Abstract
Young children’s mouthing activities thought to be among the most important exposure pathways. Unfortunately, mouthing activity studies have only been conducted in a few countries. In the current study, we used videotaping and computer-based translating method to obtain mouthing activity data for 66 children aged 7 to 35 months old in Taiwan. The median indoor hand-to-mouth and object-to-mouth frequencies were 8.91 and 11.39 contacts h−1, respectively. The median indoor hand-to-mouth and object-to-mouth hourly contact durations were 0.34 and 0.46 min h−1, respectively. The indoor object-to-mouth activities were significantly and negatively correlated with age. Children aged 12 to <24 months in the current study had lower indoor hand-to-mouth and object-to-mouth frequencies than children of same age group in the United States. We also found that indoor mouthing duration with pacifier was significantly and negatively correlated with indoor mouthing duration with other non-dietary objects. The results of the current study indicate that the mouthing behaviors might be different between different countries or populations with different ethnic or lifestyle characteristics. We conclude that using hand-to-mouth frequency values from the current literature may not be most reliable for estimating non-dietary exposures of young children living in Taiwan or even in other similar Asian countries.
Keywords: mouthing activities, non-dietary ingestion, hand-to-mouth, object-to-mouth, children
Introduction
Due to their developing physiology and unique activity patterns, children are more vulnerable to exposure through non-dietary ingestion of contaminants, such as pesticides1–3, heavy metals4–7, brominated flame retardants8–11 and microbes as well as viruses12–16. For estimating non-dietary ingestion exposures, quantified mouthing activity data of children thought to be important3; 13; 15; 17–19. In particular, these data are often used to estimate soil and/or dust ingestion rates and intake of chemicals from this exposure pathway20–24.
There are two methods which have been used in studies of children’s activities: direct observation25–28 and videotaping29–38, which is considered the most accurate way to record the children’s activities such as mouthing and hand contacts39. Compared to direct observation, videotaping can preserve the documented activities, thus allowing them to be analyzed further or confirmed at a later date. Videotaping can also provide more accurate information about the children’s activities. A computer-based method (Virtual Timing Device (VTD) software) can then be used to translate the videos into micro-level activity time series (MLATS), from which the mouthing frequency and duration can be obtained40.
Previous studies have shown that some factors, i.e. age26; 28; 31–34; 41; 42, gender29; 31; 34 and location29; 33; 34; 41; 42 may affect children’s mouthing frequency and/or duration. Moreover, the pacifier is a specific object which younger children mouth regardless of time of day. Juberg et al.26 has demonstrated that children mouth pacifiers significantly longer than other objects, regardless of age. However, there have been no published studies which investigated whether mouthing activities with pacifiers affect mouthing activities with other non-dietary objects.
Most previous studies of children’s mouthing activities were conducted in the United States. However, the culture, race, residential environment and lifestyle habits are largely different between Taiwan and the United States. To the best of our knowledge, there is no information about mouthing and hand contact frequencies for Taiwan, or the rest of Asia. There are no available studies that compare the mouthing activities between children living in Asian and Western countries43. Therefore, it is necessary to investigate children’s activity patterns for Taiwan and compare the findings to those reported by investigators elsewhere. Moreover, young children might have a greater chance of contacting soil and dust which reside on the floor or horizontal surfaces, due to their unique pediatric activity patterns. Previous studies had shown that some contaminants such as heavy metals44; 45, polycyclic aromatic hydrocarbons46 and brominated flame retardants47 were found in soil and dust in Taiwan. Such pollutant concentration data are also helpful to estimate the parameters necessary for predicting the non-dietary exposures to contaminants in soil and dust, by young children living in Taiwan.
In the current study, videotaping and the computer-based translating method were used to obtain MLATS. The principal objectives of this study were: a) to investigate the mouthing frequency and hourly mouthing duration for children aged from 7 to 35 months old in Taiwan, and b) to determine if there are significant differences by family demographics as well as by pacifier use. The secondary objective was to produce the necessary activity related input data for subsequent assessment of children’s incidental ingestion exposures to soil and dust particles or chemicals by using chemical soil/dust measurements made during the study, along with a stochastic human exposure model (i.e., the USEPA/ORD’s SHEDS model) for quantifying pathway specific exposures.
Materials and methods
The methods used for videotaping, video translation and quality control in this study were used modified from those used by Beamer et al.31. The methods are described briefly here. This study was reviewed and approved by the Taipei Medical University - Joint Institutional Review Board (Approval No: 201101026).
Children recruitment
A total of 66 children (33 boys and 33 girls) were recruited from local health centers during two periods, May to October, 2011 and July to November, 2012. Children were enrolled in this study if they met the following criteria: a) at least 1 adult lived with the children; b) the family had lived in the current residential location over 6 months, and c) the children did not have a severe illness. We obtained informed consent from adult parents and/or primary caregivers and administered a questionnaire about the demographic characteristics of the children and parents as well as the characteristics of their house.
Videotaping
Each child was videotaped for 2 hours. In general, the time of vediotapong started at 8:00a.m and ended at 13:30 p.m.. Only 4 children videotaped in the afternoon (time range from 13:00 p.m. to 18:00 p.m.) due to parents’ request. Approximately 77% children were videotaped in the on weekends (Saturday and Sunday). The videographer followed the child and tried to keep the child within view. However, due to space and children’s unpredictable behaviors, it was difficult to keep the whole body of a child in view at one time, and therefore, the videographer focused on the child’s hands and mouth to meet the objectives of this study. Moreover, the videographer kept distance as far as possible between themselves and the child to minimize affecting the taped child’s activities. The videotaping was stopped when the child napped, breast-fed or if the caregiver asked.
Videotape translation
The videotapes were translated into sequential computer text records (i.e. MLATS) in seconds using the VTD software. Each MLATS record included the location where the child visited, the contacted body part, the contacted objects/surfaces and the contact duration48. In the current study, we only focused on mouth. The mouthing contact was defined as any contact between the mouth and objects/surfaces, including objects/surfaces that slightly touched the lip, tongue or were immersed into the mouth.
To increase the reliability and accuracy of the data, many quality controls were conducted during the video translation. The videotapes were divided into 5 minutes segments. Before translating the videotapes in this study, the translator had to complete 3 practice segments. The translator needed to translate each practice segments 5 times, and the difference between the results for the 5 times had to be less than 10%. During the video translation, the translator was required to retranslate a randomly selected 5% of segments from his translated segments to increase the reliability of translations.
Quantification and analysis of MLATS data
All data were imported into Microsoft Excel 2007 (Microsoft Crop., Redmond, WA, USA) and SPSS statistics 17.0 (SPSS Inc., Chicago, IL, UAS) to perform the data analysis.
The objects were grouped into the objects/surfaces categories. There were 17 objects/surfaces categories (i.e., animal, body/skin, clothes/towel, fabric, floor, food, footwear, glass, hands, metal, non-dietary water, pacifier, paper/wrapper, plastic, rock/brick, toys, vegetation and wood) to be analyzed in the current study. Moreover, 2 super-categories (i.e. non-dietary objects (all objects other than food and hands) and all objects/surfaces) were also analyzed in the current study. The location categories were grouped into two super-categories: indoor (bathroom, bedroom, kitchen, living room) and outdoor (orchard/garden, patio, street/sidewalk, vehicle, and yard).
The mouthing frequency (contacts h−1) is the total number of contacts with a specific object category divided by the total duration in view. The hourly mouthing duration (min h−1) is the total duration of contacts with a specific object category divided by the total duration in view. The median mouthing duration (seconds) is calculated only for children who contacted the object.
Descriptive statistics were used to describe the distribution of the demographics and the mouthing data. Because the distribution of the mouthing data was right skewed, non-parametric statistical tests were used. Indoor and outdoor mouthing data were analyzed separately. The Spearman rank correlation method was used to assess the correlation between the mouthing data and children’s age. The Mann-Whitney U test was used to assess significant difference for the binomial demographic variables. The Kruskal-Wallis test was used to assess the significant difference in the trinomial demographic variables. The Dunn-Bonferroni test was used to conduct the multiple comparisons. Results were considered significant in a two-sided test if p < 0.05.
Results
Demographic
A total of 66 children (33 boys and 33 girls) were recruited in this study, including 8 children aged <12 months old, 30 children aged 12 to <24 months old and 28 children aged 24 to <36 months old. The demographic characteristics of children and parents are shown in Table 1. The average age of 66 children was 22.5 ±8.47 months. The majority of children’s primary caregivers were parents. Just under half of the children (n=25), where reported to use pacifiers by their parents. Approximately 70% of fathers and mothers had attended or graduated from college. A third of the mothers were the primary housekeeper. Half the families had monthly family income ≥NT$ 70 000 (about $2 338 US).
Table 1.
Demographic characteristics of children and parents.
| Variable | Mean (±Sd) or frequency (%)
|
p value | |||
|---|---|---|---|---|---|
| Total | <12 months | 12 to <24 months | 24 to<36 months | ||
| n | 66 | 8 | 30 | 28 | |
| Children | |||||
| Age (months) | 22.5 (±8.47) | 9.48 (±1.57) | 18.1 (±3.45) | 31.0 (±3.62) | |
| Gender | 0.8711 | ||||
| Male | 33 (50.0) | 4 (50.0) | 16 (53.3) | 13 (46.4) | |
| Female | 33 (50.0) | 4 (50.0) | 14 (46.7) | 15 (53.6) | |
| Primary caregiver | 0.2311 | ||||
| Parents | 40 (60.6) | 7 (87.5) | 16 (53.3) | 17 (60.7) | |
| The elder or nanny | 26 (39.4) | 1 (12.5) | 14 (46.7) | 11 (39.3) | |
| Average total numbers of going outside (times/week) | 0.9712 | ||||
| 1 to 3 times | 18 (27.3) | 3 (37.5) | 8 (26.7) | 7 (25.0) | |
| 4 to 6 times | 18 (27.3) | 2 (25.0) | 8 (26.7) | 8 (28.6) | |
| More than 7 times | 30 (45.5) | 3 (37.5) | 14 (46.7) | 13 (46.4) | |
| Uses pacifier | 0.0441 | ||||
| Yes | 25 (37.9) | 3 (37.5) | 14 (46.7) | 6 (21.4) | |
| No | 41 (62.1) | 5 (62.5) | 16 (53.3) | 22 (78.6) | |
| Father3 | |||||
| Age | 36.4 (±9.19) | 33.1 (±4.66) | 35.2 (±4.47) | 36.3 (±4.97) | 0.2242 |
| Education level | 0.1891 | ||||
| Senior high school or below (≤ 12 years) | 20 (31.3) | 2 (25.0) | 8 (27.6) | 10 (37.0) | |
| College (13 to ≤ 16 years) | 31 (48.4) | 6 (75.0) | 16 (55.2) | 9 (33.3) | |
| Graduate school (≥ 17 years) | 13 (20.3) | 0 (0.0) | 5 (17.2) | 8 (29.6) | |
| Occupation | 0.3921 | ||||
| Industry | 19 (29.7) | 3 (37.5) | 6 (20.7) | 10 (37.0) | |
| Public servant, businessman and teacher | 15 (23.4) | 1 (12.5) | 9 (31.0) | 5 (18.5) | |
| Doctor, nurse, military and police | 5 (7.8) | 0 (0.0) | 3 (10.3) | 2 (7.4) | |
| Housekeeper | 0 (0.0) | 0 (0.0) | 0 (0.0) | 0 (0.0) | |
| Service industry | 9 (14.1) | 3 (37.5) | 4 (13.8) | 2 (7.4) | |
| Other | 14 (23.4) | 1 (12.5) | 7 (24.1) | 8 (29.6) | |
| Mother | |||||
| Age (years) | 32.1 (±3.38) | 32.3 (±2.89) | 32.0 (±3.08) | 32.1 (±3.89) | 0.9852 |
| Education level | 0.7371 | ||||
| Senior high school or below (≤12 years) | 20 (30.3) | 2 (25.0) | 7 (23.3) | 11 (39.3) | |
| College (13 to ≤ 16 years) | 36 (54.5) | 5 (62.5) | 18 (60.0) | 13 (46.4) | |
| Graduate school (≥ 17 years) | 10 (15.2) | 1 (12.5) | 5 (16.7) | 4 (14.3) | |
| Occupation | 0.1141 | ||||
| Industry | 6 (9.1) | 0 (0.0) | 2 (6.7) | 4 (14.3) | |
| Public servant, businessman and teacher | 19 (28.8) | 0 (0.0) | 13 (43.3) | 6 (21.4) | |
| Doctor, nurse, military and police | 5 (7.6) | 0 (0.0) | 3 (10.0) | 2 (7.1) | |
| Housekeeper | 22 (33.3) | 5 (62.5) | 7 (23.3) | 10 (35.7) | |
| Service industry | 10 (15.2) | 3 (37.5) | 4 (13.3) | 3 (10.7) | |
| Other | 4 (6.0) | 0 (0.0) | 1 (3.3) | 3 (10.7) | |
| Family income (NT$/month)4 | 0.7821 | ||||
| <70 000 | 33 (50.0) | 4 (50.0) | 16 (53.3) | 13 (46.4) | |
| 70 000 to <100 000 | 14 (21.2) | 3 (37.5) | 5 (16.7) | 6 (21.4) | |
| 100 000 to <500 000 | 11 (16.7) | 0 (0.0) | 6 (20.0) | 5 (17.8) | |
| ≥500 000 | 8 (12.1) | 1 (12.5) | 3 (10.0) | 4 (14.3) | |
Statistical method: χ2 test.
Statistical method: One way ANOVA.
One 12 to <24 month-old child’s father has passed away and one 24 to <36 month-old child lived in a single parent family.
NT$70 000 was equal to about US$2 338. NT$100 000 was equal to about US$3 341. NT$500 000 was equal to about US$16 705.
The characteristics of the houses studied are shown in Table 2. Two/thirds of the children lived in a single house. More than two/thirds of the family reported that they swept floors (48 families) and mopped floors (55 families). On the contrary, only about a third of families (26 families) reported that they vacuumed floors. About half of total families (37 families) reported that they used two kinds of methods to clean their homes, and 28 families reported that they both swept and mopped floors. Only 14 families reported that they used all 3 methods, i.e. swept, mopped and vacuumed floors.
Table 2.
Household Characteristics (n=66).
| Variable | Frequency (%)
|
p value | |||
|---|---|---|---|---|---|
| Total | <12 months | 12 to <24 months | 24 to <36 months | ||
| House type | 0.2021 | ||||
| Single house | 44 (66.7) | 5 (62.5) | 17 (56.7) | 22 (78.6) | |
| Apartment | 22 (33.3) | 3 (37.5) | 13 (43.3) | 6 (21.4) | |
| Home ownership | 0.7431 | ||||
| Rent | 4 (6.1) | 0 (0.0) | 2 (6.7) | 2 (7.1) | |
| Own | 62 (93.9) | 8 (100.0) | 28 (93.3) | 26 (92.9) | |
| Peeling or chipping paint | 0.9341 | ||||
| Yes | 29 (43.9) | 4 (50.0) | 13 (43.3) | 12 (42.9) | |
| No | 37 (56.1) | 4 (50.0) | 17 (56.7) | 16 (57.1) | |
| Swept floors | 0.3281 | ||||
| Yes | 48 (72.7) | 5 (62.5) | 20 (66.7) | 23 (82.1) | |
| No | 18 (27.3) | 3 (37.5) | 10 (33.3) | 5 (17.9) | |
| Vacuumed floors | 0.0321 | ||||
| Yes | 26 (39.4) | 6 (75.0) | 13 (43.3) | 7 (25.0) | |
| No | 40 (60.6) | 2 (25.0) | 17 (56.7) | 21 (75.0) | |
| Mopped floors | 0.5081 | ||||
| Yes | 55 (83.3) | 6 (75.0) | 24 (80.0) | 25 (89.3) | |
| No | 11 (16.7) | 2 (25.0) | 6 (20.0) | 3 (10.7) | |
| Number of cleaning methods2 | 0.3231 | ||||
| 0 | 2 (3.0) | 0 (0.0) | 1 (3.3) | 1 (3.6) | |
| 1 | 13 (19.7) | 1 (12.5) | 9 (30.0) | 3 (10.7) | |
| 2 | 37 (56.1) | 5 (62.5) | 12 (40.0) | 20 (71.4) | |
| 3 | 14 (21.2) | 2 (25.0) | 8 (26.7) | 4 (14.3) | |
Statistical method: χ2 test.
The cleaning methods included sweeping, vacuuming and mopping the floors.
Mouthing frequency and duration
The average total duration of videotape footage obtained on each child was 121.92 ±3.82 minutes. In the current study, children spent 92.60 ±19.72% of total duration indoors. Only 11 children spent more than 15 minutes outdoors, with the average outdoor duration was 49.65 ±20.20 minutes among those children. The outdoor mouthing activities data were only calculated from these 11 children.
The indoor and outdoor object/surface mouthing frequencies are shown in Table 3. The complete distribution of mouthing frequency is shown in Supplementary Table S1. Children had the highest indoor median mouthing frequency with food (18.95 contacts h−1) among all objects/surfaces. The indoor median hand-to-mouth and non-dietary object-to-mouth (hereafter referred to as object-to-mouth) frequencies were 8.91 and 11.39 contacts h−1, respectively. Among the 11 children who spent more than 15 minutes outdoors, the highest outdoor median mouthing frequency (6.65 contacts h−1) was with hands among all objects/surfaces considered. Also, the median outdoor object-to-mouth frequency was 3.08 contacts h−1.
Table 3.
Indoor and outdoor object/surface mouthing frequencies (contacts/h).
| Objects/surfaces | Mouthing frequency (contacts/h)
|
|||||
|---|---|---|---|---|---|---|
| Indoor (n=66) | Outdoor (n=11)1 | |||||
|
| ||||||
| Mean | Median | Range | Mean | Median | Range | |
| Animal | -2 | - | - | - | - | - |
| Body/Skin | 2.07 | 1.47 | 0.00–14.56 | 1.60 | 1.06 | 0.00–7.38 |
| Clothes/Towel | 3.54 | 1.76 | 0.00–23.27 | 1.48 | 1.33 | 0.00–5.05 |
| Fabric | 1.32 | 0.50 | 0.00–15.43 | 0.10 | 0.00 | 0.00–1.06 |
| Floor | 0.04 | 0.00 | 0.00–1.00 | - | - | - |
| Food | 25.06 | 18.95 | 0.00–108.37 | 6.63 | 2.85 | 0.00–39.24 |
| Footwear | 0.03 | 0.00 | 0.00–1.44 | - | - | - |
| Glass | 0.02 | 0.00 | 0.00–1.00 | - | - | - |
| Hands | 13.15 | 8.91 | 0.50–47.9 | 8.35 | 6.65 | 3.08–16.88 |
| Metal | 0.98 | 0.00 | 0.00–57.77 | 0.40 | 0.00 | 0.00–3.08 |
| Non-dietary Water | - | - | - | - | - | - |
| Pacifier | 0.81 | 0.00 | 0.00–10.42 | - | - | - |
| Paper/Wrapper | 2.83 | 1.00 | 0.00–24.69 | 0.98 | 0.00 | 0.00–10.11 |
| Plastic | 2.59 | 0.55 | 0.00–39.99 | 0.37 | 0.00 | 0.00–1.67 |
| Rock/Brick | 0.03 | 0.00 | 0.00–0.97 | - | - | - |
| Toys | 7.04 | 1.68 | 0.00–153.13 | 1.31 | 1.01 | 0.00–3.34 |
| Vegetation | - | - | - | - | - | - |
| Wood | 0.44 | 0.00 | 0.00–5.59 | - | - | - |
|
| ||||||
| Non-dietary Objects | 21.74 | 11.39 | 0.50–170.57 | 6.23 | 3.08 | 1.67–21.22 |
| All Objects/Surfaces | 59.95 | 52.04 | 2.51–214.56 | 21.21 | 14.93 | 5.02–58.87 |
The outdoor mouthing frequency was only calculated from 11 children who spent more than 15 minutes outdoors.
None of children had contacted the object/surface with mouth.
The indoor and outdoor object/surface hourly mouthing durations are shown in Table 4. The complete distribution of hourly mouthing duration is shown in Supplementary Table S2. Children had the highest indoor median hourly mouthing duration with food (1.49 min h−1) among all objects/surfaces. The indoor median hand-to-mouth and object-to-mouth hourly contact durations were 0.34 and 0.46 min h−1, respectively. Among the 11 children who both spent more than 15 minutes outdoors, the highest outdoor median mouthing hourly duration (0.34 min h−1) was with their hands among all objects/surfaces identified. The outdoor median hand-to-mouth and object-to-mouth hourly mouthing duration were 0.34 and 0.07 min h−1, respectively.
Table 4.
Indoor and outdoor object/surface hourly mouthing duration (min/h).
| Objects/surfaces | Hourly mouthing duration (min/h)
|
|||||
|---|---|---|---|---|---|---|
| Indoor (n=66) | Outdoor (n=11)1 | |||||
|
| ||||||
| Mean | Median | Range | Mean | Median | Range | |
| Animal | -2 | - | - | - | - | - |
| Body/Skin | 0.04 | 0.02 | 0.00–0.24 | 0.02 | 0.00 | 0.00–0.07 |
| Clothes/Towel | 0.16 | 0.04 | 0.00–3.02 | 0.04 | 0.02 | 0.00–0.17 |
| Fabric | 0.06 | 0.00 | 0.00–1.18 | 0.00 | 0.00 | 0.00–0.02 |
| Floor | 0.00 | 0.00 | 0.00–0.01 | - | - | - |
| Food | 2.36 | 1.49 | 0.00–16.37 | 1.82 | 0.25 | 0.00–12.99 |
| Footwear | 0.00 | 0.00 | 0.00–0.06 | - | - | - |
| Glass | 0.00 | 0.00 | 0.00–0.03 | - | - | - |
| Hands | 0.69 | 0.34 | 0.02–3.86 | 0.55 | 0.34 | 0.06–2.69 |
| Metal | 0.08 | 0.00 | 0.00–5.26 | 0.01 | 0.00 | 0.00–0.05 |
| Non-dietary Water | - | - | - | - | - | - |
| Pacifier | 2.60 | 0.00 | 0.00–31.93 | - | - | - |
| Paper/Wrapper | 0.08 | 0.02 | 0.00–1.27 | 0.01 | 0.00 | 0.00–0.08 |
| Plastic | 0.17 | 0.02 | 0.00–3.96 | 0.01 | 0.00 | 0.00–0.05 |
| Rock/Brick | 0.00 | 0.00 | 0.00–0.02 | - | - | - |
| Toys | 0.53 | 0.03 | 0.00–11.12 | 0.03 | 0.00 | 0.00–0.18 |
| Vegetation | - | - | - | - | - | - |
| Wood | 0.02 | 0.00 | 0.00–0.34 | - | - | - |
|
| ||||||
| Non-dietary Objects | 3.75 | 0.46 | 0.01–31.95 | 0.11 | 0.07 | 0.00–0.32 |
| All Objects/Surfaces | 6.80 | 3.79 | 0.05–34.91 | 2.47 | 0.87 | 0.06–13.64 |
The outdoor mouthing hourly mouthing duration was only calculated from 11 children who spent more than 15 minutes outdoors.
None of children had contacted the object/surface with mouth.
The indoor and outdoor object/surface median mouthing durations are shown in Table 5. The complete distribution of median mouthing duration is shown in Supplementary Table S3. All children contacted their hands with the mouth when videotaped, and none of children contacted animal, non-dietary water and vegetation with mouth when videotaped. Children had the much higher indoor median mouthing duration with pacifier (median: 78 seconds) than other objects. The indoor median mouthing duration with objects other than pacifier was short (median range from 0.50 and 2.00 seconds). They had the highest outdoor median mouthing duration with food (median: 7.50 seconds) compared to all other objects.
Table 5.
The object/surface median mouthing duration (seconds)1.
| Objects/surfaces | Median mouthing duration (seconds)
|
|||||||
|---|---|---|---|---|---|---|---|---|
| Indoor | Outdoor 2 | |||||||
|
| ||||||||
| n | Mean | Median | Range | n | Mean | Median | Range | |
| Animal | 0 | -3 | - | - | 0 | - | - | - |
| Body/Skin | 51 | 0.98 | 1.00 | 0.00–8.00 | 6 | 0.50 | 0.00 | 0.00–2.00 |
| Clothes/Towel | 50 | 1.59 | 1.00 | 0.00–12.00 | 7 | 1.14 | 1.00 | 0.50–2.00 |
| Fabric | 31 | 2.47 | 1.00 | 0.00–32.00 | 1 | 1.00 | 1.00 | - |
| Floor | 3 | 0.50 | 0.50 | 0.00–1.00 | 0 | - | - | - |
| Food | 63 | 2.49 | 2.00 | 1.00–8.00 | 6 | 10.17 | 7.50 | 2.00–33.00 |
| Footwear | 2 | 2.00 | 2.00 | 2.00–2.00 | 0 | - | - | - |
| Glass | 2 | 1.00 | 1.00 | 0.00–2.00 | 0 | - | - | - |
| Hands | 66 | 1.72 | 1.25 | 0.00–5.50 | 11 | 2.00 | 1.00 | 0.00–6.00 |
| Metal | 9 | 1.72 | 1.00 | 0.00–4.00 | 2 | 1.00 | 1.00 | 1.00–1.00 |
| Non-dietary Water | 0 | - | - | - | 0 | - | - | - |
| Pacifier | 13 | 205.08 | 78.00 | 2.00–1007.00 | 0 | - | - | - |
| Paper/Wrapper | 40 | 1.21 | 1.00 | 0.50–4.00 | 2 | 1.75 | 1.75 | 0.50–3.00 |
| Plastic | 39 | 2.22 | 2.00 | 0.00–8.00 | 3 | 1.50 | 1.50 | 0.00–3.00 |
| Rock/Brick | 2 | 1.75 | 1.75 | 0.50–3.00 | 0 | - | - | - |
| Toys | 51 | 1.66 | 1.00 | 0.00–8.00 | 6 | 1.00 | 0.50 | 0.00–4.00 |
| Vegetation | 0 | - | - | - | 0 | - | - | - |
| Wood | 15 | 1.60 | 1.00 | 0.00–5.00 | 0 | - | - | - |
|
| ||||||||
| Non-dietary Objects | 65 | 1.48 | 1.00 | 0.50–9.00 | 11 | 0.64 | 0.50 | 0.00–2.00 |
| All Objects/Surfaces | 66 | 1.71 | 2.00 | 1.00–3.50 | 11 | 1.82 | 2.00 | 1.00–3.50 |
The median mouthing duration was only calculated from the child who contacted the objects/surfaces.
The outdoor mouthing median contact duration was only calculated from 11 children who spent more than 15 minutes outdoors.
None of children had contacted the object/surface with mouth.
Difference in location
Figure 1 provides the distribution for all objects which had statistically significant differences (p<0.05) between locations for: (a) indoor mouthing frequency, (b) indoor hourly mouthing duration and (c) indoor median mouthing duration for 11 children who both spent more than 15 minutes indoors and outdoors. The complete distributions for object/surfaces with significant differences in mouthing frequency, hourly mouthing duration and mouthing median duration (p<0.05) between locations for children who both spent more than 15 minutes indoors and outdoors are shown in Table S4. Among these 11 children, the indoor mouthing frequency and hourly mouthing duration with food (p<0.001 and 0.028, respectively), non-dietary objects (p=0.019 and 0.013, respectively) and all objects/surfaces (p<0.001 and 0.023, respectively) were both significantly higher than the outdoor mouthing frequency and hourly mouthing duration. The indoor median mouthing duration with non-dietary objects (p=0.047) was significantly higher than the outdoor median mouthing duration. However, the outdoor median mouthing duration with food (p=0.020) was significantly higher than the indoor median mouthing duration.
Figure 1.
The significant differences between locations for: (a) indoor mouthing frequency, (b) indoor hourly mouthing duration and (c) indoor median mouthing duration for 11 children who spent more than 15 minutes both indoors and outdoors.
Difference in children’s age
Because the outdoor mouthing activities were only calculated from 11 children who spent more than 15 minutes outdoor when videotaped, the following analysis for difference in demographic variables is presented only for the indoor mouthing activities.
For indoor mouthing frequency, children’s age was significantly and negatively correlated with the mouthing frequency with clothes/towel (r=−0.427, p<0.001), floor (r=−0.257, p=0.037), food (r=−0.309, p=0.011), footwear (r=−0.250, p=0.043), pacifier (r=−0.264, p=0.032), paper/wrapper (r=−0.385, p=0.001), plastic (r=−0.333, p=0.006), toy (r=−0.263, p=0.033), non-dietary objects (r=−0.559, p<0.001) and all objects/surfaces (r=−0.415, p=0.001). For indoor hourly mouthing duration, children’s age was significant negatively correlated with the hourly mouthing duration with clothes/towel (r=−0.355, p=0.003), food (r=−0.249, p=0.044), footwear (r=−0.250, p=0.043), pacifier (r=−0.251, p=0.042), paper/wrapper (r=−0.361, p=0.003), plastic (r=−0.306, p=0.012), toys (r=−0.292, p=0.017), non-dietary objects (r=−0.455, p<0.001) and all objects/surfaces (r=−0.397, p=0.001). For the median mouthing duration, children’s age was significant negatively correlated with the median mouthing duration with food (r=−0.275, p=0.029), toys (r=−0.412, p=0.003), non-dietary objects (r=−0.271, p=0.029) and all objects/surfaces (r=−0.294, p=0.017).
Children were divided into 3 age groups: <12 months, 12 to <24 months and 24 to <36 months. Figure 2 provides the distribution for all objects which had statistically significant differences (p<0.05) between the age groups, in (a) indoor mouthing frequency, (b) indoor hourly mouthing duration, and (c) indoor median mouthing duration. The complete distribution of indoor mouthing frequency, indoor hourly mouthing duration and indoor median mouthing duration for age groups are shown in Supplementary Table S5 to Table S7, respectively. The median indoor hand-to-mouth frequencies were 16.26, 8.91 and 8.14 contact h−1 for children aged <12months old, 12 to <24 months old and 24 to <36 months old, respectively. The median indoor object-to-mouth frequencies were 60.69, 11.82 and 8.96 contact h−1 for children aged <12months old, 12 to <24 months old and 24 to <36 months old, respectively. There were significant difference in indoor mouthing frequency with paper/wrapper (p=0.020), plastic (p=0.046), toys (p=0.001), non-dietary objects (p<0.001) and all objects/surfaces (p=0.002) between age groups. After conducting multi-comparison, the object-to-mouth frequency of children aged <12 months was both significantly higher than children aged 1 to <2 years old and 2 to <3 years old (p=0.007 and p<0.001, respectively). The median indoor hand-to-mouth hourly duration were 0.63, 0.31 and 0.31 min h−1 for children aged <12months old, 12 to <24 months old and 24 to <36 months old, respectively. The median indoor object-to-mouth hourly duration were 4.75, 0.63 and 0.27 min h−1 for children aged <12months old, 12 to <24 months old and 24 to <36 months old, respectively. There were significant difference in indoor hourly mouthing duration with paper/wrapper (p=0.024), toys (p=0.002), non-dietary objects (p=0.004) and all objects/surfaces (p=0.014) between age groups. After conducting multi-comparison, the object-to-mouth hourly contact duration of children aged <12 months was significantly higher than children 2 to <3 years old (p=0.004). There were significant difference in indoor mouthing median duration with food (p=0.037), toys (p=0.002) and non-dietary objects (p=0.037) between age groups. After conducting multi-comparison, the object-to-mouth contact median duration of children aged <12 months was significantly higher than children 2 to <3 years old (p=0.035).
Figure 2.
The significant differences between age groups for: (a) indoor mouthing frequency, (b) indoor hourly mouthing duration and (c) indoor median mouthing duration. • indicated the 5th/95th percentiles.
Difference by children’s gender
Figure 3 provides the distribution for each object which had significant differences (p<0.05) by children’s gender in (a) indoor mouthing frequency and (b) indoor hourly mouthing duration. The complete distribution of objects indoor mouthing frequency and indoor hourly mouthing duration by gender are shown in Supplementary Table S8. Boys had significantly greater indoor mouthing frequency and hourly duration with clothes/towel (p=0.013 and 0.036, respectively) and fabric (p=0.006 and 0.013, respectively) than girls, and girls had significantly greater indoor mouthing frequency with pacifier (p=0.036 and 0.036, respectively) than boys.
Figure 3.
The significant differences between male and female for: (a) indoor mouthing frequency and (b) indoor hourly mouthing duration. • indicated the 5th/95th percentiles.
Difference in mouthing the pacifier
We evaluated the association between mouthing activities with pacifier and other objects only in the 13 children who used the pacifier during videotaping. Among these 13 children, the mouthing frequency with pacifier (median=3.01 contacts/h) was significantly lower than the mouthing frequency with other non-dietary objects (median=13.74 contacts/h, p<0.001). The hourly mouthing duration (median=11.31 min/h) and mouthing median duration (median=78.0 seconds) with pacifier were both significantly longer than the hourly mouthing duration (median=0.43 min/h, p=0.003) and mouthing median duration (median=1.00 seconds, p<0.001) with other non-dietary objects. Furthermore, the hourly mouthing duration and mouthing median duration with pacifier was both significantly and negatively correlated with the hourly mouthing duration (r=-0.555, p=0.049) and mouthing median duration (r=-0.620, p=0.024) with other non-dietary objects.
Discussion
In the current study, we investigated the mouthing activities for 66 young children in Taiwan. We videotaped the children for 2 hours and translated the footage into MLATS using VTD software. To-date, this is the largest published study that used this method29–32; 34; 35; 37. In this study, children spent almost all of their time indoors (92.60% of total duration). Only 11 children spent more than 15 minutes outdoors. We found that the indoor object-to-mouth frequency, hourly duration and median duration were significantly higher than outdoor object-to-mouth frequency, hourly duration and median duration. We also found that the children aged <12 months had the greatest indoor object-to-mouth frequency and longest indoor hourly object-to-mouth duration, although the number of children aged <12 months was small. There were no significant difference with children’s gender in indoor hand-to-mouth and object-to-mouth frequency and hourly duration. Among the 13 children who used a pacifier during videotaping, we also found that the hourly mouthing duration and mouthing median duration with pacifier were significantly and negatively correlated with the hourly mouthing duration and mouthing median duration with other non-dietary objects.
In the current study, we found that the object-to-mouth frequency, hourly and median contact durations were significantly negatively correlated with age. This was consistent with the previous studies. Black et al.33 and a meta-analysis for children’s object-to-mouth frequency42 both indicated that the object-to-mouth frequency was decreased with the children’s age. Beamer et al.32 found that the object-to-mouth hourly contact duration was negatively correlated with age among the cohort of 1–12-year-old children. Beamer et al.31 showed that infants had higher object-to-mouth frequency and hourly contact duration. On the other hand, we found that hand-to-mouth frequency was not significantly negatively correlated with age. This was not consistent with results of the meta-analysis for children’s hand-to-mouth frequency41. Xue et al.41 had indicated that the hand-to-mouth frequency decreased with children’s age. Nevertheless, we still found that the median hand-to-mouth frequency for children aged <12 months was higher than the median hand-to-mouth contact frequency for older children.
The comparison of hand-to-month and object-to-mouth frequency, hourly contact duration and contact median duration between previous studies and the current study is shown in Table 6. For the 66 children in the current study, the indoor hand-to-mouth and object-to-mouth frequency (median: 8.91 and 11.39 contacts h−1, respectively), hourly contact durations (median: 0.34 and 0.46 min h−1, respectively) and contact median durations (median: 1.25 and 1.00 seconds, respectively) in the current study were all lower than hand-to-mouth and object-to-mouth frequency (median: 15.2 and 27.2 contacts h−1, respectively), hourly contact durations (median: 1.2 and 2.2 min h−1, respectively) and contact median durations (median: 2.0 seconds for both) in Beamer et al.31 However, this might be due to the fact that mostly younger children were studied in Beamer et al.31 (age range: 6 to 27 months). The younger children tend to exhibit the frequent mouthing behavior, i.e. repetitive contact of objects with mouth, and the longer mouthing behavior, for example sucking or biting of objects.
Table 6.
The comparison of hand-to-month and object-to-mouth frequency, hourly contact duration and contact median duration between previous studies and the current study.
| Studies | Age | Contact frequency (contacts h−1) | Hourly contact duration (min h−1) | Contact median duration (min)1 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
| |||||||||||||
| n | Mean | Median | 95th percentile | n | Mean | Median | 95th percentile | n | Mean | Median | 95th percentile | ||
| Hand-to-mouth | |||||||||||||
| The current study | 7 to <36 months | 66 | 13.15 | 8.91 | 39.79 | 66 | 0.69 | 0.34 | 3.06 | 65 | 1.65 | 1.50 | 3.70 |
| Beamer et al. (2008) | 6 to 27 months | 23 | 18.4 | 15.2 | 44.7 | 23 | 1.4 | 1.2 | 3.7 | 23 | 2.6 | 2 | 4.9 |
| The current study | <12 months | 8 | 16.73 | 16.26 | 33.51 | 8 | 0.92 | 0.63 | 2.71 | 8 | 2.25 | 2.00 | 4.00 |
| 1 to <2 years | 30 | 12.21 | 8.91 | 40.74 | 30 | 0.62 | 0.31 | 2.88 | 30 | 1.47 | 1.00 | 3.45 | |
| 2 to <3 years | 28 | 13.13 | 8.14 | 42.56 | 28 | 0.70 | 0.31 | 3.31 | 28 | 1.84 | 1.00 | 5.28 | |
| Xue et al. (2006) | 6 to <12 months | 119 2 | 18.9 | 14 | 52 | -3 | - | - | - | - | - | - | - |
| 1 to <2 years | 245 2 | 19.6 | 14 | 63 | - | - | - | - | - | - | - | - | |
| 2 to <3 years | 161 2 | 12.7 | 9 | 37 | - | - | - | - | - | - | - | - | |
| Object-to-mouth | |||||||||||||
| The current study | 7 to <36 months | 66 | 21.74 | 11.39 | 73.98 | 66 | 3.75 | 0.46 | 23.24 | 66 | 1.54 | 1.00 | 3.65 |
| Beamer et al. (2008) | 6 to 27 months | 23 | 29.2 | 27.2 | 64 | 23 | 3.5 | 2.2 | 8.5 | 23 | 2.2 | 2 | 3.9 |
| The current study | <12 months | 8 | 65.7 | 60.69 | 170.57 | 8 | 6.47 | 4.75 | 18.93 | 8 | 2.00 | 2.00 | 4.00 |
| 1 to <2 years | 30 | 18.47 | 11.82 | 62.18 | 30 | 4.14 | 0.63 | 31.58 | 29 | 1.38 | 1.00 | 3.00 | |
| 2 to <3 years | 28 | 12.68 | 8.96 | 55.84 | 28 | 2.55 | 0.27 | 22.65 | 28 | 1.43 | 1.00 | 6.30 | |
| Xue et al. (2010) | 6 to <12 months | 82 2 | 20.33 | 18.95 | 37.9 | - | - | - | - | - | - | - | - |
| 1 to <2 years | 137 2 | 14.24 | 12.3 | 34 | - | - | - | - | - | - | - | - | |
| 2 to <3 years | 95 2 | 9.89 | 8.7 | 24.4 | - | - | - | - | - | - | - | - | |
The median mouthing duration was only calculated from the child who contacted the objects/surfaces.
Number of observation.
No available data.
In the current study, the median indoor hand-to-mouth frequencies for children aged <12 months, 12 to <24 months and 24 to <36 months were 16.26, 8.91 and 8.14 contacts h−1, respectively. In the meta-analysis for children’s hand-to-mouth frequency41, the median indoor hand-to-mouth frequency for children aged 6 to <12 months (14 contacts h−1) was slightly lower than children aged <12 months in the current study. However, the median indoor hand-to-mouth frequency for children aged 12 to <24 months and 24 to <36 months in the meta-analysis (14 and 9 contacts h−1, respectively) were higher than for children ages 12 to <24 months old and 24 to <36 months old studied in the current project. In our work, the median indoor object-to-mouth frequencies for children aged <12 months, 12 to <24 months and 24 to <36 months were 60.69, 11.82 and 8.96 contacts h−1, respectively. In the meta-analysis for the U.S children’s object-to-mouth frequency42, the median indoor object -to-mouth frequency for children aged 6 to <12 months (18.95 contacts h−1) was much lower than for those children aged <12 months observed in the current study. It is possible, however, that small sample sizes for these very young kids in both of these studies may contribute to these large variations. In contrast, the median indoor object-to-mouth frequency for children aged 12 to <24 months in the U.S. meta-analysis (12.3 contacts h−1) was slightly higher than children aged 12 to <24 months old examined in the current study. The median indoor object-to-mouth frequency for children aged 24 to <36 months in the meta-analysis (8.7 contacts h−1) was similar to children aged 24 to <36 months in the current study. The results indicated children aged <12 months in the current study had higher indoor hand-to-mouth and object-to-mouth frequency than the children aged 6 to <12 months in the meta-analysis. However, the number of children aged 6 to <12 months was small in the current study. A larger study with more children aged <12 months who might have a higher hand-to-mouth and object-to-mouth frequency is needed to clarify the difference between children in Taiwan and the United States.
We found that children aged 12 to <24 months in the current study had lower indoor hand-to-mouth and object-to-mouth frequencies than children aged 12 to <24 months in the previously reported meta-analysis41; 42. A possible reason for this difference could be the influence of low birth rate and changing family structure effecting child raising in Taiwan. According to “2011 World Population Data Sheet”49, the total fertility rate of Taiwan was the lowest in the world. On average, every woman bore 0.9 children during her life in Taiwan. Moreover, Taiwan is the aging society since 1993. The elderly people (over 65 years old) were accounting for 11.2 percent of total population in 201250. Some families were lived with multiple generations due to the increasing elder population and economic pressure. In the current study, there were 56.1% of families with 1 child, and at least 51.4% of these children were lived with parents and grandparents in a house or in the neighborhood. Therefore, multiple people might take care of children together and pay more attention to the children’s behavior. Another possible reason for difference between Taiwan and the United States might be the difference in cleaning habits. Moran et al.51 investigated the cleaning habits (dry-mop hard floors, wet-mop hard floors, sweep hard floors, vacuum hard floors and vacuum carpet) for California families by telephone survey. In general, the cleaning frequency reported by families in the current study (ranged from 2.31 (vacuumed floors) to 4.06 (sweep hard floors) times/week) was higher than the frequency reported by woman in California families with children aged <5 years old (ranged from 1.61 (wet-mop hard floors) to 3.55 (sweep hard floors) times/week). Besides, approximately 77% of families reported that they used 2 or 3 kinds of clean methods. The more frequent cleaning and more kinds of cleaning methods used might reflect the more attentive care of children by their parents or caregivers. In brief, more caregivers who took care of one child and more frequent cleaning might be indirectly related to the children’s mouthing activities in Taiwan.
We also found that the 95th percentile of hand-to-mouth frequency of children aged 6 to <12 months old (33.51 contacts h−1) and 1 to <2 years old (40.74 contacts h−1) were both lower than children with similar age in the meta-analysis (52 and 63 contacts h−1 for children aged 6 to <12 months old and 1 to <2 years old, respectively)41. However, the 95th percentile of object-to-mouth frequency of children aged 6 to <12 months (170.57 contacts h−1) old, 1 to <2 years old (62.18 contacts h−1) and 2 to <3 years old (55.84 contacts h−1) were all higher than children with similar age in the meta-analysis (37.9, 34 and 24.4 contacts h−1 for children aged 6 to <12 months old, 1 to <2 years old and 2 to <3 years old, respectively) 42. The children who were at the upper-tail for distribution might have more exposure to the contaminants. The results indicated that compared to children lived in the United States, children lived in Taiwan at the upper-tail for distribution might have more object-to-mouth frequency and less hand-to-mouth frequency. This might be due to the difference of cultures between Taiwan and the United States.
Juberg et al.26 indicated that children had significantly longer mouthing duration with pacifier than other objects, which is consistent with the current study. We also found that among the 13 children who used the pacifier during videotaping, the hourly mouthing duration and mouthing median duration with pacifier were significantly and negatively correlated with the hourly mouthing duration and mouthing median duration with other non-dietary objects. These results indicate that longer duration of mouthing with pacifier might reduce mouthing duration with other non-dietary objects. However, some studies have indicated that the pacifier is a potential reservoir of infections if the pacifier is not cleaned appropriately52; 53. An additional study with a larger number of children who use pacifiers is clearly warranted in order to clarify the association between the mouthing activities with pacifier and other objects and investigate the related exposure for contaminants on the pacifier.
There are some limitations in the current study. First, the children in the current study were not sampled or recruited randomly. Therefore, our results might not be representative of all children in Taiwan with ages 7 to <36 months old. However, the number of children in the current study was more than any of the other studies, which used the VTD software to translate the videotapes, and form a good basis for our recommendations. A second limitation is that the children were aged from 7 to 35 months old in the current study. In the future, an additional study is needed with older children to understand the mouthing frequency and duration in a group of children with a larger age range living in Taiwan. Third, the children in the current study spent almost all their time indoors. Only 11 children spent more than 15 minutes outdoors. Further study is needed to investigate the outdoor mouthing activities, especially in locations (e.g., rural and suburban areas) where the children might directly contact soil more often. Finally, in the current study, only 5 children were from recent immigrant families. Generally, the recent immigrant families have lower social-economic status (SES) and lower education level. The recent immigrant mothers typically have language and cultural challenges in raising their children54; 55. Thus, we recommend performing a study to investigate children in recent often low SES immigrant families in Taiwan, who might also live in poorer environments. Despite the limitations aforementioned, this study provides the first mouthing data for children aged under 3 years old in Taiwan or in any Asian country. These data could be used in modeling soil and dust ingestion rates using the USEPA’s SHEDS soil and dust ingestion model23. As a follow-up to this study, we are conducting an additional study in which we are collecting the mouthing frequency data for older children, i.e. children aged 4 to 6 years old. Furthermore, we are also complementing this work by gathering soil transfer efficiency information from hand to mouth.
In conclusion, we found that the object-to-mouth frequency, hourly duration and median duration were significantly negatively correlated with children’s age. Children aged 12 to <24 months in the current study had lower indoor hand-to-mouth and object-to-mouth frequencies than children aged 12 to <24 months in America. The reason might be due to implications of low birth rate, changing family/caregiving structure and higher frequency of house cleaning activities in Taiwan. We also found that compared to children lived in the United States, children lived in Taiwan at the upper-tail for distribution might have more object-to-mouth frequency and less hand-to-mouth frequency. It is important to identify the contribution of soil ingestion from outdoor hand-to-mouth soil contact activities. Additional studies are also needed to further investigate the more vulnerable populations, i.e., children of new immigrant families or those living in more dusty or less maintained homes.
To the best of our knowledge, this is not only the first study to investigate the children’s mouthing behavior in Taiwan or other parts of Asia, but the first study to compare the mouthing activities data between different countries or different (i.e. Eastern vs. Western) cultures. The mouthing frequency and hourly mouthing duration are important to estimate the non-dietary ingestion exposure for children. It is particularly important for Taiwan where there is serious lack of this type of information. Given the differences observed between the results for Taiwan and the United States, additional studies are need in other countries to better understand these exposure factors and how these findings may influence environmental risks from non-dietary ingestion of contaminants, which may vary across the world.
Supplementary Material
Acknowledgments
Source of grant: This project was supported by the Taiwan Environmental Protection Administration (project no. EPA-100-G101-03-A036 and EPA-101-GA101-02-A143). The United States Environmental Protection Agency through its Office of Research and Development collaborated in the research described hereunder. Although it has been subjected to Agency review and approved for publication, it may not necessarily reflect official EPA policy. Dr. Beamer was supported by K25HL103970 from NHLBI and the Southwest Environmental Health Sciences Center (NIEHS P30 ES006694). The content is solely the work of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors would like to thanks Prof. Colin Ong from Stanford University for providing the VTD software.
Footnotes
Conflict of interest
The authors declare no conflict of interest.
Supplementary information is available at Journal of Exposure Science and Environmental Epidemiology’s website.
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