Xue et al, 2007).…”