Size distributions of soil particles adhered to children's hands.

The size distributions of the soil particles adhered to children's hands were preliminarily investigated and compared with a cutoff soil particle size recently specified in the official analytical method in Japan. To facilitate fieldworks involving child participants, we tested a methodology using a laser scattering particle size distribution analyzer and validated it for field applications. The laboratory experiments using this method showed finer soil particles tended to be adhered more efficiently to human hands. Meanwhile, our preliminary field survey revealed large variations in mass (mean 26.2 mg/hand, median 15.2 mg/hand, max 162.5 mg/hand) and size distributions (particle mode diameter of 39 +/- 26 microm) of the particles adhered to children's hands after various playing activities. Even though the ways the particles adhered were noticeably varied under actual playing situations, the adhered particles were consistently and considerably smaller than the 2-mm cutoff diameter defined by the Ministry of the Environment, Japan. Since soil contaminant concentrations are generally higher for finer soil particles, measurement of contaminant concentrations for the soil fraction including the non-adherent millimeter particles may underestimate the risk of direct soil contaminant intakes.