Abstract
BACKGROUND: Time-activity pattern data are components of EPA's efforts to develop soil and dust ingestion rate recommendations for use in risk assessment. The existing database of activity pattern data used for this purpose is comprised mostly of studies designed to estimate exposure to air pollution that are decades old, limiting their applicability to estimating soil and dust ingestion. OBJECTIVES: We aimed to generate novel time-activity pattern data germane to soil and dust ingestion for children aged 6 months to 6 years. We explore potential differences in key exposure factors by child age, sex, motor development, season, and day of the week, and we compare our estimates to the USEPA's Exposure Factors Handbook (EFH) recommendations. METHODS: Caregivers completed hourly time-activity surveys on one weekday and one weekend day in each season across one calendar year. We collected data on four microenvironments, seven activities, and several play-related parameters specific to soil and dust exposure. We assessed differences in time spent and engaged in these microenvironments and activities across day of the week, season, and calendar and developmental lifestage using clustered bootstrapping. RESULTS: We collected 1010 participant-days of time-activity pattern data representing 242 children <6 years. Children spent most of their day indoors either sleeping (51%) or playing (17%), and we observed notable differences in activity patterns across days and ages. On 97% of participant-days, children played with mean = 45 hard toys/day, while on 83% of participant-days, children played with a mean 13 soft toys/day. Comfort object use was more prevalent than pacifier use across all age groups and highest (mean = 136 minutes/day) among 2 to < 3-year-olds. Pacifier use was rarely observed among children >3 years. IMPACT: We collected novel time-activity information for children under six years, with an emphasis on characterizing exposures to chemicals in soil and dust. These contribute to efforts to refine and advance EPA's current models of soil and dust ingestion in this vulnerable lifestage.