Effect of particle size on risk assessment of direct soil ingestion and metals adhered to children's hands at playgrounds.

The quantity of heavy metals in soil is measured after 2-mm sieving in Japan for risk assessment of direct soil ingestion. A study was conducted on the relationship between the size of soil particles and quantity of heavy metals in soil, and the particle-size distribution of soil adhered to children's hands, and the risks of direct intake of soil considering the particle sizes ingested were evaluated. The results showed that smaller particles had a tendency to contain more heavy metals than bigger ones, that the particle size of approximately 90% of the soil particles from playgrounds adhered to children's hands was less than 100 μm, and that 2-mm sieving in preparation for measuring heavy metal content caused underestimation of the risk of direct soil intake. The amount of heavy metals on children's hands after playing outside was investigated. Various metals and soil were adhered to their hands, and the amount of soil adhered could be estimated from the concentration of metals. To develop accurate risk assessment, the particle-size distribution of ingested soil and more detailed scenarios of soil intake are necessary.