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Age-related changes to environmental exposure: variation in the frequency that young children place hands and objects in their mouths

Journal of Exposure Science & Environmental Epidemiology (2019) | Download Citation



Children are exposed to environmental contaminants through direct ingestion of water, food, soil, and feces, and through indirect ingestion due to mouthing hands and objects. We quantified ingestion among 30 rural Bangladeshi children <4 years old, recording every item touched or mouthed during 6-h video observations that occurred annually for 3 years. We calculated the frequency and duration of mouthing and the prevalence of mouth contacts with soil and feces. We compared the mouthing frequency distributions to those from US children to evaluate the appropriateness of applying the US data to the Bangladeshi context. Median hand mouthing frequency was 97–160 times/h and object mouthing 23–50 times/h among the five age groups assessed. For more than half of the children, >75% of all hand mouthing was associated with eating. The frequency of hand mouthing not related to eating was similar to the frequency of all hand-mouthing among children in the US. Object-mouthing frequency was higher among Bangladeshi children compared to US children. There was low intra-child correlation of mouthing frequencies over our longitudinal visits. Our results suggest that children’s hand- and object-mouthing vary by geography and culture and that future exposure assessments can be cross-sectional if the goal is to estimate population-level distributions of mouthing frequencies. Of all observations, a child consumed soil in 23% and feces in 1%.

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We gratefully acknowledge the participating study families, as well as collaborators responsible for video translation software, data collection and video translation: Robert Canales, Carla Bustos, Rita Chowdhury, Nisa Sultana, Eashmat Annay, Shamima Islam Mina, Nusrat Jahan, Akhe Nur Begum, and Md. Sajjad Rahman. This study was funded by the Stanford Center for Innovation in Global Health and the World Bank; the WASH Benefits Study, in which it was embedded, was funded by the Bill & Melinda Gates Foundation. This material is based upon work supported by the Stanford Wood’s Institute for the Environment Goldman Graduate Fellowship and the National Science Foundation Graduate Research Fellowship under Grant No. DGE-114747. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation.

Author information


  1. Department of Civil and Environmental Engineering, Stanford University, Stanford, CA, USA

    • Laura H. Kwong
    •  & Jennifer Davis
  2. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, USA

    • Ayse Ercumen
  3. Division of Epidemiology and Biostatistics, University of California, Berkeley, CA, USA

    • Ayse Ercumen
  4. Department of Civil and Environmental Engineering, Tufts University, Medford, MA, USA

    • Amy J. Pickering
  5. International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh

    • Leanne Unicomb
  6. Woods Institute for the Environment, Stanford University, Stanford, CA, USA

    • Jennifer Davis
    •  & Stephen P. Luby


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Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

Caregivers of the participating children provided informed written consent before the observations. The study was conducted in accordance with the Declaration of Helsinki and received ethics clearance from Stanford University (Protocol 25863), University of California, Berkeley (2011-09-3652), and the International Centre for Diarrhoeal Disease Research, Bangladesh (PR-11063).

Corresponding author

Correspondence to Laura H. Kwong.

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