Mass and particle size distribution of household dust on children's hands.

Background: Children are vulnerable to household dust exposure; however, to date, a handful of studies simultaneously report both the mass and particle size of household dust found on children's hands after natural indoor play activities.

Objective: Evaluate a new approach to measure dust loading and characterize particle size on a child's hands using a Coulter Counter.

Methods: The volume of particles rinsed off children's hands was measured through counting and sizing particles (using a Coulter Counter), followed by multiplying the particle volume by the density of dust collected from the home. This mass was then normalized per total hand surface area to obtain dust loading on children's hands. Results were compared by region (North Carolina, Florida, Arizona), age groups (6 months to 6 years), and social demographics (gender, race, ethnicity) for 101 children.

Results: The estimated median density for household dust was 1.54 g/cm³, with an average of 1.58 g/cm³ (SD = 0.43). The overall median dust loading on children's hands was 11.13 μg/cm² (per total hand surface area), with a range of 0.004-167.6 μg/cm². No statistical difference was observed by region, age, nor social demographics (p > 0.05). The majority of particles (90%) from children's hand rinses had a diameter (D_90,v) <35 μm; however, these small particles represent a fraction of the total mass. This new approach succeeded at obtaining dust loadings and particle size simultaneously from the same sample, in contrast to current methods that would have required multiple methods and sample types.

Impact statement: Children are vulnerable to household dust due to their play behavior; however, to date, limited measurements are available for the mass and particle size of dust on children's hands after natural indoor play activities. We propose a new approach to facilitate dust loading measurements, while also obtaining the particle size of dust, through the usage of a Coulter Counter. Results showed that 90% of particles were <35 μm, which is four times smaller than the current guidelines threshold (150 μm) for risk assessments that utilize estimates for particles found on hands.